ANTIBIOTICS

When antibiotics were first discovered they were called “wonder drugs”

Antibiotic is a drug that fights bacterial infection

Dr. PANCHUMARTHY RAVI SANKAR

M. Pharm, Ph.D.

Professor & HOD

Vignan pharmacy college,

Vadlamudi- Guntur, A.P, India.

““AntibioticsAntibiotics are defined as chemical substances or are defined as chemical substances or compounds produced by various species of compounds produced by various species of microorganisms such as bacteria and fungi, which in low microorganisms such as bacteria and fungi, which in low concentrations destroy, kill or inhibit the growth of other concentrations destroy, kill or inhibit the growth of other species of microorganisms.”species of microorganisms.” Greek words Greek words anti = against ; bios = lifeanti = against ; bios = life Vuillemin to define antibiotics literally meaning “against Vuillemin to define antibiotics literally meaning “against life”life”In 1942 Waksman proposed the widely cited definition that “an antibiotic In 1942 Waksman proposed the widely cited definition that “an antibiotic is a substance produced by microorganisms, which has the capacity of is a substance produced by microorganisms, which has the capacity of inhibiting the growth and even of destroying other microorganisms”. inhibiting the growth and even of destroying other microorganisms”. The word antibiotic came from the word The word antibiotic came from the word antibiosisantibiosis a a term coined in term coined in 18891889 by Louis Pasteur's by Louis Pasteur's pupil pupil Paul Paul Vuillemin Vuillemin which means a process by which which means a process by which life could be life could be used to destroy lifeused to destroy life..However, by acylating it with various acid derivatives, more than However, by acylating it with various acid derivatives, more than 50,00050,000 semisynthetic penicillins have been made, of which semisynthetic penicillins have been made, of which less than 30 less than 30 are currently used in medicine.are currently used in medicine.

DEFINITION:

Requirements for a substance to be considered as an Requirements for a substance to be considered as an antibioticantibiotic

-It should have a -It should have a wide spectrumwide spectrum of activity with the of activity with the ability to destroy ability to destroy or inhibit or inhibit many different species of pathogenic organisms.many different species of pathogenic organisms.

-It should be -It should be eliminated completelyeliminated completely from the body. from the body. -It should -It should not produce adverse and side effectsnot produce adverse and side effects.. -It should -It should antagonizes the growth antagonizes the growth or survival of one or more speciesor survival of one or more species of micro- organisms.of micro- organisms. -It should be -It should be highly effectivehighly effective in low concentrations. in low concentrations. -It should be -It should be nonallergenicnonallergenic to the host. to the host. -It should -It should notnot eliminate the eliminate the normal floranormal flora of the host. of the host. -It should be -It should be able to reachable to reach the part of the human body where the part of the human body where the infection is occurring. the infection is occurring. -It should be -It should be inexpensiveinexpensive and and easy to produceeasy to produce. . -It should be -It should be chemically-stablechemically-stable (have a long shelf-life). (have a long shelf-life). -It is a product of metabolism (although it may be duplicated or even have -It is a product of metabolism (although it may be duplicated or even have

been anticipated by chemical synthesis).been anticipated by chemical synthesis).

HHistory of antibiotics can be described in istory of antibiotics can be described in two segmentstwo segments early history and modernearly history and modern historyhistory..

Most important is the discovery of penicillin by SIR Most important is the discovery of penicillin by SIR Alexander Fleming.Alexander Fleming. EARLY HISTORYEARLY HISTORY:: During ancient timesDuring ancient times:: Long ago before 20Long ago before 20thth century there was no proper treatment for diseases. century there was no proper treatment for diseases. The diseases caused by The diseases caused by Mycobacterium tuberculosis, Mycobacterium lepraeMycobacterium tuberculosis, Mycobacterium leprae were not were not

identifiedidentified.. Over 2,500 Over 2,500 years ago , Chinese used years ago , Chinese used plants and moldy cheese used plants and moldy cheese used to treat infected to treat infected

wounds.wounds. As early as 500 to 600 BC, molded curd of soybean was used in Chinese folk medicine to As early as 500 to 600 BC, molded curd of soybean was used in Chinese folk medicine to

treat boils and carbuncles.treat boils and carbuncles. The ancient The ancient Egyptians used honey + lint (softEgyptians used honey + lint (soft cotton cloth covering and protecting cotton cloth covering and protecting

wounds)+wounds)+lard lard (melted fat of pigs) used as ointment (melted fat of pigs) used as ointment for dressing wounds.for dressing wounds.

EgyptiansEgyptians have often been found have often been found onions in body cavities of mummiesonions in body cavities of mummies. They used onions,. They used onions, garlic and radish herb therapeutically. Infact they have garlic and radish herb therapeutically. Infact they have anti-infective properties.anti-infective properties.

GreeksGreeks and Indians used and Indians used moulds moulds and other plants to treat infections. and other plants to treat infections.

In In Greece and Serbia, moldy breadGreece and Serbia, moldy bread was traditionally used to treat wounds and was traditionally used to treat wounds and infections. infections.

Warm soilWarm soil was used by was used by RussiansRussians to cure infected wounds. to cure infected wounds. Sumerian doctorsSumerian doctors gave patients gave patients beer soup mixed with turtle shells and snake beer soup mixed with turtle shells and snake

skinsskins. . Babylonian doctorsBabylonian doctors healed the eyes using a mixture of healed the eyes using a mixture of frog bile and sour milkfrog bile and sour milk. . Sri Lankan armySri Lankan army used used oil cake (sweetmeat)oil cake (sweetmeat) to serve as antibacterial. to serve as antibacterial.

TREATMENT OF INFECTIOUS DISEASES PRIOR TO ANTIBIOTICS.Centuries earlier, humans had learned to use crude preparations for the

topical treatment of infections.

Modern History Modern History Late 1800’s = Search for antibiotics began with the growing acceptance of the germ theory of Late 1800’s = Search for antibiotics began with the growing acceptance of the germ theory of disease(disease(Louis Pasteur was one of the first recognized physicians who observed that bacteria could be Louis Pasteur was one of the first recognized physicians who observed that bacteria could be used to kill other bacteria)used to kill other bacteria)

1871 = The surgeon joseph lister found urine contaminated with 1871 = The surgeon joseph lister found urine contaminated with mould couldn't kill the bacteria.mould couldn't kill the bacteria. 1890’s = German doctors Rudolf emmerich, oscar low made 1890’s = German doctors Rudolf emmerich, oscar low made pyocyansepyocyanse from microbes. It was the first antibiotic used from microbes. It was the first antibiotic used in hospitals but the drug did not work.in hospitals but the drug did not work. 1909 =First modern chemotherapeutic agent 1909 =First modern chemotherapeutic agent SALVARSANSALVARSAN for the for the treatment of syphilis.(Paul Ehrlich)treatment of syphilis.(Paul Ehrlich) 1928 1928 = Scottish bacteriologist = Scottish bacteriologist Sir Alexander Fleming discovered enzyme Sir Alexander Fleming discovered enzyme lysozyme and the antibiotic substance penicillin.lysozyme and the antibiotic substance penicillin. 1932 = Gerhard Domagk discovered 1932 = Gerhard Domagk discovered ProntosilProntosil a prodrug. a prodrug. 1936 = Sulfanilamide the first synthetic sulfonamide in human medicine.1936 = Sulfanilamide the first synthetic sulfonamide in human medicine. 1940 = 1940 = Invention of Modern Drug Discovery: Ehrlich & The Magic Bullet means compound that selectively targets a disease causing organism while having no negative effect on human tissue.no negative effect on human tissue. 1940 =First therapeutic use of penicillin by Floury.1940 =First therapeutic use of penicillin by Floury. 1944 = Selman waksman made Streptomycin from soil bacteria.1944 = Selman waksman made Streptomycin from soil bacteria. 1948 = Chlortetracycline.1948 = Chlortetracycline. 1957 = Nystatin (fungal infections)1957 = Nystatin (fungal infections) 1970’s = New 4-quinolones(pipemidic acid,oxolinic acid,cinoxacin)1970’s = New 4-quinolones(pipemidic acid,oxolinic acid,cinoxacin) 1980 =Norfloxacin, the first fluoroquinolone.1980 =Norfloxacin, the first fluoroquinolone. 1980 =Enroflocacin.1980 =Enroflocacin. 1998 =Smithkline Beecham patented Amoxicillin/clavulanate potassium tablets 1998 =Smithkline Beecham patented Amoxicillin/clavulanate potassium tablets the first sold antibiotic under the trade names of Amoxil and trimox. the first sold antibiotic under the trade names of Amoxil and trimox.

CLASSIFICATIONCLASSIFICATION: : Antibiotics are classified in many ways based on chemical structure, source,its Antibiotics are classified in many ways based on chemical structure, source,its spectrum of activity and Mechanism of action (MOA).spectrum of activity and Mechanism of action (MOA).

*Based on the chemical structure:*Based on the chemical structure: 1.1.β-lactam antibioticsβ-lactam antibiotics: Penicillin's, Cephalosporin's, carbapenams, monobactams. : Penicillin's, Cephalosporin's, carbapenams, monobactams. 2.2. Amino glycoside antibioticsAmino glycoside antibiotics: Streptomycin, Neomycin, Kanamycin, Gentamycin, Tobramycin, : Streptomycin, Neomycin, Kanamycin, Gentamycin, Tobramycin,

Amikacin.Amikacin. 3.3. Tetracyclines Tetracyclines:: Tetracycline, Chlortetracycline, Oxytetracycline, Doxycycline, Tetracycline, Chlortetracycline, Oxytetracycline, Doxycycline,

Minocycline,Minocycline, methacycline, meclocycline.methacycline, meclocycline. 4.4. Macrolide antibioticsMacrolide antibiotics: : (i.e., large macrolide structure)(i.e., large macrolide structure)::EryErythromycin, thromycin, ClariClarithromycin, thromycin, AziAzithromycinthromycin, ,

RoxiRoxithromycin.thromycin. 55. . PolypeptidePolypeptide antibioticsantibiotics: Actinomycin, Bacitracin, Colistin, Polymyxin B, tyrothricin: Actinomycin, Bacitracin, Colistin, Polymyxin B, tyrothricin 6. 6. Polyenes: Polyenes: Amphotericin B, Nystatin.Amphotericin B, Nystatin. 7. 7. Lincomycin: Lincomycin: Clindamycin.Clindamycin. 8.8. MiscellaneousMiscellaneous: Chloramphenical, Novobiocin, Mupirocin, Fucidic acid.: Chloramphenical, Novobiocin, Mupirocin, Fucidic acid. *Based on the source*Based on the source: : They are divided in to They are divided in to Natural antibioticsNatural antibiotics: : Penicillium chrysogenum-Penicillium chrysogenum---- Penicillin. --- Penicillin. Bacillus subtilis Bacillus subtilis --------------- Bacitracin.--------------- Bacitracin. Bacillus polymyxa Bacillus polymyxa ------------- Polymyxin.------------- Polymyxin. Stryptomyces griseus-Stryptomyces griseus---------- Stryptomycin.--------- Stryptomycin. Streptomyces aureofaciens Streptomyces aureofaciens ---Chlortetracyclines---Chlortetracyclines Streptomycers erythreus Streptomycers erythreus -------Erythromycin-------Erythromycin Streptomyces venezulae-Streptomyces venezulae------- Chloramphenicol.------ Chloramphenicol. Semisynthetic antibioticsSemisynthetic antibiotics: These antibiotics are commercially synthesized by adding chemical : These antibiotics are commercially synthesized by adding chemical

compounds, amides etc., to the natural antibiotics. In these the main part of the chemical structure is compounds, amides etc., to the natural antibiotics. In these the main part of the chemical structure is obtained from the micro-organisms which are then modified by adding various chemical moieties as obtained from the micro-organisms which are then modified by adding various chemical moieties as the side chain.the side chain.

Ex: Ex: Ampicillin, Amoxacillin, Oxacillin, Cloxacillin, Dicloxacillin, Carbencillin. Methicillin.Ampicillin, Amoxacillin, Oxacillin, Cloxacillin, Dicloxacillin, Carbencillin. Methicillin. **Spectrum ActivitySpectrum Activity:: Broad spectrumBroad spectrum: These antibiotics inhibit the growth of wide range (i.e. More than one species) of : These antibiotics inhibit the growth of wide range (i.e. More than one species) of

microorganisms. Some antibiotics can inhibit both Gram- positive and Gram-negative bacteria.microorganisms. Some antibiotics can inhibit both Gram- positive and Gram-negative bacteria. EX: EX: Cephalosporins, Chloramphenicol, Tetracycline’sCephalosporins, Chloramphenicol, Tetracycline’s.. Narrow spectrumNarrow spectrum: : These antibiotics are effective mainly against a single species of microorganism either These antibiotics are effective mainly against a single species of microorganism either Gram +ve (or) Gram –ve bacteria. EX: - Gram +ve (or) Gram –ve bacteria. EX: - Bacitracin, Nystatin, PenicillinBacitracin, Nystatin, Penicillin..

Antibiotic activity Antibiotic activity :Based on their activity against different m.o’s they are divided in :Based on their activity against different m.o’s they are divided in toto

a. Antibacterial antibiotics: a. Antibacterial antibiotics: The chemotherapeutic agents which kill or inhibit the growth of The chemotherapeutic agents which kill or inhibit the growth of bacteria bacteria

are called antibacterial antibiotics. (penicillins, cephalosporins, tetracyclines, aminoglycosides)are called antibacterial antibiotics. (penicillins, cephalosporins, tetracyclines, aminoglycosides) 1. 1. Bactericidal antibiotics Bactericidal antibiotics : : These are more effective in killing harmful microorganisms These are more effective in killing harmful microorganisms

particularly bacterialparticularly bacterial species. (species. (Kill the bacteria directlyKill the bacteria directly) ) ExamplesExamples are ….. are …..

22. Bacteriostatic antibiotics: . Bacteriostatic antibiotics: These are effective in abolishing or preventing the growth These are effective in abolishing or preventing the growth of of

bacterial species. (bacterial species. (stop the bacteria from growingstop the bacteria from growing):): EX: Tetracyclines, Chloramphenicol, Clindamycin.EX: Tetracyclines, Chloramphenicol, Clindamycin. b. b. Antifungal antibioticsAntifungal antibiotics: Griseofulvin, Amphoterisin B, Nystatin.: Griseofulvin, Amphoterisin B, Nystatin. c . c . Anthelmintic agents Anthelmintic agents : Ivermectin.: Ivermectin. d. d. Anticancer antibioticsAnticancer antibiotics: Bleomycin, Dactinomycin, Doxorubicin. : Bleomycin, Dactinomycin, Doxorubicin.

Based on Mechanism of action (MOA) : Based on Mechanism of action (MOA) : Cell wall synthesis inhibitors Cell wall synthesis inhibitors : Penicillins, Cephalosporins, Carbapenams, Aztreonam.: Penicillins, Cephalosporins, Carbapenams, Aztreonam. Microbial cell membrane inhibitors : Microbial cell membrane inhibitors : Polymyxin B and E, Colistin, Polyene, Imidazole.Polymyxin B and E, Colistin, Polyene, Imidazole. Protein synthesis inhibitors: Protein synthesis inhibitors: Aminoglycosides, Macrolides, Tetracyclines.Aminoglycosides, Macrolides, Tetracyclines.

Penicillins and Cephalosporins Are Very cidal For Microbes

Penicillins Cephalosporins

Aminoglycosides

Vancomycin

Fluoroquinolones

Mietronidazole

Beta-lactam antibiotics will be examined in four Beta-lactam antibiotics will be examined in four groups, including groups, including penicllinspenicllins, cephalosporins, , cephalosporins, monobactams, and carbapenems. monobactams, and carbapenems. The beta-lactam ring is joined to a five-membered The beta-lactam ring is joined to a five-membered thiazolidine ring in penicillin, thiazolidine ring in penicillin, Six-membered dihydrothiazine ring in Six-membered dihydrothiazine ring in cephalosporins. cephalosporins. In carbapenems, the beta-lactam ring is also In carbapenems, the beta-lactam ring is also joined to a five-membered ring, although it is joined to a five-membered ring, although it is carbocyclic.carbocyclic.Monobactams have a monocyclic betalactam Monobactams have a monocyclic betalactam structure, and the side sulfo-group is joined to a structure, and the side sulfo-group is joined to a nitrogen atom.nitrogen atom.All of these contain a four-membered beta-lactam All of these contain a four-membered beta-lactam ring, which is necessary for exhibiting antibacterial ring, which is necessary for exhibiting antibacterial activity. activity.

Four groups Beta-lactam antibiotics

Penicillin was discovered in Penicillin was discovered in 19281928 by by Alexander FlemingAlexander Fleming, who noticed that , who noticed that one of his experimental cultures of one of his experimental cultures of staphylococcusstaphylococcus was contaminated with was contaminated with mold, which caused the bacteria to lyse. Since mold belonged to the family mold, which caused the bacteria to lyse. Since mold belonged to the family PenicilliumPenicillium, he named the antibacterial , he named the antibacterial substance substance penicillin.penicillin.

About a decade later, a group of researchers at Oxford University isolated a About a decade later, a group of researchers at Oxford University isolated a crude substance made up of a few low-molecular substances, which were crude substance made up of a few low-molecular substances, which were penicillins (penicillins (F, G, K, O, V, XF, G, K, O, V, X).).

PENICILLINSPENICILLINS

Penicillium mould(penicillium notatum)

Historical background of penicillinsHistorical background of penicillins Alexander Fleming was born in Loudon, Scotland on 6 August, Alexander Fleming was born in Loudon, Scotland on 6 August,

1881 in a farming family. 1881 in a farming family. He carried on his schooling at He carried on his schooling at regent streetregent street polytechnicpolytechnic after his after his

family moved to London in 1895. family moved to London in 1895. He joined He joined St. Mary's medical schoolSt. Mary's medical school and became research assistant and became research assistant

to renowned Sir Almroth Wright, after he got to renowned Sir Almroth Wright, after he got distinctiondistinction in 1906. in 1906. He completed his degree He completed his degree (M.B.B.S.)(M.B.B.S.) with with gold medalgold medal in 1908 from in 1908 from

the University of London and lectured at St. Mart till 1914. the University of London and lectured at St. Mart till 1914. He served as He served as captain captain during the during the World War IWorld War I and worked in and worked in

battlefield hospitals in France. After the war he returned to St. Mary battlefield hospitals in France. After the war he returned to St. Mary in 1918 and got elected as in 1918 and got elected as Professor of bacteriology in 1928. Professor of bacteriology in 1928.

He discovered natural antiseptic enzyme in 1921, which he named He discovered natural antiseptic enzyme in 1921, which he named lysozymelysozyme. This substance existed in tissues and secretions like . This substance existed in tissues and secretions like mucus, tears and egg-white but it did not have much effect on the mucus, tears and egg-white but it did not have much effect on the strongly harmful bacteria.strongly harmful bacteria.

It was in 1928 when he observed while experimenting on It was in 1928 when he observed while experimenting on influenza influenza virusvirus that a common fungus inhibiting the growth of organism. that a common fungus inhibiting the growth of organism.

It was a It was a Serendipitous observation(fortuitous accident)Serendipitous observation(fortuitous accident) i.e (happening i.e (happening by chance) in his laboratory in the basement of St. Mary's Hospital in by chance) in his laboratory in the basement of St. Mary's Hospital in London ( now part of imperical college).London ( now part of imperical college).

On Friday, September 28, in 1928, Fleming left the lid off of one of On Friday, September 28, in 1928, Fleming left the lid off of one of his Petri dishes for several weeks, and a fungal spore landed on it (the his Petri dishes for several weeks, and a fungal spore landed on it (the culture became contaminated). After returning from vacation, culture became contaminated). After returning from vacation, Fleming noticed that his Fleming noticed that his StaphylococcusStaphylococcus culture was contaminated culture was contaminated with this fungus but instead of throwing the Petri dish away, he with this fungus but instead of throwing the Petri dish away, he carefully examined it first. carefully examined it first.

There was an inhibited bacterial growth around the mould. Fleming There was an inhibited bacterial growth around the mould. Fleming concluded that the mould (fungal colony) was releasing a concluded that the mould (fungal colony) was releasing a antibacterial substance which was spreading into the surrounding area antibacterial substance which was spreading into the surrounding area where the bacterial colonies were dying. i.e. lysing the bacteria.where the bacterial colonies were dying. i.e. lysing the bacteria.

He grew a pure culture and discovered that it was a He grew a pure culture and discovered that it was a PenicilliumPenicillium mould, now known to be mould, now known to be Penicillium notatum.Penicillium notatum.

Penicillium mould must be secreting an antibacterial substance, Penicillium mould must be secreting an antibacterial substance, which he isolated first in crude form of the active substance and which he isolated first in crude form of the active substance and named it as penicillin.named it as penicillin.

This newly discovered active substance(penicillin) was effective This newly discovered active substance(penicillin) was effective even when diluted up toeven when diluted up to 800 800 times. times.

Unfortunately, the substance was also Unfortunately, the substance was also unstable and Fleming was unstable and Fleming was unableunable to isolate and purify the compoundto isolate and purify the compound. He therefore came to . He therefore came to the conclusion that penicillin was too unstable to be used clinically.the conclusion that penicillin was too unstable to be used clinically.

Florey and Chain in 1938Florey and Chain in 1938 by using processes such as by using processes such as freeze-drying freeze-drying and chromatographyand chromatography which allowed isolation of pure form of which allowed isolation of pure form of penicillins.penicillins.

Fleming, Florey, and Chain shared the Fleming, Florey, and Chain shared the 1945 Nobel Prize1945 Nobel Prize for their for their medicinal work on penicillin.medicinal work on penicillin.

In june 1942 availability of penicillin was just to treat 10 patients.In june 1942 availability of penicillin was just to treat 10 patients. After fermentation research 2.3 million doses had been increased in After fermentation research 2.3 million doses had been increased in

U.S.U.S.

Commercial production of antibioticsCommercial production of antibiotics

The general scheme may be divided into six stepsThe general scheme may be divided into six steps1.1. Preparation of a pure culture of the desired organism for use in inoculation of the Preparation of a pure culture of the desired organism for use in inoculation of the

fermentation medium.fermentation medium.2.2. Fermentation, during which the antibiotic is formed.Fermentation, during which the antibiotic is formed.3.3. Isolation of the antibiotic from the culture medium.Isolation of the antibiotic from the culture medium.4.4. Purification.Purification.5.5. Assays for potency, sterility, absence of pyrogens, and other necessary data.Assays for potency, sterility, absence of pyrogens, and other necessary data.6.6. Formulation into acceptable and stable dosage forms.Formulation into acceptable and stable dosage forms.

1943 the mass production of penicillin began. As the production increased the cost dropped Correspondingly. When penicillin was first available, 100,000 units sold for $20. currently, the same quantity costs less than a penny

Once the penicillin is released from the fungal cells, the Once the penicillin is released from the fungal cells, the compound is isolated from the fermenter's contents and compound is isolated from the fermenter's contents and purified by special biochemical processes.purified by special biochemical processes.

Such commercial production results in more than Such commercial production results in more than 100,000,000 pounds of penicillin production per year. 100,000,000 pounds of penicillin production per year.

Bulk production of pencillins

Biological sources of penicillinBiological sources of penicillin The first naturally occurring benzyl penicillin (penicillin G is also The first naturally occurring benzyl penicillin (penicillin G is also

referred to as referred to as gold standard penicillin gold standard penicillin ) was obtained by the ) was obtained by the fermentation of fungus fermentation of fungus Penicillium notatumPenicillium notatum. .

At present it is obtained from a highly yielding strain called At present it is obtained from a highly yielding strain called PenicilliumPenicillium chrysogenumchrysogenum and other penicillum species. and other penicillum species.

30 different biosynthetic penicillin's have been isolated from various 30 different biosynthetic penicillin's have been isolated from various strains of strains of Penicillium notatium Penicillium notatium and and Penicillum chrysogenum. Penicillum chrysogenum.

5 Classes of Penicillins

Natural Penicillins (Fermentation derived penicillins)Penicillin G ,Penicillin V

Semi synthetic Penicillinase Resistant Penicillins (parenteral)MethicillinNafcillinIsoxazolyl Penicillins (Cloxacillin / Dicloxacillin / Oxacillin / Flucloxacillin)

Amino penicillins ( Semisynthetic penicillinase sensitive broad spectrum penicillins)Ampicillin , Amoxicillin

Carboxy penicillins ( Synthetic penicillins sensitive to broad spectrum, Parenteral penicillins.)

Carbencillin, Carbencillin phenyl, Carbencillin indanyl. Ticarcillin

UreidopenicillinsPiperacillin , Mezlocillin, Azlocillin

R =

STRUCTURE

OF PENICILLINS

Penicillin G (Benzylpenicillin)Penicillin G (Benzylpenicillin) Penicillin G is also referred to as Penicillin G is also referred to as gold standard penicillingold standard penicillin.. Penicillin G is not acid resistant it is acid sensitive.Penicillin G is not acid resistant it is acid sensitive. 3 reasons for the acid sensitivity of penicillin G.3 reasons for the acid sensitivity of penicillin G. 11. . Ring strainRing strain. ( 4 membered betalactam ring + 5 membered thiazolidine ring) As a result penicillins . ( 4 membered betalactam ring + 5 membered thiazolidine ring) As a result penicillins

suffers large angle and torsional strains. Acid catalyzed ring opening relieves these strains by breaking suffers large angle and torsional strains. Acid catalyzed ring opening relieves these strains by breaking open the more highly open the more highly ββ –lactam ring. –lactam ring.

22. . Highly reactive corbonyl groupHighly reactive corbonyl group. . The resonance stabilization is impossible for the The resonance stabilization is impossible for the ββ –lactam ring because –lactam ring because of the increase in angle strain that would result in having a double bond within of the increase in angle strain that would result in having a double bond within ββ –lactam ring. So the –lactam ring. So the angle of the angle of the ββ –lactam ring constrained to 90 –lactam ring constrained to 9000 . So the lone pair is localized on the N atom, and the . So the lone pair is localized on the N atom, and the carbonyl group is more electrophilic than one would expect for a tertiary amide. carbonyl group is more electrophilic than one would expect for a tertiary amide.

Influence of the acyl side chainInfluence of the acyl side chain: Acyl group open up the lactam ring . So Penicillin G has a self-destruct : Acyl group open up the lactam ring . So Penicillin G has a self-destruct mechanism built in its structure.mechanism built in its structure.

Benzylpenicillin is broken down by stomach acidBenzylpenicillin is broken down by stomach acid and destroyed by staphylococcus penicillinase.and destroyed by staphylococcus penicillinase. So it can be given by IV.So it can be given by IV.

Therapeutic uses:Drugs of the penicillin group are effective for infections caused by Gram-positive bacteria(streptococcus, pneumococcus, and others), spirochaetae, and other pathogenic microorganisms.Drugs of this group are ineffective with respect to viruses, mycobacteria tuberculosis, fungi, and the majority of Gram-negative microorganisms. Benzylpenicillin is the drug of choice for infections caused by sensitive organisms. This includes streptococci infections (except enterococci), gonococci, and meningococci that do not produce beta-lactam anaerobes. Benzylpenicillin is used for croupous and focal pneumonia, skin infections, soft tissue and mucous membranes, periotonitis, cystisis, syphilis, diphtheria, and other infectious diseases.

Benzyl groupN

S

COOHH

CH3

CH3

HH

O

HNCH2C

O

N

S

COOHH

CH3

CH3

HH

O

HNCH2C

O

O

It withdraws the electrons away from the corbonyl oxygen and reduce the tendency to act as a nucleophile

Phenoxy methyl Penicillin ( Penicilln V)

•By placing electron with drawing group in the side chain which could draw electrons away from the corbonyl oxygen and reduce its tendency to act as a nucleophile.•Penicillin- V has electro –ve oxygen on the acyl side chain with electron withdrawing effect. It has more acid stability than penicillin G .•It is more stable in acid in the stomach, so it can be given orally.•Infact acid sensitivity can be solved by having an electron withdrawing group on the Acyl side chain.

PENICILLIN- V

N

S

COOHH

CH3

CH3

HH

O

HNCH2C

O

OCH3

OCH3

Strategy is putting two ortho- methoxygroups on the aromaticring.

Bulky groups

"Steric shields” can be added to penicillins to protect them from bacterial Betalactamase (peicillinase) enzymes.By placing bulky groups on the side chain, bulky groups can prevent the betalactamase or penicillinase enzyme to Reach the beta lactamase or penicillinase active site.Because of betalactamases bacteria can gain resistance to penicillin.Betalactamases hydrolyse the ester link and open the pencillin. 1000 penicillin molecules are hydrolysed per second.Infact steric shield should not be too bulkey. If it is too bulkey it also prevents the penicillin from attacking the transpeptidase target enzyme.It should not be too small enough.. Methicillin is also not a ideal drug. Infact methicillin has no electron withdrawing group on the side chain. Methicillin is acid sensitive and has to be injected.

Penicillinase resistant penicillins

METHICILLIN

OC2H5

R Group

Nafcillin.

(Narrow spectrum Antistaphylococcal penicillins)

Methicillin in USA not ued clinicallyMethicillin produces Interstitial Nephritis (damages the kedney).

Nafcillin also some times produces Interstitial Nephritis.it also Produces Neutropenia (Low level of Neutrophils)

Isoxazoyl Penicillins Penicillinase- resistant penicillins or β- lactamase- resistant penicillins

R1 R2

Oxacillin H HCloxacillin Cl HDicloxacillin Cl ClFlucloxacillin Cl F

N

S CH3

CH3

COOH

O

HN

O

NO

CH3

R1

R2

H

H HBulkyand electronwithdrawing group

Isoxazolyl ring

The incorporation of an isoxazolyl ring in to the penicillin side chain lead to orally activecompounds which were stable to -lactamase enzymes of S. aureus.The isoxazolyl ring acts as the steric shiels but it is also electron-withdrawing, giving thestructure acid stable.

The β-Lactamase resistant penicllins tend to be comparativelylipophilic molecules that do not penetrate well into Gram –vebacteria.α- acyl carbon could be part of an aromatic ( phenyl or Naphthyl or heteroaromatic (e.g., 4-isoazoyl) system.

To sum up acid resistant penicillins would be the drugs of first choice against an infection. If the bacteria proved resistance due to the presence of a Penicillinase enzyme Penicillin resistant S. aureus therapy would be changed to penicillinase resistant penicillins. Hydrophobic groups on the side chain(pen-G) favor gram +ve but Poor activity against gram-

ve. Enhancement of gram -ve activity is found if hydrophilic Groups – NH2, - OH, -COOH are

attached to the alpha carbon from the carbonyl group on the side chain. Those Penicillins have useful activity against gram +ve and gram -ve.

Hydrophilic groups on the side chain have little effect on Gram-positive activity (e.g. penicillin T) or cause a reduction of activity (e.g. penicillin N)

However, they lead to an increase in activity against Gram-negative bacteria.

The acidic stability of the ampicillin also attributes the electron withdrawing character of the primary amino group which prevents the hydrolysis of the β-lactum bond. It is susceptible to degradation by β-lactamase enzymes. Hence it is given in Combination with inhibitors like sulbactum.

Hydrophobic groups on the side chain( Ex: penicillin G) favor activity against Gram-positive bacteriaHydrophilic groups on the side chain have increase in activity against Gram –negative bacteria.If the hydrophilic group is (NH2,OH,COOH group) attached to the carbon, alpha to the carbonyl group on the side chain. All have an alpha hydrophilic group which aids the passage of these penicillins through the porins of the Gram-ve Bacterial outer cell membrane.

Uses: Ampicillin and Amoxicillin HELPS to clear the Enterococci.H – Haemophilus Influenzae.E – Escherichia Coli.L – Listeria monocytogenes.P- Proteus.S – Salmonella Typhi.

Amino Penicillins ( Ampicllin, Amoxicillin )

AMPICILLIN

N

S CH3

CH3

COOH

O

HN

O

CH

H HNH2

H

Amoxicillin (Amoxil) (p-hydroxy Ampicillin)

Amoxicillin is the very similar in structure like ampicillin, the only difference beingan extra phenol group on amoxicillin.*similar spectrum of activity to penicillin G, but more active against Gram-ve bacteria*Acid resistant due to the –NH2 group and therefore orally active.*Non toxic, *Sensitive to β-lactamase (No shield).---Can cause diarrhea due to poor absorption through the gut wall, is due to dipolar nature of the moleculeIt has both free carboxylic acid and amino function. This problem can be solved by using a prodrugPivampicillin, talampicillin, bacampicillin are prodrugs of ampicillin. acyloxymethyl esters are used to mask the -COOH groups. Its spectrum of activity is increased when administered with clavalunic acid.Amoxicillin + clavalunic acid = Augmentin tablets.

Broad spectrum activity is associated with thepresence of an alpha hydrophilic group on the acyl side chain of penicillin. Extra phenol group is present on amoxicillin.If you compare with ampicillin, amoxicillin Is better absorbed through gut wall.

Uses:BronchitisPneumoniaTyphoidEnteric feverGonorrhoeaUrinary tract infactions.

N

S CH3

CH3

COOH

O

HN

O

CH

H HNH2

H

HO

Ampicillin synthesis:A method of directly acylating 6-APA with phenylglycine chloride hydrochloride

Ampicillin

Amoxicillin synthesis:The direct reaction of D-()-2-(4-hydroxyphenyl) glycine chloride hydrochloride with trimethylsylil ester of 6-APA

Amoxicillin

Nomenclature of PenicillinsNomenclature of PenicillinsNomenclature of penicillins was done in different systemsNomenclature of penicillins was done in different systems..

Chemical abstract system(CAS):•According to this system penicillins are numbered starting from “S” atom. Sulphur atom is assigned the 1st position and “N” atom is assigned number 4.

1 2

34

56

7

Bicyclic ring system

1-thia-4-azabicyclo [3.2.0] heptane

United States Pharmacopoeia (USP system):•The USP system of naming penicillins is the reverse of CAS.•According to this system the nitrogen atom is given the 1st position and “S” atom is assigned the 4th position.

1 2

3456

74-thia-1-azabicyclo [3.2.0] heptane

1 22

34

56

7

1 2

3456

7

As derivatives of Penam:Unsubstituted bicyclic system together with amide corbonyl group has been named as penam.According to this method penicillins are named as4- Thia-1-azabicyclo[3.2.0] heptane-7-one.

4. As derivatives of penicillanic acid: In this method penicillins are named as derivatives of penicillanic acid ring system with 5- acyl amino -2,2’-dimethyl penam -3- carboxylic acid.

1

5. As derivatives of penicillins (on the basis of “R” group) … TRIVAL SYSTEMIn this system 6-corbonyl amino penicillanic acid portion of the molecule is namedas penicillin and the different penicillins are distinguished on the basis of “R” groupon the acyl amino side chain.

4

56

7

This system of naming of penicillins is simple and serves as a good measure for naming and

comparing closely related penicillin structures. However this system is not well suited for compounds

having the ring Modified Derivatives.

Stereo chemistryStereo chemistry The penicillin molecule contains three chiral carbon atoms at C-3, C-5 and The penicillin molecule contains three chiral carbon atoms at C-3, C-5 and

C-6.C-6. All natural and synthetic penicillins have the same absolute configuration All natural and synthetic penicillins have the same absolute configuration

about these three centers.about these three centers. The 6The 6thth carbon atom bearing the acyl amino group has the L-configuration, carbon atom bearing the acyl amino group has the L-configuration,

where as the carbon to which the carboxyl group was attached has the where as the carbon to which the carboxyl group was attached has the D- configuration.D- configuration.

Thus the acyl amino group and carboxyl group are trans to each other, with Thus the acyl amino group and carboxyl group are trans to each other, with the former the former αα and latter in the and latter in the ββ orientation relative to penam ring. orientation relative to penam ring.

The absolute stereochemistry of the penicillins was designated as The absolute stereochemistry of the penicillins was designated as 3S:5R:6R.3S:5R:6R.

The atoms composing the 6-aminopenicillanic acid are biosynthetically The atoms composing the 6-aminopenicillanic acid are biosynthetically derived from two amino acids, L-cysteine and D-valine.derived from two amino acids, L-cysteine and D-valine.

Reactions: Hydrolysis of penicillins by hot and cold dilute mineral acidReactions: Hydrolysis of penicillins by hot and cold dilute mineral acid

There are also a variety of acylases that have been isolated from some bacteria, and

these enzymes cleave the acylamino sidechain of the antibiotic, a modification which also

inactivates the molecule. 

N

S

COOH

CH3

CH3

HH

O

HNCR

O

Thiazolidine ring-Lactam

ring

Cis orientation of hydrogens(stereochemistry) are essential

Bicyclic system essential Free corboxylate essential

Amide essential or acylaminoside chain essential

Strained -lacturmring,which is necessary for exhibiting antibacterial activity

(The corboxylate ion bindsto the charged ammoniumion of a lysine residue in thebinding site)

Sulfur is usual but notessential

Presence of one-orientation andone -orientation is essential for activity

Presence of N is essentialany modification upon nitrogen it will results lack of activity.

Highly reactiveketonic group at7th position alsoessential any modification lackof activity.

Amino group presenton the 6th position should be trans whichis very essential.

12

34

56

7

Bicyclic system confers further strainon-lactam ring. Greater the stran, the greaterthe activity,but greater the instability of the molecure to other factors.

6-Aminopenicillanic acid

The “R”groupdetermines theStability andImproved spectrumof activity and Pharmacokineticadvantages.

BASIC CHEMISTRY= -LACTRUM RING + THIAZOLIDINE RING

STRUCTURE - ACTIVITY RELATION SHIP (SAR) OF PENICILLINSGENERAL STUCTURE OF PENICILLIN OR PENICILLIN CORE STRUCTUREPENICILLIN NUCLEUS OR BASIC STRUCTUREOF PENICILLIN

cysteine

Valine(aminoacid)

ByProf. Ravisankar

Site of penicillinase action(break in beta lactum ring(that bond is broken by betalactamase or penicillinaseEnzyme.(the bond b/n C and N is broken by ß-lactamase (or) penicillinase enzme.

Key features of structure 1. β-lactam ring a. "Lactam" is a word for any cyclic amide (the word "lactone" is used for

a cyclic ester) b. a β-lactam means that the nitrogen is joined to the carbon which is beta

to the carbonyl c. this creates strain in the ring, since it is a four membered ring d. b-lactam becomes good acylating agent for active site serine of

penicillin binding protein 2. Carboxylate: a. Negatively charged at neutral pH b. Anchors drug in active site pocket (positively charged) 3. Acylamide side chain: a. Necessary for biological potency b. Proper stereochemistry of attachment to ring essential for activity c. Variation at side chain can dramatically affect biological activity against

various strains of bacteria D. Common Early Penicillins 1. Penicillin G had to be administered parenterally, since it isn't acid stable. 2. Penicillin V has more acid stability, and can be administered orally

Penicillins are…. a group of antibiotics that contain 6-amino penicillanic acid side chain attachedto the 6-amino group.•The penicillin nucleus is the chief structural requirement for biological activity.•The side chain structure determines the many of the antibacterial and pharmacological characterstics.•The strained β-lactum ring is essential.•Penicillin contains β-lactum ring is fused with thiazolidine ring.•The free carboxylic acid is essential. The carbolated ion is binds to the charged ammonium ion of lysine residue in the binding site.•The bicyclic system is important. The greater the strain, the greater the activity.•The acyl amino side chain is essential.•Sulfur is usual but not essential.•The cis- stereo chemistry of bicyclic ring with respect to the acyl amino side chain is important.•Oxidation of sulphur to a sulfone or sulfoxide will decrease the activity.•The methyl groups at position 2 are essential.•β- lactum corbonyl group at position “7” is must.•The carboxylic acid is changed to an alcohol or ester activity is decreased.•“N” at position 4 is must for antibacterial activity.•Penicillin molecule contains a ‘3’ chiral carbon atome c-3,c-5,c-6. Disruption of•These spacial arrangements results in loss of activity.

SAR of “R” group:SAR of “R” group: C-6 amino west end substitution:C-6 amino west end substitution: The design and development of the west-end substituents hasThe design and development of the west-end substituents has been aimed at strengthening of activity, stability, resistance, absorption and distribution.been aimed at strengthening of activity, stability, resistance, absorption and distribution. Placing the electron withdrawing group in the side chain which could draw electrons away Placing the electron withdrawing group in the side chain which could draw electrons away

from the carbonyl oxygen and reduce the tendency to act as a nucleophile and allows a from the carbonyl oxygen and reduce the tendency to act as a nucleophile and allows a greater stability and oral availability. Ex: penicillin V, Ampicillin.greater stability and oral availability. Ex: penicillin V, Ampicillin.

Stereic shields can be added to penicillin to protect them from bacterial β-lactamase Stereic shields can be added to penicillin to protect them from bacterial β-lactamase enzymes.enzymes.

By placing bulky groups on the side chain it prevent the penicillin from entering the By placing bulky groups on the side chain it prevent the penicillin from entering the penicillinase or β-lactamase active site. penicillinase or β-lactamase active site.

Infact if the stereic shield was too bulky then it also prevents the penicillin from Infact if the stereic shield was too bulky then it also prevents the penicillin from attacking the transpeptidase target enzyme, It should be ideal shield.attacking the transpeptidase target enzyme, It should be ideal shield. but it should not be too small enough…but it should not be too small enough… Ex: Methicillin.Ex: Methicillin. Indeed Methicillin has no electron with drawing group on the side chain. It is acid sensitive Indeed Methicillin has no electron with drawing group on the side chain. It is acid sensitive

and has to be injected.and has to be injected. Incorporation of isoxazolyl ring in to the penicillin side chain lead to the development of Incorporation of isoxazolyl ring in to the penicillin side chain lead to the development of

better penicillinase resistant agents. In fact isoxazolyl ring acts as the stereic shield but also better penicillinase resistant agents. In fact isoxazolyl ring acts as the stereic shield but also electron withdrawing group giving the structure acid stability.electron withdrawing group giving the structure acid stability.

Ex: Oxacillin, Cloxacillin, Dicloxacillin, Flucloxacillin.Ex: Oxacillin, Cloxacillin, Dicloxacillin, Flucloxacillin.

Broad spectrum activity is associated with the presence of Broad spectrum activity is associated with the presence of αα-hydrophilic -hydrophilic group on the acyl side chain of penicillin.group on the acyl side chain of penicillin.

Enhancement of Gram –ve activity is increased hydrophilic groupEnhancement of Gram –ve activity is increased hydrophilic group (-NH(-NH22,OH,-COOH group), attached to the Carbon,,OH,-COOH group), attached to the Carbon,αα to the carbonyl group to the carbonyl group

on the side chain. These penicillin's are having useful activity against both on the side chain. These penicillin's are having useful activity against both remove and gram-Vet bacteria are known as broad spectrum antibiotics.remove and gram-Vet bacteria are known as broad spectrum antibiotics.

EX: Ampicillin and Amoxicillin.EX: Ampicillin and Amoxicillin. The spectrum of activity was further extended with introducing strong The spectrum of activity was further extended with introducing strong

acidic group is attached to the carbon acidic group is attached to the carbon αα- to the carbonyl group on the side - to the carbonyl group on the side chain.chain.

αα - carboxy penicillins are broad spectrum penicillins and wider range of - carboxy penicillins are broad spectrum penicillins and wider range of gram-ve activity than ampicillin.gram-ve activity than ampicillin.

EX: Carbencillin,Ticarcillin.EX: Carbencillin,Ticarcillin. The acylation of the ampicillin west-end amine functionality with The acylation of the ampicillin west-end amine functionality with certain polar groups leads to cyclic urea derivatives. certain polar groups leads to cyclic urea derivatives. Urido penicillins have a urea functional group at Urido penicillins have a urea functional group at αα-position. In fact they -position. In fact they

are more active than the carboxy Penicillins against streptococci andare more active than the carboxy Penicillins against streptococci and Haemophilus species. Presence of urea group gives improved penetration Haemophilus species. Presence of urea group gives improved penetration

in to gram-ve species.in to gram-ve species. EX: Azocillin, Mezlocillin, Piperacillin.EX: Azocillin, Mezlocillin, Piperacillin.

Plasma membrane

Peptidoglycan cell wall(rigid coating around the membrane)

Lipopolysaccharide layer(LPS)

Gram +ve Gram –ve

Thick Thin

One of the major difference between 2 types of bacteria is the amount of peptidoglyconThey have on the cell wall.Gram +ve bacteria has a lot of peptidoglycon and this actually holds the gram stain inThat’s why it is gram +ve.Gram –ve bacteria has a very thin layer of the peptidoglycon and gram stain leaks out

Cell membrane (or)Outer membrane

Since the penicillin's inhibits peptidoglycon synthesis it is much better an attacking gram+ve bacteria such as Staphylococci, and streptococci than gram –Ve bacteria like E-coli.

Beta-lactam antibiotics are relativelyBeta-lactam antibiotics are relativelynon-toxic to humans why?non-toxic to humans why?

One of the important point is penicillin is acting as a mimic One of the important point is penicillin is acting as a mimic for a D-Ala-D- Ala moiety, this provides another explanation for a D-Ala-D- Ala moiety, this provides another explanation for its lack of toxicity.for its lack of toxicity.

There is no D-Ala- D-Ala amino acids or D-Ala- D-Ala There is no D-Ala- D-Ala amino acids or D-Ala- D-Ala segments in any human protein. That’s why any of the body's segments in any human protein. That’s why any of the body's serine protease enzymes does not recognize penicillin. serine protease enzymes does not recognize penicillin.

As a result penicillin is only selective for bacterial As a result penicillin is only selective for bacterial transpeptidase enzyme and ignored by the body’s own serine transpeptidase enzyme and ignored by the body’s own serine protease.protease.

Mechanism of action of penicillinsMechanism of action of penicillins The primary mechanism of the action of beta-lactam antibiotics is the inhibition of synthesis of The primary mechanism of the action of beta-lactam antibiotics is the inhibition of synthesis of cell walcell wall of bacteria, which causes l of bacteria, which causes

them to quickly die.them to quickly die. The cell membrane protects bacteria cells from lysis, which can occur as a result of different osmotic pressures between the The cell membrane protects bacteria cells from lysis, which can occur as a result of different osmotic pressures between the

cytoplasm and the surrounding medium..cytoplasm and the surrounding medium.. The main component of bacterial cell membranes is a mixed polymer known as The main component of bacterial cell membranes is a mixed polymer known as murein or peptidoglycanmurein or peptidoglycan. Peptidoglycon is a long . Peptidoglycon is a long

polysaccharide chain that is cross-linked with short peptides.polysaccharide chain that is cross-linked with short peptides. Polysaccharide chains are made up of two varying aminosugars—Polysaccharide chains are made up of two varying aminosugars—N-acetylglucosamineN-acetylglucosamine and and N-acetylmuraminic acidN-acetylmuraminic acid. There are significant differences between Gram +ve and Gram –ve bacteria. The cell wall in Gram . There are significant differences between Gram +ve and Gram –ve bacteria. The cell wall in Gram

+ve bacteria consists of +ve bacteria consists of 50-10050-100 peptidoglycon layers where as Gram –ve bacteria it consists only peptidoglycon layers where as Gram –ve bacteria it consists only 2 layers2 layers. . Beta-lactam antibiotics specifically bind with a number of proteins of cytoplasmic membranes known as Beta-lactam antibiotics specifically bind with a number of proteins of cytoplasmic membranes known as penicillin-binding penicillin-binding

proteins (PBP).proteins (PBP). The enzyme responsible for the cross-linking reaction is known as the The enzyme responsible for the cross-linking reaction is known as the transpeptidase enzyme.transpeptidase enzyme. Beta-lactam antibiotics must pass through the outer layer of the cell in order to get the desired PBP to the surface of the membrane.Beta-lactam antibiotics must pass through the outer layer of the cell in order to get the desired PBP to the surface of the membrane. About 30 enzymes are involved in the overall biosynthesis of cell wall but final cross linking reaction which is inhibited by About 30 enzymes are involved in the overall biosynthesis of cell wall but final cross linking reaction which is inhibited by

penicillin. This leads to a cell wall framework that is no longer interlinked. As a result, the wall becomes fragile and can no longer penicillin. This leads to a cell wall framework that is no longer interlinked. As a result, the wall becomes fragile and can no longer prevent the cell from prevent the cell from swelling and bursting.swelling and bursting.

It has been proposed that It has been proposed that penicillin has a conformation which is similar penicillin has a conformation which is similar to the transition state conformation taken up by the to the transition state conformation taken up by the D-Ala- D-Ala- D-Ala moiety D-Ala moiety during cross linking reaction. The enzyme mistakes penicillin for D-Ala- D-Ala and binds to the active site.during cross linking reaction. The enzyme mistakes penicillin for D-Ala- D-Ala and binds to the active site.

Once bound, penicillin is subjected to Once bound, penicillin is subjected to nucleophilic attack by serinenucleophilic attack by serine. The enzyme can attack the . The enzyme can attack the ββ- lactam rung of penicillin and - lactam rung of penicillin and open it in the same way as it did with the peptide bond. However penicillin is a cyclic and as a result the molecule is open it in the same way as it did with the peptide bond. However penicillin is a cyclic and as a result the molecule is not split in not split in two two and nothing leaves the active site.and nothing leaves the active site.

Transpeptidase connects the little peptide chains perpendicular to the NAM chains.Transpeptidase connects the little peptide chains perpendicular to the NAM chains. Without the grid the rapidly growing bacteria can’t maintain the strong cell wall.Without the grid the rapidly growing bacteria can’t maintain the strong cell wall. There is a high pressure inside the cell i.e. 10-20 atm. pressure which means if the cell wall is There is a high pressure inside the cell i.e. 10-20 atm. pressure which means if the cell wall is

not present, the rigid coating bacteria can swell and burst.not present, the rigid coating bacteria can swell and burst. β – lactam antibiotics like penicillins act by inhibiting the transpeptidase (or) PBPs by β – lactam antibiotics like penicillins act by inhibiting the transpeptidase (or) PBPs by

covalently bonding to the serine residues within the active sites and prevent the cell wall covalently bonding to the serine residues within the active sites and prevent the cell wall synthesis.synthesis.

(Peptidoglycan cell wall)

N-acetylglucosamine

N-acetylmuramic acid

Transpeptidase locatedwithin the cell membraneare responsible for cross linking thePeptidoglycon chains

Transpeptidases(Penicillin Binding Proteins)

In order to make the rigid grid, There is an enzyme called Transpeptidase, which connects the Little peptide strings perpendicular to the NAM and NAG chains.

Cell membranePBP’S (or) transpeptidase help to build Or construct maintain the peptidoglyconLayer.

Cross-linking of bacterial cell walls inhibited by penicillin

Sugars contained in the cell wall structure of bacteria. Sugars contained in the cell wall structure of bacteria. N-acetylglucosamine (NAG)N-acetylglucosamine (NAG) N- acetylmuramic acid (NAM)N- acetylmuramic acid (NAM)

PEPTIDOGLYCAN STRUCTURE OF BACTERIAL CELL WALLS

Mechanisms of transpeptidase crosslinking and penicillin inhibition.

Microbial resistance to Microbial resistance to ββ-lactam antibiotics -lactam antibiotics like penicillins, cephalosporins occurs like penicillins, cephalosporins occurs mainly mainly due to the production of an enzyme known as due to the production of an enzyme known as ββ-lactamases.-lactamases.

ββ-lactamases act by breaking the -lactamases act by breaking the ββ-lactam ring by catalyzing the hydrolysis of -lactam ring by catalyzing the hydrolysis of ββ--lactum ringlactum ring, which results in the loss of antibacterial property of antibiotics. Thus , which results in the loss of antibacterial property of antibiotics. Thus micro-organisms exhibit resistance.micro-organisms exhibit resistance.

ββ-lactamase inhibitors are -lactamase inhibitors are ββ-lactam structures that have negligible antibacterial -lactam structures that have negligible antibacterial activity but inhibit activity but inhibit ββ-lactamases-lactamases..

They can be administered along with penicillins They can be administered along with penicillins to protect them from to protect them from ββ-lactamases -lactamases and broaden(increase) their spectrum of activityand broaden(increase) their spectrum of activity..

ββ-lactamase inhibitors such as -lactamase inhibitors such as Clavulanic acid, Sulbactam, Tazobactum act as Clavulanic acid, Sulbactam, Tazobactum act as suicide substrates for suicide substrates for ββ-lactamase enzymes.-lactamase enzymes.

Suicide substrates are agents which are converted to highly reactive species when Suicide substrates are agents which are converted to highly reactive species when they ungergo an enzyme-catalyzed reaction. They form they ungergo an enzyme-catalyzed reaction. They form covalent bonds to the covalent bonds to the enzyme and inhibit irreversiblyenzyme and inhibit irreversibly..

The agents Clavalunic acid, sulbactam and tazobactam have also been developed as

β-lactamase inhibitors.

Sulbactum + ampicillin = unasyn.

Amoxycillin + Clavulanic acid = Clavulin

Ticarcillin + Clavulanic acid = Timentin

Piperacillin + Tazobactam = Tazocin

Allow the “real” drug to get through to bind to the PBP’s

Regain gram negative spectrum of activity otherwise lost dueto β-lactamase production

Clavulanic acid:Clavulanic acid: clavalunic acid was isolated from streptomyces clavuligerus by clavalunic acid was isolated from streptomyces clavuligerus by

Bechams in 1976.Bechams in 1976. It has weak and unimportant antibiotic activity, but it is powerful and It has weak and unimportant antibiotic activity, but it is powerful and

irreversible inhibitor of most β-lactamases and as such it is now usedirreversible inhibitor of most β-lactamases and as such it is now used in combination with penicillins such as amoxicillinin combination with penicillins such as amoxicillin( Augmentin)( Augmentin) The structure of clavulanic acid was the first example of a naturally The structure of clavulanic acid was the first example of a naturally

occuring β-lactam ring that was not fused to a sulfur-containing ring. occuring β-lactam ring that was not fused to a sulfur-containing ring. It is fused instead to an oxazolidine ring structure.It is fused instead to an oxazolidine ring structure. ESSENTIAL REQUIREMENTS FOR ESSENTIAL REQUIREMENTS FOR ββ-lactamase inhibition are:-lactamase inhibition are: Strained Strained ββ-lactam ring.-lactam ring. Enol ether.Enol ether. The double bond of the enol ether has the Z configuration(Activity is reducedThe double bond of the enol ether has the Z configuration(Activity is reduced but not eliminated if the double bond is E)but not eliminated if the double bond is E) No substitution at C-6No substitution at C-6 R- Stereochemistry at positions 2 and 5. R- Stereochemistry at positions 2 and 5. Carboxylic acid group.Carboxylic acid group.

Resistance to the B-lactam Antibiotics

1. Differences in PBP’s- Decreased affinity of the PBP for the binding of the Abx- Increased production / concentration of PBP’s produced

2. B-lactamase production- Spectrum of activity of various B-lactamases- Concentration of B-lactamases produced

3. Decreased ability to penetrate to the PBP target- Primarily due to the LPS layer of gram –ve bacteria

Penicillin’s may be used to treat infections such as urinary tract infections.Penicillin’s may be used to treat infections such as urinary tract infections. Septicaemia, meningitis, intra-abdominal infection, respiratory infections, ear, Septicaemia, meningitis, intra-abdominal infection, respiratory infections, ear,

nose and throat infections.nose and throat infections. Skin and Soft tissue infections. Examples of infectious micro organisms (bacteria) Skin and Soft tissue infections. Examples of infectious micro organisms (bacteria)

that may respond to penicillin therapy include that may respond to penicillin therapy include * Streptococcal infections* Streptococcal infections

* Pneumococcal infections* Pneumococcal infections* Meningococcal infections* Meningococcal infections* Gonorrhoea* Gonorrhoea* Syphilis* Syphilis* Diphtheria* Diphtheria* Tetanus and gas gangrene* Tetanus and gas gangrene DRUG OF CHOICE for *Anaerobic anthrax* DRUG OF CHOICE for *Anaerobic anthrax** Actinomycosis* Actinomycosis* Trench mouth* Trench mouth* Rat bite fever* Rat bite fever* Listeria monocytogenes* Listeria monocytogenes* Pasteurella multocida * Pasteurella multocida

Penicillins are available only with a prescription. Penicillin’s are useful against Penicillins are available only with a prescription. Penicillin’s are useful against infections in many parts of the body, including the mouth and throat, skin and infections in many parts of the body, including the mouth and throat, skin and soft tissue, tonsils, heart, lungs, and ears. For example, dentists often prescribe soft tissue, tonsils, heart, lungs, and ears. For example, dentists often prescribe penicillin to prevent infections after dental surgery. penicillin to prevent infections after dental surgery.

Biosynthetic penicillins are important in chemotherapy. They are used in Biosynthetic penicillins are important in chemotherapy. They are used in treating streptococcal sore throat, tonsillitis, pneumococcal pneumonia, treating streptococcal sore throat, tonsillitis, pneumococcal pneumonia, endocardities caused by some streptococci, syphilis, gonorrhoea, meningococcal endocardities caused by some streptococci, syphilis, gonorrhoea, meningococcal infections and infections that are caused by some anaerobic organisms.infections and infections that are caused by some anaerobic organisms.

The drug Augmentin, for example, contains a combination of The drug Augmentin, for example, contains a combination of amoxicillin(500mg) and a β-lactamase inhibitor, clavulanic acid (125mg) amoxicillin(500mg) and a β-lactamase inhibitor, clavulanic acid (125mg) used used in the treatment of Feverish patients with neutropenia from cancer in the treatment of Feverish patients with neutropenia from cancer chemotherapy. chemotherapy. It is also useful in treating the sinusitis. Animal/human It is also useful in treating the sinusitis. Animal/human bite wounds, otitis media in children.bite wounds, otitis media in children.

There are several types of penicillins, each used to treat different kinds of There are several types of penicillins, each used to treat different kinds of infections.infections.

These drugs will not work for, flu, and other infections caused by viruses.These drugs will not work for, flu, and other infections caused by viruses.

Adverse/toxic effects of penicillins:- Although most penicillins are safe for the majority of people, some people

may experience side effects. Once an individual is allergic to one penicillin, he or she is most likely allergic to all of the penicillins.

The most serious allergic reaction is anaphylaxis that can be fatal which is not treated properly.

a severe allergic reaction that can cause skin rash, itching, difficulty breathing, a severe allergic reaction that can cause skin rash, itching, difficulty breathing, shock, and unconsciousness.shock, and unconsciousness.

An early sign of anaphylaxis is a feeling of warmth and flushing. If any of An early sign of anaphylaxis is a feeling of warmth and flushing. If any of these occurs, the medicine should be stopped and emergency help sought these occurs, the medicine should be stopped and emergency help sought immediately.immediately.

Anaphylactic shock occurs more frequently after parenteral administration but Anaphylactic shock occurs more frequently after parenteral administration but can occur with oral use.can occur with oral use.

After 7 days this allergy occurred her after penicillin has been taken for throat Infection. That is Late hypersensityvity.

Nausea

Headache

Vomiting

Giddiness

Diarrhoea

Angioedema

Bronchospasm

Skin rashes

COMMON SIDE EFFECTS OF PENICILLINS

Less common side effects of penicillins are 1. Nausea 2. Diziness 3. Head ache 4. skin rashes 5. Bronchospasm 6. vasculitis 7.

inflammation of blood vessels 8. constriction of the airways of the lungs 9. fever 10. Angioedema or swelling of lips, face and tongue.

Other most common side effects are mild diarrhoea, vomiting, headache, vaginal itching and discharge, sore mouth or tongue, or white patches in the mouth or on the tongue. These problems usually go away as the body adjusts to the drug and do not require medical treatment unless they continue or they are bothersome.

Occasionally, certain types of penicillin may cause the tongue to darken or discolour. This condition is temporary and will go away when the medicine is stopped.

Effect on GITEffect on GIT: Broad spectrum penicillins like Ampicillin, when administered orally, : Broad spectrum penicillins like Ampicillin, when administered orally, alters the bacterial flora in the intestines and leads to GIT disturbances like diarrhoea .alters the bacterial flora in the intestines and leads to GIT disturbances like diarrhoea .

On rare occasions some types of penicillin may cause severe abdominal or stomach On rare occasions some types of penicillin may cause severe abdominal or stomach cramps, pain, or bloating or severe or bloody diarrhoea. Other rare side effects include cramps, pain, or bloating or severe or bloody diarrhoea. Other rare side effects include fever, increased thirst, severe nausea or vomiting, unusual tiredness or weakness, fever, increased thirst, severe nausea or vomiting, unusual tiredness or weakness, weight loss, seizures, or unusual bleeding or bruising .weight loss, seizures, or unusual bleeding or bruising .

Over dosage/Acute ToxicityOver dosage/Acute Toxicity - Acute oral penicillin overdoses are unlikely to cause - Acute oral penicillin overdoses are unlikely to cause significant problems other than GI distress, but other effects are possible .In humans, significant problems other than GI distress, but other effects are possible .In humans, very high dosages of parenteral penicillin’s, especially in patients with renal disease, very high dosages of parenteral penicillin’s, especially in patients with renal disease, have induced CNS effects.have induced CNS effects.

Hypersensitivity or allergic reactions : Hypersensitivity to penicillin’s is caused by the degradation

products of penicillins. The degradation products of penicilloic acid, sodium benzyl penicilloate (of β-lactum ring) binds ie combines to serum proteins initiating an IgE and initiates the IgE mediated inflammatory reactions

It occurs in about 5-8% of the patients and according to estimation, 300-500 people have been dieing each year form penicillin induced anaphylaxis.

Hypersensitivity reactions are classified into A) Immediate Hypersensitivity b) Accelerated Hypersensitivity C) Late Hypersensitivity

A)A) Immediate hypersensitivity Immediate hypersensitivity: : -- This occurs This occurs within 20 minwithin 20 min. of parenteral . of parenteral administration of penicillin and is characterized by the prurities, skin administration of penicillin and is characterized by the prurities, skin rashes, wheezing, rhinitis, sneezing.rashes, wheezing, rhinitis, sneezing.

These reactions are transformed in to anaphylaxis (extreme from of These reactions are transformed in to anaphylaxis (extreme from of immediate hypersensitivity reaction) that it is characterised by hypotensive immediate hypersensitivity reaction) that it is characterised by hypotensive shock, angioneurotic oedema, choking, loss of consciousness and finally shock, angioneurotic oedema, choking, loss of consciousness and finally death.death.

Serious anaphylaxis reactions require immediate emergency treatment with Serious anaphylaxis reactions require immediate emergency treatment with ephedrine, oxygen, IV steroids and airway management, including ephedrine, oxygen, IV steroids and airway management, including intubations should also be administered as indicated.intubations should also be administered as indicated.

B)B) Accelerated Hypersensitivity Accelerated Hypersensitivity: : - It occurs - It occurs within few hourswithin few hours after after penicillin has been administered. Accelerated hypersensitivity reactions are penicillin has been administered. Accelerated hypersensitivity reactions are characterized by skin rashes, fever, urticaria, angioneurotic oedema. Death characterized by skin rashes, fever, urticaria, angioneurotic oedema. Death is a rare consequence.is a rare consequence.

c) c) Late HypersensitivityLate Hypersensitivity:: It occurs It occurs after 72 hoursafter 72 hours after penicillin has after penicillin has been administered. This reaction is mediated by IgE and IgM antibodies been administered. This reaction is mediated by IgE and IgM antibodies and manifested by and manifested by utricaria, skin rashes similar to measles, local utricaria, skin rashes similar to measles, local inflammation, serum sickness and coomb’s positive haemolytic anaemiainflammation, serum sickness and coomb’s positive haemolytic anaemia

Penicillin's advantages and disadvantagesPenicillin's advantages and disadvantages Penicillin's disadvantagesPenicillin's disadvantages:: Acid liability - most of these drugs are destroyed by gastric acid.Acid liability - most of these drugs are destroyed by gastric acid. Short duration of action - because of this short half-life, the penicillin's must be at short Short duration of action - because of this short half-life, the penicillin's must be at short

intervals, usually every 4 hours.intervals, usually every 4 hours. Lack of activity against most gram-negative organisms.Lack of activity against most gram-negative organisms. Drug hypersensitivity - about 10 % of population has allergy.Drug hypersensitivity - about 10 % of population has allergy. Many patients experience GI upset.Many patients experience GI upset. Painful if given intramuscularly.Painful if given intramuscularly.

penicillin's advantagespenicillin's advantages:: Bactericidal against sensitive strains.Bactericidal against sensitive strains. Relatively nontoxic.Relatively nontoxic. Have excellent tissue penetration.Have excellent tissue penetration. Efficacious in the treatment of infections.Efficacious in the treatment of infections. Relatively inexpensive in comparison with other antibiotics. Relatively inexpensive in comparison with other antibiotics. Newer penicillin's are resistant to stomach acid, such as penicillin v, or have a broader Newer penicillin's are resistant to stomach acid, such as penicillin v, or have a broader

spectrum, such as Ampicillin and Amoxicillin.spectrum, such as Ampicillin and Amoxicillin.

Key pointsKey points

Penicillins have a Penicillins have a bicyclic structurebicyclic structure consisting of a consisting of a ββ-lactam ring fused to a Thiazolidine ring.-lactam ring fused to a Thiazolidine ring.

The strained The strained ββ-lactam ring reacts irreversibly with the transpeptidase enzyme responsible for -lactam ring reacts irreversibly with the transpeptidase enzyme responsible for the final cross-linking of the bacterial cell wall.the final cross-linking of the bacterial cell wall.

Penicillin can be made more resistant to acid conditions by incorporating an Penicillin can be made more resistant to acid conditions by incorporating an electronelectron withdrawing groupwithdrawing group into the acyl side chain. into the acyl side chain.

Stereic shieldStereic shield can be added to penicillins to protect them from bacterial can be added to penicillins to protect them from bacterial ββ-lactamase enzymes.-lactamase enzymes.

Broad spectrum activityBroad spectrum activity is associated with the presence of an is associated with the presence of an αα-hydrophilic group on the acyl -hydrophilic group on the acyl side chain of penicillins.side chain of penicillins.

Prof. Panchumarthy Ravisankar