Antimicrobial Agents(General Considerations)

Prof. R. K. DixitPharmacology and Therapeutics

K.G.M.U. Lucknowdixitkumarrakesh@gmail.com

Objectives• After this lecture you will be able to answer

– What are antimicrobials, antibiotics, chemotherapeutic agents (Terminologies used in antimicrobial treatment)

– Classification of antimicrobials • Chemicals• Mechanism• Spectrum

– Mechanisms of action of antimicrobials– Resistance development in antimicrobials– Multidrug resistant microorganisms

A naturopath tells “One should never take antibiotics

Except in Pneumonia, a kidney infection, boils, meningitis, encephalitis, osteomyelitis, occular infections, or other serious illness………………………………………………….”

Allopath is Lucky to have the help of Antimicrobials

But This Luck may not last long due to reasons……– Inappropriate use,… Overuse…..– Antimicrobial resistance– Reduced immunity and worsening of environment – patients having co morbid illnesses like diabetes,

malnutrition………………..– Less interest of pharmaceuticals in this field– Costly new antimicrobials

Antimicrobials , Antimicrobials , Antimicrobials , Antimicrobials, Antimicrobials , Antimicrobials

Antimicrobials!!!

Penicillin, ampicillin, amoxycillin, ticarcillin, piperacillin, flucloxacillin, dicloxacillin, oxacillin, methicillin, nafcillin, carbenicillin, eryhtromycin, clindamycin, roxythromycin clarithromycin, tetracycline, doxycycline, minocycline, vancomycin, teicoplanin, augmentin, gentamicin, tobramycin, amikacin, streptomycin, azithromycin, aztreonam, cephalexin, cefotaxime, cephamandole, cefepime, ceftriaxone, ceftazidime, cefpirome, imipenem, chloramphenicol, cotrimoxazole, ciprofloxacin, norfloxacin, trimethoprim,……. ………………………………………………………………………………………………………………………………………………….. hundreds of different antimicrobial agents on the market.

TerminologyTerminology

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Chemotherapy –

Use of drugs to treat infections and malignancy. (Antimicrobials and Antineoplastic agents)

Pharmacodynamic agents-

Drugs regulating physiological process of body and act on the body cells.

Chemotherapeutic agents-

Selectively acting against microbes or malignant cells. (Don’t touch body cells)

Antimicrobials –

Used in treating infectious diseases.

Antibiotics –

Produced from microbes to inhibit or kill other microbes. (Antimicrobials from microbes)

All antibiotics are antimicrobials but all antimicrobials are not antibiotics

Bacteriostatic- Stop the growth of bacteria

Bactericidal- Kill the bacteria

PAE- Post antibiotic effect

Minimum Inhibitory Concentration (MIC)- Which stops the growth

Minimum Bactericidal Concentration (MBC)- Which kills by 99.99%

(Bactericidal -less value of MBC-MIC, Bacteriostatic - more value of MBC-MIC)

• Prebiotics- – Stimulate the growth of intestinal commensals and

prevent multiplication and establishment of pathogenic bacteria.

– Lactulose, Lactitol, Inulin• Probiotics-

– Live microbial substances used as supplements to maintain or improve the intestinal bacterial flora.

– Lactobacilli and Bifidobacteria

Gram positive & Gram Negative

• Gram positive bacteria have – thick cell wall– Peptidoglycan directly accessible from environment

• Gram negative bacteria have – Thin cell wall– Surrounded by inner and outer membrane– Of lipopolysaccharide, phospholipids, and proteins– Outer membrane is a barrier to diffusion of antibiotics

• Limited antibiotics may diffuse through porins

Historical Perspectives• Chenopodium-

– for intestinal worms• Mouldy curd –

– for boils• Chaulmoogra oil-

– for Leprosy• Mercury –

– for Syphilis• Cinchona Bark-

– for Malaria

Historical perspectives• Pasteur- (1877)

– Phenomenon of antibiosis• Paul Ehrlich- (1906)

– Father of Chemotherapy, Coined term chemotherapy• Domagk- (1935)

– Discovery of sulfonamides (Prontosil to sulphanilamide)• Fleming, Chain, Florey-

– Penicillin (1929, 39, 41) from penicillium• Waksman-

– Streptomycin, from actinomycetes, – Coined term antibiotic

Introduction of Class of antimicrobial agents (SPECTM)• 1935 - Sulphonamides• 1941 - Penicillins• 1944 - Aminoglycosides• 1945 - Cephalosporins• 1949 - Chloramphenicol• 1950 - Tetracyclines• 1952 - Macrolides• 1956 - Glycopeptides• 1957 - Rifamycins• 1959 - Nitroimidazoles• 1962 - Quinolones• 1968 - Trimethoprim• 2000 - Oxazolidinones• 2003 - Lipopeptides

Antimicrobial Classification• Chemical structure• Mechanism of Action• Organism type • Spectrum of activity• Static or Cidal• Origin of antimicrobials

Chemical Classification (Public Loves GOOD Quality BATSMAN)• Polypeptides- Polymyxin, Colistin, Bacitracin• Poyene antibiotics- Nystatin, Amphotericin-B, Hamycin• Lincosamide- Lincomycin, Clindamycin• Glycopeptides- Vancomycin, Teicoplanin• Oxazolidinone- Linezolid• Others-----------------Riampicin, Griseofulvin, etc• Diaminopyrimidines- Trimethoprim, Pyrimethamine• Quinolones- Nalidixic acid, ciprofloxacin• Beta-lactam- Penicillins, Cephalosporins, Monobactams, Carbapenems• Aminoglycosides- Streptomycin, Gentamycin• Tetracyclines- Oxytetracycline, Doxycycline• Sulphonamides- Sulfadiazine, Sulfamethoxazole, • Macrolides- Erythromycin, Clarithromycin• Azoles- Fluconazole, Clotrimazole• Nitroimidazoles- Metronidazole, Tinidazole• Nicotinic acid derivatives- Isoniazide, Pyrizinamide, Ethionamide• Nitrobenzene derivaties- Chloramphenicol• Nitrofuran derivatives- Nitrofurantoin, Furazolidone

Organism affected• Anti-viral• Anti-bacterial• Anti-fungal• Anti-protozoal• Anthelmintic

Sources• Fungi-

– Penicillin– Cephalosporins– Griseofulvin

• Bacteria- – Polymyxin B– Colistin– Bacitracin

• Actinomycetes- – Most common– Aminoglycosides,

Tetracyclines, Chloramphenicol

– Macrolides

Spectrum• Narrow

– Penicillin G– Streptomycin– Erythromycin

• Broad– Tetracycline– Chloramphenicol

• Extended– Ampicillin– Amoxicillin– Most……..

Bacteristatic– Sulfonamides and Trimethoprim– Tetracyclines– Macrolides (Erythromycin)– Chloramphenicol– Ethambutol– Nitrofurantoin

Bactericidal– Cotrimoxazol– Penicillins– Cephalosporins– Aminoglycosides– Vancomycin, Daptomycin – Fluroquinolones (ciprofloxacin)– INH, Rifampicin, Pyrazinamide– Polymixins, Bacitracin– Metronidazole

Spectrum(Narrow, Broad, Extended)

Mechanism of action• Cell Wall synthesis inhibition-

– Beta-lactams, Vancomycin, Cycloserines

• Cell membrane Leakage-– Polypeptides, Polyenes

• Folate Synthesis inhibition-– Sulfonamides, Pyrimethamine, Cotrimaxazole, PAS, Ethambutol

• DNA gyrase and Topoisomerase inhibition- – Fluroquinolones

• RNA polymerase inhibition- – Rifampicin,,

• Protein Synthesis Inhibition- (ATT)– Aminoglycosides, tetracyclines, Chloramphenicol, Macrolides,

Clindamycin, Linezolid

Differences between human cells Vs Bacterial Cells (Makes the antibacterial selective)

• Human cells don’t posses wall – (Peptidoglycans = peptides + sugar)

• Human cell membrane is different – ( Bacteria Contain Hypanoids in place of Sterol)

• Human cells take preformed dihydrofolic acid – (no need of PABA in human)

• Dihydrofolic acid reducatase enzyme is different – (thousand time affinity)

• Topoisomerase II are different– (in bacteria IV, DNA Gyrase)

• DNA dependent RNA polymerase is different• Ribosome 60S subunit (in bacteria 50S)• Ribosome 40S subunit (in bacteria 30S)

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Cell Wall

Beta Lactams

Protein SynthesisChloramphenicol-Macrolides- Erythromycin, Azithromycin etc.

Aminoglycosides. Gentamicin, Amikacin, etc.

• DNA gyrase (Gyrase) belongs to DNA topo-isomerases

• DNA gyrase, referred to simply as gyrase, • DNA gyrase also known as DNA

topoisomerase IV (In bacteria). • In human Topoisomerase II

Quinolones

PABA

Dihydrofolic acid

Tetrahydrofolic acid

Purines and PyrimidinesDNA And RNA

DNA unwinding (DNA gyrase)

Threads sepeartion (Topoisomerase IV)

DNA dependent RNA Polymerase

tRNA +Amino Acids

Ribosome unit (50S)

Ribosome unit (30S)Protein Synthesis

Dihydro-folic acid Synthetase

Dihydro-folic acid reductase

DNA multiplication

mRNA

Sulphonamides (PABA analogue and inhibitor of DHFAS)

Trimethoprim and Pyrimethamine (inhibitor of DHFAR)

Quinolones (Inhibitor of DNA gyrase and Topoisomerase IV)

Rifampicin (inhibitor of DNA dependant RNA Polymerase)

Chloramphenicol, Macrolides (50S)

Aminoglycosides, Tetracyclines (30S)

DNA unwinding (DNA gyrase)

Threads sepeartion (Topoisomerase IV)

PABA

Dihydrofolic acid

Tetrahydrofolic acid

Purines and PyrimidinesDNA And RNA

Dihydro-folic acid Synthetase

Dihydro-folic acid reductase

RNA Polymerase

tRNA +Amino Acids

Ribosome unit (50S)

Ribosome unit (30S)Protein SynthesismRNA

Sulphonamides (PABA analogue and inhibitor of DHFAS)

Trimethoprim and Pyrimethamine (inhibitor of DHFAR)

Quinolones (Inhibitor of DNA gyrase and Topoisomerase IV)

Rifampicin (inhibitor of DNA dependant RNA Polymerase)

Chloramphenicol, Macrolides (50S)

Aminoglycosides, Tetracyclines (30S)

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Cell Wall synthesis inhibition- Beta-lactams, Vancomycin, Cycloserines

Cell membrane Leakage- Polypeptides, Polyenes

PABA

Dihydrofolic acid

Tetrahydrofolic acid

Purines and PyrimidinesDNA And RNADNA unwinding (DNA gyrase)

Threads sepeartion (Topoisomerase IV)

RNA Polymerase

mRNAtRNA + Amino Acids

Ribosome unit (50S)Ribosome unit (30S)

Protein Synthesis

Dihydro-folic acid Synthetase

Dihydro-folic acid reductase

DNA multiplication

Sulphonamides (PABA analogue and inhibitor of DHFAS)

Trimethoprim and Pyrimethamine (inhibitor of DHFAR)

Quinolones (Inhibitor of DNA gyrase and Topoisomerase IV)

Rifampicin (inhibitor of RNA Polymerase)

Chloramphenicol, Macrolides (50S)

Aminoglycosides, Tetracyclines (30S)

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ANTIBIOTICSDose-dependent (With PAE) Time-dependent

Antibacterial effect directly depends on their concentrations in the locus of infection (high doses 1-2 times/24h)

•Aminoglycosides •Fluoroqinolones•Metronidazol•Amphotericin B

Effectiveness depends on a period of time, during which concentration in blood overwhelms MIC for a particular causative agent(constant i.v. infusion or 3-6 times/24h)

•Beta-lactames•Glycopeptides•Macrolides•Tetracyclines•Vancomycin

Post-Antibiotic Effect• The capacity to inhibit the growth of bacteria

after removal of the drug from the culture (body)

• Provides additional time for the immune system to remove bacteria that might have survived antibiotic treatment before they can eventually regrow after removal of the drug.

• Cell mebrane – Polypeptides and Polyenes– Polymyxin, Colistin, Bacitracin, Nystatin, Amphotericin-B, Hamycin

• Cell Wall synthesis by acting on cross linking– Penicillins, Cephalosporins, Monobactams, Carbapenems, Vancomycin, Teicoplanin,

• Cell wall synthesis by acting on inhibition of mycolic acid (Long Fatty acid present in mycobacterial family)

– Isoniazide, Pyrizinamide, Ethambutol• Interfering with folic acid metabolism

– Sulphonamides- Sulfamethoxazole, Sulfadoxine, – Diaminopyrimidines- Trimethoprim, Pyrimethamine

• DNA gyrase and topoisomerase IV inhibitors– Quinolones- Nalidixic acid, ciprofloxacin, Ofloxacin, Pfloxacin, Gatifloxacin, Sparfloxacin

• Inhibition of DNA dependeant RNA Polymerase– Rifampicin,

• Acting on 50S ribosome– Macrolides- Erythromycin, Clarithromycin, Azithromycin, Roxithromycin, – Chloramphenicol, Lincomycin, Clindamycin, Linezolid

• Acting on 30 S ribosome– Aminoglycosides- Streptomycin, Gentamycin, Kanamycin, Amikacin, Tobramycin– Tetracyclines- Oxytetracycline, Doxycycline

Antibacterial - Co-trimoxazoleAntimalarial- Co-trimazine

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Mechanisms Of Resistance ResistanceIntrinsic Acquired

Mutation Transferred

Conjugation Transformation Transduction

Not Dangerous/less clinical importance

Dangerous/clinical importance

Inherent Resistance(Not Much of clinical importance)

• Bacteria naturally resistant – e.g., Gram-negative bacteria resistant to penicillins– Genes transferred to the bacterial progeny.

• Bacteria may be resistant because – No mechanism to transport the drug into the cell. – Do not contain antibiotic’s target process or protein.

Acquired Resistance• Due to exposure of antimicrobials• Horizontal evolution:

– Resistance genes pass from resistant to nonresistant strain,

– Antibiotics- a selective pressure.– Gene transfer mechanisms:

• Conjugation.• Transduction.• Transformation.

Cellular Resistance

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• • ATTACK OF THE SUPERBUGS:

ANTIBIOTIC RESISTANCE By Grace Yim, Science Creative Quarterly.

Jan 07

Mechanisms of Resistance• Enzyme-based resistance–

– Break down of antimicrobials.

• Ribosomal modifications–– Methylation of ribosome interferes with antibiotic binding.

• Protein modifications–– Mutations leave target protein unrecognizable to antibiotic

• Metabolic resistance–– Overcome competitive inhibition by alternate pathway.

• Efflux–– Pumps antimicrobials out.

Resistance to Antibiotics

Resistance in some antibiotics• Beta-lactams: - Hydrolysis , mutant PBP• Tetracycline: - Active efflux from the cell• Aminoglycosides- Inactivation by enzymes• Sulfonamides- Alternate pathway, • Fluoroquinolones- Mutant DNA gyrase• Chloramphenicol- Reduced uptake into cell • Macrolides - RNA methylation, drug efflux

Factors favoring Resistance•Prescription related factors:•Overuse•Early discontinuation•Over continuation•Less dose, duration

•Livestock doping:•Animals exposure

Superbugs (Microorganisms with multiple resistance)

• MRSA - Methicillin-resistant Staphylococcus aureus• VISA - Vancomycin intermediate resistant Staphylococcі• VRE - Vancomycin-resistant enterococci• ESBLs - Extended-spectrum beta-lactamases

(microorganisms – resistant to cephalosporins and monobactams)

• PRSP - Penicillin-resistant Streptococcus pneumoniae• MRPA (MDR-PA)- Multidrug resistant Pseudomonas

aeruginosa• MRAB (MDR-AB) - Multidrug resistant Acinetobacter

baumannii

Why worry?n MDRO are dangerous

– Difficult to treat– More virulent– Increase mortality and morbidity

n Resource-intensive – More expensive and toxic antibiotics– Increase length of hospitalization– Increase demand for isolation-facilities

Thanks