LECTURE 2

Nomenclature:Every drug has three names:

1) Chemical Name:

The drug is named according to its

chemical structure.

2) Generic name (common name):

Non proprietary name is assigned to the

drug to be easy to remember.

It should reflect some important pharmacologic

or chemical characteristics of the drugs.

3) Brand name (trade name):

Proprietary name is privately owned by the

manufacturer to distinguish certain drug

product from the other.

The name may have an indication to its

therapeutic use or the name of the

manufacture.

e.g. AspirinChemical name:Acetyl salicylic acidGeneric name:AspirinBrand name:RivoAspocidJuspirinAlexoprin

e.g. AcetaminophenChemical name:N-acetyl-p-amino phenolGeneric name:Acetaminophen (USP) or Paracetamol (BP)Brand name:AbimolParamolPanadol

e.g. KetoprofenChemical name2-(3-benzoylphenyl)propanoic acidGeneric name:KetoprofenBrand name:KetofanAlcofanProfenid

PharmacodynamicsHow do drugs act?

Drugs can produce their effects through one or more of the following mechanisms.

1) Drug-receptor interactions: The cells in certain tissue contain

structures called receptors. Receptors are macromolecules

component of the cell that bind the drug to produce a response.

Receptors are located at cell membranes or in the cell nucleus.

The drug is thought to fit onto a receptor like a key fits a lock.

The ability of the drug to bind to the receptor depends on the bond formed between the drug and the receptor.

[D] + [R] [DR] Response

Agonist:

A drug which can bind to

a receptor to produce a

response.

Antagonist:

A drug which bind to

receptor and produce no

effect (compete with the

agonist and inhibit its

effect).

2) Antimetabolites/cytotoxic:

Drug act by impairing cell reproduction.

This means that the affected cells may

remain alive and may continue to carry

out many of their functions, but are

unable to reproduce successfully, leading

to cell death (Methotrxate,

Cyclophosphamide).

The drug may resemble substances which are

used by the cells for nutrition and when

absorbed, the cells can not used them and so

failed to multiply.

The sulphonamides which are used to stop the

multiplication of bacteria are good example.

They are very similar in structure to para-

aminobenzoic acid and certain bacteria can not

distinguish between them and absorb the

sulphonamides and stop generation.

3) Action on enzymes:

Enzymes are substances which speed up

many chemical processes within the body.

Drugs may produce their effects through

inhibition or stimulation of certain enzymes.

Sulphonamides are used as antibacterial

agents as they inhibit folate synthase

enzyme so decrease the synthesis of folic

acid by bacteria death

4) Action on cell membrane:

The action of nerves and muscles

depends on ions passing across the

membranes surrounding these cells.

Certain drugs interfere with the

movement of these ions and thus prevent

nerve or muscle function (local

anaesthetics).

5) Chelating agents:

Adsorb drugs, electrolytes or biological

substances in the intestine to form non-

absorbable complex that is excreted in the

feces (Cholestyramine).

Activated charcoal is used as a non-specific

antidote in treatment of poisoning as it

adsorbs poisons on its surface and inhibit

their absorption from the GIT.

Pharmacokinetics

I. Drug Absorption

II. Drug Distribution

III.Drug Metabolism

IV. Drug Excretion

These factors

determine the drug

dose and frequency

of administration

I. Drug AbsorptionAbsorption is the transport of drug from the site of administration to the blood stream.Drugs must be librated and dissolved before it can be absorbed into systemic circulation.Absorption involves the passage of the drug across cell membranes.

II. Drug Distribution After the drug reaches the

blood stream, the drug is

distributed through the body

fluids and tissues.

Drugs exist in two forms: bound

and unbound (free) forms.

The protein-bound drug is

inactive and not subjected to

metabolism or excretion.

The binding capacity of plasma protein is limited.

Once saturation has been reached, a small increase in drug dose increase in free drug concentration pharmacological activity.

Competition of drugs for binding to plasma protein serious drug interactions.

Aspirin + Warfarin

Aspirin displaces warfarin from plasma protein

bleeding.