Drug Metabolism

A- Sequential metabolism: A drug can be metabolized to a metabolite which is further metabolized to a second metabolite.
Each metabolic pathway has its own rate constant.

Drug:

Oxidation

Metabolite-1

Conjugation

Metabolite-2

Example:

Phenytoin
(PPH)

Oxidation

Other metabolites

p-hydroxy-PPH
(p-HPPH)

Conjugation

p-HPPH-glucuronide

B- Parallel metabolism: A drug can be metabolized to several metabolites simultaneously. Each metabolic pathway has its own rate constant.

Drug

km1

Metabolite-1

km2

Metabolite-2

Example:

Aspirin

Hydrolysis

Salicylic acid

gentisuric acid

Conjugation

other metabolites

gentisic acid

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