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PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(

 Because of a faster rate of drug metabolism, the dose of warfarin will need to

be increased.

 If the patient should for some reason discontinue the barbiturates, the blood level
of warfarin will rise, perhaps leading to a bleeding disorder.

Examples:

✓ Phenobarbitone,
✓ Phenytoin,
✓ Carbamazepine,

✓ Griseofulvin,
✓ Testosterone,
✓ Tobacco smoking, ethyl alcohol (chronic).

• Importance of enzyme induction:

a) It decreases the effect of other drug.

b) Tolerance is sometimes explained by a drug inducing its own metabolism, e.g.

ethyl alcohol, phenobarbitone.

c) Phenobarbitone induces bilirubin conjugation so used in treatment of

hyperbilirubinemia in newborn.

Enzyme Inhibition

 Many compounds (eg, cimetidine) may inhibit the enzymes that metabolize other

drugs in the body.

 An inhibitor may decrease the rate of drug metabolism by several different

mechanisms.

 The inhibitor may combine with a cofactor such as NADPH2 needed for enzyme

activity,

 Interact with the drug or substrate, or interact directly with the enzyme.

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