Enzyme inhibitors

Enzyme inhibitors act mainly in the liver to inhibit the action of the cytochrome P450 enzyme. Inhibition of cytochrome P450 cause decreased metabolism of other drugs. In most cases this causes the drug to stay in the body for longer in its active form, and therefore have increased action. When enzyme inhibitors are taken at the same time as drugs with narrow therapeutic ranges (warfarin, theophylline, phenytoin) this significantly increases the risk of toxicity or adverse effects. The effects of enzyme inhibitors will be seen approximately 2-3 days. Important enzyme inhibitors are listed below:

1. Isoniazid

2. Cimetidine

3. Grapefruit juice

3. Dilsulfuram

4. Sulphonamides

5. Quinolones (Erythromycin and Ciprofloxacin)

6. Fluconazole

7. Sodium Valporate

others include, omeprazole, verapamil, itraconazole, ketoconazole, fluoxetine, allopurinol, metronidazole, clarithromycin.

　

Enzyme inducers

Enzyme inducers have the opposite effect from enzyme inhibitors, they induce enzyme activity in the liver, therefore more active drugs are being changed into their inactive form, this causes a decrease in the action of other medication being taken at the same time. As with enzyme inducers this is particularly important in drugs with low a therapeutic range, e.g Rifampicin may decrease the effectiveness of an anti-epileptic drug, therefore reducing its action and leading to an increase risk of convulsions in the patient.

1. Phenytoin

2. Carbamazepine

3. Rifampicin

4. Griseofulvin