CYP

Abbreviation for cytochrome P450 enzymes; usually followed by an arabic numeral, a letter, and another arabic numeral ( e.g., C. 2D6). These enzymes are found in and on the smooth endoplasmic reticulum of liver and other cells and are responsible for a large number of drug biotransformation reactions.

- C. 1A2 microsomal enzyme, the substrates of which include theophylline, antidepressants, and tacrine. It is inhibited by grapefruit juice and quinolones, and induced by smoking, phenobarbital, phenytoin, rifampin, and omeprazole.

- C. 2C9 microsomal enzyme responsible for the oxidation of S-warfarin, phenytoin, and numerous NSAIDs. Inhibitors include azole antifungals ( e.g., ketoconazole, itraconazole, metronidazole); induced by rifampin.

- C. 2C19 microsomal enzyme partially responsible for the oxidation of clomipramine, diazepam, propranolol, imipramine, and omeprazole. Inhibited by fluoxetine, sertraline, omeprazole, and ritinovir.

- C. 2D6 the isoenzyme that metabolizes many antidepressants, antipsychotic agents, beta adrenergic blockers, and codeine. It is inhibited by cimetidine and several antidepressants and antipsychotics.

- C. 2E1 microsomal enzyme that participates in the oxidation of ethanol and acetaminophen. Inhibited by disulfiram and induced by ethanol and isoniazid (INH). Believed to be responsible for the hepatotoxic metabolite of acetaminophen.

- C. 3A a cytochrome P450 isoform found in the gastrointestinal tract as well as hepatic and other cells; substrates include benzodiazepines, calcium channel blockers, antihistamines, steroid hormones, and protease inhibitors. Inhibited by antidepressants, azole antifungals, cimetidine, and erythromycin. Induced by phenobarbital, phenytoin, rifampin, and carbamazepine.

* * *

cyclophilin; cyproheptadine; cytochrome P