CYTOCHROME P450 - An important group of isoenzymes in the liver that metabolize many medications used clinically. Inhibition or induction (stimulation) of the cytochrome P450 isoenzymes is a relatively common mechanism be which clinically important drug interactions occur. Drugs that induce the cytochrome P450 system can enhance the metabolism (and clearance) of other drugs that are metabolized by the same pathway. In some cases this can limit their clinical effectiveness. Alternatively, those drugs which inhibit cytochrome P450 system of isoenzymes can interfere with the breakdown of medications normally metabolized via this pathway. In this case, drug toxicity may result. Some drugs (e.g. tacrine, omeprazole) can both inhibit and induce cytochrome P450 isoenzymes. See cytochrome P450 inducers and cytochrome P450 inhibitors for additional information.