Serious adverse interactions between drugs continue to be reported.1 Many of these are due to inhibition or induction of cytochrome P450 (CYP) enzymes, particularly CYP3A4. CYP3A is thought to be involved in the metabolism of more than 50 percent of currently prescribed drugs.2 CYP3A4, which is more abundantly expressed than CYP3A5, accounts for most CYP3A activity in vivo.

TESTING —The FDA has established standards for in vitro testing of new drugs to predict CYP-related interactions.3 Liver microsomes and CYP3A-overexpressing cells can be used to assess metabolism by and inhibition or induction of CYP3A. In addition to in vitro testing, targeted clinical drug interaction studies in healthy volunteers may be required.

CYP3A — The clinical consequences of altering any pathway of drug elimination depend ... more      

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