SEPTEMBER 1998

NUMBER ONE

P450 Metabolism
Managing Drug Interactions

Today, there are several updated p450 pharmacology charts on the Internet to help health providers assess potential drug interactions. The following chart tells you what p450 liver pathway is used by a given drug. If two drugs use the same pathway, they could affect one another. In general, a P450 substrate is any drug that uses the cytochrome p450 enzyme pathway. P450 inhibitors (INH) generally increase concentrations of other drugs. P450 inducers (IND) generally decrease concentrations of other drugs. P450 enzymes are classified using Roman numerals and letters. Almost half of all human drugs use p450 3A4; another 30 percent use p450 2D6.

On the Web
Regularly updated p450 drug-interaction sites include the American College of Clinical Pharmacology (www.accp.com/p450.html), Georgetown Medical Center (www.dml.georgetown.edu/depts/pharmacology/davetab.html), and San Francisco General Hospital (insite.ucsf.edu). There are also excellent practical guides for managing HIV drug interactions at the Health Care Communications Group website (www.healthcg.com/hiv/treatment/interactions), and Project Inform (www.projinf.org).

Tip: Discuss possible drug interactions with your doctor before taking any new drug. Read the package insert for a drug to find out if it's cytochrome p450 metabolized, or ask a pharmacist for help.

Updated as of June 20, 1998 (extrapolated from clinical pharmacology p450 tables: ACCP, Georgetown, Healthcare Communications Group, etc. See "When Drugs Fail").