John R. Horn, PharmD, FCCP

The last in the series of cytochrome P450 enzyme articles ends with the most important enzyme-CYP3A4, which metabolizes approximately half of all the drugs on the market.

The level at which prescribers accurately identify and manage drug?drug interactions has recently been debated. Pharmacists are in a key position to help avoid common drug?drug interactions.

The enzyme CYP2D6 affects the metabolism of many drugs, and its effect is altered by genetic variability.

Genetic variations can impact warfarin metabolism.

Drugs metabolized by CYP2C19 often have other pathways. An individual's genetic makeup may alter the activity of CYP2C19; it also is involved in important drug interactions.

By careful monitoring of patients who are prescribed clopidogrel, drugs likely to reduce its effectiveness can be avoided.

An in-depth look at CYP2C9, an enzyme involved in many clinically important drug interactions.

Awareness prevents complex drug interaction with carbamazepine.

Pharmacists have a key role to play in educating patients about the risk of stopping certain medications.

Pharmacists are an important source of drug interaction information for patients wishing to use complementary and alternative medications. In addition to discussing the possible benefits, the pharmacist can carefully evaluate the patient's medical record for potential interactions.

This enzyme is increasingly involved in drug interactions as new medications metabolized by it are released.