Drugs that may Interact with Protease Inhibitors
via CYP3A Metabolism

The following is a list of medications that may potentially interact with ritonavir therapy via cytochrome P450, specifically CYP3A4 isoenzyme (CYP3A ) metabolism. Clinical trials measuring the magnitude of these potential interactions have not been conducted. Additionally both saquinavir and indinavir are metabolized via CYP3A. The extent of these interactions is unknown at this time. Therefore, it may be appropriate to use therapeutic drug concentration monitoring and/or increased monitoring of therapeutic and adverse effects when concomitantly administering any of the following medications with portease inhibitors, especially for agents with narrow therapeutic margins. Dosage reductions may be required for those medications that are extensiviely metabolized by CYP3A.

Please refer to Norvir™ product labeling information for further details regarding other potential drug interactions via CYP2D6, CYP2C9/19, glucuronidation and other pathways.

Drug Category	Drugs that interact with Protease Inhibitors via CYP3A
Analgesics, Narcotics	alfentanil (Alfenta) fentanyl (Sublimase/Innovar)
Antriarrhythmics	disopyramide (Rythmodan) lidocaine (Xylocaine, others)
Anticoagulant	R-warfarin (Coumadin)
Anticonvulsants	carbamazepine (Tegretol) clonazepam (Klonopin) ethosuximide (Zarontin)
Antihistamine	loratadine (Claritin)
Antidepresants, other	nefazodone (Serzone) setraline (Zoloft) trazodone (Desyrel)
Antiemetics	dronabinol (Marinol) ondansetron (Zofran)
Antimycobacterial	rifampin (Rifadin, others)
Antiparasitics	quinine (various)
Calcium Channel Blockers	amlodipine (Norvasc) diltiazem (Cardizem, Diltiazem) felodipine (Plendil) isradipine (DynaCirc) nicardipine (Cardene) nifedipine (Adalat, Procardia) nimodipine (Nimotop) nisoldipine (Sular) verapamil (Calan, Isoptin)
Cancer Chemotherapeutic Agents	etoposide (VePesid) paclitaxel (Taxol) tamoxifen (Nolvadex, others) vinblastine (Velban) vincristine (Oncovin)
Corticosteriods	dexamethasone (Decadron, others) prednisone (various)
Hypolipidemics	lovastatin (Mevacor) pravastatin (Pravachol)
Immunosuppresants	cyclosporine (Sandimmune, Neoral) tacrolimus (Prograf)

Reference: Norvir™ Prescibing Information (March 1, 1996)