Drug Interaction Report

MONITOR: Coadministration with teriflunomide may decrease the plasma concentrations and therapeutic effects of drugs that are substrates of CYP450 1A2. The proposed mechanism is increased clearance due to teriflunomide-mediated induction of CYP450 1A2. Multiple doses of teriflunomide decreased mean Cmax and AUC of caffeine, a known CYP450 1A2 substrate, by 18% and 55%, respectively.

MANAGEMENT: Caution is advised if teriflunomide is used concomitantly with drugs that are substrates of CYP450 1A2. Dosage adjustments as well as clinical and laboratory monitoring should be considered whenever teriflunomide is added to or withdrawn from therapy with these drugs.

MONITOR: Coadministration with thiabendazole may increase the plasma concentrations of caffeine. The mechanism is thiabendazole inhibition of the CYP450 1A2 metabolism of caffeine. In ten healthy, nonsmoking volunteers, administration of a single 136.5 mg dose of caffeine in combination with a single 500 mg dose of thiabendazole resulted in a nearly 60% increase in the area under the plasma concentration-time curve (AUC) of caffeine compared to administration without thiabendazole. In addition, the half-life of caffeine was increased from 11.9 to 28.6 hours, and oral clearance was reduced by 67% during coadministration with thiabendazole. The formation of paraxanthine from caffeine, which is primarily mediated by CYP450 1A2, was almost completely abolished until after the thiabendazole was cleared from the system.

MANAGEMENT: Patients should be advised that pharmacologic effects of caffeine may be increased during coadministration with thiabendazole.

MONITOR: Smoking cessation may lead to elevated plasma concentrations and enhanced pharmacologic effects of drugs that are substrates of CYP450 1A2 (and possibly CYP450 1A1) and/or certain drugs with a narrow therapeutic index (e.g., flecainide, pentazocine). One proposed mechanism is related to the loss of CYP450 1A2 and 1A1 induction by polycyclic aromatic hydrocarbons in tobacco smoke; when smoking cessation agents are initiated and smoking stops, the metabolism of certain drugs may decrease leading to increased plasma concentrations. The mechanism by which smoking cessation affects narrow therapeutic index drugs that are not known substrates of CYP450 1A2 or 1A1 is unknown. The clinical significance of this interaction is unknown as clinical data are lacking.

MANAGEMENT: Until more information is available, caution is advisable if smoking cessation agents are used concomitantly with drugs that are substrates of CYP450 1A2 or 1A1 and/or those with a narrow therapeutic range. Patients receiving smoking cessation agents may require periodic dose adjustments and closer clinical and laboratory monitoring of medications that are substrates of CYP450 1A2 or 1A1.