Drug interaction studies have been completed with both INVIRASE and saquinavir soft gel capsules. Observations from drug interaction studies with saquinavir soft gel capsules may not be predictive for INVIRASE/ritonavir. Because ritonavir is coadministered with INVIRASE, prescribers should also refer to the prescribing information for ritonavir regarding drug interactions associated with this agent.

The combination INVIRASE/ritonavir is a potent inhibitor of CYP3A and may significantly increase the exposure of drugs primarily metabolized by CYP3A. Drugs that are contraindicated specifically due to the observed or expected magnitude of interaction and potential for serious or life-threatening adverse events are listed in Table 1 [see Contraindications ]. Coadministration with other CYP3A substrates may require a dose adjustment or additional monitoring (see Table 3).

The metabolism of saquinavir is mediated primarily by CYP3A. Additionally, saquinavir is a substrate for P-glycoprotein (P-gp). Therefore, drugs that affect CYP3A and/or P-gp may modify the pharmacokinetics of saquinavir. Coadministration with drugs that are potent inducers of CYP3A (e.g., phenobarbital, phenytoin, carbamazepine) may result in decreased plasma concentrations of saquinavir and reduced therapeutic effect.

Based on the finding of dose-dependent prolongations of QT and PR intervals in healthy volunteers receiving INVIRASE/ritonavir, additive effects on QT and/or PR interval prolongation may occur with certain members of the following drug classes: antiarrhythmics class IA or class III, neuroleptics, antidepressive agents, PDE5 inhibitors (when used for pulmonary arterial hypertension), antimicrobials, antihistaminics and others. This effect might lead to an increased risk of ventricular arrhythmias, notably torsades de pointes. Therefore, concurrent administration of these agents with INVIRASE/ritonavir is contraindicated [see Contraindications ].

Table 3 provides a listing of established or potentially clinically significant drug interactions. Alteration in dose or avoidance of the combination may be recommended depending on the interaction^[1]

Adapted from the FDA Package Insert.