Drug Interactions between rifampin and solifenacin

MONITOR: Theoretically, coadministration with inducers of CYP450 3A4 may decrease the plasma concentrations of solifenacin, which has been shown to be a substrate of the isoenzyme in vitro. In addition, when two or more medications with similar adverse effect profiles are given concurrently, the likelihood of experiencing these adverse reactions may be increased. For example, coadministration with other agents that can prolong the QT interval (e.g., apalutamide, encorafenib, enzalutamide) may result in additive effects and an increased risk of ventricular arrhythmias like torsade de pointes.

MANAGEMENT: Pharmacologic response to solifenacin should be monitored more closely whenever a CYP450 3A4 inducer is added to or withdrawn from therapy, and the solifenacin dosage adjusted if necessary. If the CYP450 3A4 inducer also carries a risk of prolonging the QT interval, then obtaining more frequent electrocardiograms (ECGs) to monitor the QT interval may be advisable. Patients should be counseled to seek immediate medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, syncope, palpitations, irregular heartbeat, and/or shortness of breath. The prescribing information for the concomitant CYP450 3A4 inducers should be consulted for specific recommendations.