Drug Interactions between etrasimod and Nuedexta

GENERALLY AVOID: Coadministration with potent CYP450 2D6 inhibitors (e.g., quinidine, terbinafine) may significantly increase the plasma concentrations of dextromethorphan in patients who are extensive metabolizers of this isoenzyme (approximately 93% of Caucasians and more than 98% of Asians and individuals of African descent). The proposed mechanism is inhibition of the CYP450 2D6-mediated O-demethylation of dextromethorphan. Studies in humans have shown an increase in systemic exposure of dextromethorphan of up to 43-fold when given concurrently with quinidine. Increased plasma concentrations increase the risk of dextromethorphan-related adverse effects (e.g., agitation, confusion, tremor, insomnia, diarrhea, and respiratory depression) and serotonin syndrome. However, this interaction has also been used clinically, with dextromethorphan in combination with quinidine indicated by some authorities for the treatment of pseudobulbar affect. Data evaluating the impact of this interaction in patients who are poor metabolizers of CYP450 2D6 are limited; most studies include extensive metabolizers of this isoenzyme. It is expected that poor metabolizers would have elevated dextromethorphan levels without concurrent quinidine

MANAGEMENT: The combination of dextromethorphan with potent CYP450 2D6 inhibitors should be generally avoided. Some manufacturers consider the concomitant use of dextromethorphan and selective serotonin reuptake inhibitors contraindicated. If use is considered necessary, the patient should be monitored for signs of dextromethorphan adverse effects (e.g., agitation, confusion, tremor, insomnia, diarrhea, and respiratory depression) and serotonin syndrome, and advised to notify their health care professional if these adverse effects develop or worsen. Dose reduction of dextromethorphan may also be required.

MONITOR CLOSELY: Due to the risk of bradycardia and atrioventricular (AV) block, the risk of QT prolongation and torsade de pointes arrhythmia may be increased during initiation of etrasimod treatment in patients receiving drugs that prolong the QT interval. Etrasimod may cause a transient decrease in heart rate during initiation of therapy. In the randomized placebo-controlled studies in patients with ulcerative colitis UC-1 and UC-2, following an initial dose of 2 mg on day 1, the greatest mean decrease from baseline in heart rate of 7.2 bpm occurred at hour 2 (UC-2) and hour 3 (UC-1). In studies UC-2 and UC-3, bradycardia was reported on day 1 in 2.9% of patients on etrasimod compared to none in the placebo group. On Day 2, bradycardia was reported in 1 patient (0.3%) treated with etrasimod compared to none in the placebo group. Overall, subjects who experienced bradycardia were generally asymptomatic. Few subjects experienced symptoms such as dizziness, and these symptoms resolved without intervention. Initiation of etrasimod treatment has also resulted in transient AV conduction delays. In the UC-1 study, after 2 mg of etrasimod on day 1 of treatment, first- or second-degree Mobitz type I AV blocks were observed in 0.7% of etrasimod- treated subjects compared to none in the placebo group. In studies UC-2 and UC-3, Mobitz type I AV blocks were observed in 0.8% of etrasimod-treated subjects compared to none in the placebo group. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). In addition, the extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s).

MANAGEMENT: Because bradycardia and AV block are recognized risk factors for QT prolongation and torsade de pointes arrhythmia, advice from a cardiologist should be sought if treatment with etrasimod is considered in patients with significant QT prolongation (QTcF greater than 450 msec in males or 470 msec in females), patients with arrhythmias requiring treatment with Class 1a or Class III antiarrhythmic agents, or in patients on concurrent therapy with QT prolonging drugs with a known risk of torsades de pointes or drugs that slow heart rate or AV conduction. Temporary interruption of anti-arrhythmic therapy may be required prior to initiation of etrasimod, depending on the patient's resting heart rate. Some authorities state that treatment with an anti-arrhythmic agent may be initiated in patients who have been stabilized on etrasimod therapy for at least 7 consecutive days. The manufacturer's product labeling or local treatment protocols should also be consulted for additional guidance.