Drug Interaction Report

GENERALLY AVOID: Coadministration with drugs that cause moderate inhibition of CYP450 2C9 and moderate or strong inhibition of CYP450 3A4 may increase the plasma concentrations of siponimod, which is primarily metabolized by these isoenzymes. This interaction includes concomitant use of siponimod with a moderate CYP450 2C9/3A4 dual inhibitor or a moderate CYP450 2C9 inhibitor in combination with a separate moderate or strong CYP450 3A4 inhibitor. In healthy CYP450 2C9*1/*1 genotype volunteers, coadministration of a moderate CYP450 2C9/3A4 dual inhibitor (fluconazole 200 mg daily at steady-state) and siponimod (a single 4 mg dose) resulted in 2-fold and 50% increases in siponimod AUC and terminal half-life, respectively. According to in silico (computer-based) evaluation, use of fluconazole resulted in a 2- to 4-fold increase in the steady-state AUC of siponimod across different CYP450 2C9 genotypes. The CYP450 2C9 genotype influences the fractional contributions of CYP450 2C9 and 3A4 to overall elimination. If the metabolic activity of CYP450 2C9 is decreased, a larger contribution of CYP450 3A4 can be anticipated.

MANAGEMENT: Concomitant use of siponimod with a moderate or strong CYP450 2C9/3A4 dual inhibitor (e.g., fluconazole, mifepristone) or a moderate CYP450 2C9 inhibitor (e.g., abiraterone, amiodarone, fenofibrate, gemfibrozil, nitisinone, oxandrolone) in combination with a moderate or strong CYP450 3A4 inhibitor (e.g., amprenavir, aprepitant, atazanavir, boceprevir, ceritinib, chloramphenicol, ciprofloxacin, clarithromycin, cobicistat, conivaptan, crizotinib, dalfopristin-quinupristin, darunavir, delavirdine, diltiazem, dronedarone, erythromycin, fedratinib, fluvoxamine, fosamprenavir, fosaprepitant, fosnetupitant, fusidic acid, idelalisib, imatinib, indinavir, isavuconazole, itraconazole, ketoconazole, letermovir, mibefradil, nefazodone, nelfinavir, netupitant, posaconazole, ribociclib, ritonavir, saquinavir, stiripentol, telaprevir, telithromycin, troleandomycin, verapamil, voriconazole, voxelotor) is not recommended. Caution is advised if siponimod is used in combination with moderate CYP450 2C9 inhibitors.

ADJUST DOSING INTERVAL: According to the manufacturer, coadministration with a meal high in calories, fat, and protein reduces the absorption of indinavir. In ten patients given indinavir in this manner, the peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of indinavir decreased by an average of 84% and 77%, respectively. In contrast, grapefruit juice may have only minor effects on the oral bioavailability of indinavir. The manufacturer's package labeling states that administration of a single 400 mg dose of indinavir with 8 oz. of grapefruit juice decreased indinavir AUC by an average of 26%. Likewise, a study consisting of 14 HIV-infected subjects found no uniform nor significant changes in steady-state indinavir AUC during administration with double-strength grapefruit juice compared to water. There was, however, a delay in absorption (Tmax) due to grapefruit juice that is unlikely to be of clinical significance.

MANAGEMENT: To ensure maximal oral absorption, indinavir should be administered without food but with water 1 hour before or 2 hours after a meal. Alternatively, indinavir may be administered with other liquids such as skim milk, juice, coffee, or tea, or with a light meal (e.g., dry toast with jelly, juice, and coffee with skim milk and sugar; corn flakes, skim milk and sugar).