Drug Interactions between lefamulin 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.

CONTRAINDICATED: When administered orally, lefamulin may significantly increase the plasma concentrations of drugs that are primarily metabolized by CYP450 3A4. Increased exposure to sensitive CYP450 3A4 substrates that can prolong the QT interval may increase the risk of ventricular arrhythmias including torsade de pointes and sudden death. Based on interaction with midazolam, a sensitive CYP450 3A4 substrate, lefamulin may be a moderate CYP450 3A4 inhibitor. When oral midazolam was administered concomitantly with and at 2 or 4 hours after administration of lefamulin tablets, mean midazolam peak plasma concentration (Cmax) and systemic exposure (AUC) increased by approximately 100% and 200%, respectively. No clinically significant differences in the pharmacokinetics of midazolam were observed when administered concomitantly with lefamulin injection.

Because lefamulin itself may cause prolongation of the QT interval, the potential for a pharmacodynamic interaction with other agents that can prolong the QT interval should also be considered. In two randomized, double-blind, double-dummy, active-controlled (moxifloxacin 400 mg once daily) studies, a concentration-dependent QTc prolongation effect of lefamulin was observed. The mean change from baseline QTcF around Tmax on day 3 or 4 was 13.6 msec for lefamulin 150 mg administered twice daily by infusion and 9.3 msec for lefamulin 600 mg administered twice daily orally, compared to 16.4 msec for moxifloxacin 400 mg administered once daily by infusion and 11.6 msec for moxifloxacin 400 mg administered once daily orally. 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: Concomitant use of oral (but not intravenous) lefamulin with sensitive CYP450 3A4 substrates that can prolong the QT interval is considered contraindicated. However, because lefamulin itself can also cause QT prolongation regardless of the route of administration, concomitant use with other drugs that can prolong the QT interval should generally be avoided even when lefamulin is administered intravenously.