Drug Interactions between mephenytoin and zuranolone

ADJUST DOSING INTERVAL: Phenytoin bioavailability may decrease to subtherapeutic levels when the suspension is given concomitantly with enteral feedings. The mechanism may be related to phenytoin binding to substances in the enteral formula (e.g., calcium, protein) and/or binding to the tube lumen. Data have been conflicting and some studies have reported no changes in phenytoin levels, while others have reported significant reductions.

MONITOR: Acute consumption of alcohol may increase plasma phenytoin levels. Chronic consumption of alcohol may decrease plasma phenytoin levels. The mechanism of this interaction is related to induction of phenytoin metabolism by ethanol during chronic administration. Other hydantoin derivatives may be similarly affected by ethanol.

MANAGEMENT: Some experts have recommended interrupting the feeding for 2 hours before and after the phenytoin dose, giving the phenytoin suspension diluted in water, and flushing the tube with water after administration; however, this method may not entirely avoid the interaction and is not always clinically feasible. Patients should be closely monitored for clinical and laboratory evidence of altered phenytoin efficacy and levels upon initiation and discontinuation of enteral feedings. Dosage adjustments or intravenous administration may be required until therapeutic serum levels are obtained. In addition, patients receiving phenytoin therapy should be warned about the interaction between phenytoin and ethanol and they should be advised to notify their physician if they experience worsening of seizure control or symptoms of toxicity, including drowsiness, visual disturbances, change in mental status, nausea, or ataxia.

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ADJUST DOSING INTERVAL: Food enhances the oral bioavailability of zuranolone. When administered with a low-fat meal (e.g., 400 to 500 calories, 25% fat), zuranolone peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 3.5- and 1.8-fold, respectively, compared to administration under fasted conditions. Zuranolone was administered with food in the premarketing study population. The efficacy of zuranolone when administered in the fasted state is unknown.

GENERALLY AVOID: Concomitant use of zuranolone with central nervous system (CNS) depressants, including alcohol, may potentiate adverse effects such as somnolence, confusion, dizziness, and gait disturbance.

MANAGEMENT: Zuranolone must be administered with fat-containing food (e.g., 400 to 1,000 calories, 25% to 50% fat) according to the manufacturer. Patients should also be advised to avoid or limit consumption of alcohol and to avoid activities requiring mental alertness such as driving or operating hazardous machinery until at least 12 hours after administration of zuranolone.

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