Drug Interaction Report

MONITOR: Coadministration with modafinil (the racemate) or armodafinil (the R-enantiomer) may increase the plasma concentrations of drugs that are primarily metabolized by the CYP450 2C19 isoenzyme. The mechanism is decreased clearance due to inhibition of CYP450 2C19 activity by modafinil and armodafinil. In pharmacokinetic studies, coadministration of a single 400 mg dose of armodafinil with omeprazole 40 mg increased systemic exposure to omeprazole by approximately 40%. A case report implicated modafinil in the development of clozapine toxicity characterized by dizziness, ataxia, and tachycardia. Clozapine serum levels increased from 761 ng/mL to 1400 ng/mL several weeks after initiation of modafinil therapy.

MANAGEMENT: Caution is advised if modafinil or armodafinil must be used concurrently with medications that undergo metabolism by CYP450 2C19, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever modafinil or armodafinil is added to or withdrawn from therapy.

ADJUST DOSING INTERVAL: Food may interfere with the absorption of esomeprazole. The manufacturer reports that the area under the concentration-time curve for esomeprazole following a single 40 mg dose was 33% to 53% lower when administered after food intake as opposed to during fasting conditions.

MANAGEMENT: Esomeprazole should be taken at least one hour before meals. When administered to patients receiving continuous enteral nutrition, some experts recommend that the tube feeding should be interrupted for at least 1 hour before and 1 hour after the dose of esomeprazole is given.

Administration with food may delay the absorption of modafinil (the racemate) and armodafinil (the R-enantiomer) without significantly affecting their overall bioavailability. According to the product labeling, modafinil's absorption may be delayed by approximately one hour if taken with food. Similarly, the time to reach peak plasma concentration (Tmax) of armodafinil may be delayed by approximately 2 to 4 hours in the fed state.