Drug Interaction Report

MONITOR: Coadministration with oxcarbazepine may increase the plasma concentrations of drugs that are substrates of the CYP450 2C19 isoenzyme. The mechanism is decreased clearance due to inhibition of CYP450 2C19 activity by oxcarbazepine and its active metabolite 10-monohydroxy derivative, or MHD. In vivo, the plasma levels of phenytoin, a CYP450 2C19 substrate, increased by up to 40% when oxcarbazepine was given at dosages above 1200 mg/day.

MANAGEMENT: Caution is advised if higher dosages of oxcarbazepine 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as well as clinical and laboratory monitoring may be appropriate for some drugs whenever oxcarbazepine is added to or withdrawn from therapy.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.