Drug interactions between Lamictal and Symbyax

fluoxetine ↔ lamotrigine

Applies to:Symbyax (fluoxetine/olanzapine) and Lamictal (lamotrigine)

MONITOR: Central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking multiple drugs that cause these effects, especially in elderly or debilitated patients.

MANAGEMENT: During concomitant use of these drugs, patients should be monitored for potentially excessive or prolonged CNS and respiratory depression. Ambulatory patients should be counseled to avoid hazardous activities requiring 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.

lamotrigine ↔ olanzapine

Applies to:Lamictal (lamotrigine) and Symbyax (fluoxetine/olanzapine)

Coadministration with olanzapine may slightly decrease the plasma concentrations of lamotrigine. The mechanism of interaction has not been described. In 16 healthy male volunteers, addition of olanzapine (15 mg once daily) decreased the peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of lamotrigine (200 mg once daily) by 20% and 24%, respectively, compared to administration of lamotrigine alone in 12 healthy male volunteers. These alterations are unlikely to be of clinical significance. In another study, olanzapine 5 mg had no effect on the Cmax and AUC of lamotrigine (25 mg daily for 5 days, then 50 mg daily for 13 days) in 14 healthy volunteers, but significantly increased the mean time to reach peak plasma concentration (Tmax) of lamotrigine from 1.9 to 4.0 hours. This effect may be attributable to the anticholinergic properties of olanzapine. Mild sedation was the only adverse effect reported during lamotrigine and olanzapine coadministration. Lamotrigine has no effect on the pharmacokinetics of olanzapine.