Abstracts

RATIONALE:During AED polytherapy replacement of(CBZ) or pheenytoin(PHT), strong enzyme inducers, with oxcarbazepine(OXC),a relatively weak enzyme inducer,can result in altered plasma levels of other AEDs. METHODS:Over 200 patients on AED polytherapy has their CBZ or PHT replaced with OXC. Clinical observations and blood level monitoring were recorded for up to two weeks following the switch. RESULTS: Switching patients treated with CBZ or PHT to OXC was aassociated with adverse events if the patients were concomitantly treated with lamotrigine,topiramate,valproate or tiagabine. Within two to fourteen days following the switch,adverse events such as headache,nausea and difficulty going to sleep were associated with increased blood levels of concomitant AEDs. These adverse events disaappeared when the dose of the comcomitant AEDs were reduced. CONCLUSIONS: When strong inducing AEDs such as CBZ, PHT, PB are replaced by OXC in a polytherapy setting, clinicians should be aware of the potential for de-induction of the liver which could occur as early as twenty four hours after the switch. This may result in increased plasma levels of the comcomitant AEDs leading to adverse events. Patients should be observed closely and decreases in concomitant AEDs should be considered earlier on after making the switch.