Fluorescent dyes invalidate this assay. Co-administration of phenytoin, barbiturates, benzodiazepines, succinimides, and valproic acid may induce lower serum levels, but seizure control is possible because the active metabolite, carbamazepine epoxide has anticonvulsant activity.
Clinical effects are difficult to predict.
Likewise carbamazepine administration may decrease plasma levels of phenytoin and warfarin. Toxic effects may occur with apparently therapeutic levels if given with phenytoin or barbiturates. Carbamazepine can rarely produce serious side effects which may not be dose related. The most widely feared side effect is bone marrow depression. The drug should be withdrawn at the first sign of leukopenia or thrombocytopenia.