Routine therapeutic monitoring of the active metabolite of carbamazepine: Is it really necessary?

Carbamazepine epoxide/carbamazepine (CBZ-E/CBZ) ratios significantly increase in patients taking CBZ with phenytoin, phenobarbital, primidone and valproic acid (Polytherapy II) compared to patients on monotherapy or patients taking CBZ with other anticonvulsants (Polytherapy I).