Effect of lamotrigine on the pharmacokinetics of carbamazepine and its active metabolite in dogs

The effect of lamotrigine (LTG) on the pharmacokinetics of carbamazepine (C BZ) and its active metabolite; carbamazepine-epoxine (CBZ-E), was investiga ted in dogs. Five male dogs received CBZ (2 x 200 mg tab, p.o.) daily for a period of I week. After the end of this period, blood samples were collect ed serially for up to 24 hrs. After a wash-out period of 1 week, LTG (100 m g tab, p.o.) was coadministered with the CBZ dose (2 x 200 mg tab, p.o.) fo r 7 days. Blood samples were again serially collected and plasma levels of CBZ and CBZ-E were analysed by high performance liquid chromatography (HPLC ). Concurrent administration of LTG with CBZ did not have any significant e ffect on the pharmacokinetic parameters of CBZ. There was also no significa nt difference between the plasma concentration ratio (CBZ-E to CBZ) vs time profiles in the two schedules of drug administration signifying the absenc e of pharmacokinetic interaction between LTG and CBZ or its active metaboli te in this animal model.