Brain concentrations of carbamazepine and carbamazepine-10,11-epoxide in epileptic patients.

Carbamazepine (CBZ) and carbamazepine-10,11-epoxide (CBZ-Epoxide) in the temporal lobe were measured in five epileptic patients undergoing unilateral temporal lobectomy. The patients had been under CBZ treatment from 6 months to 6 years and all were in steady state at the time of operation. The brain tissue concentration of CBZ in all patients was higher than the plasma concentration; the brain/plasma ratio ranged from 1.4--1.6. Brain/plasma ratios of CBZ-Epoxide ranged from 0.6--1.5. The ratio for CBZ was similar in patients treated with CBZ alone or in combination with other anticonvulsants, but for the CBZ-Epoxide a higher ratio was found in patients on combined treatment. The results may mean that other antiepileptic drugs, too, can influence the brain concentration of an active metabolite, which could have a bearing on the enhanced therapeutic effect often seen on combining CBZ treatment with other antiepileptic drugs.