Single-drug therapy with carbamazepine in patients with epilepsy: serum levels and clinical effect.

Carbamazepine (CBZ) was given as the only drug to 62 epileptic patients with mainly simple and complex partial seizures. Twenty-four of the patients were given CBZ as the only drug from the beginning of therapy, while 38 patients had formerly received other antiepileptic drugs. Serum concentrations of CBZ and CBZ-10,11-epoxide were determined by enzyme immunoassay and gas chromatography, respectively, in fasting morning blood specimens. Twenty of the 24 patients given CBZ from the beginning were seizure-free at follow-up 7-48 months later. These patients had a mean daily dose of CBZ of 7.5 (+/- 0.56) mg/kg and mean CBZ and epoxide serum concentrations of 23.4 (+/- 1.16) and 2.4 (+/- 0.20) mumoles/liter, respectively. The corresponding values for 25 of the 38 patients previously treated with other antiepileptic drugs were 10.3 +/- 0.66 mg/kg and 29.4 +/- 1.60 and 3.1 +/- 0.18 mumoles/liter. The follow-up in these patients was 11-58 months. Thirteen patients had poor seizure control, although they had serum CBZ and epoxide concentrations within the ranges giving seizure control in the rest of the patients. The concentrations of the epoxide in serum were significantly correlated to the concentrations of CBZ (r = 0.63, p < 0.01). The therapeutic range, 13-51 mumoles/liter, indicates great interindividual differences in optimal levels of CBZ. Accordingly, individually tailored drug regimens are necessary to achieve optimal therapeutic effects with CBZ.