Pharmacokinetics of 10-OH-carbazepine, the main metabolite of the antiepileptic oxcarbazepine, from serum and saliva concentrations

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Abstract
After administration of 600 mg of the antiepileptic oxcarbazepine to 7 healthy volunteers, serum and stimulated saliva samples were collected for the next 72 h. Concentrations of 10-OH-C [10-hydroxy-carbazepine] were determined by an HPLC [high pressure liquid chromatography] method. The time-concentration curves showed a median Tmax [peak concentration time] of 8 h followed by a plateau until 24 h indicating saturable kinetic processes. Based on the curves, the pharmacokinetic parameters were calculated. The half-life of 10-OH-C in saliva, 13.8 .+-. 3.7 (SD) h, was significantly shorter than in serum, 19.3 .+-. 6.2 (SD) h. The half-life of 10-OH-C in serum was inversely correlated to the free fraction, estimated by the ratio saliva/serum concentrations. Calculation of the free fraction by this method showed that 53.1 .+-. 14.4 (SD)% of 10-OH-C is unbound in serum. There was a good correlation (r = 0.914) between serum and saliva concentrations of 10-OH-C from 8-72 h after administration of oxcarbazepine. Saliva concentrations may prove useful, as has been shown for carbamazepine, in therapeutic monitoring of oxcarbazepine treatment.

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