The kinetics of an enteric-coated formulation of carbamazepine-10,11-epoxide (CBZ-E) were studied in healthy subjects. A single oral dose of 100 mg of CBZ-E was given to eight subjects. Four of them were also given a single oral dose of 200 mg of CBZ-E. Plasma concentrations of CBZ-E and urinary excretion of the end metabolite trans-10,11-dihydroxy-10,11-dihydrocarbamazepine (trans-CBZ-diol) were determined by high performance liquid chromatography. Plasma kinetics of CBZ-E fitted an open one-compartment model with plasma elimination half-life of 7.4 ± 1.8 h (mean ± SD). The clearance was 105 ± 17 ml/kg/h and the apparent volume of distribution 1.1 ± 0.2 L/kg assuming complete bioavailability. There was no indication of dose-dependent elimination of CBZ-E. The recovery of trans-CBZ-diol in urine collected for 3 days was 67 ± 9% of the given dose. This enteric-coated formulation may thus in the future be used for the evaluation of the clinical effects of CBZ-E in patients. The effects of valpromide on amitriptyline (AMT) and nortriptyline (NT) plasma levels were examined in 20 depressed inpatients. They all were treated with AMT, 125 mg once daily, and 10 patients also received 600 mg of valpromide daily after 10 days on AMT. In the 10 patients receiving valpromide in addition to AMT, the mean AMT level increased from 70.5 ± 35 to 105.5 ± 49 ng/ml (p < 0.0003) and the mean NT level from 61.0 ± 34 to 100.5 ± 65 ng/ml (p < 0.01). This increase was not related to valpromide metabolite plasma levels, nor to the age of the patients. The addition of valpromide to a stable AMT regimen may result in an increase of antidepressant plasma level with clinical implications.
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Spina et al. (1988) studied this question.