Potent therapeutic effect of carbamazepine-10,11-epoxide in trigeminal neuralgia

The clinical effects of carbamazepine-10,11-epoxide were assessed in six patients with trigeminal neuralgia. The patients were first given an optimal therapeutic dose of carbamazepine. Part of or the entire carbamazepine dose was then exchanged for the metabolite carbamazepine-10,11-epoxide for three to six days. The patients were unaware of changes in the therapeutic regimen (single-blind). Carbamazepine dosages ranged from 400 to 1,400 mg/day and carbamazepine-10,11-epoxide dosages ranged from 300 to 1,000 mg/day. The clinical effects were assessed by the patients' recordings of pain attacks. When carbamazepine-10,11-epoxide and carbamazepine were given in similar doses, the pain control was comparable. On a plasma concentration basis, carbamazepine-10,11-epoxide had a considerably higher pain-relieving potency than carbamazepine. During carbamazepine treatment, the epoxide metabolite contributes to the antineuralgic effect to an extent that might be comparable to that of the parent drug. No side effects were seen during carbamazepine-10,11-epoxide therapy.