Oxcarbazepine. A review of its pharmacology and therapeutic potential in epilepsy, trigeminal neuralgia and affective disorders.

Oxcarbazepine is the 10-keto analogue of carbamazepine but has a distinct pharmacokinetic profile. In contrast to the oxidative metabolism of carbamazepine, oxcarbazepine is rapidly reduced to its active metabolite, 10,11-dihydro-10-hydroxy-carbamazepine. With the possible exception of the P450IIIA isozyme of the cytochrome P450 family, neither oxcarbazepine nor its monohydroxy derivative induce hepatic oxidative metabolism. Direct comparison of oxcarbazepine and carbamazepine has shown no difference in efficacy between these 2 agents in terms of reducing seizure frequency in patients with partial epilepsy with or without secondary generalisation, or with tonic-clonic seizures. Substitution of oxcarbazepine for carbamazepine in multiple antiepileptic drug regimens improved seizure control in some patients with refractory epilepsy; however, the rise in serum concentrations of concurrent antiepileptic agents secondary to elimination of carbamazepine-associated hepatic enzyme induction may have also played a role. Substitution of oxcarbazepine for carbamazepine was associated with improved cognition and alertness in some patients with epilepsy. Limited data indicate that oxcarbazepine may be a useful alternative to carbamazepine in the management of trigeminal neuralgia. Experience in patients with acute mania is promising, but the value of oxcarbazepine in managing affective disorders, particularly as a prophylactic agent, is not established. Oxcarbazepine may be better tolerated than carbamazepine; however, the current published database is small and the potential for oxcarbazepine to induce the type of serious idiosyncratic reactions occasionally associated with carbamazepine is unknown. Hyponatraemia has been reported in patients treated with oxcarbazepine. Although apparently asymptomatic, fluid restriction may be deemed necessary in some patients to reduce the risk of precipitating seizures secondary to low serum sodium. Thus, oxcarbazepine appears to be an effective substitute for carbamazepine in those patients intolerant of this agent, or experiencing significant drug interactions. Wider clinical experience should help clarify the long term efficacy and tolerability of oxcarbazepine. Pharmacokinetic advantages over current antiepileptic drugs, carbamazepine in particular, may then favour oxcarbazepine for consideration as a first-line agent in the management of partial and tonic-clonic epilepsy.