Oxcarbazepine Cimetidine

Cimetidine, erythromycin, and dextropropoxyphene had no effect on the pharmacokinetics of MHD. Results with warfarin show no evidence of interaction with either single or repeated doses of oxcarbazepine. 

Therefore, plasma concentrations for drugs metabolized by these isoforms will be affected (see Chapter 10). Thus, the addition of phenytoin to an AED regimen can reduce their plasma levels by inducing their CYP3A4 metabolism for carbamazepine, felbamate, lamotrigine, oxcarbazepine, tiagabine, valproate, and zonisamide. Other drugs for which metabolism is induced by phenytoin include methadone, theophylline, warfarin, and oral contraceptives. On the other hand, plasma phenytoin levels are increased by carbamazepine, felbamate, cimetidine, warfarin, chloramphenicol, isoniazid, and disulfiram. Plasma phenytoin levels are decreased by rifampin, antacids, and valproate (free phenytoin levels remain the same). 

The serum levels of those taking long-term carbamazepine may transiently increase, possibly accompanied by an increase in adverse effects, for the first few days after starting to take cimeti-dine, but these adverse effects rapidly disappear. Cimetidine does not appear to have this effect on oxcarbazepine levels. Ranitidine appears not to interact with carbamazepine. 

No changes in the pharmacokinetics of a single 600-mg oral dose of oxcarbazepine were seen in 8 healthy subjects who took cimetidine 400 mg twice daily for 7 days. ... 

Kermien T, JoUdccnen J, JQosterskov-Jensen P, Menge GP. Oxcarbazepine does not interact with cimetidine inhesllhy voluateers. Acta Neurol Scand ( 992) 85,239-42. 

Carbamazepine toxicity, associated with marked rises in serum carbamazepine levels, has been described in other reports. " Some of the patients were also taking sodium valproate, which does not seem to be implicated in the interaction, and in one case cimetidine, which was thought to have potentiated the interaction. See also Carbamazepine or Oxcarbazepine + H2-receptor antagonists , p.529. 

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