H2-RECEPTOR ANTAGONISTS AND PHENYTOIN
Phenytoin serum levels are raised by cimetidine (maximum rise of 280% over 3 weeks). Very rarely bone marrow depression develops on concurrent use. Limited evidence suggests that low (non-prescription) doses of cimetidine may not interact. Fospheny- toin, a prodrug of phenytoin, may interact similarly.
Monitor phenytoin levels and adjust the dose accordingly. Alternatively other H2- receptor antagonists (ranitidine, famotidine, nizatidine) do not usually interact, although isolated cases have been reported. Be alert for signs of phenytoin toxicity (e.g. blurred vision, nystagmus, ataxia or drowsiness) when these H2-receptor antagonists are first given.
Monitor phenytoin levels and adjust the dose accordingly. Alternatively other H2- receptor antagonists (ranitidine, famotidine, nizatidine) do not usually interact, although isolated cases have been reported. Be alert for signs of phenytoin toxicity (e.g. blurred vision, nystagmus, ataxia or drowsiness) when these H2-receptor antagonists are first given.