Contraindicated with hypersensitivity to hydantoins, sinus bradycardia, sinoatrial block, second- or third-degree AV heart block, Stokes-Adams syndrome, pregnancy (data suggest an association between use of antiepileptic drugs by women with epilepsy and an elevated incidence of birth defects in children born to these women; however, do not discontinue antiepileptic therapy in pregnant women who are receiving therapy to prevent major seizures—this is likely to precipitate status epilepticus, with attendant hypoxia and risk to both mother and unborn child), lactation.

Use cautiously with hypotension, severe myocardial insufficiency, porphyria, hepatic dysfunction.