Phenytoin is contraindicated in patients who are hypersensitive to phenytoin, or its inactive ingredients, or other hydantoins.
Because of its effect on ventricular automaticity, phenytoin is contraindicated in sinus bradycardia, sinoatrial block, second- and third-degree atrioventricular (AV) block, and in patients with Adams-Stokes syndrome.
Co-administration of phenytoin with delavirdine is contraindicated due to the potential for loss of virologic response and possible resistance to delavirdine or to the class of non-nucleoside reverse transcriptase inhibitors.