Phenytoin (brand name: Dilantin) is used to prevent and treat seizures. Blood levels of phenytoin can become too high and cause toxicity. Thus, patients who start phenytoin should be made aware they will need blood monitoring from time to time while on this medication. Phenytoin is not associated with hallucinations or delusions, but is associated with an increased risk of suicidal ideation. Phenytoin injection is contraindicated in patients with sinus bradycardia, sick sinus syndrome, QT interval prolongation, second and third degree heart block and other arrhythmias. It is not associated with sinus tachycardia. Phenytoin is not a sulfa drug.