Fosphenytoin may cause hemodynamically unstable bradydysrhythmias.

The prodrug fosphenytoin (FOS) was recently introduced as an alternative to phenytoin (PTN) and has since become a first line therapy for status epilepticus. Unlike PTN, FOS generally has been considered to be safe from cardiac toxicity. To better characterize cardiac toxicity associated with FOS administration, we performed a review of the Food and Drug Administration's Adverse Event Reporting System databank for reports of possible FOS toxicity from 1997-2002. There were 29 applicable reports of adverse cardiac events likely related to FOS infusion, including 10 cardiac deaths. Among survivors, there were four cases of high-grade atrioventricular block, and five cases of transient sinus arrest. Our data suggest that FOS may produce more cardiac toxicity than previously thought. Clinicians should consider administering intravenous FOS in a monitored setting for selected high-risk patients.