Incidence and risk factors of hypotension after intravenous fosphenytoin administration.

Abstract

Fosphenytoin (FOS) administered intravenously offers several benefits over intravenously administered phenytoin, including a faster infusion rate, decreased pain and irritation at the infusion site, and fewer cardiovascular complications. However, some studies suggest that the intravenous administration of FOS in some patients may also induce adverse cardiovascular events. Here, we investigated the clinical characteristics of patients who experienced hypotension following an intravenous infusion of a FOS loading dose. We reviewed the medical records of consecutive patients who received an intravenous (IV) dose of FOS between July 2013 and June 2015. Various clinical and demographic parameters were analysed, including comorbidities, drug history, seizure aetiology and type, incidence of hypotension/cardiac arrhythmia and the dosing data (ie the total dose, concentration and FOS IV infusion rate). Hypotension was defined as a ≥20mm Hg decrease in systolic blood pressure or a ≥10mm Hg decrease in diastolic blood pressure during or after FOS IV infusion. These parameters were compared between patients with and without hypotension. Of the 28 included patients, 11 (39%) had hypotension associated with an IV infusion of FOS, two of whom also had an atrioventricular block. Most patients (22/28, 79%) who received an IV infusion of FOS had status epilepticus (SE). The presence of SE was significantly associated with the development of hypotension (P=.026); hypotension occurred in half of the patients with SE, but did not occur in six patients without SE. Hypotension was also associated with old age (≥60years, P=.034) and the presence of a systemic infection (P=.04). Our study shows that hypotension associated with an IV infusion of FOS is not a rare adverse event, especially in patients with SE. Moreover, we found that old age and the presence of a systemic infection increased the risk of hypotension. These findings suggest that FOS should be infused under careful cardiovascular monitoring, especially in patients who are at higher risk of developing hypotension.