Impact of Obesity on Fosphenytoin Volume of Distribution in Pediatric Patients.

The impact of body habitus on fosphenytoin pharmacokinetics is poorly understood in pediatric patients. This retrospective, single-center review examined differences in fosphenytoin volume of distribution (VD) between children with normal and obese body habitus. From 2013 to 2015, patients 2 to 18 years of age who received a loading dose of fosphenytoin were identified. Thirty-seven patients met inclusion criteria. Mean total serum phenytoin concentration was 25.3 ± 6.5 μg/mL in the nonobese group and 29.5 ± 7.6 μg/mL in the obese group ( P = .09). VD was not significantly different between obese and nonobese groups, 0.92 ± 0.26 L/kg and 0.97 ± 0.48 L/kg ( P = .76), respectively. In contrast to adult studies, these data suggest that fosphenytoin dose adjustments for obese children may be unnecessary.