Hyperphosphatemia due to fosphenytoin in a pediatric ESRD patient

Fosphenytoin is indicated for the treatment of generalized convulsions and seizures occurring during neurosurgery. Metabolites of fosphenytoin include phenytoin, phosphate, and formaldehyde. The drug monograph recommends caution in administering fosphenytoin to patients in whom phosphate restriction is necessary. Additionally, fosphenytoin has altered pharmacokinetics in end-stage renal disease patients. We report a 17-year old African-American male with end-stage renal disease who developed acute hyperphosphatemia to 3.9 mmol/L (12.1 mg/dL) following the intravenous administration of 1000 mg of fosphenytoin for an idiopathic complex partial seizure. To our knowledge, this is the first report of acute hyperphosphatemia due to fosphenytoin administration. Due to this risk of hyperphosphatemia, we recommend that fosphenytoin should be used with caution in the end-stage renal disease population.