Rapid intravenous administration of phenytoin (>50 mg/min in adults or 1 mg/kg/min in children) may produce hypotension, AV block, and cardiovascular collapse, probably owing to the propylene glycol diluent. Fosphenytoin is readily soluble and does not contain propylene glycol, and therefore a hypotensive response is not expected. However, a few cases of bradycardia and asystole have been reported after very large IV doses of fosphenytoin.
Extravasation of phenytoin may result in local tissue necrosis and sloughing. Phenytoin may induce the “purple glove” syndrome (edema, discoloration, and pain) after peripheral IV administration. This can occur hours after infusion, in the absence of clinical signs of extravasation, and can lead to limb ischemia and necrosis from a compartment syndrome. Elderly patients receiving large multiple doses are at risk; other risk factors include use of small IV catheters, high infusion rates, and use of the same catheter site for two or more IV push doses. Extravasation problems have not been observed with fosphenytoin.
Drowsiness, ataxia, nystagmus, and nausea may occur.
Use in pregnancy. No assigned FDA category. Congenital malformations (fetal hydantoin syndrome) and hemorrhagic disease of the newborn have occurred with chronic use. However, this does not preclude acute, short-term use in a seriously symptomatic patient (See Introduction in Section III).