Maintenance of Therapeutic Phenytoin Plasma Levels via Intramuscular Administration

Abstract

A parenteral dosing regimen was designed for the immediate attainment and maintenance of therapeutic plasma levels of phenytoin in patients requiring anticonvulsant therapy, but not able to tolerate oral medication. An i.v. dose of 10.7 mg/kg body wt infused at a rate of 25 mg/min immediately followed by an i.m. dose of 12.7 mg/kg body wt were administered initially. This was followed by daily i.m. maintenance doses, generally 8.6 mg/kg body wt, until oral medication could be tolerated. Due to variability between subjects, primarily in metabolism, the predicted maintenance doses had to be adjusted in approximately 1/3 of the patients. This regimen for the dosing of phenytoin was evaluated in 98 patients and consistently yielded therapeutic levels.