Maintenance of therapeutic phenytoin plasma levels via intramuscular administration.

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 intravenous dose of 10.7 mg/kg body weight infused at a rate of 25 mg/min immediately followed by an intramuscular dose of 12.7 mg/kg body weight were administered initially. This was followed by daily intramuscular maintenance doses, generally 8.6 mg/kg body weight, until oral medication could be tolerated. Due to variability between subjects, primarily in metabolism, the predicted maintenance doses had to be adjusted in approximately one third of the patients. This regimen for the dosing of phenytoin was evaluated in 98 patients and consistently yielded therapeutic levels.