Phenytoin, Free

Phenytoin is used singly or in combination with other anticonvulsants to treat grand mal epilepsy. Monitoring the serum levels of antiepileptic drugs has increased the efficiency and safety of drug therapy in epilepsy. It facilitates individualization of dosage regimen, reveals irregular drug intake and identifies the responsible agent in intoxicated patients on multiple drug therapy. Free phenytoin is especially useful in patients with altered phenytoin binding to protein, e.g., uremia or individuals having abnormally low levels of albumin, such as nephrotic syndrome. Free phenytoin in serum correlates better with the various other free compartments of the body than does the total drug and is probably a better estimate of the “active drug level” at the receptor site and agrees more with the clinical response.