Phenytoin encephalopathy as probable idiosyncratic reaction: case report.

A case of phenytoin (DPH) encephalopathy with increasing seizures and EEG and mental changes is described. Despite adequate oral dosage of DPH (5 mg/kg/daily) the plasma level was very low (2.8 microgramg/ml). The encephalopathy was probably an idiosyncratic and not toxic or allergic reaction. In fact the concentration of free DPH was normal, the patient presented a retarded morbilliform rash during DPH treatment, the protidogram was normal, and an intradermic DPH injection had no local effect. The authors conclude that in a patient starting DPH treatment an unexpected increase in seizures, with EEG and mental changes occurring simultaneously, should alert the physician to the possible need for eliminating DPH from the therapeutic regimen, even if plasma concentrations are low.