Influence of type I and type II diabetes mellitus on phenytoin steady-state levels.

Phenytoin kinetics was studied in male type I and type II diabetic patients, ten in each group. Age and sex matched epileptic patients receiving phenytoin alone served as control groups. Steady-state concentration of phenytoin was significantly lower in both types of diabetics compared to respective controls. The Vmax and Vmax/Km of phenytoin were significantly increased in type I diabetics. The Vmax was unaltered in type II diabetics but the Vmax/Km was higher in them. Protein binding of the drug was decreased in both groups. It is concluded that phenytoin kinetics is increased in both types of diabetics which may be responsible for the lower steady-state concentration of the drug.