Effect of glycated albumin on phenytoin binding in elderly patients with type II diabetes mellitus

We evaluated the effect of glycated albumin on phenytoin protein binding in 36 elderly (age range 63-94 yrs) patients with type II diabetes mellitus (DM) under diet management. Serum was spiked with 15 mg/L phenytoin and incubated. A serum ultrafiltrate was obtained from each sample for determining total and free phenytoin concentrations. Glycated hemoglobin was determined by boronate-affinity chromatography, and glycated albumin was separated from nonglycated fractions with boronate-agarose gel. Glycated hemoglobin in the study group ranged from 4.3-14.6% (mean 7.8 +/- SD 2.1%) and glycated albumin ranged from 3.7-12.5% (7.4 +/- SD 2.6%). We observed no correlation between glycated albumin and the percentage of free phenytoin (r2 = -0.14; p = 0.419). The concentration of nonglycated albumin ranged from 0.66-4.28 g/dl (mean 3.45 +/- 0.67 g/dl) and was calculated from measured total and glycated albumin concentrations. A correlation between the free fraction of phenytoin and nonglycated albumin was not demonstrated (r2 = 0.22, p = 0.22). In addition, a correlation was not observed between total glycated albumin and the free fraction of phenytoin (r2 = -0.095; p = 0.58). We conclude that elderly patients with type II DM under diet control do not have significant alterations in phenytoin protein binding. The use of total serum phenytoin levels therefore appears appropriate for determining phenytoin dosages in elderly patients with well controlled type II DM.