VPA daily dose and total VPA concentrations for 146 elderly (> or =65 years) nursing home residents collected from June 1998 to December 2000 in homes located throughout the United States are presented. Average age was 78.5+/-8.0 years old. The mean VPA daily dose was 16.2+/-11.2mg/kg and mean total VPA concentration was 48.5+/-24.8 mg/L. The majority (56.2%) of the VPA residents are being maintained at total VPA levels <50mg/L. Mean daily dose (19.4+/-11.4, 16.3+/-12.1, and 11.3+/-7.6 mg/kg/day; p=0.003) and total VPA concentration (56.4+/-25.8, 47.7+/-22.6, and 38.7+/-23.1mg/kg/day; p=0.003) decreased by age groups (65-74, 75-84, and > or =85 years). Daily dose and total VPA concentration were not different in residents receiving inhibitory or inducing co-medications, between men and women, or by albumin level. Total VPA clearance was similar between men and women, among age groups, or according to inducing or inhibiting co-medications.