Effect of age, gender, and obesity on midazolam kinetics

The effects of age, sex, and obesity on the kinetics of single intravenous (iv) and oral doses of midazolam were evaluated in healthy volunteers who received 2.5-5 mg of iv midazolam on one occasion and 5-10 mg orally on another. Kinetics were determined from multiple plasma midazolam concentrations measured during 24 h after dosage. Midazolam elimination half-life (t1/2) after iv dosage was significantly prolonged in elderly (aged 60-74 yr) versus young (24-33 yr) males (5.6 vs. 2.1 hours, P less than 0.01) and total clearance was significantly reduced (4.4 vs. 7.8 ml X min-1 X kg-1, P less than 0.01), leading to increased systemic availability of the oral dose (50% vs. 41%, P less than 0.05). However total volume of distribution calculated by the area method (Vd) (1.6 vs. 1.3 1/kg) and protein binding (3.5 vs. 3.4% unbound) did not differ between groups. Among women there were no significant differences between elderly (64-79 yr) and young (23-37 yr) volunteers in t1/2 (4.0 vs. 2.6 h), clearance (7.5 vs. 9.4 ml X min-1 X kg-1), Vd (2.1 vs. 2.0 1/kg), protein binding (3.7% vs. 3.7% unbound), or oral bioavailability (38% vs. 36%). In obese volunteers (mean weight 117 kg; 173% of ideal weight) versus control subjects of normal weight (66 kg, 95% of ideal weight) matched for age, sex, and smoking habits, midazolam Vd was increased significantly (311 vs. 114 1, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)