Thiopental disposition as a function of age in female patients undergoing surgery

The effect of age on the disposition kinetics of thiopental was studied in 22 lean female patients having a body mass index (weight (kg/height(m)2) less than 30 and whose age ranged between 25 to 83 years. Patients underwent primarily abdominal surgery. A strong positive correlation between age and the apparent volumes of distribution, V beta and Vss, was found (P less than 0.001). No significant relationship was found between total body clearance and age. The elimination half-life (t1/2) of thiopental increased with age, and was primarily a function of volume of distribution. The free or unbound fraction of thiopental in serum (alpha) ranged between 0.168 and 0.276 and was significantly correlated with age (P less than 0.005). Multiple regression analysis indicated that age was the independent variable which contributed most the variability in t1/2, V beta, and Vss. No conclusion can be reached concerning the potential differences in anesthetic induction doses required as a function of age; however, these data suggest that care may be required in the use of a balanced anesthetic technique in the elderly as a result of prolonged elimination.