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, Vβ and V(ss), was found (P<0.001). No significant relationship was found between total body clearance and age. The elimination half-life (t 1/2 ) of thiopental increased with age, and was primarily a function of volume of distribution. The free or unbound fraction of thiopental in serum (α) ranged between 0.168 and 0.276 and was significantly correlated with age (P<0.05). Multiple regression analysis indicated that age was the independent variable which contributed most to the variability in t 1/2 , Vβ, and V(ss). 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.