Pharmacokinetics of propofol as an induction agent in geriatric dogs

The pharmacokinetics of propofol were investigated in six unpremedicated dogs aged between eight-and-a-half and 10.5 years. After the induction of anaesthesia with a bolus dose of 5 mg kg-1 propofol administered intravenously, the trachea was intubated and anaesthesia was maintained with halothane in a gas mixture of oxygen and nitrous oxide. The mean (sd) t1/2 beta was 83.9 (14.8) minutes, the mean (SD) residence time was 99.0 (10.8) minutes, the mean body clearance was 34.5 (12.1) ml kg-1 minute-1 and the mean volume of distribution at steady state was 3864 (1647) ml kg-1. The dose of propofol was lower than that recommended in the data sheet (6.5 mg kg-1) and was associated in some of these dogs over eight years of age with post-induction apnoea. The clearance of propofol was also slower than that previously reported in young dogs. These results have implications for infusion rates when propofol is used to maintain anaesthesia in dogs.