Pharmacokinetics of propofol infusions, either alone or with ketamine, in sheep premedicated with acepromazine and papaveretum.

The pharmacokinetics of propofol were investigated in two groups of five Scottish blackface sheep undergoing surgery for the implantation of subcutaneous tissue pouches. After premedication with acepromazine and papaveretum, anaesthesia was induced with either propofol at 4 mg kg-1 intravenously (group 1) or with a mixture of propofol at 3 mg kg-1 and ketamine at 1 mg kg-1 intravenously (group 2). Anaesthesia was maintained with a variable infusion rate of either propofol alone (group 1) or propofol and ketamine (group 2). Both regimens produced satisfactory conditions for superficial surgery of the body surface. The mean (SD) duration of anaesthesia was 64.8 (3.1) minutes for group 1 and 60 (0) minutes for group 2; the mean total dose of propofol given to the sheep in group 1 was 801 (84) mg, and the sheep in group 2 received 470 (46) mg of propofol and 267 (30) mg of ketamine. The mean elimination half-life of propofol was 56.6 (13.1) minutes in group 1 and 50.3 (21.4) minutes in group 2; the mean volume of distribution at steady state was 1.037 (0.480) litre kg-1 in group 1 and 1.515 (0.939) litre kg-1 in group 2; the mean body clearance was 85.4 (28.0) ml kg-1 min-1 in group 1 and 128.0 (35.0) ml kg-1 min-1 in group 2; the mean residence time corrected for a bolus injection was 12.1 (4.2) minutes in group 1 and 11.9 (6.6) minutes in group 2; for the infusion, the mean residence time was 72.1 (4.2) minutes in group 1 and 69.9 (7.9) minutes in group 2. There were wide variations in the blood propofol concentrations reached in individual sheep by using this standard dosing regimen. All the sheep recovered quickly from anaesthesia; the mean times to extubation, sternal recumbency and standing for the animals in group 1 were 2.8 (0.4), 6.3 (1.2) and 10.9 (1.6) minutes from the end of the infusion, and the times for group 2 were 5.3 (0.9), 11.2 (1.7) and 15.1 (2.2) minutes.