Prolongation of epidural anaesthesia in dogs with bupivacaine in a lipid emulsion

An aqueous solution and a lipid emulsion of bupivacaine were administered e pidurally in doses of 1-8 mg/kg to six beagle dogs following a randomised t wo-phase crossover design. The aqueous solution was absorbed rapidly and th e mean (sd) peak venous plasma concentration of bupivacaine, 1-4 (0.4) mug/ ml, was detected after five minutes. After administration of the lipid emul sion, the peak plasma concentration of bupivacaine, 0.6 (0.2) mug/ml, was d etected after 30 minutes. The mean (sd) t(1/2 beta) of the aqueous preparat ion was 149.1 (32.6) minutes, and of the lipid emulsion 119.2 (34.0) minute s. Both preparations had a similar bioavailability. The mean time to the on set of motor block after the administration of the aqueous solution, 2.3 (2 .2) minutes, was significantly shorter (P=0.028) than after the administrat ion of the lipid emulsion, 9.4 (1.9) minutes, and the duration of the motor block induced by the lipid emulsion, 217.6 (26.2) minutes, was significant ly longer (P=0.043) than for the aqueous solution, 158 (48.8) minutes. Duri ng anaesthesia, the plasma concentrations of bupivacaine ranged between 1.3 and 0.2 mug/ml. Non-significant changes in systolic blood pressure and hea rt rate were observed which coincided with the peak plasma concentrations o f bupivacaine.