Effects of clonidine pretreatment on the local anaesthetic activity of bupivacaine in mice

This study was designed to document possible changes in bupivacaine local anaesthetic activity in mice after a single injection of clonidine (0.1 or 1 mg kg(-1), i.p.). The local anaesthetic activity was evaluated during 60 min, according to a previously reported technique, using sciatic nerve blockade by injection of bupivacaine in the area of the sciatic nerve. Clonidine pretreatment modified the local anaesthetic activity of bupivacaine dose-dependently. The time of recovery was higher for clonidine-pretreated mice (40.00 +/- 7.24 min, 0.1 mg kg(-1) clonidine: 50.0 +/- 9.35 min 1 mg kg(-1) clonidine) compared with controls 27.22 +/- 1.21 min, P = 0.02). The maximal effect (E(max)) was significantly lower for the pretreated group (1.15 +/- 0.13 units, 0.1 mg kg(-1); 1.35 +/- 0.09 units, 1 mg kg(-1)) compared with the control group (1.72 +/- 0.13. P = 0.01). Our data indicate a significant decrease in the duration of anaesthetic activity of bupivacaine in clonidine-pretreated mice.