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 mgkg-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 mgkg-1 clonidine: 50.0 +/- 9.35 min, 1 mgkg-1 clonidine) compared with controls (27.22 +/- 1.21 min, P = 0.02). The maximal effect (Emax) was significantly lower for the pretreated group (1.15 +/- 0.13 units, 0.1 mgkg-1; 1.35 +/- 0.09 units, 1 mgkg-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.