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 (E_max) 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. 1995 Royal Pharmaceutical Society of Great Britain