THE INFLUENCE OF THE TIMING OF BUPIVACAINE INFILTRATION ON THE TIME-COURSE OF INFLAMMATION-INDUCED BY 2 CARRAGEENAN INJECTIONS 7 DAYS APART

The mechanical allodynia and edema related to a subcutaneous carrageen in injection are increased by a conditioning carrageenin injection 7 d ays before (Guilbaud et al., 1992). In the present study, the possibil ity of preventing this by bupivacaine infiltration was tested. In the first part of the experiment, the time course of a carrageenin induced inflammation of the right hind paw was assessed in animals receiving local anesthetic injection (0.2 ml of bupivacaine 0.5% solution with e pinephrine) either 5 min before (BUPI PRE group) or 60 min after (BUPI POST group) the carrageenin injection (0.2 ml of 1% solution). Contro l groups received saline (0.2 ml) with the same timing. In the second part of the experiment, 7 days later, a carrageenin injection was perf ormed either in the right or the left hind paw. Mechanical allodynia a nd edema were evaluated by the vocalization threshold to paw pressure (VTPP) and paw circumference (PC) in both hind paws at 1, 2, 4, 24 h a nd 7 days after both carrageenin injections. The first carrageenin inj ection induced mechanical allodynia and edema maximal at 240 min (42% reduction of VTPP; 23% increase in PC) and the influence of bupivacain e on the VTPP and PC was similar to previous results (Fletcher et al., 1996). The second ipsilateral carrageenin injection induced a more pr onounced inflammation in the control groups and BUPI POST group than t he first injection (P < 0.001). In contrast, the increase in allodynia and edema was less intense in the BUPI PRE group than in the other gr oups (P < 0.0001 and P < 0.02 respectively). Bupivacaine injections ha d no effect on allodynia and edema related to a second contra-lateral carrageenin injection. These results suggest that bupivacaine infiltra tion, when administered before the first conditioning injection of car rageenin, can prevent the reinforcement of mechanical allodynia and ed ema related to a second ipsilateral injection of carrageenin 7 days la ter.