Preoperative versus postoperative pethidine for extraction of impacted third molars

We have studied the pre-emptive analgesic effects of pethidine by comparing its analgesic effects given before or immediately after operation in a randomized, double-blind study of 40 patients undergoing removal of bilateral impacted third molars under general anaesthesia. Group 1 patients received pethidine 50 mg as a 1 ml injection 1 to 2 hours before operation and normal saline 1 ml intramuscularly immediately after surgery. Group 2 patients received normal saline 1 ml intramuscularly before operation and pethidine 50 mg as a 1 ml injection immediately after surgery. Outcome measures included perception of pain on a visual analogue scale (VAS), the number of patients who required postoperative pethidine, time to first postoperative pethidine injection and total dose of pethidine given. Four patients in group 1 compared to 8 in group 2 required postoperative pethidine but this was not statistically significant. The VAS scores, time to first postoperative pethidine injection and total dose of pethidine also did not differ significantly between the 2 groups. We concluded that preoperative administration of pethidine intramuscularly did not confer additional analgesic effects compared with a similar dose given after surgery.