Effect of preoperative i.m. administration of diclofenac on suxamethonium-induced myalgia.

We have studied the effects of preoperative administration of diclofenac on suxamethonium-induced myalgia, plasma met-enkephalin-like activity (E-LA), prostaglandin E2-like activity (PGE2-LA), leukotriene C4-like activity (LTC4-LA) and histamine-like activity (H-LA). Thirty-four ASA I patients undergoing elective ophthalmic surgery were allocated randomly to two groups to receive either saline placebo or diclofenac 75 mg i.m. 20 min before operation, in a double-blind design. Anaesthesia was induced with thiopentone 5-7 mg kg-1 followed by suxamethonium 1.5 mg kg-1 and maintained with 67% nitrous oxide and halothane in oxygen. Plasma PGE2-LA, LTC4-LA, H-LA and E-LA were measured before premedication, 1 min after the administration of suxamethonium and 24 h after operation. Muscle fasciculations, intubation conditions and postoperative myalgia were graded numerically. Postoperative myalgia in the diclofenac group was significantly (P < 0.05) less (47.1%) than in the control group (76.5%). Post-suxamethonium and 24-h concentrations of plasma PGE2-LA and LTC4-LA were also significantly (P < 0.05) greater than baseline in the control group. Plasma H-LA was increased in both groups after suxamethonium and this increase was significant (P < 0.05) in the control group. We conclude that diclofenac reduces significantly the incidence and intensity of suxamethonium-induced myalgia.