INTERACTION OF MAGNESIUM-SULFATE WITH VECURONIUM-INDUCED NEUROMUSCULAR BLOCK

We have investigated the interaction between magnesium sulphate 40 mg kg(-1) i.v. and vecuronium. First, we determined the effect of pretrea tment with magnesium on the potency of vecuronium using a single bolus dose-response technique. In addition, we compared the time course of vecuronium-induced neuromuscular block (vecuronium 100 mu g kg(-1)) wi th and without magnesium pretreatment. For both parts, neuromuscular b lock was assessed by electromyography. In addition, the effect of magn esium pretreatment on vecuronium-induced neuromuscular block was inves tigated in the context of rapid sequence induction of anaesthesia. We found that the neuromuscular potency of vecuronium was increased by pr etreatment with magnesium sulphate. The ED(50) and ED(90) of vecuroniu m with MgSO4 were 25% lower than MgSO4 (ED(50): vs 26.9 mu g kg(-1); 3 4.2 vs 45.7 mu g kg(-1); P < 0.05 for both). Mean onset time was 147.3 (SD 22.2) s in the MgSO4-vecuronium group vs 297.3 (122) s for contro ls (P < 0.05). Clinical duration was prolonged (MgSO4-vecuronium 43.3 (9) min vs 25.2 (5.1) min for controls; P < 0.05). This was also true for the recovery index (20.1 (6.6) min vs 10.6 (3.4) min; P < 0.05) an d duration to 75% recovery (63.4 (9.9) min vs 35.8 (6.9) min; P < 0.05 ). in the context of rapid sequence induction, pretreatment with MgSO4 improved the intubating score of vecuronium compared with vecuronium without MgSO4, reaching the same quality as that with suxamethonium 1 mg kg(-1). We conclude that magnesium pretreatment increased the neuro muscular potency of vecuronium, in addition to modifying the time cour se of its neuromuscular block.