Pretreatment with magnesium sulphate enhances vecuronium-induced neuromuscular block

The interaction between magnesium sulphate (MgSO4) and vecuronium was investigated during isoflurane-nitrous oxide-oxygen anesthesia. Neuromuscular function was evaluated by recording the single twitch of the abductor policis muscle. Anesthesia was induced with thiamylal followed by injection of vecuronium. The effects of pretreatment with MgSO4 (20 or 40 mg.kg-1) on the potency of vecuronium were compared with observations in patients without MgSO4 pretreatment (control). We also examined the serum concentration of magnesium ions after administration of MgSO4. We found that the neuromuscular effect of vecuronium was not influenced by pretreatment with MgSO4 20 mg. On the contrary, the onset time of vecuronium was decreased and the duration of action until 25% recovery was increased by pretreatment with MgSO4 40 mg. The serum concentration of magnesium ions after administration of MgSO4 40 mg was significantly higher than that after 20 mg. We conclude that pretreatment with MgSO4 40 mg but not 20 mg enhances vecuronium-induced neuromuscular block.