To determine how pretreatment with magnesium sulfate (MgSO₄) potentiates neuromuscular blocking agents. We investigated how the onset and recovery characteristics of cisatracurium are changed by pretreatment with MgSO₄.

After Institutional Review Board approval, a total of 48 ASA I and II patients were devided into 2 groups. Patients in each group received either the MgSO₄ 30 mg/kg (group M) in 0.9% normal saline (total volume 100 ml) or 0.9% normal saline (control group C) alone intravenously for 15 min before induction of anesthesia with propofol, remifentanil and cisatracurium 0.15 mg/kg. Anesthesia was maintained with propofol and remifentanil. Electromyographical responses were measured by train-of-four. Lag time, onset time, total recovery time, clinical duration, recovery index, and recovery time were measured. The mean arterial blood pressure, heart rate, and ionized magnesium were also measured.

The lag time and onset time were significantly shorter in the MgSO₄ group than the control group (P < 0.05). Recovery index, recovery time, clinical duration, and total recovery time showed no significant differences in the MgSO₄ group compared to the control group (P > 0.05). Mean arterial pressure was more significantly increased in the MgSO₄ group than in the control group at the time point immediately after the administration of MgSO₄. Heart rate showed no significant changes in both groups. The concentrations of ionized magnesium were significantly more increased at the all time point (P < 0.05).

MgSO₄ results in about 29% shortening of onset time of cisatracurium (0.15 mg/kg) without prolongation on the recovery of neuromuscular block.