Do antiarrhythmic doses of magnesium potentiate vecuronium?

The purpose of this study was to investigate whether magnesium sulfate (MgSO4) at a dose commonly used to treat arrhythmias potentiates vecuronium. After Institutional Review Board approval, 20 randomly assigned, consenting patients received a bolus of either MgSO4 (30 mg/kg) or placebo in a blinded fashion. Immediately after receiving the bolus of either MgSO4 or placebo, the study patients were taken to the operating room (OR) and anesthetized. The ED95 of vecuronium was determined in both groups by administering 10 micrograms/kg boluses of vecuronium until 95% twitch depression was measured. Delay to 25% twitch height recovery (indicating that the neuromuscular block could be reversed for extubation) was measured in 10 patients. Ultrafilterable magnesium levels were measured in a total of 13 patients. Magnesium levels were drawn before the magnesium/placebo bolus, 5 minutes after bolus, and 30 minutes after bolus. The data did not demonstrate any relationship between the use of MgSO4 at 30 mg/kg doses and either the ED95 or the duration of vecuronium. A 30 mg/kg bolus of MgSO4 roughly doubled ultrafilterable magnesium levels from baseline. The limited sample size precluded making any firm conclusions from this data. The data trend suggested that antiarrhythmic doses of MgSO4 may not potentiate vecuronium.