Intravenous magnesium sulfate for bronchial hyperreactivity: A randomized,controlled, double-blind study

Background: Magnesium has been shown to be helpful in the treatment of acut e exacerbations of asthma. Conflicting data exist concerning the effect of magnesium on bronchial hyperreactivity: Methods: We performed a randomized, double-blind, placebo-controlled study to investigate the effect of intravenous magnesium sulfate on bronchial rea ctivity to metacholine in 30 subjects with bronchial hyperreactivity. Two d ays after baseline metacholine provocation, 20 subjects received 0.3 mmol/k g/h of intravenous magnesium sulfate and 10 subjects received normal saline solution. Metacholine provocation was repeated 30 minutes after the initia tion of the magnesium or placebo infusion. Results: The difference of the postinterventional minus the baseline provoc ative dose of metacholine required to decrease the forced expiratory volume in 1 second by 20% (PC20) was significantly higher in the magnesium group compared with the placebo group (0.48 +/- 0.46 mg/mL versus 0.05 +/- 0.73 m g/mL, P =.028), In the magnesium group, the PC20 significantly increased (f rom 0.83 +/- 0.54 mg/mL to 1.31 +/- 0.66 mg/mL, P =.0001), whereas there wa s no change in the placebo group (0.86 +/- 0.52 mg/mL to 0.91 +/- 0.54 mg/m L, P =.83). Conclusions: In the magnesium group, 30% of the subjects reached a normal P C20 compared with 10% in the placebo group. We conclude that intravenous ma gnesium sulfate significantly improved bronchial hyperreactivity and may se rve as an adjunct to standard treatment.