Magnesium bolus or infusion fails to improve expiratory flow in acute asthma exacerbations.

HYPOTHESIS Intravenous magnesium sulfate improves objective measures of expiratory flow in patients with acute severe exacerbations of asthma. DESIGN Randomized, double-blind, placebo-controlled trial. SETTING Urban emergency department. PARTICIPANTS Forty-eight asthmatic patients aged 18 to 60 years with initial peak expiratory flow rate (PEFR) < 200 L/min who failed to double their initial PEFR after two standardized albuterol treatments. INTERVENTIONS Subjects were randomized to three groups: a loading dose of magnesium sulfate, 2 g IV over 20 min followed by 2 g/h over 4 h (infusion), magnesium sulfate, 2 g over 20 min followed by placebo infusion (bolus), or placebo loading dose and infusion (placebo). All subjects received standardized aminophylline and steroid therapy. MEASUREMENTS The PEFR and FEV1 were measured at the start of the loading dose, and 20, 50, 80, 140, 200, and 260 min later using a water-displacement spirometer. Changes from baseline were compared by one-way analysis of variance for repeated measures. RESULTS Magnesium sulfate administration did not at any time significantly improve either FEV1 (F = 0.036, p = 0.96) or PEFR (F = 0.51, p = 0.61). This study had the power to detect a PEFR difference of 26 L/min and a FEV1 difference of 0.19 L between groups (beta = 0.20, alpha = 0.05 two-tailed significance). CONCLUSION Use of IV magnesium sulfate in addition to standard therapy does not provide clinically meaningful improvement of objective measures of expiratory flow in patients with moderate to severe asthma exacerbations.