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.