In a double-blind study, 30 children at Rhode Island Hospital with moderate to severe acute asthma exacerbations and peak expiratory flow rates (PEFR) < 70% predicted after 3 treatments with nebulized albuterol or ipratropium bromide (or both) were randomized to receive either 40 mg/kg (maximum dose 2 gm) of magnesium sulfate intravenously over 20 minutes (16 patients, 11 male, mean age 10.9 years) or normal saline (14 patients, 7 male, mean age 12 years). The children were given intravenous steroids if they had not already received steroids when the IV catheter was placed. Additional nebulized treatments were given at the discretion of the provider. Peak expiratory flow rate (PEFR), forced expiratory volume in 1 sec (FEV1), forced vital capacity (FVC), clinical asthma scores, and vital signs were recorded at baseline, before administration of magnesium or placebo, 10 minutes into the infusion, at completion of the infusion (20 minutes), 50 minutes and 110 minutes after starting the study. There was no statistical difference between the groups at baseline.
The absolute change in PEFR was 8.6% in the magnesium sulfate group vs 0.3% in the saline group at 20 minutes (P<.001), and 25.8% vs 1.9% at 110 minutes (P<.001). The authors report a similar degree of improvement in FEV1 at 20, 50 and 110 minutes for the magnesium sulfate treated patients. The magnesium sulfate group received an average of 1.6 additional albuterol treatments during the study vs 1.2 for the saline group (NS). None of the children had clinically significant changes in blood pressure. Half (8/16) of the magnesium treated patients were discharged home while all 14 saline treated patients were admitted to the hospital (P=.002).
Magnesium relaxes smooth muscle and may reduce histamine-induced bronchoconstriction.1 Studies in the 1980s and 1990s in adults with asthma produced conflicting results and an expert panel from the National Institutes of Health concluded that the efficacy of magnesium sulfate had not been established.2 However, the panel listed magnesium sulfate as a therapy to consider in severe inpatient asthma exacerbations that do not respond to established therapy.
In comparison with a similar study3 in which children received a smaller dose of magnesium sulfate (25 mg/kg), the improvement in peak flow reported in this study was twice as great, suggesting a dose response curve for magnesium-mediated bronchodilatation. The reported change from baseline of 80% in this study was possible, in part, because the baseline was so low. The authors did not report the actual peak flow after the baseline measurements. The initial asthma management included 3 inhalation treatments. The paper does not state the dose of inhaled albuterol or if the dose differed between treatment groups. After the initial therapy, the average PEFR remained less than 50% predicted, suggesting severe airway obstruction. In that situation, many providers...