WELLINGTON, NEW ZEALAND—Studies have suggested that intravenous (IV) magnesium sulfate can be used as a bronchodilator for severe asthma; however, IV administration can be unpleasant and requires careful monitoring. Thus, some clinicians have wondered: Can the isotonic nebulized form of the drug be beneficial as well? Recent evidence suggests yes, but only in certain patients.[1]

According to Richard Beasley, MD, “isotonic nebulized magnesium sulfate has a number of possible mechanisms of action in addition to its established role as a smooth muscle relaxant. Our study determined only that magnesium sulfate has an effect in severe asthma, but its range of activity needs further study.” Dr. Beasley is a Professor at the Medical Research Institute of New Zealand.

OBJECTIVE MEASURES OF IMPROVEMENT

The study by Dr. Beasley and his colleagues included 52 adult patients with severe asthma who were randomized to receive 2.5 mg of nebulized albuterol mixed with either 2.5 mL isotonic nebulized magnesium sulfate or isotonic nebulized saline; the drugs were administered at three 30-minute intervals. All the patients studied were experiencing severe asthma exacerbations (their forced expiratory volume in one second [FEV1] was less than 50% of predicted after administration of 2.5 mg nebulized albuterol). “We did not assess patients with less severe asthma as IV magnesium had not been shown to be of benefit in this group,” explained Dr. Beasley.

Primary outcomes measured were FEV1 at 90 minutes after administration of magnesium or saline, and number of hospital admissions. “We wanted objective measures of improvement,” noted Dr. Beasley; subjective variables such as symptom amelioration were not examined. At 90 minutes, FEV1 was 51.2% of predicted in the magnesium group and 41.3% of predicted in the saline group. Compared with baseline measurements, these numbers represent an improvement of 0.72 L in the magnesium group but of only 0.35 L in the saline group. Additionally, the number of hospital admissions was significantly lower in the magnesium group than in the saline group (12 vs 17).

MOST SEVERELY ILL BENEFIT MOST

Among the 24 patients in the study with life-threatening asthma (FEV1 of less than 30% of that predicted at baseline), the 12 treated with magnesium experienced a mean 0.83-L increase in FEV1 from baseline; those administered saline had only a 0.19-L increase. “In severe life-threatening asthma, magnesium sulfate plus albuterol equals a greater effect than albuterol alone,” Dr. Beasley added.

Nebulized magnesium has not been studied in pediatric patients, but Dr. Beasley believes that this form of therapy should be a research priority. If found to be safe and effective in children, “nebulized magnesium sulfate may be better than IV because no needles are necessary, and it is easier to administer,” Dr. Beasley pointed out. The drug also has promise for treating chronic obstructive pulmonary disease (COPD), as some studies have suggested it has a beneficial effect on the condition. “COPD patients are a group that warrants further investigation,” commented Dr. Beasley.

There were no adverse events among the participants treated with magnesium, though Dr. Beasley cautioned that “the magnesium sulfate solution must be isotonic, since hypertonic and hypotonic solutions can promote bronchoconstriction.” Although further research is needed to determine whether administration of isotonic nebulized magnesium should be standard emergency department procedure for the treatment of severe asthma, the initial results look encouraging for its use as a potent bronchodilator, especially in patients with the life-threatening form of the disease.

—Tamara Gibb