Studies of the effects of inhaled magnesium on airway reactivity to histamine and adenosine monophosphate in asthmatic subjects

Background Magnesium is a cation with smooth muscle relaxant and anti-inflammatory effects and may therefore have a role in the therapy of asthma. Several studies have investigated the effects of intravenous magnesium in acute or stable asthma, but little is known about the effects of inhaled magnesium. Objective To measure the effects of a single inhaled nebulized dose of 180 mg magnesium sulphate on airway reactivity to a direct-acting bronchoconstrictor (histamine) and an indirect-acting bronchoconstrictor (adenosine monophosphate [AMP]) in asthmatic subjects. Methods Two separate randomized, double-blind, placebo-controlled crossover studies, each involving 10 asthmatic subjects. In the histamine study, airway reactivity to histamine was measured and lung function allowed to recover spontaneously over 50 min before administering nebulized magnesium sulphate or saline placebo. Airway reactivity to histamine was then measured at 5 and 50 min. In the AMP study, a single measurement of airway reactivity was made 5 min after magnesium or placebo. Results In the histamine study, the provocative dose required to reduce FEV1 by 20% (PD20FEV1) was significantly lower after magnesium than after placebo, by a mean (95% CI) of 1.02 (0.22-1.82) doubling doses at 5 min (P=0.018), and 1.0 (0.3-1.7) doubling doses at 50 min (P=0.01). In the AMP study, PD20FEV1 was also significantly lower at 5 min after magnesium than after saline, by 0.64 (0.12-1.16) doubling doses (P=0.023), though this difference was not statistically significant after adjustment for differences in baseline FEV1 on the two study days. Conclusions Inhaled magnesium did not protect against the effects of these direct and indirect bronchoconstrictor stimuli in subjects with asthma, and may have increased airway reactivity to histamine.