Dose-related effect of inhaled magnesium sulfate on histamine bronchial challenge in asthmatics.

The effects of various doses of inhaled MgSO4 on the histamine bronchoprovocation test were studied in nine asthmatics in clinical remission (FEV1 greater than 80% of predicted). The minimal effective dose of MgSO4 was 0.20 mmol, which increased the dose of histamine which produced a 20% decrease in control FEV1 (PD20) from 2.88 +/- 1.4 to 5.62 +/- 1.38 mumol, p less than 0.05. A greater increase of histamine PD20 was observed after inhalation of MgSO4 at 0.40 mmol (6.90 +/- 1.6 mumol of histamine, p less than 0.05 in comparison with baseline PD20). The decrease in bronchial hyper-reactivity produced by MgSO4 suggests that it influences smooth muscle contractility and may prove to be clinically important in the treatment of asthma.