The effect of inhaled RS 7540, a xanthone, on exercise-induced asthma.

The effect of 71 oxo-7-thiomethoxyxanthone-2-carboxylic acid sodium salt (RS 7540) in inhibiting exercise-induced asthma was compared with that of placebo in a double-blind crossover study. Single doses of 40 mg were given by inhalation to 12 patients. Ten of these subsequently received a dose of 20 mg. RS 7540 at both dose levels had a statistically significant effect in giving total or partial protection from exercise-induced bronchospasm; however, no dose relationship was apparent.