Background: Although long-term administration of 14-membered macrolide antibiotics is a therapeutic alternative in asthma, both its pharmacologic mechanism of action and association with the pathogenesis of asthma remain obscure.
Objective: This study investigated the suppressive effect of clarithromycin on airway responsiveness to methacholine provocation testing and examined whether chrarithromycin's antiasthmatic activity is associated with a reduction in eosinophilic inflammation.
Methods: For 8 weeks, patients received 200 mg of clarithromycin or identical-appearing placebo twice daily. We assessed the effects of treatment with clarithromycin on bronchoconstriction precipitated by inhalation of methacholine in 17 adults with mild or moderate bronchial asthma who were in stable clinical condition. A double-blind, randomized, crossover design was used. Eosinophil counts and eosinophilic cationic protein (ECP) levels were determined in blood and sputum samples obtained on the morning of the methacholine provocation testing day.
Results: After 8 weeks of treatment with clarithromycin, patients' symptoms, blood and sputum eosinophils counts and sputum ECP levels were significantly decreased compared with both placebo and baseline. Furthermore, values of PC20 methacholine improved in all patients after clarithromycin treatment.
Conclusions: Clarithromycin has a bronchial anti-inflammatory effect associated with decreased eosinophilic infiltration. This study suggests interesting therapeutic possibilities for bronchial asthma that warrant further trials.