Efficacy of the combination of doxycycline and azithromycin for the treatment of foals with mild to moderate bronchopneumonia.

Abstract

Given the importance of rifampin in treatment protocols for tuberculosis in people, its use in veterinary medicine is under increasing scrutiny in some countries and alternatives might be needed in the near future. This study was set up to evaluate whether azithromycin combined with doxycycline is effective for the treatment of bronchopneumonia in foals and noninferior to the combination of azithromycin and rifampin. This is a controlled, randomised and double-blinded clinical trial. Two hundred and forty foals on a farm endemic for infections caused by Rhodococcus equi were involved. Foals with ultrasonographic pulmonary lesions (lesion score 10-15cm) were allocated to 3 groups: azithromycin-doxycycline orally (n=81); azithromycin-rifampin orally (n=81); or untreated controls (n=78). Physical examination and thoracic ultrasonography were performed by individuals unaware of treatment group assignment. Foals that worsened were considered treatment failures and removed from the study. The proportion of foals that recovered was significantly higher for foals treated with azithromycin-doxycycline (80 of 81) or azithromycin-rifampin (81 of 81) compared with that of control foals (57 of 78). The difference in the percentage of efficacy of azithromycin-rifampin vs azithromycin-doxycycline was 1.2% (90% CI=-0.78% to 3.5%) which did not cross the predetermined noninferiority limit of 10%. Therefore, azithromycin-doxycycline was noninferior to azithromycin-rifampin within the predetermined noninferiority limit. The study was performed on a single farm, and recovery rates may differ in other locations. Azithromycin-doxycycline was noninferior to azithromycin-rifampin for the treatment of bronchopneumonia in this farm.