LAUSR

Background There is conflicting data regarding the efficacy of tulathromycin for the treatment of foals with bronchopneumonia. Hypotheses Tulathromycin is effective for the treatment of bronchopneumonia in foals and noninferior to the combination of azithromycin and rifampin. Animals A total of 240 foals on a farm endemic for infections caused by Rhodococcus equi. Methods In a controlled, randomized, and double‐blinded clinical trial, foals with ultrasonographic pulmonary lesions (abscess score 10–15 cm) were allocated to 3 groups: 1—tulathromycin IM q 7 days (n = 80); 2—azithromycin‐rifampin, orally q24h (n = 80); or 3—untreated controls (n = 80). 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. Results The proportion of foals that recovered was significantly higher for foals treated with tulathromycin (70 of 79) or azithromycin‐rifampin (76 of 80) compared to that of control foals (22 of 80). The difference in the percentage of efficacy of azithromycin‐rifampin versus tulathromycin was 6.4% (90% CI = −0.72–13.5%). Given that the confidence interval crossed the predetermined noninferiority limit of 10%, the null hypothesis that the response rate in the azithromycin‐rifampin group is superior to that of the tulathromycin group could not be rejected. Resolution of ultrasonographic lesions occurred faster in foals treated with azithromycin‐rifampin than in foals treated with tulathromycin. Conclusion and clinical importance Tulathromycin was effective for the treatment of bronchopneumonia in foals at this farm but not as effective as the combination of azithromycin‐rifampin.