Efficacy of Gamithromycin Injectable Solution for Control of Pneumonia in Cattle Challenged with Histophilus somni after Treatment

Recently weaned calves transported to the feedlot are at risk of infection, illness and even death from Histophilus somni and other pathogens associated with bovine respiratory disease (BRD) throughout the feeding period. Gamithromycin is an azalide 15-membered semi-synthetic macrolide antimicrobial that is licensed in the European Union and Canada for therapeutic and preventative treatment of BRD associated with Mannheimia haemolytica, Pasteurella multocida, and H. somni. This placebocontrolled study evaluates the efficacy of gamithromycin injectable solution administered subcutaneously to cattle at 6.0 mg/kg body weight for control of the development of pneumonia in cattle challenged with H. somni approximately 6 hours post-treatment. Mean depression and respiratory scores were significantly lower (P<0.01) for the gamithromycin treated group than for the saline control group throughout the 7-day evaluation period. Mean rectal temperatures were significantly lower (P<0.01) for gamithromycin treated calves from Day 1 through Day 6. Total weighted percentage lung consolidations were significantly (P<0.01) lower in the gamithromycin group than in the saline group. In total, 16 calves in the saline control group, and seven from the gamithromycin group had one or more bacterial pathogens cultured from lung samples collected at necropsy. In this study, gamithromycin treated calves had an excellent safety and tolerability profile compared to those calves receiving saline. Results of this study indicate that gamithromycin administered subcutaneously at 6.0 mg/kg was significantly efficacious in the prevention of clinical and pathological disease induced by