Efficacy of DRAXXIN (tulathromycin) Injectable Solution for treatment of naturally occurring infectious bovine keratoconjunctivitis associated with Moraxella bovis in beef and dairy calves

Infectious bovine keratoconjunctivitis (IBK or pinkeye) is a common, highly contagious condition affecting primarily calves.1,2 The incubation period is typically 2 to 3 days, with a small opaque area appearing on the cornea within 2 days. Elevated body temperature and intense pain depress the appetite, and deep corneal ulceration can develop within 6 days. Most infected eyes heal within 3 to 6 weeks, although perforation of the cornea can lead to permanent blindness and disfigurement. Natural outbreaks usually peak in the third or fourth week, when as much as 80% of a herd may be infected.2 Moraxella bovis is probably the best characterized bacterial agent causing IBK. The organism produces pilus adhesions that facilitate attachment and colonization of corneal and conjunctival epithelium, and produces hemolytic and cytolytic bacterial toxins, which cause epithelial damage and necrosis of neutrophils, resulting in typical eye lesions. IBK varies from mild eye irritation to severe necrotizing inflammation, resulting in permanent scarring and vision loss, to the more severe consequences of corneal rupture and complete loss of the eye. Non-pathogenic strains of Moraxella bovis exist. Strains that do not produce pili for rapid absorption, extensive distribution into tissue, and slow elimination.7 Following label indications, DRAXXIN requires only a single dose, which conveniently reduces cattle handling. Second, DRAXXIN demonstrated in vitro antimicrobial activity against the Moraxella bovis isolates cultured from calves enrolled in this study. Cytolytic toxins produced by actively growing Moraxella bovis induce neutrophil necrosis and degranulation in the cornea, leading to neutrophil-induced corneal necrosis. Part of the equation resulting in diminished lesion severity and shorter time to improvement is likely to be reduction in bacterial numbers and reduction in the toxin and neutrophil-mediated corneal damage. Halting progression of corneal lesions and their rapid resolution are important to reduce the chance of lost value due to permanent changes causing partial or complete blindness. DRAXXIN also achieved excellent in vivo efficacy with a low MIC90 for these Moraxella bovis isolates (0.5 μg/mL; range: 0.25 to 1.0 μg/mL). Concentrations of tulathromycin in lacrimal secretions, corneal or palpebral tissues were not determined in this study.