It isn’t for lack of effort that the equine industry still doesn’t have new options for treating Rhodococcus equi pneumonia in foals. According to Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM, professor of equine medicine at Texas A&M University, he and his colleagues are well aware that veterinarians are in dire need of better antibiotic alternatives. “Treatment of foals with R. equi pneumonia is generally prolonged, making treatment both expensive and labor-intensive,” said Cohen in his presentation at the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md. “Currently, the treatments of choice are a combination of the drug rifampin with azithromycin, clarithromycin, or erythromycin.”

The latter three drugs are members of a family known as macrolides. Cohen explained the significance of macrolides, noting, “To date, alternatives to macrolides for effective treatment of R. equi pneumonia in foals have not been identified. Thus, when new macrolide treatments are developed, there is considerable interest among equine practitioners and farm managers about the prospects of using these new macrolides to treat foals with pneumonia.”

One of the disadvantages of azithromycin, clarithromycin, or erythromycin is that these must be administered at least every 24 hours. Because treatment is generally prolonged, availability of a macrolide that could be administered less frequently to foals is desirable.

Tulathromycin is a long-acting injectable macrolide antibiotic, and data from Germany has suggested tulathromycin was useful for managing abscessing pneumonia in foals at a large breeding farm