Bronchopneumonia in foals is a common concern in many equine facilities. In most cases, this condition is caused by Rhodococcus equi, a Gram-positive facultative intracellular pathogen. R. equi can also cause various extrapulmonary infections.1 Although R. equi is present in the environment of nearly all horse farms, clinical disease in foals may be endemic in some farms and rare in others. 

The R. equi bacteria are ubiquitous in soil. Inhalation of virulent R. equi is the major route of pulmonary infection in foals between three weeks and five months of age, although infections are also extremely rare in adult horses. Ingestion of the organism is an important route of exposure, but rarely leads to pneumonia unless a foal has multiple exposures to extremely large numbers of bacteria.1

Manure from infected foals is the chief source of bacteria contaminating the environment, and foals are usually exposed to R. equi during the first week of life. R. equi infections progress slowly, with signs of disease being difficult to detect until lung lesions reach a certain point. When this occurs, foals will exhibit decreased appetite, lethargy, fever, and rapid breathing. Cough may also be present, with nasal discharge being less common.

A wide variety of antimicrobials are effective in vitro against R. equi. However, because of the intracellular location of R. equi and its development within pyogranulomatous lesions, drugs that are effective in vitro may not be effective in vivo.3 Some data indicate that the combination of penicillin and gentamicin is ineffective, however, in some countries, this combination is still used with apparent success to treat affected foals.2

Where to buy Rifampin 

Rifampin is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. 

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

1Stieler A.L., et. al. Effects of clarithromycin, azithromycin and rifampicin on terbutaline-induced sweating in foals. Equine Vet J. 2017 Sep;49(5):624-628.

2Giguère S, et. al. Retrospective comparison of azithromycin, clarithromycin, and erythromycin for the treatment of foals with Rhodococcus equi pneumonia. J Vet Intern Med. 2004 Jul-Aug;18(4):568-73. 

3Sweeney C.R., et. al. Rhodococcus equi pneumonia in 48 foals: Response to antimicrobial therapy. Vet Microbiol 14:326-329, 1987.