Equine Science Update by: Mark Andrews
Pneumonia caused by Rhodococcus equi is an insidious, often fatal, infection of foals. It causes abscesses in the lungs and can prove challenging to treat. A combination of two antimicrobials, azithromycin (AZM) and rifampicin (RIF), is widely used for treatment. Combination therapy is necessary as bacteria rapidly develop resistance to rifampicin if it is used on its own.
However, rifampicin is important for treatment of tuberculosis in humans, and there is mounting pressure to reduce its use in veterinary medicine. This has led to a search for alternative treatments.
A report in the Equine Veterinary Journal by Wetzig and colleagues has shown that a different combination of antibiotics is no less effective for treating Rhodococcus equi bronchopneumonia in foals.
In their study, they found that foals treated with azithromycin (AZM) and doxycycline (DOX) responded similarly to those treated with AZM – RIF.
A total of 240 foals with mild to moderate bronchopnenumonia were included in the controlled, randomised and double‐blinded clinical trial. They were divided into three treatment groups:
AZM (5mg/kg) + DOX (10mg/kg) twice daily
AZM (10mg/kg) + RIF (10mg/kg) once daily
Progress of the condition was monitored by physical examination and thoracic ultrasonography, performed by individuals unaware of which treatment each foal was receiving.
Foals whose condition worsened were considered treatment failures and were removed from the study.
The research team found little difference between the recovery rate of foals in the two treatment groups. Of the AZM-DOX group, 80 of 81 foals recovered, compared with all 81 foals in the AZM-RIF group. Only 57 of 78 control foals recovered without treatment.
The researchers conclude that AZM-DOX is as effective as AZM-RIF in treating mild-moderate bronchopneumonia in foals. They suggest that doxycycline is likely to be a suitable alternative to rifampicin in such cases.
For more details, see:
Efficacy of the combination of doxycycline and azithromycin for the treatment of foals with mild to moderate bronchopneumonia
M. Wetzig, M. Venner, S. Giguère
Equine Vet Journal (2019)