The association of erythromycin ethylsuccinate with acute colitis in horses in Sweden.

A study conducted in Sweden suggests that low doses of erythromycin ethylsuccinate, an antibiotic, could cause severe colitis in horses, with Clostridium difficile identified as a potentially causative agent.

Research Context

• The study was generated by reports in Sweden of mares developing acute colitis (inflammation of the colon) when their foals were being treated for Rhodococcus equi pneumonia using a combination of antibiotics, namely erythromycin and rifampicin.
• Researchers found that such cases necessitated an investigation into the relationship between erythromycin ethylsuccinate and acute colitis in horses.

Research Methodology

• In the study, six adult horses were given low oral dosages of the mentioned antibiotics, either singly or in combination.
• Observations were made to document any changes in horses’ health, primarily looking for symptoms of colitis.
• Additionally, faecal samples were analyzed to detect the presence of pathological bacteria known to induce colitis.

Research Findings

• Within three days post administration of erythromycin, two horses developed severe colitis, one of which was a fatal case. This included one case involving a combination treatment with rifampicin.
• Clostridium difficile was isolated from one of the horses, though no specific pathogens were identified in the other.
• Both of these horses displayed typical changes in blood parameters, namely those indicative of acute colitis.
• A third horse, which was administered a lower dose of erythromycin in combination with rifampicin, had Clostridium difficile isolated from its faeces. Though this horse exhibited very mild clinical symptoms, it recovered spontaneously.
• The fourth horse, which was only given erythromycin, was found to have very high numbers of Clostridium perfringens.
• No clinical symptoms were observed in the horses that were only given rifampicin, and no significant changes were identified in their faecal flora.

Study Conclusion

• The research concluded that low doses of erythromycin ethylsuccinate can cause severe colitis in horses and can result in significant changes to the intestinal microflora.
• The bacterium, Clostridium difficile, was identified as a potential causative agent in antibiotic-induced acute colitis.

Implications of the Study

• This study emphasizes the need to reassess and review treatment methods involving erythromycin for horses, considering the potential for severe colitis.
• The findings could contribute towards the development of safer alternative treatment methods and preventative measures against Rhodococcus equi pneumonia in young horses.