VETERINARY
The downsides to antibiotic therapy
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HERE are many different classes and types of antibiotics, all of which may result in complications. Horses can develop allergies to an antibiotic and some antibiotics can be toxic, with compromised kidney or liver function. However, one of the most frequently observed adverse effects of antibiotic therapy in horses is diarrhoea. Antibiotic-associated diarrhoea can range from mild signs requiring no treatment to severe diarrhoea, which may require hospitalisation with intensive care and it may be life threatening. Overuse of antibiotics will also lead to the development of resistance, an important emerging threat in equine medicine.
The Hippocratic oath, which encapsulates the concept that it may be better to provide no treatment than to intervene but as a result do more damage, is a central tenet of medicine introduced by the Ancient Greeks. Antibiotics are widely used to treat or prevent infections and can be life saving. However, they have potential to do great harm, and this can be easy to overlook until the worst happens. WORDS: Celia MaRR, eDitOR,equine VeteRinaRy JOuRnal, neWMaRket, SuffOlk & DR BOnnie BaRR, VMD, DaCViM PHOtOS: ROSSDale equine HOSPital, SHutteRStOCk
Antibiotic-associated Diarrhoea The mechanism whereby antibiotics lead to diarrhoea is relatively straightforward: when antibiotics are administered, their effects are not confined to stopping the infection that the horse is suffering from. They can also kill off the population of normal gastrointestinal bacterial, allowing harmful bacteria to grow. The over-growth of harmful bacterial results in an abnormal gastrointestinal environment, inflammation, and abnormal water and electrolyte secretion within the intestinal tract. This in turn results in depression, fever, and diarrhoea. Toxic molecules derived from bacterial cell walls can enter the bloodstream, trigger widespread and severe inflammation, and lead to failure of multiple organs, a process known as endotoxaemia. This process usually begins when horses are treated with antibiotics themselves, but mares can develop diarrhoea when their foals are under treatment with oral medicines, most likely because during administration, rather than swallowing the whole dose, the foal can end up with some of the drug on its face or lips and the dam ingests it. For this reason, it
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is always sensible to clean any excess drug off the foal after administration. The Equine Veterinary Journal recently published a study in which researchers in the United States attempted to determine how often antibiotic-associated diarrhoea occurs and examine whether some drugs are more risky than others. Researchers at private