Medicine side effects are under the spotlight, in the latest research from Peter Green MRCVS
FOR years, equine vets and owners have been familiar with painkiller phenylbutazone (bute), but we now know it is not the harmless medicine it was once perceived to be – and should not be given long term or as a routine medication.
Bute is classed as a non-steroidal anti-inflammatory drug (NSAID) and other medicines in the same family have recently been developed to treat inflammation and pain – such as meloxicam and flunixin, which have fewer side effects.
Vets in Denmark studied horses given these NSAIDs when they were treated at the veterinary hospital in Copenhagen; those with no history of colic, low worm burdens and under treatment for issues such as lameness and respiratory problems received these as part of their therapy.
Within two days of starting their course, some horses developed thickening of the colon wall and, during the course of treatment, most showed signs of mild colic or diarrhoea. However, none of the control horses – which received no NSAIDs – showed any of these signs.
These findings show that even the newer, “kinder” NSAIDs are likely to cause some irritation or inflammation of the bowel. The Danish vets point out that the side effects were mild and that all the horses needed the pain relief the medicines provided. Withholding NSAIDs from horses in pain would be cruel, but we must be aware that using them to excess, or unnecessarily, can present real risks.
VETS in Canada have reviewed all published evidence on the use of glucocorticoids (also known as corticosteroids, or GCs) in horses with equine asthma.
Medicines like prednisolone and dexamethasone are the mainstay of therapy for many equine asthma patients. There are long-standing suspicions, however, that these drugs are occasionally associated with serious side effects, such as severe laminitis and immunosuppression. Some powerful GCs, like triamcinolone, are usually only used for injection into joints because of the risk of such side effects.
The vets confirmed that there are risks of side effects with GCs given by mouth, or by injection into the muscle or bloodstream. The risk of laminitis seems to be greatest in patients that have suffered laminitis before, or if the patient is particularly stressed. However, they concluded that there is no risk of laminitis if the GCs are given by inhalation, using nebulised preparations.
One rather quirky finding was that powerful GCs like triamcinolone have a positive effect on lung function, even when they are injected into joints. The vets suggest that some sport horses that appear to perform more effectively after their joints are injected are actually improving because their lungs – not their joints – are working better.
NSAIDs: Journal of Equine Veterinary Science: doi.org/10.1016/j.jevs.2021.103451
GCs: Journal of Veterinary Internal Medicine: doi.org/10.1111/jvim.16189
This feature can also be read in Horse & Hound magazine, on sale date 24 June 2021
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