April newsletter: The misuse of anti-inflammatories and painkillers – user Beware!

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Your horse has had a hard work-out, show or tournament, or has an undiagnosed swelling and mild lameness. You feel bad and decide to treat it with an anti-inflammatory for a few days and see how it goes – isn’t that what everyone does?

Dr Adrienne Viljoen, European board certified Equine Internal Medicine Specialist, discusses the reasons against simply self-treating without proper veterinary advice, due to potential long term damage to the horse, sometimes resulting in organ failure and even death!

Like humans, horses will need the odd anti-inflammatory throughout their career to treat conditions such as colic and musculoskeletal pain. We, as horse owners, should however realise that these drugs can be harmful and that we should be using them with caution when administering them to our beloved animals. Seeking veterinary attention prior to administering one of these anti-inflammatory drugs is strongly advised, and preferably these drugs should not be given as “just a precaution” without real knowledge of each drug’s action and the many side effects associated with them.

What is inflammation?

Inflammation is a natural, series of biochemical reactions that takes place in all animals as a response to injury. Inflammation is the first stage of healing and involves complex reactions between local damaged cells, blood vessels, inflammatory cells and biochemical signals.

Initial results of inflammation include opening of blood vessels to the area (reddening and heat), increased permeability of blood vessels (swelling), and attraction of infection fighting white blood cells to the site.
Products of inflammation include prostaglandins and other inflammatory “mediators” that help bring about these effects. Some of these mediators directly cause pain. All of these products of inflammation are intended to rid the body of infection or injury, and to prepare it to for healing.

Inflammation is a natural process and is critical for survival but the problem is that often this process becomes excessive, creating a vicious cycle and causing more tissue damage and pain than the injury itself might.
This is where anti-inflammatory drugs may be helpful. Their role is to dampen inflammation by reducing the formation of these mediators, and thus reducing the signs of disease (swelling, pain and fever, for example) while still allowing healing to take place.

What are nonsteroidal anti-inflammatory drugs (NSAIDs)?

These are the most commonly used drugs to treat pain and inflammation in the horse and include drugs such as finadyne, phenylbutazone, meloxicam, ketofen and aspirin. NSAIDs exert their effect and reduce inflammation by stopping the formation of prostoglandins, by inhibiting the enzyme cyclo-oxygenase (COX). COX converts arachadonic acid to prostaglandins, thromboxane and prostacyclin.

By blocking this conversion of arachadonic acid, they reduce the formation of certain pain-causing products of inflammation, and they also reduce swelling and fever. They thus have value in treating a wide range of conditions in horses, from abdominal pain (colic) to joint injury and laminitis.

Although these beneficial effects of blocking prostaglandin synthesis are why we would consider administering these drugs to horses, it is the same mechanism of action that can also result in undesirable and potentially fatal side effects.
A higher incidence of NSAID toxicity occurs in neonates and dehydrated animals and these drugs should be used even more cautiously in such cases.

Prostaglandins come in many types. Some are products of the inflammatory cascade, while others have vital maintenance functions in the body. For example, one has the role of protecting the stomach and intestinal lining from acid and digestive enzymes and also has a protective role in the kidneys. Unfortunately, NSAIDS not only decrease the production of prostaglandins causing inflammation, they also reduce the formation of these beneficial prostaglandins and can cause problems to organs normally protected.

NSAID Toxicity

NSAID toxicity in horses may be associated with inappropriately large doses, but one should keep in mind that these side effects may also occur when appropriate dosages are administered.

Renal toxicity, oral and gastrointestinal ulceration and right dorsal colitis have all been associated with NSAIDs use in horses:

  • Intestinal and stomach side effects including gastric and colonic ulcers. Foals are especially sensitive to the intestinal side effects and easily develop ulcers from the use of these medications.
  • Kidney problems. This is especially true of young horses, but caution should always be used, especially in old horses and those that are otherwise ill or dehydrated.
  • Importantly, NSAIDS have the ability to “mask” a problem, making it look less severe than it really is and give cause for false hope and delayed treatment.

GASTRIC ULCERATION

Prostaglandin inhibition by NSAIDs results in decreased mucosal blood flow and disruption of the mucous bicarbonate layer in the stomach and therefore mucosal integrity resulting in gastric ulceration.

Figure 1: This horse presented for further management of a chronic heel bulb injury which had been ongoing for a few weeks. The horse had a history of chronic NSAID administration. Within 24 hours after admission severe colic symptoms were noted, unresponsive to analgesia, and colic surgery was performed. No abnormalities could be detected during surgery. A few hours post-operatively signs of endo-toxaemia and shock were observed. Humane euthanasia was carried out. Post mortem examination revealed a perforated gastric ulcer resulting in acute peritonitis. This is a good example of a horse that never displayed any signs of gastric ulcer disease, but in which the disease ultimately led to his death.

 

RIGHT DORSAL COLITIS

NSAID induced gastrointestinal toxicity can also result in right dorsal colitis. Treatment of this condition is intensive and mainly symptomatic. Right dorsal colitis is an inflammatory condition of the wall of the right dorsal colon. Loss of mucosal integrity of the colon wall can result in loss of proteins and electrolytes. Pain is another symptom associated with this condition and has to be managed with opioid analgesics to avoid further injury to the colon wall. Recovery is usually slow, and in severe cases the prognosis is always guarded (Figures 2 and 3).

Figure 2: A horse presented for further management of colic and diarrhoea. A diagnosis of right dorsal colitis was made based on a history of NSAIDs administration and ultrasonographic images of the colon wall. Another complication associated with this disease is laminitis due to the toxin absorption through the now permeable gut wall.

 

Figure 3: Note the severely thickened colon wall imaged next to the liver on the right side of the abdomen.

 

RENAL DISEASE

Renal toxicity is another potential side effect associated with NSAID use. Prostaglandins are vital for renal perfusion, especially under conditions of reduced renal function and dehydration. Administration of NSAIDs to dehydrated and toxaemic animals may contribute further to renal hypo-perfusion by exacerbating reduced renal blood flow. In some cases it may be severe enough to cause intrinsic renal damage and acute renal failure (Figure 4). Concurrent administration of other potential nephrotoxic drugs such as Forray 65 and antibiotics such as Gentamicin increases the risk for renal damage.

Figure 4: This 3-month old foal presented with lethargy of a few days duration. A detailed history revealed that the foal sustained a musculoskeletal injury a few weeks prior to presentation. Further investigation revealed that the foal was self-medicated at home and received a 4 times overdose of phenylbutazone on more than one occasion. Serum biochemistry parameters confirmed that this foal was in renal failure which was managed successfully for two years through diet modification, easy access to clean water and avoidance of any potential nephrotoxic drugs. Unfortunately the damage sustained was severe enough that humane euthanasia had to be carried out later on, all related to the initial kidney insult sustained due to NSAID overdose.

 

“Bute” was banned for use in all animals by the SA Vet Council in South Africa in May 2014 and is thus illegal to have in your possession.
Finadyne (flunixin meglumine) is now often the alternative for managing pain and a variety of inflammatory disorders in horses.
Finadyne is probably best known for its use in horses with abdominal pain –i.e. colic. This drug is a potent pain reliever and it has extra anti-inflammatory benefits that make it especially good for treating intestinal problems. It is thought to break the pain-dysfunction cycle that occurs commonly in colic cases, thereby allowing the gut to regain function.

Unfortunately, this drug is also excellent at masking the signs of colic, giving horse owners the false belief that they have fixed the colic only to find their horse is critically ill or even dead the next day.

Colic is the horse’s way of demonstrating abdominal pain of any cause, from ulcers to spasmodic colic. If the cause of colic pain is simply gas or a spasm, a “simple shot of Finadyne” may be all it takes to break the cycle and solve the problem.

HOWEVER, if there is a mechanical problem in the gut such as an impaction or displacement, injecting Finadyne without a proper diagnosis might temporarily make the horse look better but does nothing to fix the underlying problem. Unfortunately, this improvement can mislead horse owners into believing their horse has been cured but the resultant time wasted in getting appropriate veterinary attention can be the difference between life and death.

Even though pharmacological agents can aid us in many ways, a basic understanding of the mechanism of action of these drugs is essential to try and limit side effects associated with administration thereof. We may have our companion’s best interest at heart when administering these agents to them, but one should always be aware of the potential toxic effects of each and every drug we administer. Clinical signs associated with some of the side effects can be subtle and only recognised further along into the disease process when medical therapy may no longer be of benefit. It may be necessary to ask ourselves the question as to whether or not it is essential to administer these pharmacological agents, or are we just giving them for our own peace of mind?

Considering the environment

Another consideration for cautious use of NSAIDs (as much as we may not want to think about it) is the disposal of horse carcasses into the environment. A large majority of dead horses are sent to predator and vulture conservation centres. This is an important source of feed for them and if we think about it as part of the circle of life, it provides a natural and environmentally sustainable way of disposing of a large animal.
Unfortunately drugs used to treat horses while sick, or at the time of euthanasia, can be highly toxic and deadly to many animals and birds, and vultures are especially sensitive.

It is thus very important to inform any centre that may be collecting a carcass of ANY drugs that have been administered to that animal within the past few weeks. Not revealing drugs used could potentially kill any other animals in the food-chain.
Any horses put down by use of Euthanase injection will not be able to be used by any animals for feed and would need to be cremated. Ingesting Euthanase will prove fatal to all creatures.

Finadyne is also toxic to most predators and many centres will not be able to feed a carcass injected with Finadyne.
Thus, indiscriminate use of NSAIDs is not only potentially damaging to our own horses that we are trying to help, it can also have a knock on effect in the environment that we would like to protect.

As always, please feel free to contact any of our team of vets with questions or concerns.
Fourways Equine Clinic is available to assist you 24 hours a day, 7 days a week.

Fourways Equine Clinic: 011 4683393
www.fourwaysequineclinic.co.za and follow us on Facebook
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