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Safe Use of NSAIDs in Small Animals

 Article by Dr. Jim Lloyd

Prescription of non-steroidal anti-inflammatory drugs (NSAIDs) has increased markedly over the past decade. Both acute and chronic pain in small animals can be managed with NSAIDs. As with all drugs, adverse effects to NSAIDs can occur. Patient selection, drug selection, dosage selection, and ongoing patient monitoring are therefore paramount for appropriate usage of NSAIDs.

We now have a greater range of products, and more animals are being treated with NSAIDs than ever before. Pets with a longer life expectancy have a correlating increased incidence of chronic conditions (such as liver and kidney disease), which can also increase risks associated with NSAID use. We need to ensure that these increases do not cause an increase in the number of adverse effects we see in practice.

Some key points that increase the likelihood of adverse effects are:

• A diagnosis has not been made
• Steroids are given concurrently
• Higher than prescribed dosages are given
• Different NSAIDs are used on the patient, especially where this change between drugs is caused by a perceived lack of effect or the occurrence of a side effect using the initial NSAID.

NSAIDs have analgesic, anti-inflammatory and anti-pyretic action through their inhibition of the action of prostaglandins and leukotrienes. Central to their pharmacological action is the inhibition of cyclo-oxygenase enzymes (COX). COX inhibition has the potential to affect physiological processes such as gastroprotection, blood clotting, renal development and immune responses.

COX1 has long been thought to be involved in physiological functions, including cytoprotective effects, whereas COX2 is predominantly inducible and production is associated with inflammation. As such, COX1 inhibition has been implicated in the cause of most NSAID side effects. Newer NSAIDs, thought to show preferential COX2 inhibition are now in use to decrease the likelihood of adverse effects from NSAID usage.

The primary indication for NSAIDs in small animal medicine is in the management of pain. NSAIDs appear to act synergistically with opioids, which may allow a reduction in the amount of opioid analgesia required in managing mild to moderate pain. Their duration (dosage is usually every 12-24 hours) and efficacy makes them ideal for treating acute and chronic pain, including both post-operative pain and pain associated with osteoarthritis.

NSAIDs are metabolised in the liver and excreted predominantly by the kidneys in urine. It is important that both liver and kidney function are considered when NSAIDs are prescribed.

The administration of NSAIDs prior to surgery so as to achieve adequate drug levels in the immediate post surgical period remains controversial. Untoward events (which can occur with any anaesthetic) during surgery or immediately post-op may increase the risk of adverse drug effects associated with NSAIDs given pre-operatively.

The increase in NSAID usage has prompted some recommendations for their use, namely:

• Only use NSAIDs as the sole analgesic where the indications include relief of mild to moderate pain in association with osteoarthritis, soft tissue inflammation or injury, musculoskeletal injury, post-operative pain and pain associated with some cancers.
• Only use in conditions where a cause of pain has been established and a diagnosis has been made. NSAIDs should not be used where more appropriate treatment may be delayed.
• NSAIDs should not be used as the sole analgesic for animals in severe pain.
• Dosage should never exceed recommendations. NSAID dosages can be reduced based on clinical response. (Most injectable NSAIDs are labelled for single use only)
• Orally administered NSAIDs should be withheld if the animal is inappetant.
• Any switch to an alternative product should only be made after an appropriate time which allows for clearance of the initial NSAID.
• Ongoing monitoring should always occur in the case of long term NSAID therapy.
• Advice should be given on the potential adverse effects of NSAID therapy. Vomiting and inappetance associated with NSAID therapy should never be ignored.
• NSAIDs are not reversible, so general health should always be considered prior to prescribing NSAIDs.
• NSAID usage should be avoided if possible in patients with:
• Hypovolaemia
• Major or multisystemic trauma
• Brain trauma
• Hepatic disease
• Renal disease
• Gastrointestinal disease
• Inappetance
• Coagulopathies
• Cardiac Failure

If appropriate consideration is given to patient selection, choice of drug, dosage, and ongoing monitoring, many potential adverse effects of NSAIDs can be avoided. Used discerningly NSAIDs will provide improved quality of life to many patients otherwise suffering debilitating disease.