Carprofen – brand name Rimadyl – is a very widely used pain medication classified as a non-steroidal anti-inflammatory medication (NSAID). Many owners see the benefit their dogs exhibit when on the medication, especially pets with chronic pain issues such as osteoarthritis.
While veterinarians prescribe this medication for a wide range of reasons including post surgical pain, trauma, and degenerative joint issues, there are serious side effects that can occur both with sort term and long term use. Below is a discussion about the drug so pet owners can understand some of the risks involved using this medication.
Background
NSAIDs are used for pain relief successfully in humans but the development of safe NSAIDs for dogs has only been achieved relatively recently and continues to be problematic in the cat. With the possible exception of aspirin, none of the human drugs listed above can be safely used in pets and even aspirin (without very careful dosing) has its issues.
Problems have in the past been related to:
- Stomach ulceration – even perforation and rupture of the stomach can occur. This is not only painful but potentially lethal.
- Platelet deactivation – platelets are the cells controlling the ability to clot blood and, as a general rule, it is preferable not to promote bleeding. We would prefer platelets to remain active and able to function should we need them.
- Decreased blood supply to the kidney – this could tip a borderline patient in to kidney failure.
The veterinary profession had been in need of an NSAID that could effectively relieve pain without the above risks. Carprofen is one of the safer veterinary drugs in this class that answer this need in dogs.
This new plane of safety is made possible by new scientific knowledge. Many of the biochemicals responsible for the pain and inflammation we want to alleviate are produced by an enzyme called cyclo-oxygenase 2. The goal is to inhibit this enzyme without inhibiting its counterpart cyclo-oxygenase 1. Both enzymes produce prostaglandins but we want to keep our constitutive prostaglandins that help maintain our bodies (these come from COX-1) but not make the inflammatory prostaglandins that come from COX-2. NSAIDs like aspirin inhibit all COX enzymes, good and bad alike. Most human bodies are okay with this but most dogs and cats are not.
Carprofen is what is called a COX-preferential NSAID, which means that it inhibits COX-2 much more strongly than COX-1 and this new plane of safety has enabled dogs to have long term oral pain relief with minimal side effects potential. Many canine lives have been extended with good quality because of the advent of this class of pain relief.
How This Medication Is Used
Carprofen can be given as one single daily dose or the daily dose can be divided such that half is given in the morning and half in the evening.
A dog that is potentially a candidate for long-term use of carprofen should have a complete examination by the veterinarian, a screening blood panel to establish baseline biochemical values, and ideally some kind of recheck testing two weeks after starting carprofen. This is because most adverse reactions, unusual as they may be, occur within this initial time frame and it is important that they be recognized before they get out of hand. After this initial period, complete blood panels should be screened every 6 months, an important step with any medication for long term use, not just the NSAIDs.
Carprofen is approved only for use in dogs and was designed for long-term use in dogs. Cats are more sensitive to NSAID side effects than dogs and require different pain relief regimens. This drug should never be used in cats.
Side Effects
Stomach upset: vomiting, diarrhea, and/or appetite loss are the important side effects to watch for, especially in the three weeks or so after beginning long term carprofen. These symptoms can have multiple meanings so it is important to sort them out.
- Some dogs are simply sensitive to NSAIDs, despite the COX-preferential nature of carprofen described above. These dogs simply need nausea relief in the short term and a different pain management regimen after recovery.
- Some dogs have an unrecognized liver problem. Carprofen is removed from the body by the liver which means that the liver on carprofen has extra work. This is not a problem for a normal liver but a diseased liver could be tipped into failure from the extra load. This is why screening tests are so important prior to long term use.
- Another problem manifesting with upset stomach is an idiosyncratic hepatopathy (a liver condition that is not dose-dependent or predictable in any way). While this only occurs in 1 in 5000 dogs, it is a more serious problem which likely would require hospitalization.
If a dog on carprofen develops an upset stomach, discontinue the medication and report the problem to your veterinarian. It is prudent to check liver enzymes (a blood test) to rule out the two liver side effect issues that could manifest with upset stomach.
Other side effects typically require other pre-existing conditions that could be made worse by giving an NSAID (even a COX-preferential one). See the Concerns and Cautions section.
Stomach upset occurs in less than 2 percent of dogs taking carprofen but should be taken seriously to be on the safe side.
Interactions With Other Drugs
Multiple drugs of the NSAID class should not be used concurrently as the potential for NSAID side effects increases. This means greater chance of exactly what we had hoped to avoid by using a COX-preferential NSAID instead of a non-preferential NSAID: stomach irritation/ulceration, altered kidney function, inappropriate bleeding.
For similar reasons, NSAIDS should not be used in conjunction with corticosteroid hormones such as prednisone, dexamethasone, etc. A 5 to 7 day rest period is recommended when changing over to carprofen or to another NSAID from carprofen.
Aspirin poses an exception due to its strong platelet inactivating abilities so 10 to 14 days is recommended when switching to carprofen from aspirin. Allow at least one week between prednisone and carprofen.
If carprofen is used concurrently with phenobarbital, it is especially important that appropriate liver monitoring be performed. I recommend bile acids testing every 6 months for dogs on phenobarbital. These two drugs interact such that neither may work well if they are used together.
ACE inhibitors such as enalapril or benazepril may not be as effective in the presence of carprofen (ACE inhibitors are used to treat hypertension or heart failure). This is because ACE inhibitors depend on the dilation of blood vessels in the kidneys and such dilation can be interfered with by NSAIDs).
In 9 percent of all adverse reactions reported regarding carprofen, concurrent use with corticosteroids was reported.
Concerns And Cautions
Carprofen is available as a chewable tablet which is highly palatable to animals. This increases the potential for accidental overdose should a pet gain access to a large amount of chewable tablets. Keep chewable carprofen out of the reach of children and pets.
