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RIMADYL UPDATE
by Ross Becker
Posted with permission from Good Dog! Magazine
January/February 1998 Issue

Copyright 1998 Good Dog! Magazine. All rights reserved. For a free sample issue, call 1-800-968-1738 or e-mail your name and earth-mail address to: gooddogmag@aol.com (This article MAY be downloaded, copied for personal use and reposted electronically, as long as the complete copyright notice is included. Any commercial use or print publication must be cleared with the publisher.)

In the November/December 1997 issue of GOOD DOG!, Wendy Houtz wrote a glowing review of her test of Rimadyl(R) (carprofen) for dogs with arthritis. The new drug was working wonderfully to eliminate her dog, Fisher's, pain, resulting in a complete change of personality. That kept Fisher from being put to sleep for aggressive behavior. The drug had been shown to be quite safe in all of its safety and toxicity studies, and the FDA approved it for sale in the U.S. It seemed a veritable fountain of youth for arthritic dogs. But for a few dogs, there's been a high price. With about 500,000 dogs now having taken Rimadyl, some adverse reactions have shown up that weren't seen in the original clinical trials. Some dogs who were taking Rimadyl have even died. Because many dogs receiving Rimadyl are older, Pfizer Animal Health is now recommending that a geriatric examination and appropriate lab tests be given prior to using Rimadyl. Here at Good Dog! we now think it's important to establish that kind of baseline for ANY DOG who is going to be taking Rimadyl.

Rimadyl is an NSAID - a non-steroidal anti-inflammatory. Other NSAIDs include aspirin, ibuprofen, ketoprofen, and acetaminophen. If it's a pain reliever or anti-inflammatory and it's not a steroid, it's an NSAID. As a class of drugs, the NSAIDs tend to have some common side effects, including stomach irritation, and potentially, liver and kidney problems. Of course, there's risk involved whenever any medication is taken. As you read all of these adverse reactions, remember that only a few dogs will have these reactions, and that they have not yet been definitively linked to Rimadyl usage. There may have been other causes, especially since the average Rimadyl user tends to be an older dog.

The most serious side effect seen is a rare liver reaction. Dogs that experience this reaction - one out of every few thousand taking Rimadyl - usually do so after they have been on the drug between two and six weeks. When a drug reaction is seen, it's because the drug is metabolized into something that is toxic to that individual's liver. It causes death of some of the liver cells. Liver problems show up first as a loss of appetite, vomiting, or diarrhea. Veterinary exams have revealed jaundice (yellow color due to liver malfunction), acute hepatic (liver) toxicity, hepatic enzyme elevation, and abnormal liver function test results. Of the 40 or so dogs with liver problems, about half were Labrador Retrievers. It's not clear whether this indicates a problem in the breed's metabolism of Rimadyl or if it's because there are so many Labs on the drug. Interestingly, liver reactions also occur in some people who take NSAIDs. These reactions, while rare, are serious and potentially life-threatening. Whether dog or person, if a reaction occurs, stop the NSAID and get medical help. The sooner the condition is recognized, the more likely the chances of recovery. Late last summer, Pfizer sent a letter to all veterinarians alerting them to the liver complications. They recommended that liver function be evaluated, especially in older dogs, before they are started on Rimadyl.

A variety of urine changes have also been reported, all indicative of kidney malfunction. These include blood in the urine (hematuria), sugar in the urine (glucosuria, or sweet-smelling urine), an overabundance of urine (polyuria), urinary incontinence (urine accidents in the house), urinary tract infection, and renal tubular acidosis (RTA), which can also lead to the formation of kidney stones. Excessive thirst (polydipsia) has also been seen. Gastrointestinal (GI) symptoms - vomiting, diarrhea, or loss of appetite - are the most commonly reported side effects in dogs taking Rimadyl. In addition, there is a small risk of gastric ulcers. All NSAIDs have the potential to cause ulcers in people as well as dogs, but dogs seem especially susceptible. That's why you can't use most human NSAIDs in dogs - they can cause serious GI ulcers or even fatal perforations. Although Rimadyl seems to be safer than most NSAIDs for dogs, there are still some reports of dogs with ulcers. If ulcers develop, they can bleed into the digestive tract, causing black, tarry stools that indicate digested blood (melena) or bright red blood or flecks of blood in the vomit (hematamesis).

All NSAIDs can affect blood clotting, which is why Rimadyl is not recommended for dogs with bleeding disorders. Adverse blood-related reactions from Rimadyl include immune-mediated hemolytic anemia. That's the destruction of the red blood cells in an immune system reaction to the drug. Another immune system reaction is immune-mediated thrombocytopenia. Here, the immune system reduces the number of blood platelets. Thrombocytopenia is the most common cause of bleeding disorders. Dogs treated with Rimadyl have also been seen with blood loss anemia.

A number of other symptoms have been reported, and are mentioned in the package insert that comes with Rimadyl. Because these are rare, with 1 to 3 reports per 10,000 dogs treated, it's unclear whether these were caused by the drug or merely coincidental. Behavioral reactions include drowsiness (sedation), lethargy, hyperactivity, restlessness and aggressiveness. Nervous system (neurologic) reactions include a few dogs who staggered or stumbled in an uncoordinated way (ataxia), weakness or partial paralysis (paresis), full paralysis, seizures, and ear-related dizziness or loss of balance (vestibular signs).

Dermatological reactions have included itching (pruritus), an increase in shedding, bald or thin spots in the hair coat (alopecia), hot spots (pyotraumatic moist dermatitis), and belly bruises (ventral ecchymosis). There have also been cases of allergic reactions, including facial swelling, hives (urticaria) and redness (erythema).

If your dog is on Rimadyl and has any of these symptoms, get him off the drug immediately and see your veterinarian as soon as possible. Appropriate action has saved "the vast majority of patients," according to Pfizer's latest drug information brochure. Unfortunately, it didn't save the life of George, an 11-year old Chocolate Labrador Retriever owned by a Good Dog! reader. (Your vet is supposed to file an adverse reaction report with Pfizer.)

Many veterinarians are now recommending that Rimadyl be used intermittently for a few weeks at a time, with a few weeks off for the liver to recover. Others are tinkering with the dosage to find the minimum amount of Rimadyl necessary to restore mobility and pain-free movement.

Is Rimadyl the fountain of youth for dogs? Well, it certainly seems to have miraculous effects on many dogs. Unfortunately, it also proves our thesis that tests are wonderful, but real life often throws a curveball.

Our recommendation: If you're thinking about trying your dog on Rimadyl, have a complete battery of lab tests run BEFORE YOU START. This is a baseline for later comparison, and will show you if there are any possible problems lurking in the liver and kidneys.

Ask your veterinarian to see how small a dose of Rimadyl you can use and still have a positive effect on the pain. If the arthritis is mild or intermittent, take your dog off Rimadyl when it is not needed, in order to give the liver and kidneys a rest.

Have some more bloodwork done once or twice a year to make sure everything is still all right. And if you see any of the symptoms described in this article, see your veterinarian immediately. Rimadyl may not be right for your dog.

If you have a Labrador Retriever, we advise extra caution until more is understood about Rimadyl's effects on Labs.

Rimadyl is still a great drug for the majority of dogs with arthritis. Just keep a close eye on your dog's health, particularly in the first two to six weeks.*

Copyright (c) 1998 Good Dog! Magazine. All rights reserved. For a free sample issue, call 1-800-968-1738 or e-mail your name and earth-mail address to: gooddogmag@aol.com (This article MAY be downloaded, copied for personal use and reposted electronically, as long as the complete copyright notice is included. Any commercial use or print publication must be cleared with the publisher.)

*Senior Dogs Project Coordinator's Note: Since the appearance of this article, we have had reports of dogs having reactions after significantly longer periods.