BRAND NAME: RIMADYL (ZENECARP IN THE U.K.)
AVAILABLE IN 25 mg, 75 mg & 100 mg CAPLETS and chewable tablets
BACKGROUND
Carprofen is a member of the class of drugs known as NSAIDS (non-steroidal anti-inflammatory drugs), the same class as such common over-the-counter remedies as Advil (Ibuprofen), Aleve (Naproxen), Orudis (ketoprofen), and Aspirin. The chief use for such drugs in the dog has been pain relief, usually joint pain or post-surgical pain relief.
The problem with this class of drugs has been unacceptable (even life-threatening) side effects. 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 life-threatening.
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 has been in need of an NSAID that could effectively relieve pain without the above risks. In 1997, Pfizer Animal Health released this medication for dogs in the U.S. as the answer to this need. This medication had been available in the U.K. since 1994 and has earned a reputation for effectiveness and safety.
HOW THIS MEDICATION IS USED
Carprofen is used in the treatment of pain and is usually given twice a day. It takes 1-3 hours after oral administration for a dose of carprofen to reach its maximum effect.
Carprofen is approved only for canine use officially and dogs may safely take this medication long term with no ill effects. Injectable carprofen, only available in the U.K., is commonly used for post-operative pain relief in the cat but only one or two doses are typically given.. Do not use this medication in a cat without specific veterinary guidance.
SIDE EFFECTS
There is an approximately 4% or less chance of a dog on Carprofen showing any of the following side effects: nausea, appetite change, diarrhea, lethargy or constipation. If a dog develops nausea, vomiting, or appetite loss while on carprofen, it is important that the medication be discontinued and that blood testing be done to rule out a liver necrosis syndrome that occurs in one in 5000 dogs on carprofen. This syndrome is rare but can be fatal if early warning signs are ignored. This syndrome has been described primarily in Labrador retrievers taking carprofen for longer than 3 weeks.
Platelet deactivation was not found in the testing of this medication; however, Carprofen is not recommended for animals with known bleeding disorders.
Carprofen should not be used in patients with pre-existing liver disease, inflammatory bowel disease, or with known tendency towards GI ulceration.
INTERACTIONS WITH OTHER DRUGS
Drugs of the NSAID class should not be used concurrently as the potential for the aforementioned side effects increases. For similar reasons, NSAIDS should not be used in conjunction with corticosteroid hormones such as prednisone, dexamethasone etc. The University of California at Davis recommends a two week “rest” period when changing from any NSAID to carprofen or from carprofen to another NSAID.
If carprofen is used concurrently with phenobarbital, it is especially important that appropriate liver monitoring be performed. (Our hospital recommends bile acids testing every 6 months for dogs on phenobarbital.)
ACE inhibitors such as enalapril or captopril may not be as effective in the presence of carprofen. (ACE inhibitors are used in the treatment of hypertension or heart failure.)
CONCERNS AND CAUTIONS
Carprofen has not been tested in pregnant or nursing females and thus is not recommended for use in such individuals.
Hepatic necrosis syndrome in large breed dogs (especially Labrador retrievers) is a rare condition (one in 5000 at most). It is important to put this in proper perspective and follow the guidelines as described here. Many exaggerated reports and rumors have surfaced on the internet and it is important to consider only confirmed and properly investigated information.
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CVM Update
December 1, 1999
UPDATE ON RIMADYL®
FDA's Center for Veterinary Medicine (CVM) has recently compiled and reviewed adverse drug experience (ADE) reports received for 1998. During
this period, the Center received a substantial number of ADE reports for carprofen (trade name Rimadyl®) and consumer inquiries regarding the safety
of this product.
CVM has released the "1998 Annual Adverse Drug Experience (ADE) Summary" which includes information about ADEs to all veterinary drugs,
including Rimadyl®. This ADE summary is on our Home Page . Copies are also available from CVM's Communications Staff at FDA/Center for
Veterinary Medicine, HFV-12, 7500 Standish Place, Rockville, MD 20855, 301-594-1755. FDA also published a descriptive overview of the 1998
ADE reports in the November/December issue of the FDA Veterinarian. This report also is available from the Communications Staff and our Home
Page at the above address.
FDA approved Rimadyl® for dogs on October 25, 1996, after a comprehensive review of the product’s safety and efficacy. Rimadyl® is a
non-steroidal anti-inflammatory drug (NSAID) indicated for use in relief of pain and inflammation associated with osteoarthritis in dogs. NSAIDs are
commonly used in human medicine for relief of pain and include such drugs as aspirin, ibuprofen, and naproxen. Rimadyl® is one of two NSAID
products currently approved for use in dogs. The active ingredient in Rimadyl®, carprofen, is not approved for use in humans. The drug is available by
veterinary prescription only. The approved drug sponsor is Pfizer Animal Health of Exton, PA.
Pre-approval studies for Rimadyl® included a clinical trial involving 297 dogs administered either the drug or a placebo for 14 days. Similar adverse
clinical signs were observed in both the carprofen and placebo-treated groups. These signs included an increase in vomiting, diarrhea, lethargy,
behavioral changes, constipation, and an increase in liver enzymes. Safety studies revealed no remarkable side effects associated with long-term drug
administration. Based on the studies submitted to CVM, the risk of Rimadyl® was thought to be negligible.
Of all the ADE reports CVM received in 1998, thirty-nine percent (39%) or 3626 involved Rimadyl®. The number of ADE reports received by CVM
for Rimadyl® is considerably more than that received for other animal drugs. For any one ADE report, there is no absolute certainty that the suspected
drug caused the effect. The adverse effects in these reports are consistent with those expected for NSAIDs. They typically involve the gastrointestinal
system, renal/urinary system, hematopoietic (blood) system, neurological system, and the liver. Approximately 13% of the 1998 Rimadyl® ADE
reports for dogs involved death of the dog, either on their own or by means of euthanasia.
In spite of the high standards for safety and effectiveness that exist for FDA approval, not everything is known about a drug when it is first marketed.
Due to the limited number of animals and controlled nature of pre-marketing clinical trials, only the most common adverse effects will be observed.
Uncommon effects or problems may not be discovered until after the drug has been widely used.
Based on adverse experience reports received since Rimadyl® was marketed, a number of actions have been taken to provide the most current
product safety information to veterinarians and dog owners. In 1997, shortly after Rimadyl® was marketed, CVM began receiving ADE reports
involving the drug. In May 1997, CVM asked Pfizer to change the adverse reaction section of the label.
CVM also asked Pfizer to send a "Dear Doctor" letter to veterinarians informing them of the adverse effects reported with product use. In August
1997, Pfizer mailed a "Dear Doctor" letter to all veterinarians who had purchased the product. By September 1997, Pfizer had revised Rimadyl®
labeling to include an extensive adverse reaction section. The possibility of a fatal outcome was mentioned elsewhere on the label, but death was also
added to the adverse reactions section in the spring of 1999. In addition, at CVM’s request, Pfizer developed and distributed an information sheet
containing safety information for veterinarians to give to owners at the time Rimadyl® is dispensed.
A number of factors might contribute to the high number of ADE reports received for Rimadyl®:
type of drug – NSAIDs as a pharmaceutical class are commonly associated with adverse affects on a variety of body systems, particularly the
gastrointestinal system. Adverse effects on the kidney and liver have also been documented.
wide use -- Rimadyl® has been administered to 2.5 million dogs over its first two years of marketing. This represents a high level of use for a recently
approved drug.
duration of use -- Rimadyl® is intended for daily administration to dogs, possibly on a long-term basis. While Rimadyl®-related adverse effects are
reported to occur shortly after drug initiation, long-term use may result in a higher risk for adverse effects. A substantial portion of dogs receive
Rimadyl® continuously for more than 30 days.
senior dog use – Over 85% of Rimadyl® ADE reports involved dogs greater than six years of age. Rimadyl® is intended for use in osteoarthritis, a
disease condition more pronounced in older dogs. Older dogs in general may be more susceptible to carprofen-related adverse effects.
marketing of the drug -- Pfizer’s direct-to-consumer marketing strategy and professional support encourages the submission of a higher number of
ADE reports. For instance, Rimadyl® is one of the few animal drugs that provides a toll-free number on the label for reporting ADE reports to the drug
company, which facilitates reporting.
Most of the ADEs reported by owners directly to CVM involved owners of dogs who said they were not aware of the potential adverse effects
associated with Rimadyl® use. Adequate communication between the veterinarian and client should result in an awareness of the risk and benefit of
drug use and alternate therapies that are available. Additionally, communication should establish the importance of evaluation of the dog prior to
Rimadyl® initiation and the necessity of periodic follow-up evaluations if drug use is continued long-term. Animal owners have told CVM that adequate
communication is not occurring in many instances.
CVM will continue to evaluate ADE reports received for Rimadyl® compared to the benefits of NSAID therapy. In many dogs, the use of NSAIDs is
not an elective therapeutic choice, but the primary therapy available for maintaining an acceptable standard of life due to the long-term debilitating
effects of osteoarthritis. As an NSAID with potentially serious side effects, however, the use of Rimadyl® should be carefully considered before being
incorporated in any therapeutic plan. Moreover, dog owners should have an active role in making that decision. CVM, along with drug sponsors, is
actively pursuing a number of avenues to improve the management of NSAID safety issues in order to minimize the risks and maximize the benefits of
using these products in dogs.
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Hepatocellular Toxicosis Associated with Administration of Carprofen in 21 Dogs
<<J Am Vet Med Assoc 212[12]:1895-1901 Jun 15'98 Reports of Original Studies 27 Refs
* Catriona M. MacPhail, DVM; Michael R. Lappin, DVM, PhD; Dennis J. Meyer, DVM; Steven G. Smith, DVM; Cynthia R. L. Webster, DVM, MS; P. Jane Armstrong, DVM, MS
* Dept. of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523
- A diagnosis of hepatocellular toxicosis attributable to carprofen administration was made in 21 dogs on the basis of development of clinical signs and clinicopathologic abnormalities associated with hepatic disease and histopathologic documentation of hepatic necrosis. Clinical signs of toxicosis were anorexia, vomiting, and icterus. Hyperbilirubinemia and high serum activities of alanine transaminase, alkaline phosphatase, and aspartate transaminase were the most notable clinicopathologic abnormalities. In 7 of 9 dogs in which urinalyses were performed, abnormalities suggestive of renal tubular disease were detected. Clinical course of toxicosis was variable; however, most dogs had resolution of clinical signs and improvement or resolution of biochemical abnormalities with discontinuation of the drug and administration of supportive care. As with any medication, clients should be informed of possible adverse effects and reactions associated with administration of carprofen. In the event of those signs, clients should be instructed to immediately discontinue administration of carprofen to their dog and contact their veterinarian.