Chemistry - A propionic acid derivative non-steroidal antiinflammatory agent, carprofen occurs as a white crystalline compound. It is practically insoluble in water and freely soluble in ethanol at room temperature.
Storage/Stability/Compatibility - The commercially available caplets should be stored at room temperature (15-30°C).
Pharmacology - Like other NSAIDs, carprofen exhibits analgesic, anti-inflammatory, and antipyretic activity probably through its inhibition of cyclooxygenase, phospholipase A2 and inhibition of prostaglandin synthesis.
Uses/Indications - Carprofen is indicated for the relief of pain and inflammation in dogs. It may also prove to be of benefit in other species as well, but data are scant to support its safe use at this time. In Europe, carprofen is reportedly registered for single dose use in cats, but there have been reported problems (e.g., vomiting) with cats receiving more than a single dose.
Pharmacokinetics - When administered orally to dogs, carprofen is approximately 90% bioavailable. Peak serum levels occur between 1-3 hours post dosing. The drug is highly bound to plasma proteins (99%) and has a low volume of distribution (0.12 - 0.22 l/kg). Carprofen is extensively metabolized in the liver primarily via glucuronidation and oxidative processes. About 70-80% of a dose is eliminated in the feces; 10-20% eliminated in the urine. Some enterohepatic recycling of the drug occurs. Elimination half-life of carprofen in the dog is approximately 8-12 hours.
Contraindications/Precautions/Reproductive Safety - Carprofen is contraindicated in dogs with bleeding disorders (e.g., Von Willebrand’s), those that have had prior serious reactions to it or other propionic-class antiinflammatory agents. It should be used with caution in geriatric patients or those with preexisting chronic diseases (e.g., inflammatory bowel disease, renal or hepatic insufficiency).
Adverse Effects/Warnings - Although adverse effects appear to be uncommon with carprofen use in dogs, they can occur. Mild gastrointestinal effects are the most likely to appear, but serious effects (hepatocellular damage and/or renal disease; hematologic and serious gastrointestinal effects) have been reported. Geriatric dogs or dogs with chronic diseases (e.g., inflammatory bowel disease, renal or hepatic insufficiency) may be at greater risk for developing toxicity while taking this drug. Although not proven to be statistically significant, Labrador Retrievers have been associated with 1/3 of the initial cases associated with the reported hepatic syndrome. Before initiating therapy, pretreatment patient evaluation and discussion with the owner regarding the potential risks versus benefits of therapy are strongly advised.
Overdosage - In dog toxicologic studies, repeated doses of up to 10X resulted in little adversity. Some dogs exhibited hypoalbuminemia, melena or slight increases in ALT. However, post-marketing surveillance suggests that there may be significant interpatient variability in response to acute or chronic overdoses.
Drug Interactions - Note: Although the manufacturer does not list any specific drug interactions in the package insert, it does caution to avoid or closely monitor carprofen’s use with other ulcerogenic drugs (e.g., corticosteroids or other NSAIDs). In humans, there are many interactions possible with NSAIDs. Because clinical experience is limited in dogs, the following may or may not be clinically significant: Because carprofen is highly bound to plasma proteins (99%) it may displace other highly bound drugs. Increased serum levels and duration of actions of phenytoin, valproic acid, oral anticoagulants, other anti-inflammatory agents, salicylates, sulfonamides, and the sulfonylurea antidiabetic agents may occur.
When aspirin is used concurrently with carprofen, plasma levels of carprofen could decrease and an increased likelihood of GI adverse effects (blood loss) could occur. Concomitant administration of aspirin with carprofen cannot be recommended. Probenecid may cause a significant increase in serum levels and half-life of carprofen. Serious toxicity has occurred when NSAIDs have been used concomitantly with methotrexate; use together with extreme caution.
Carprofen may reduce the saluretic and diuretic effects of furosemide and increase serum levels of digoxin. Use with caution in patients with severe cardiac failure.
As an antiinflammatory/analgesic:
a) 2.2 mg/kg PO twice daily; round dose to nearest half caplet increment (Package Insert; Rimadyl®—Pfizer)
b) For surgical pain: 4 mg/kg IV initially once; 2.2 mg/kg PO, IV, subQ or IM, repeat in 12 hours if needed.
For chronic pain: 2.2 mg/kg PO q12h (Johnson 1996)
Monitoring Parameters - 1) Baseline (especially in geriatric dogs or dogs with chronic diseases or those where prolonged treatment is likely): physical exam, CBC, Serum chemistry panel (including liver and renal function tests), UA 2) Clinical efficacy 3) Signs of potential adverse reactions: inappetence, diarrhea, vomiting, melena, polyuria/polydipsia, anemia, jaundice, lethargy, behavior changes, ataxia or seizures 4) Chronic therapy: Consider repeating CBC, UA and serum chemistries on an ongoing basis
Client Information - Although rare, serious adverse effects have been reported with the use of this drug. Clients should be informed of the risks associated with its use and be alerted to monitor for signs of potential adverse effects (see above). Should these signs present, clients should stop the drug immediately and contact their veterinarian.
Dosage Forms/Preparations/FDA Approval Status -
Carprofen 25 mg, 75 mg & 100 mg scored caplets in bottles of 100 or 250; Rimadyl® (Pfizer); (Rx). Approved for use in dogs.
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