Risk factors for carprofen toxicosis
A variety of risk factors exist for carprofen toxicosis. Animals with any previous reaction to the drug are at risk. Aged animals may have documented compromise of the liver or kidneys or subclinical disease that becomes clinical with the toxicosis.1
Any condition that results in dehydration can reduce blood flow to the kidneys and exacerbate the potential for acute renal failure, decreasing the dosage of concern for renal toxicosis to as little as 30 mg/kg (ASPCA APCC Database: Unpublished data, 2001-2009). Examples include patients with congestive heart failure receiving diuretic therapy or those with reduced cardiac output regardless of medical therapy. Unreplaced fluids lost through vomiting or diarrhea with carprofen toxicosis or underlying gastrointestinal disease may hasten the onset of renal damage.
Because the liver and kidneys are responsible for carprofen's metabolism and clearance, any preexisting disease involving these organs is likely to amplify the toxic risk by increasing the half-life and plasma drug concentration.2Concurrent administration of drugs that are also highly protein-bound may result in worsening carprofen toxicosis or create an additional toxicosis with the second agent. Some examples include phenytoin, valproic acid, oral anticoagulants, other NSAIDs, glucocorticoids, salicylates, sulfonamides, sulfonylureas, methotrexate, and digoxin.2,3
Because of the potential for changes in platelet function and coagulopathies associated with fulminant liver failure, animals with underlying coagulation disorders such as von Willebrand's disease may be at increased risk for carprofen toxicosis. The manufacturer has not specifically tested the drug in these patients but warns against its use in those animals.1
1. Pfizer Animal Health: Rimadyl Chewable Tablets package insert. Exton, Pa.
2. Plumb DC. Veterinary drug handbook. 6th ed. Stockholm, Wis: PharmaVet Inc, 2008.
3. Talcott PA. Nonsteroidal antiinflammatories. In: Peterson ME, Talcott PA, eds. Small animal toxicology. 2nd ed. St. Louis, Mo: Elsevier/Saunders, 2006;902-933.