In the last 10 years, an ever-expanding number of veterinary NSAIDs have been approved, much to the benefit of our patients,
especially dogs. In the North American market, these include drugs such as deracoxib (Deramaxx—Novartis Animal Health; United
States), carprofen (Rimadyl—Pfizer Animal Health; United States and Canada), meloxicam (Metacam—Boehringer Ingelheim and Merial;
United States and Canada), etodolac (Etogesic—Fort Dodge Animal Health; United States), tepoxalin (Zubrin—Schering-Plough
Animal Health; United States), tolfenamic acid (Tolfedine—Vétoquinol; Canada), and ketoprofen (Anafen—Merial; Canada). Other
drugs are occasionally used in companion animals and include aspirin (ArthriCare—Veterinary Products Laboratories) (approved
for and primarily used in dogs), acetaminophen (dogs only, not veterinary approved), and piroxicam (dogs and cats, not veterinary
approved). Table 1 provides NSAID dosages commonly used for treating chronic cancer pain [For clarity, all drugs listed in Table 1 will be referred to as NSAIDs in the text].
Table 1. NSAIDs Used to Treat Cancer Pain in Dogs and Cats
It is recommended to perform a complete blood cell count, serum chemistry profile, and urinalysis to evaluate renal and liver
function before administering NSAIDs long-term in veterinary patients. It is especially important to measure serum urea nitrogen
and creatinine concentrations, urine specific gravity, liver enzyme activities (alkaline phosphatase and alanine transaminase),
and, occasionally, serum bile acid concentrations (preprandial and postprandial) when liver enzyme activities are elevated.
Obtain baseline values, followed by a recheck after two to four weeks and then periodic reassessment every two to four months
with long-term therapy. Instruct owners to look for specific signs such as melena, vomiting, lethargy, decreased appetite,
depression, yellow discoloration of mucous membranes and sclera, and altered water intake and urine output. The most common
side effects of all NSAIDs remain gastrointestinal irritation and nephrotoxicosis. Hepatotoxicosis can also occur with acetaminophen
or because of idiosyncratic reactions to NSAIDs. Antithrombotic effects can also occur with aspirin.
Few NSAIDs are approved for cats, and their use has been rendered difficult because of marked differences in metabolism when
compared with dogs. Species differences in the glucuronidation pathways play an important role in the metabolism of many such
drugs and account for the prolonged half-life of NSAIDs in cats when compared with that in dogs.45 The NSAIDs labeled for use in cats in North America currently include meloxicam, tolfenamic acid, and ketoprofen (Table 1). Although drugs such as carprofen and piroxicam are not approved in cats, studies have been performed, and relatively safe
dosages and dosing intervals have been reported.45-47 Using the lowest effective dose and avoiding their use in cats with altered renal function are the basics of safe NSAID administration
in cats.11 Acetaminophen is extremely toxic in cats and should never be used.