PRETREATMENT DIAGNOSTIC TESTS
Ideally, any animal with acute carprofen exposure expected to result in moderate or severe clinical signs should undergo pretreatment
baseline diagnostic tests to better assess the patient's risk and to tailor the treatment. This assessment is especially true
for carprofen exposure because a variety of underlying illnesses may complicate the toxicosis (see "Sidebar: Risk factors for carprofen toxicosis"). A complete blood count to obtain a baseline packed cell volume; a serum chemistry profile to assess blood urea nitrogen
(BUN), creatinine, and electrolyte concentrations as well as liver enzyme activities; and a urinalysis to evaluate the urine
specific gravity would be ideal.
Treatment involves instituting decontamination, protecting the gastrointestinal tract and kidneys, providing supportive care,
and monitoring gastrointestinal, renal, and hepatic function.
If the exposure history indicates a potential for adverse effects, decontamination is warranted. If a patient presents within
a couple of hours of ingesting an overdose of carprofen and has no condition that precludes it, induce emesis. In dogs, administer
2.2 ml/kg of 3% hydrogen peroxide (maximum 45 ml) orally. You may repeat this dose if the patient fails to vomit within 15
minutes (ASPCA APCC Database: Unpublished data, 2001-2009). Alternatively, apomorphine can be given intravenously (0.04 mg/kg),
subcutaneously (0.08 mg/kg), or in the conjunctival sac (0.25 mg/kg).2 Examining the vomitus often does not allow quantification of recovered medication because the residue of the chewable Rimadyl
is often indistinguishable from partially digested food. Nevertheless, it is advisable to attempt to reevaluate the exposure
by examining the vomitus.
Inducing emesis is an unpredictable endeavor in cats. The response to hydrogen peroxide is typically poor; apomorphine can
stimulate the central nervous system, and xylazine (0.44 mg/kg intramuscularly) can cause central nervous system depression
and increase the risk of aspiration.2 Decontamination with activated charcoal (e.g. ToxiBan—Vet-a-Mix) may be the best first step in cats.
After emesis has stopped, orally administer the first dose of activated charcoal. The ToxiBan label recommends 10 to 20 ml/kg
for a small animal.22 Because of concerns for hypernatremia, however, the ASPCA APCC recommends a lower dose of 6.6 to 11 ml/kg of the 10% solution
(alternatively, 1 to 2 g/kg of the 100% granules). A formulation containing a cathartic such as sorbitol is recommended for
the first dose.
An experimental study in beagles involving an overdose of 16 mg/kg carprofen given orally documented the efficacy of administering
2.5 g/kg activated charcoal 30 minutes after exposure. The plasma carprofen concentration was significantly reduced with activated
charcoal administration relative to the control group.23 Because of carprofen's enterohepatic circulation, multiple doses of activated charcoal can be beneficial. Subsequent doses
without cathartic are given every eight hours and at a reduced dose (3.3 to 5.5 ml/kg of the 10% solution) to minimize the
potential for osmotic diarrhea and hypernatremia. To further minimize the potential for these adverse effects, the number
of doses of activated charcoal is typically limited to three, even with the most extreme overdoses.24
Aggressive administration of gastrointestinal mucosa protectants (Table 3) is warranted as a precaution for seven to 10 days after exposure to carprofen overdoses (ASPCA APCC Database: Unpublished
data, 2001-2009). The prostaglandin E1 analogue, misoprostol, is recommended for dogs, especially if the carprofen dose exceeds 20 mg/kg or the patient is exhibiting
signs consistent with ulceration. Misoprostol is available in 100- and 200-μg tablets. Side effects include diarrhea, abdominal
pain, vomiting, and flatulence, which may be confused with the underlying carprofen toxicosis. Because of the potential for
adverse effects after several days of use, the veterinarians at the ASPCA APCC limit misoprostol administration to three to
five days after exposure (ASPCA APCC Database: Unpublished data 2001-2009). Misoprostol is also used as an abortifacient,
so its use is not recommended in pregnant dogs. Veterinary personnel or pet owners who may be concerned with this potential
should wear gloves when administering the drug or avoid handling it altogether.2
TABLE 3: GI Protectants and Antiemetics Used in Dogs and Cats with Carprofen Toxicosis
Additionally, gastric acid production can be decreased with an H2 antagonist, such as famotidine, or the proton pump inhibitor omeprazole.
A third measure to minimize the potential for ulcerative effects is to administer sucralfate, which reacts with hydrochloric
acid in the stomach to form a protective paste at the site of ulceration.2 Sucralfate administration is recommended 30 minutes before an H2 antagonist or proton pump inhibitor since it requires an acidic environment to be efficacious.2