Toxicology Brief: Naproxen toxicosis in dogs - Veterinary Medicine
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Toxicology Brief: Naproxen toxicosis in dogs
At high doses, naproxen, an NSAID commonly found in our medicine cabinets, can be harmful in dogs. Be prepared to recognize and treat this toxicosis in your canine patients.



Most cases surveyed in the literature on naproxen toxicosis in dogs report repeated exposure over multiple days. In one of these case reports, a 13-year-old male basenji was treated with 125 mg of naproxen orally twice a day for seven days for joint stiffness, arthritis, and mandibular swelling.5 The patient's weight was not included in the report; however, assuming a weight of 20 to 25 lb (9.07 to 11.34 kg), the daily dosage would have been about 22 to 28 mg/kg.

This patient developed anorexia, weight loss, abdominal pain, melena, and anemia (most likely related to GI hemorrhage since no other sources of blood loss or destruction were identified). Urinalysis showed numerous granular and hyaline casts indicating renal tubular damage. Results of a serum chemistry profile showed a normal blood urea nitrogen (BUN) concentration of 22 mg/dl (reference range2 = 7 to 26 mg/dl). The serum creatinine concentration was not reported. Naproxen was discontinued.

At the three-week recheck, the dog had improved and gained weight. The melena resolved. No other treatment was documented in the case report.5

A second case report describes a 9-year-old male Samoyed that received 5.6 mg/kg naproxen once daily for seven days for periodic shoulder stiffness.6 The patient developed vomiting and melena. Clinical pathology changes included anemia, increases in BUN and serum creatinine concentrations, increases in alkaline phosphatase (ALP) and alanine transaminase (ALT) activities, and a urine specific gravity of 1.019. The patient was treated with intravenous fluids for four days, a blood transfusion, antacid therapy (dimethicone, calcium carbonate and magnesium hydroxide combination), and cimetidine. The dog subsequently recovered.6

The only case report in a dog after a single dose of naproxen involved an elderly dachshund that received 35.7 mg/kg of the drug.7 The next day the dog became lethargic and developed abdominal discomfort, vomiting, diarrhea, and profuse hematemesis and melena. The dog recovered after receiving supportive treatment. Detailed treatment information was not included in the report.7

ASPCA Animal Poison Control Center data

The ASPCA Animal Poison Control Center (APCC) database contains 4,404 cases of naproxen exposures in dogs dating from 2001 to 2011.8 Only the single-exposure cases that the APCC staff determined had a high or medium likelihood of causing the patient's clinical findings are included here. The most commonly reported signs after ingestion of naproxen in dogs were vomiting, lethargy, diarrhea, and anorexia.8

In dogs, single doses ranging from 1 to 7 mg/kg resulted in vomiting and lethargy. In a 1-year-old dog, 7.7 mg/kg of naproxen resulted in multiple episodes of vomiting that eventually became bloody. In two elderly dogs, 7.4 mg/kg of naproxen resulted in diarrhea, inappetence, and melena in one dog, and melena and a mildly increased BUN concentration (likely due to GI bleeding) in the other dog.8 Hemorrhage into the GI tract is catabolized by the body similar to any other dietary protein source, leading to increased urea.9

In a 2-year-old dog, ingestion of 13.4 mg/kg of naproxen resulted in mild increases in BUN (38 mg/dl; reference range = 7 to 26 mg/dl) and serum creatinine (2 mg/dl; reference range = 0.6 to 1.4 mg/dl) concentrations. Whether these increases in BUN and serum creatinine concentrations were prerenal or renal in origin was not determined; however, no GI effects, such as vomiting and diarrhea, associated with increased risk for dehydration were reported in this patient.

In two 5-year-old dogs, doses of about 14 mg/kg of naproxen resulted in azotemia. In the first dog, 13.9 mg/kg of naproxen resulted in melena, inappetence, and a mild increase in serum creatinine concentration (2 mg/dl; reference range = 0.6 to 1.4 mg/dl). Because of the presence of GI signs in this dog, it is possible that the azotemia was prerenal in origin. In the second dog, 14.2 mg/kg of naproxen resulted in vomiting and azotemia. Urine specific gravity was 1.008, the BUN concentration was 64 mg/dl (reference range = 7 to 26 mg/dl), and the serum creatinine concentration was 5.8 mg/dl (reference range = 0.6 to 1.4 mg/dl), which can be interpreted as renal in origin based on the isosthenuria.

In both cases, APCC treatment recommendations included GI-protectant medications (sucralfate, H2 blockers, and misoprostol) and fluid diuresis. The actual treatments and outcomes subsequent to consultation were not reported for these patients.8

The APCC data suggest that a one-time dose of 7 mg/kg or greater can cause clinical signs of GI irritation and ulceration (vomiting, diarrhea, melena, anorexia), whereas azotemia is possible at doses ranging from 13 to 15 mg/kg. GI effects most frequently develop within two to 24 hours, and renal effects develop within 24 to 48 hours.8 The risk of adverse GI or renal effects increases with concurrent use of other NSAIDs or corticosteroids.4 Elderly patients also may be at increased risk for adverse renal effects if renal insufficiency is already present.4


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