Aspirin for Animals

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Aspirin

Aspirin, or acetylsalicylic acid, is a salicylate NSAID with analgesic, anti-inflammatory and antipyretic actions. At lower exposure it is also used to inhibit platelet function. Veterinary use has declined for many painful conditions because other agents offer more suitable species-specific evidence or tolerability.

Analgesic and antiplatelet uses involve different therapeutic objectives and exposure requirements. Platelet response is variable in animals, and species differences in salicylate elimination substantially affect persistence and accumulation.

Group

Salicylate NSAID; antiplatelet agent

Mechanism of Action

Aspirin irreversibly acetylates cyclooxygenase enzymes, reducing formation of prostaglandins from arachidonic acid. Lower prostaglandin production reduces inflammatory sensitization of pain pathways and contributes to analgesia, anti-inflammatory activity and antipyresis. Reduced protective prostaglandins also explain important gastrointestinal and renal effects.

In platelets, inhibition of COX-1 reduces thromboxane A2 formation and thereby limits platelet activation and aggregation. Because platelets cannot readily replace the acetylated enzyme, inhibition can persist beyond the presence of aspirin in plasma. The degree of suppression is nevertheless inconsistent among veterinary patients.

After absorption aspirin is hydrolyzed to salicylate, which contributes additional pharmacologic effects and is eliminated at markedly different rates between species. Aspirin’s platelet action is therefore distinct from simply selecting any NSAID, and an analgesic dose is not automatically an appropriate antithrombotic regimen.

Dose Rates

Dogs

Use / stageDoseRouteScheduleInstructions
Mild analgesia10 mg/kgPOEvery 12 h
Anti-inflammatory treatment20–25 mg/kgPOEvery 12 h
Antiplatelet treatment – typical amount1–5 mg/kgPOTypical amount is listed without an explicit repeat interval; clinical benefit is inconsistent.
Antiplatelet treatment – higher-dose course5–10 mg/kgPOEvery 24–48 hClinical antiplatelet benefit is not consistently demonstrated.
Antiplatelet treatment – research regimen0.5 mg/kgPOEvery 12 hPlatelet aggregation impairment was observed in research dogs; clinical benefit is not established.
Anti-inflammatory treatment – frequent alternative25 mg/kgPOEvery 8 h
Antipyresis10 mg/kgPOEvery 12 h
IMHA antithrombotic adjunct0.5 mg/kgPOEvery 12 hLow-dose adjunct; evaluate gastrointestinal and bleeding risk, especially with corticosteroids.
Glomerular disease antithrombotic adjunct0.5 mg/kgPOEvery 24 h
IMHA antithrombotic – daily alternative0.5 mg/kgPOEvery 24 hDescribed with azathioprine and glucocorticoids; monitor bleeding.
Perioperative ocular analgesic – incomplete route6.5 mg/kgPOTwo or three times daily before elective intraocular surgery; route is not explicitly stated and surgical bleeding risk requires assessment.

Cats

Use / stageDoseRouteScheduleInstructions
Mild analgesia10 mg/kgPOEvery 48 h
Anti-inflammatory treatment10–20 mg/kgPOEvery 48 h
Antiplatelet treatment80 mg/animalPOEvery 48 hNo clinical efficacy study validates this fixed feline dose.
Antiplatelet treatment – 5 mg alternative5 mg/animalPOEvery 72 hReported alternative; no clinical study establishes efficacy.
Antiplatelet treatment – 80 mg alternative80 mg/animalPOEvery 72 hReported alternative; no clinical study establishes efficacy.
Analgesia – fixed tablet alternative81 mg/animalPOEvery 48–72 h
Arterial thromboembolism prophylaxis40 mg/animalPOEvery 72 hHigher-dose historical alternative; clinical efficacy is uncertain.
Arterial thromboembolism prophylaxis – 81 mg alternative81 mg/animalPOEvery 72 hHistorical alternative; often less effective than other antithrombotic options.

Cattle

Use / stageDoseRouteScheduleInstructions
Analgesic and anti-inflammatory treatment100 mg/kgPOEvery 12 h
High-dose historical listing333 mg/kgPOAmount up to 333 mg/kg is described without a repeat interval; not a routine recommended course.

Sheep

Use / stageDoseRouteScheduleInstructions
Analgesic and anti-inflammatory treatment100 mg/kgPOEvery 12 h

Goats

Use / stageDoseRouteScheduleInstructions
Analgesic and anti-inflammatory treatment100 mg/kgPOEvery 12 h

Pigs

Use / stageDoseRouteScheduleInstructions
Analgesic and anti-inflammatory treatment10 mg/kgPOEvery 6–8 h
Analgesia – frequent alternative10 mg/kgPOEvery 4 h

Horses

Use / stageDoseRouteScheduleInstructions
Analgesic and anti-inflammatory treatment25–50 mg/kgPOEvery 12 hDo not exceed 100 mg/kg per day. A total daily body-weight cap cannot be encoded as an amount-only max_daily_dose.
Analgesia – initial and maintenance course — Initial25 mg/kgPOEvery 12 hThen reduce to 10 mg/kg daily.
Analgesia – initial and maintenance course — Maintenance10 mg/kgPOEvery 24 h
Analgesia – daily alternative15–100 mg/kgPOEvery 24 h
Laminitis antiplatelet adjunct5–10 mg/kgPOEvery 24–48 h
Laminitis antiplatelet – extended interval20 mg/kgPOEvery 96–120 h

Ferret

Use / stageDoseRouteScheduleInstructions
Analgesia10–20 mg/kgPOEvery 24 hDuration of effect can be short.

Rabbit

Use / stageDoseRouteScheduleInstructions
Low-grade analgesia5–20 mg/kgPOEvery 24 h

Mouse

Use / stageDoseRouteScheduleInstructions
Analgesia – historical small-rodent course100–150 mg/kgPOEvery 4 hSpecies-specific historical regimen; do not extrapolate to dogs, cats or other mammals.

Rat

Use / stageDoseRouteScheduleInstructions
Analgesia – historical small-rodent course100–150 mg/kgPOEvery 4 hSpecies-specific historical regimen; do not extrapolate to dogs, cats or other mammals.

Gerbil

Use / stageDoseRouteScheduleInstructions
Analgesia – historical small-rodent course100–150 mg/kgPOEvery 4 hSpecies-specific historical regimen; do not extrapolate to dogs, cats or other mammals.

Hamster

Use / stageDoseRouteScheduleInstructions
Analgesia – historical small-rodent course100–150 mg/kgPOEvery 4 hSpecies-specific historical regimen; do not extrapolate to dogs, cats or other mammals.

Guinea pigs

Use / stageDoseRouteScheduleInstructions
Analgesia – interval unspecified87 mg/kgPORepeat interval is not supplied.

Indications

  • Selected mild painful and inflammatory conditions, including historical osteoarthritis management.
  • Adjunctive anti-inflammatory treatment where aspirin is appropriate for the species and condition.
  • Selected antiplatelet treatment in patients at risk of platelet-associated thrombosis; response and clinical outcome evidence vary by indication.

Contraindications

  • Avoid in animals predisposed to gastrointestinal ulcers.
  • Use cautiously with coagulopathies.
  • Cats clear salicylates slowly and are especially susceptible to intoxication.
  • Heartworm-associated thromboembolism prevention lacks convincing benefit and may be inappropriate.
  • Aspirin hypersensitivity or active bleeding ulcers.
  • Use cautiously in asthma, renal or severe hepatic dysfunction, hypoalbuminemia and neonates.
  • Avoid during pregnancy, particularly late gestation; it can delay parturition.

Interactions

  • Corticosteroids increase gastrointestinal adverse-effect risk.
  • Other drugs that impair coagulation increase bleeding risk.
  • Other NSAIDs increase ulcer risk; allow an appropriate washout when changing therapy.
  • Can increase digoxin exposure or methotrexate toxicity; anticoagulants increase bleeding.
  • Urinary acidifiers can reduce salicylate elimination. Carbonic-anhydrase inhibitors can worsen systemic acidosis despite increasing urinary excretion.
  • Furosemide can delay elimination, phenobarbital can increase metabolism and spironolactone diuresis may be reduced.

Adverse effects

  • Vomiting, gastrointestinal ulceration and bleeding.
  • Platelet inhibition and increased bleeding tendency.

Toxicity

Salicylate poisoning can cause vomiting, hyperthermia, hyperventilation, acid–base disturbances, weakness, seizures and coma. Monitor blood gases, electrolytes, hydration and renal function. Decontamination, gastrointestinal protection and carefully monitored urinary alkalinization may be indicated; dialysis may be considered for severe poisoning.

Preparations

PreparationFormStrengthRoute
Aspirin 81 mg tabletTablet81 mg / tabletPO
Aspirin 325 mg tabletTablet325 mg / tabletPO
Aspirin 3900 mg tabletTablet3900 mg / tabletPO
Aspirin 15600 mg tabletTablet15600 mg / tabletPO
Aspirin 31200 mg tabletTablet31200 mg / tabletPO
Durlaza extended-release 16.2 mg capsule
Swallow intact; do not open or break.		Capsule16.2 mg / capsulePO

Monitoring and Administration

Monitor gastrointestinal signs and bleeding. Enteric-coated absorption in dogs can be erratic and incomplete; buffering does not prevent serious ulceration or perforation.

Aspirin can suppress measured thyroid hormone values after 2–4 weeks; values returned to baseline about 14 days after stopping in the described observation.

Keep tightly sealed and dry at room temperature; moisture causes hydrolysis. Extended-release Durlaza capsules must not be opened or broken.

For an avian drinking-water preparation, 5 g in 250 mL as the sole water source is described; exposure depends on intake. Because of hydrolysis, prepare fresh every 12 hours at room temperature or every 4 days refrigerated at 5°C. Monitor PCV and fecal blood when indicated; stop before planned surgery when clinically appropriate, with 1 week described for platelet recovery.

Routine aspirin after heartworm adulticide treatment lacks convincing clinical benefit and can be inappropriate; it is not a preferred prophylactic protocol. Use the metric strength of the exact bolus rather than an assumed grain conversion.

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