Aspirin: veterinary dose and monograph

At a glance

Drug class

Analgesic

Also known as

Acetylsalicylic acid, ASA, Bayer Aspirin, Disprin

Species with doses

Dogs, Cats, Cattle, Horses, Pigs, Rabbits and Ferrets

General dose range

5–25 mg/kg PO q12–48h (variable by species) — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Antiplatelet — feline HCM thromboprophylaxis (low dose ~5 mg/cat q72h)
• Antiplatelet — canine IMHA, heartworm-associated thrombosis (low dose)
• Analgesia / antipyresis (mild — newer NSAIDs preferred)
• Anti-inflammatory (musculoskeletal — replaced by carprofen / meloxicam)
• Post-adulticide heartworm therapy (dogs, low dose) — controversial

Aspirin dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Analgesia (Plumb's, modest): Plumb’s p.115 (Lascelles 2003): analgesia 10 mg/kg PO q12h. Use buffered or enteric-coated tablets to reduce GI irritation; do not combine with other NSAIDs or corticosteroids; stop 1 week before surgery (platelet effect).
• Anti-inflammatory / antirheumatic: Plumb’s p.116 (Holland & Chastain 1995): 25 mg/kg PO q8h. Papich 5e: 20–25 mg/kg q12h PO. Use buffered aspirin; monitor for GI ulceration. Do not combine with other NSAIDs or corticosteroids.
• Antiplatelet (low dose): Plumb’s p.116: IMHA adjunct 0.5 mg/kg PO q12–24h (Noonan 2009; Weinkle 2004); glomerular disease 0.5 mg/kg q24h. Papich 5e: typically 1–5 mg/kg, as high as 5–10 mg/kg q24–48h — convincing evidence of clinical benefit is lacking.

Cats

• Analgesia (cautious): Papich 5e: analgesia 10 mg/kg q48h PO; anti-inflammatory 10–20 mg/kg q48h PO. Plumb’s p.116: 10 mg/kg PO every other day (Holland & Chastain) or q48–72h in food (Hardie). Never more often — cats lack glucuronidation capacity.
• Thromboprophylaxis — low dose: Plumb’s p.116: 5 mg TOTAL per cat PO every 72 h (Smith 2003; Fuentes 2009). This is per CAT, not per kg. Efficacy of either low or high dose is not proven (Papich).
• Thromboprophylaxis — high dose: Plumb’s p.116: 40 mg per cat q72h (Fuentes 2009) or one 81 mg tablet q72h (Meurs 2006). Papich 5e: 80 mg/cat q48h PO. Cats clear salicylate slowly — never dose daily.

Cattle

• Analgesia (extra-label): Papich 5e (ruminants) and Plumb’s p.116 (Walz 2006): 100 mg/kg PO q12h; doses up to 333 mg/kg have been given to cattle. WITHDRAWAL — Plumb’s: aspirin predates FDA approval requirements, so no meat or milk withdrawal is listed; the author suggests a MINIMUM of 1 day for milk and meat. The 1 d / 24 h recorded here is that minimum, not a regulatory withdrawal — contact FARAD.

Horses

• Antiplatelet — laminitis prevention: Plumb’s p.116 (Brumbaugh 1999): antiplatelet adjunct in laminitis 5–10 mg/kg PO q24–48h, or 20 mg/kg PO every 4–5 days.
• Analgesia / anti-inflammatory: Papich 5e: 25–50 mg/kg q12h PO (up to 100 mg/kg/day). Plumb’s p.116: 25 mg/kg PO q12h initially, then 10 mg/kg once daily (Jenkins 1987). ARCI Class 4.

Pigs

• Anti-inflammatory / antipyretic (mini/pet pig): Papich 5e: swine 10 mg/kg q6–8h PO. Plumb’s p.116: 10 mg/kg PO q4–6h (Jenkins; Davis). Carpenter’s (miniature pigs): 10–20 mg/kg PO q6–8h; use enteric-coated tablets.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Analgesia (extra-label): Papich 5e (ruminants) and Plumb’s p.116 (Walz 2006): 100 mg/kg PO q12h; doses up to 333 mg/kg have been given to cattle. WITHDRAWAL — Plumb’s: aspirin predates FDA approval requirements, so no meat or milk withdrawal is listed; the author suggests a MINIMUM of 1 day for milk and meat. The 1 d / 24 h recorded here is that minimum, not a regulatory withdrawal — contact FARAD.

Rabbits

• Low-grade analgesia: Plumb’s p.116 (Ivey & Morrisey 2000): rabbits 5–20 mg/kg PO once daily for low-grade analgesia. (The previous 10–100 mg/kg q8h was not from a rabbit reference.)

Ferrets

• Analgesia / anti-inflammatory: Plumb’s p.116 (Williams 2000): ferrets 10–20 mg/kg PO once daily (short duration of activity).

Contraindications

GI ulcers / haemorrhage. Bleeding disorders (von Willebrand, severe hepatic failure, DIC). Severe renal insufficiency / dehydration. Last trimester pregnancy. Hypersensitivity. CATS: extreme dose caution — long half-life; toxicity at small dose increments.

Species-specific warnings

Cats: LONG half-life ~38 h. Dose q48–72h ONLY. ~5 mg per cat (1/16 of 81 mg tablet) for antiplatelet.

Dogs: Modern NSAIDs (carprofen, meloxicam) preferred for analgesia. Aspirin remains useful for low-dose antiplatelet.

Adverse effects

• GI ulceration / haemorrhage
• Renal injury (especially with dehydration)
• Hypersensitivity (rare)
• Bleeding tendency (irreversible platelet effect — lasts platelet lifespan ~7–10 days)
• Cats: salicylate toxicity — anorexia, vomiting, depression, hyperthermia, metabolic acidosis

Drug interactions

• Other NSAIDs (including bute, flunixin): additive GI / renal toxicity — DO NOT combine
• Corticosteroids: additive GI ulceration
• Warfarin / heparin: additive bleeding risk
• ACE inhibitors / diuretics: additive renal injury
• Methotrexate: aspirin reduces methotrexate clearance
• Antacids: reduce aspirin absorption

Pregnancy and lactation

Avoid in late pregnancy — premature ductus arteriosus closure, prolonged labour, neonatal bleeding. Earlier pregnancy: weigh risk/benefit. FDA Category C (D in third trimester).

Monitoring

• PCV / haemoglobin every 1–2 weeks for first month
• Faecal occult blood
• BUN / creatinine — baseline + monthly on chronic therapy
• Cats: clinical signs of toxicity (anorexia, vomiting, depression) — assume toxicity until proven otherwise

Toxicity and overdose

CATS especially vulnerable — long half-life leads to accumulation. Salicylate toxicity: vomiting, depression, hyperventilation, metabolic acidosis, hyperthermia, seizures. Therapeutic range narrow in cats; signs at >50 mg/kg single dose. Dogs: GI ulceration at high doses.

Management: Decontamination if recent ingestion (emesis, activated charcoal). IV fluids with bicarbonate to alkalinise urine (target urine pH >7.5) → enhances salicylate excretion. Vitamin K1 if bleeding. Glucose and supportive care for severe acidosis. GI protection (sucralfate, omeprazole). Severe cases: dialysis.

Clinical pearls

• Feline HCM with left atrial enlargement: aspirin ~5 mg/cat PO q72h (1/16th of adult tablet) for antiplatelet — clopidogrel 18.75 mg/cat PO q24h is now first-line, aspirin is second-line
• Canine IMHA: aspirin 0.5–1 mg/kg PO q24h for antiplatelet; combine with prednisone
• CATS: never give aspirin daily — toxicity will accumulate. q48–72h dosing only.
• Always use buffered or coated aspirin if you must use it — reduces GI ulceration
• For analgesia in dogs / cats, prefer modern NSAIDs (carprofen, meloxicam, robenacoxib) — better safety profile
• Equine laminitis prophylaxis: low-dose aspirin 5–10 mg/kg PO q24h as thromboprophylaxis adjunct

Mechanism of action

Irreversibly acetylates cyclooxygenase-1 (COX-1) — permanently inactivates the enzyme for the life of the cell. Platelets (no nucleus) cannot regenerate COX → antiplatelet effect lasts ~7–10 days. Endothelial COX-1 (nucleated cells) recovers in hours → preserves prostacyclin production at low doses. COX-2 inhibition gives anti-inflammatory effect at higher doses.

Formulations and products

• Aspirin tablet 75 / 81 / 162 / 325 / 500 mg
• Aspirin buffered tablet 325 mg (Bufferin)
• Aspirin powder 50 % (500 mg/g) in flavoured base — equine (Plumb’s p.117)
• Aspirin granules 2.5 g per scoop (Arthri-Eze, equine — Plumb’s p.117)

Storage

15–25 °C protected from light and moisture.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other analgesics

• Amantadine
• Bupivacaine
• Buprenorphine
• Butorphanol
• Codeine
• Dipyrone (Metamizole)
• Fentanyl
• Gabapentin

Frequently asked questions