# Aspirin: veterinary dose and monograph

> Aspirin is a veterinary analgesic. Oldest NSAID — irreversible COX inhibitor. Indications include antiplatelet — feline HCM thromboprophylaxis (low dose ~5 mg/cat q72h); antiplatelet — canine IMHA, heartworm-associated thrombosis (low dose); analgesia / antipyresis (mild — newer NSAIDs preferred). This monograph lists 12 reference doses for dogs, cats, cattle, horses, pigs and rabbits and 1 more species, each with route, frequency and source, plus meat and milk withdrawal periods for food animals.

Source: https://vetmasterji.com/drugs/aspirin · Last reviewed: 2026-10-01

## 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

*Aspirin doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Analgesia (Plumb's, modest) | 10 mg/kg | PO | q12h | — |
| Anti-inflammatory / antirheumatic | 25 mg/kg | PO | q8h | — |
| Antiplatelet (low dose) | 0.5–5 mg/kg | PO | q12–24h | — |

- 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

*Aspirin doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Analgesia (cautious) | 10–20 mg/kg | PO | q48–72h | — |
| Thromboprophylaxis — low dose | 5 mg/cat | PO | q72h (every 3rd day) | — |
| Thromboprophylaxis — high dose | 40–81 mg/cat | PO | q72h (Papich: 80 mg q48h) | — |

- 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

*Aspirin doses for cattle*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Analgesia (extra-label) | 100 mg/kg | PO | q12h | — | 1d slaughter / 24h milk |

- 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

*Aspirin doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Antiplatelet — laminitis prevention | 5–10 mg/kg | PO | q24–48h | — |
| Analgesia / anti-inflammatory | 25–50 mg/kg | PO | q12h | — |

- 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

*Aspirin doses for pigs*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Anti-inflammatory / antipyretic (mini/pet pig) | 10–20 mg/kg | PO | q6–8h | — | Withdrawal NOT established — treat as extra-label |

- 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.

*Aspirin doses for buffalo*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Analgesia (extra-label) | 100 mg/kg | PO | q12h | — | 1d slaughter / 24h milk |

- 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

*Aspirin doses for rabbits*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Low-grade analgesia | 5–20 mg/kg | PO | q24h | — |

- 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

*Aspirin doses for ferrets*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Analgesia / anti-inflammatory | 10–20 mg/kg | PO | q24h | — |

- 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

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

> **Caution:** 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

> **Caution:** 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](https://vetmasterji.com/drugs/amantadine)
- [Bupivacaine](https://vetmasterji.com/drugs/bupivacaine)
- [Buprenorphine](https://vetmasterji.com/drugs/buprenorphine)
- [Butorphanol](https://vetmasterji.com/drugs/butorphanol)
- [Codeine](https://vetmasterji.com/drugs/codeine)
- [Dipyrone (Metamizole)](https://vetmasterji.com/drugs/dipyrone)
- [Fentanyl](https://vetmasterji.com/drugs/fentanyl)
- [Gabapentin](https://vetmasterji.com/drugs/gabapentin)

## Frequently asked questions

### What is the dose of Aspirin for dogs?

Reference doses for Aspirin in dogs: 10 mg/kg PO q12h (Analgesia (Plumb's, modest)); 25 mg/kg PO q8h (Anti-inflammatory / antirheumatic); 0.5–5 mg/kg PO q12–24h (Antiplatelet (low dose)). Confirm against the label and the patient before use.

### What is the dose of Aspirin for cats?

Reference doses for Aspirin in cats: 10–20 mg/kg PO q48–72h (Analgesia (cautious)); 5 mg/cat PO q72h (every 3rd day) (Thromboprophylaxis — low dose); 40–81 mg/cat PO q72h (Papich: 80 mg q48h) (Thromboprophylaxis — high dose). Confirm against the label and the patient before use.

### What is the dose of Aspirin for cattle?

Reference doses for Aspirin in cattle: 100 mg/kg PO q12h (Analgesia (extra-label)). Confirm against the label and the patient before use.

### What is the withdrawal period for Aspirin?

Cattle, PO (Analgesia (extra-label)): 1d slaughter / 24h milk; Pigs, PO (Anti-inflammatory / antipyretic (mini/pet pig)): Withdrawal NOT established — treat as extra-label. Follow the product label and national regulations where they differ.

### When should Aspirin not be used?

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.

### What are the side effects of Aspirin in animals?

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.

## Sources

- Plumb's Veterinary Drug Handbook
- Papich, Papich Handbook of Veterinary Drugs, 5th edition
- Carpenter, Exotic Animal Formulary

---

VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.