Aspirin (acetylsalicylic acid)

What is this medication for?

• Analgesia/antipyresis/anti-inflammatory (buffered products); antiplatelet adjunct (IMHA, glomerular disease, heartworm post-adulticide thromboprophylaxis)
• Analgesia/antipyretic (cautious dosing); ATE prophylaxis in cardiomyopathy

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• None commonly reported; call your clinic with any concern.

Worth a phone call to your veterinarian

• stomach/intestinal ulceration/bleeding (Dogs relatively sensitive even at antiplatelet doses)
• Toxicity (tinnitus-analog, CNS, acid-base, overheating) (Overdose/accumulation)
• Hepatotoxicity (High-dose chronic)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Hypersensitivity; active stomach/intestinal bleed/bleeding ulcers
• has or has had: Bleeding disorders, asthma, renal insufficiency (though low-dose used in glomerular disease)
• has or has had: Hypoalbuminemia (↓ dose); stop ~1 week pre-surgery; caution with severe hepatic/renal disease; do NOT combine with other NSAIDs

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Other NSAIDs / corticosteroids
  • Anticoagulants (heparin, warfarin), clopidogrel
  • Highly protein-bound drugs
  • Urinary acidifiers
  • Carbonic anhydrase inhibitors, methotrexate

Storage and handling

Room temperature; buffered formulations preferred for canine oral use.

Good to know

• Cat dosing interval is every 2–3 DAYS, not daily — the 27–45 h feline half-life (glucuronidation deficiency) makes daily dosing a classic overdose trap.
• Aspirin's COX-1 inhibition in platelets is irreversible (platelets cannot resynthesize COX) → antiplatelet effect lasts the platelet lifespan (~7 days).
• Aspirin resistance documented: low doses may fail to inhibit aggregation in some animals (COX-2-derived thromboxane) — clopidogrel adds independent, superior inhibition in cats.
• Heartworm thromboprophylaxis benefit is unproven; some evidence suggests aspirin may be contraindicated in heartworm disease (Papich).
• Overdose: alkalinize urine (↑excretion), hemodialysis if available.