Azathioprine

What is this medication for?

• IMHA, pemphigus, IBD, other immune-mediated diseases (steroid-sparing)
• Refractory IBD/skin disease only, with extreme caution

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.

• Taper dogs off slowly (over months) after remission of IMHA specifically — abrupt discontinuation risks rebound hemolytic crisis.

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

• Bone marrow suppression (low white blood cell counts, low red blood cell counts, low platelet counts) (Principal adverse effect)
• stomach/intestinal upset, poor hair growth, pancreatitis, liver damage (Reported)

⚠️ 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
• has or has had: Cats — extreme caution, many avoid altogether; hepatic dysfunction; taper slowly after remission (rapid withdrawal can trigger rebound hyperimmune response, esp. IMHA)

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Allopurinol
  • ACE inhibitors, TMP/sulfa, cyclophosphamide
  • Corticosteroids
  • Warfarin

Storage and handling

Room temperature, tight container. Compounded suspension stable 60 days.

Good to know

• Cats are disproportionately sensitive due to low TPMT activity — most clinicians avoid azathioprine in cats altogether, using chlorambucil instead for feline immunosuppression.
• Taper dogs off slowly (over months) after remission of IMHA specifically — abrupt discontinuation risks rebound hemolytic crisis.
• Onset of clinical benefit can take weeks — don't judge treatment failure too early.