Azathioprine
Azathioprine is used mainly in dogs with immune-mediated disease, often alongside a glucocorticoid. Clinical effects are delayed, and marrow or liver toxicity can precede obvious clinical deterioration.
Group
Thiopurine immunosuppressant
Mechanism of Action
Conversion to mercaptopurine and thioguanine metabolites interferes with purine metabolism and nucleic-acid synthesis, suppressing proliferating lymphocytes.
Dose Rates
Dog
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Immune-mediated disease — Initial | 2 mg/kg | PO | Every 24 h | Continue the initial schedule only until the planned clinical and laboratory reassessment; benefit is delayed. |
| Immune-mediated disease — Maintenance | 0.5–1 mg/kg | PO | Every 48 h | After response or as part of the tapering plan; continue CBC and liver monitoring. |
Horse
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Immune-mediated disease | 3 mg/kg | PO | Every 24 h | Limited equine clinical experience; monitor CBC and hepatic indices. |
Indications
- Selected immune-mediated hemolytic anemia, pemphigus and chronic inflammatory enteropathy in dogs.
- Selected immune-mediated disease in horses where a suitable alternative is unavailable.
Contraindications
- Avoid in cats because of marked susceptibility to myelosuppression.
- Pre-existing marrow suppression, serious active infection or major hepatic dysfunction.
- Avoid use in animals intended for food.
Interactions
- Allopurinol inhibits thiopurine breakdown and can cause severe marrow toxicity; avoid routine coadministration.
- Other myelosuppressive agents increase cytopenia risk.
- Concurrent corticosteroids increase immunosuppression and infection risk.
Adverse effects
- Myelosuppression and cytopenias.
- Hepatotoxicity, particularly early in treatment.
- Vomiting, diarrhea and secondary infection.
- Possible pancreatitis.
Toxicity
Obtain baseline CBC and hepatic indices and repeat early and periodically, including at about two weeks. Withhold or adjust treatment for cytopenia or liver injury; recovery may lag after discontinuation. Include platelet counts in serial hemograms. CBC checks every 1–2 weeks during initiation are commonly used; monitoring during maintenance remains necessary because delayed cytopenias can occur. Interpret trends with clinical findings when deciding whether to reduce or withhold treatment.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Azapure 50 mg tablet | Tablet | 50 mg / tablet | PO |
| Azofit 50 mg tablet | Tablet | 50 mg / tablet | PO |
