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Allopurinol

Prescription
Xanthine oxidase inhibitor
Last reviewed 21 Apr 2026 · PetCare.AI Editorial Team
Species
Dog, Cat
Brands
4 available
Interactions
1 documented
Formulations
2

Mechanism of action

Inhibits xanthine oxidase, the enzyme that converts hypoxanthine to xanthine and xanthine to uric acid; reduces uric acid production and is used to prevent urate urolithiasis and treat Leishmania

At a glance

Class
Xanthine oxidase inhibitor
Schedule
Prescription
Storage
Below 25°C, protect from moisture and light

Dosing

🐕

Dog

Urate urolithiasis prevention (Dalmatians, portosystemic shunts), leishmaniasis adjunct
Dose
10–20 mg/kg
Route
PO
Frequency
BID to TID
Max dose
300 mg/dose; 900 mg/day
Duration: Long-term for urate prevention; with antimonials for Leishmania
🐈

Cat

Urate urolithiasis (rare)
Dose
10–15 mg/kg
Route
PO
Frequency
SID
Max dose
100 mg
Duration: Long-term as needed

Formulations

💊

Tablet — 2

Strength
100mg
Available in India
Strength
300mg
Available in India

Storage

Below 25°C, protect from moisture and light

Safety

Absolute contraindications — do not use

  • Known hypersensitivity to allopurinol
  • Concurrent azathioprine
    Allopurinol inhibits xanthine oxidase metabolism of azathioprine — FATAL myelosuppression; reduce azathioprine dose by 50–75% if absolutely necessary
    azathioprine6-mercaptopurine

Adverse effects

Common
Xanthine urolithiasis (if purine intake not restricted)
Serious
Hepatotoxicity
Vasculitis
Xanthine stone formation

Monitoring parameters

Serum uric acidUrinalysisImaging for stonesHepatic enzymesLow-purine diet compliance

Interactions

Major — 1

Azathioprine
major
Allopurinol inhibits xanthine oxidase which metabolizes azathioprine's active metabolite 6-MP. Concurrent use causes severe 6-MP accumulation and life-threatening myelosuppression.
Management: Reduce azathioprine dose by 25-33% when combined with allopurinol. Monitor CBC every 1-2 weeks. Some references recommend avoiding combination entirely.

Brands

International

Zyloprim
Prometheus
Aloprim
Various

India

Zyloric
GSK India
Allopurinol
Cipla

FAQs

Frequently asked questions

›What is Allopurinol?
Allopurinol is a xanthine oxidase inhibitor used in pets. Inhibits xanthine oxidase, the enzyme that converts hypoxanthine to xanthine and xanthine to uric acid; reduces uric acid production and is used to prevent urate urolithiasis and treat Leishmania
›What is Allopurinol used for in pets?
Allopurinol is used in veterinary medicine for: Urate urolithiasis prevention (Dalmatians, portosystemic shunts), leishmaniasis adjunct; Urate urolithiasis (rare).
›What is the Allopurinol dose for dogs?
For dogs, Allopurinol is typically dosed as follows — Urate urolithiasis prevention (Dalmatians, portosystemic shunts), leishmaniasis adjunct: 10–20 mg/kg PO BID to TID. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Allopurinol dose for cats?
For cats, Allopurinol is typically dosed as follows — Urate urolithiasis (rare): 10–15 mg/kg PO SID. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What are the side effects of Allopurinol?
Common: Xanthine urolithiasis (if purine intake not restricted). Serious (call your vet immediately): Hepatotoxicity, Vasculitis, Xanthine stone formation.
›Does Allopurinol need a prescription?
Yes. Allopurinol is a prescription medication and should only be administered under veterinary supervision.
›When should Allopurinol not be used?
Do not use Allopurinol if: Known hypersensitivity to allopurinol; Concurrent azathioprine.

References

References

Textbooks & handbooks

  • Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
  • Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
  • Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
  • National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
  • The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/

Clinical guidelines & consensus

  • Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
  • American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.

Journals & peer-reviewed studies

  • Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
  • Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
  • ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control

Regulatory & approvals

  • Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/

Databases

  • Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →