Allopurinol: veterinary dose and monograph

At a glance

Drug class

Antiparasitic

Also known as

Zyloric, Zyloprim, Ciplaric

Species with doses

Dogs, Cats, Birds and Reptiles

General dose range

10–15 mg/kg PO q12h — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Canine leishmaniasis — long-term maintenance (with/after antimonial or miltefosine)
• Urate urolith prevention/dissolution — Dalmatians, portosystemic shunt dogs, urate stone-formers
• Hyperuricaemia / tumour-lysis prophylaxis

Allopurinol 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

• Leishmaniasis (maintenance): Papich 5e: 10 mg/kg PO q12h for at least 4–6 months; some use 15 mg/kg q12h then 7–10 mg/kg q12–24h once responding. Plumb’s p.53: 10 mg/kg PO q12h for 6–12 months with meglumine antimoniate or miltefosine, or alone (Solano-Gallego); 20 mg/kg q12h for 9 months (Brosey); 5 mg/kg q12h with renal insufficiency (Font). Watch for xanthine urolithiasis — feed a low-purine diet.
• Urate urolith dissolution / prevention: Papich 5e: 10 mg/kg PO q8h, then reduce to 10 mg/kg q24h. Plumb’s p.53: dissolution 15 mg/kg PO q12h with a low-purine diet; prevention 10–20 mg/kg/day, preferably relying on diet alone (Osborne); 7–10 mg/kg PO q8h (Senior). Prolonged high doses cause xanthine stones; reduce with renal impairment.

Cats

• Leishmaniasis: Plumb’s 10e p.38 (extra-label): feline leishmaniasis — 10–20 mg/kg PO every 12 or 24 hours long-term. This is the only cat dose in Plumb’s 10e; Papich 5e gives none. Monitor for xanthine urolithiasis and renal function.

Birds

• Gout / hyperuricaemia: Plumb's p.54: budgies/cockatiels/parakeets — crush one 100 mg tablet in 10 mL water, add 20 drops per ounce of drinking water (McDonald 1989; Clubb 1986). ⚠ Red-tailed hawks are SENSITIVE — 50 mg/kg caused vomiting/hyperuricaemia/renal dysfunction; 25 mg/kg was safe but ineffective.

Reptiles

• Gout / renal hyperuricaemia: Plumb's p.54: lizards with elevated uric acid / gout 20 mg/kg PO once daily (de la Navarre 2003; Johnson-Delaney 2005); green iguanas 25 mg/kg PO daily (Hernandez-Divers 2008). A mainstay for the very common reptilian visceral/articular gout — pair with rehydration and diet correction.

Contraindications

Concurrent high-purine diet with urate-prevention use (xanthine urolith risk). Significant renal impairment (reduce dose — renally excreted). Known hypersensitivity. Concurrent azathioprine/6-mercaptopurine (allopurinol blocks their metabolism → severe toxicity — major interaction). Pregnancy (caution).

Species-specific warnings

Dogs: On urate-prevention therapy, monitor for XANTHINE uroliths and feed a low-purine diet; in leishmaniasis, continue long-term and watch for relapse.

Adverse effects

• XANTHINE urolithiasis (if urate over-suppressed on a high-purine diet) — pair with low-purine diet
• GI upset (vomiting, diarrhoea)
• Hypersensitivity/skin reactions (uncommon)
• Rare hepatic/haematologic effects on long-term use

Drug interactions

• Azathioprine / 6-mercaptopurine: allopurinol blocks their xanthine-oxidase metabolism → severe, potentially fatal toxicity — avoid or drastically reduce their dose
• Meglumine antimoniate / miltefosine: complementary anti-leishmanial partners
• High-purine diet: promotes xanthine stones during urate suppression
• Warfarin/theophylline: levels may rise (reduced metabolism)

Pregnancy and lactation

Limited data; use in pregnancy only if clearly needed.

Monitoring

• Leishmaniasis: clinical response, serology/PCR, relapse surveillance over months
• Urate use: urinalysis for urate AND xanthine crystals/stones; imaging
• Renal function (dose adjustment) and a LOW-PURINE diet
• Never co-administer with azathioprine/6-MP without major dose reduction

Toxicity and overdose

Generally well tolerated long-term; the characteristic problem is XANTHINE urolithiasis when uric-acid production is over-suppressed (especially on a high-purine diet) — hence dietary pairing. GI upset and, rarely, hypersensitivity/hepatic/haematologic effects occur. Accumulates in renal impairment (reduce dose). The dangerous drug interaction is with azathioprine/6-MP.

Management: No specific antidote. Supportive care; ensure hydration/urine output and monitor for xanthine crystalluria/stones. For the azathioprine interaction, manage as thiopurine toxicity (marrow suppression). Reduce dose in renal impairment. Decontaminate large recent ingestions.

Clinical pearls

• Two hats: the long-term maintenance drug for canine LEISHMANIASIS (with/after an antimonial) and a URATE-stone preventive (Dalmatians, portosystemic shunts)
• For urate prevention, ALWAYS pair it with a low-purine diet — over-suppressing urate on a purine-rich diet just swaps urate stones for xanthine stones
• Classic dangerous interaction: allopurinol + azathioprine/6-MP → severe marrow suppression (avoid or slash the thiopurine dose)
• Well tolerated for months; reduce the dose in renal impairment and monitor urine crystals

Mechanism of action

Allopurinol (and its active metabolite oxypurinol) competitively inhibits XANTHINE OXIDASE, the enzyme that converts hypoxanthine → xanthine → uric acid — lowering uric-acid production (the basis of urate-stone prevention). In Leishmania, allopurinol is misincorporated as a purine analogue into the parasite's RNA (which cannot synthesise purines de novo and relies on salvage), disrupting protein synthesis and inhibiting parasite growth. The xanthine-stone risk reflects accumulation of the poorly soluble precursor xanthine when uric-acid formation is over-blocked.

Formulations and products

• 100 mg tablet
• 300 mg tablet
• Zyloric — 100 / 300 mg tablet, Tablet (human-label)
• Ciplaric / Zyloprim — 100 / 300 mg tablet, Tablet (human-label)

Storage

Tablets: 15–30 °C, dry, protect from light.

Before you use this dose

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.

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Frequently asked questions