# Allopurinol: veterinary dose and monograph

> Allopurinol is a veterinary antiparasitic. A xanthine-oxidase inhibitor with two important veterinary roles: (1) long-term treatment of canine LEISHMANIASIS — it blocks parasite purine metabolism and is the cornerstone maintenance drug (usually with, then continued after… Indications include 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. This monograph lists 5 reference doses for dogs, cats, birds and reptiles, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/allopurinol · Last reviewed: 2026-10-01

## 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

*Allopurinol doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Leishmaniasis (maintenance) | 10–15 mg/kg | PO | q12h | at least 6–12 months (often longer) |
| Urate urolith dissolution / prevention | 10–15 mg/kg | PO | q8–12h (dissolution), then q24h (prevention) | — |

- 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

*Allopurinol doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Leishmaniasis | 10–20 mg/kg | PO | q12–24h | long-term |

- 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

*Allopurinol doses for birds*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Gout / hyperuricaemia | One 100 mg tablet crushed in 10 mL water; 20 drops per ounce of drinking water | PO | in drinking water | — |

- 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

*Allopurinol doses for reptiles*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Gout / renal hyperuricaemia | 20–25 mg/kg | PO | q24h | — |

- 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

> **Caution:** 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

> **Caution:** 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

### What is the dose of Allopurinol for dogs?

Reference doses for Allopurinol in dogs: 10–15 mg/kg PO q12h for at least 6–12 months (often longer) (Leishmaniasis (maintenance)); 10–15 mg/kg PO q8–12h (dissolution), then q24h (prevention) (Urate urolith dissolution / prevention). Confirm against the label and the patient before use.

### What is the dose of Allopurinol for cats?

Reference doses for Allopurinol in cats: 10–20 mg/kg PO q12–24h for long-term (Leishmaniasis). Confirm against the label and the patient before use.

### What is the dose of Allopurinol for birds?

Reference doses for Allopurinol in birds: One 100 mg tablet crushed in 10 mL water; 20 drops per ounce of drinking water PO in drinking water (Gout / hyperuricaemia). Confirm against the label and the patient before use.

### When should Allopurinol not be used?

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).

### What are the side effects of Allopurinol in animals?

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.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.