Diclazuril
Also known as: Protazil · Clinicox · Vecoxan · diclazurilo · diclazurilum · R 64433
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Coccidiosis | 25 mg/kg PO once | PO | once | — | 🌎 NA |
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Coccidiosis | 25 mg/kg PO once | PO | once | — | 🌎 NA |
| Coccidiosis in kittens | 1 mL (2.5 mg) PO of the sheep solution per 4 kg body mass | PO | once | — | 🌎 NA |
| Isospora spp. infections | 25 mg/kg PO once | PO | once | — | 🌎 NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of equine protozoal myeloencephalitis (S. neurona) | Top dress at the rate of 1 mg/kg bodyweight | PO | q24h | 28 days | 🌎 NA |
- Treatment of equine protozoal myeloencephalitis (S. neurona): Using the oral pellets and the provided cup. If horse's bodyweight is in between two graduations on the dosing cup, fill the cup to the higher of the two marks.
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| As an aid to control coccidiosis (calves) | 1 mg/kg (1 mL of the 2.5 mg/mL suspension per 2.5 kg bodyweight) PO as a single dose | PO | once | — | 🌎 NA |
- As an aid to control coccidiosis (calves): Administer 14 days after moving into a potentially high risk environment. Recommended to treat all calves in pen.
Sheep
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Therapeutic use (lambs) | 1 mg/kg (1 mL of the 2.5mg/mL suspension per 2.5 kg bodyweight) PO once | PO | once | — | 🌎 NA |
| Preventative use (lambs) | 1 mg/kg PO | PO | once | — | 🌎 NA |
- Therapeutic use (lambs): Recommended to treat all lambs in flock.
- Preventative use (lambs): Administer at about 4-6 weeks of age at the time that coccidiosis can normally be expected. Under high infection pressure, a second treatment may be indicated about 3 weeks after the first dosing.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Diclazuril is a potent, broad-spectrum antiprotozoal agent belonging to the triazine (benzeneacetonitrile) class.
Key clinical applications include:
- Horses: FDA-approved for the treatment of Equine Protozoal Myeloencephalitis (EPM) caused by Sarcocystis neurona.
- Livestock & Poultry: Used extensively as a coccidiostat in broiler chickens, calves, and lambs.
- Small Animals: Off-label use for treating resistant coccidiosis, Neospora caninum, and Toxoplasma infections in dogs and cats.
Clinical Pearl: While highly effective at clearing the protozoal infection in EPM, diclazuril cannot reverse pre-existing neurological damage caused by the parasite's migration through the central nervous system.
Mechanism of action
Diclazuril specifically targets the apicoplast (a plastid-like organelle) found uniquely in the Apicomplexa phylum (which includes Sarcocystis, Toxoplasma, and Eimeria).
- Mechanism: It disrupts essential metabolic pathways within the apicoplast (likely involving lipid and heme biosynthesis) → halts intracellular schizogony and gametogony → parasiticidal effect.
- Potency: It is highly potent, with in vitro concentrations required to inhibit 95% of S. neurona being exceptionally low (~1 ng/mL).
Safety & warnings
Contraindications
- Hypersensitivity to diclazuril
- Safe use in horses used for breeding, during pregnancy, or in lactation has not been evaluated
Adverse effects
- Severe diarrhea (rarely, in highly susceptible lambs)
Precautions
The safe use of Protazil in horses used for breeding purposes, during pregnancy, in lactation, or with other therapies has not been evaluated. Use with caution in highly susceptible lambs as severe diarrhea may occur on rare occasions.
Monitoring
- Clinical efficacy (neurologic exams)
Pharmacokinetics
Half-life
Absorption
In horses, oral bioavailability is about 5%.
Distribution
CSF levels are approximately 15% of those found in plasma.
Overdose
Limited information is available, but the drug appears to have a large safety margin in animals. Normal horses dosed up to 50 mg/kg/day (50X) for 42 days developed only marginal effects (decreased weight gain, increased creatinine, BUN). Doses of up to 60X in lambs and calves did not cause any demonstrable side effects.
Available products
Formulations
- Oral pellets
- Medicated feed
- Oral suspension
Veterinary
- Diclazuril Oral Pellets 1.56% (Protazil)
- Diclazuril 0.2% Type A Medicated Feed Article (Clinicox)
- Diclazuril oral suspension 2.5 mg/mL (Vecoxan)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Diclazuril pellets should be stored at room temperature (15-30°C). Oral suspension should be stored below 30°C.
Client information
For Horses with EPM:
- Strict Compliance: The medication must be given daily for the entire 28-day course to effectively clear the parasite.
- Expectations: While the drug kills the organism causing EPM, it does not heal existing nerve damage. Some horses may not return completely to their 'normal' baseline.
General Administration:
- Pellets: Top-dress on the animal's feed. Use the provided measuring cup accurately.
- Suspension: Shake vigorously before use to ensure the medication is evenly mixed.
- Storage: Keep pellets at room temperature and suspensions below 30°C (86°F).
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.