Clorsulon
4-amino-6-trichloroethenyl-1,3-benzenedisulfonamide
Also known as: Curatrem · Ivomec Plus · Normectin Plus · MK-401
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
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Fasciola hepatica infections | 7 mg/kg PO | PO | Single dose | — | 🌎 NA |
| Fasciola hepatica infections, round worms, lungworms, cattle grubs, sucking lice, mange mites | Inject 1mL per 110 lb. body weight SC behind the shoulder | SC | Single dose | — | 🌎 NA |
- Fasciola hepatica infections: Deposit suspension over the back of the tongue
- Fasciola hepatica infections, round worms, lungworms, cattle grubs, sucking lice, mange mites: Combination product with ivermectin
Sheep
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Fasciola hepatica infections | 7 mg/kg PO | PO | Single dose | — | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Clorsulon is a highly effective, narrow-spectrum antiparasitic agent primarily used as a flukicide.
- Primary Indication: FDA-approved for treating immature and adult liver flukes (Fasciola hepatica) in cattle.
- Off-label Uses: Frequently utilized in sheep and camelids (llamas) for similar fluke infections.
- Limitations: It is ineffective against flukes younger than 8 weeks, rumen flukes (Paramphistomum spp.), and lacks complete efficacy against Fasciola magna in sheep.
Clinical Pearl: Because of its narrow spectrum, clorsulon is often formulated in combination with macrocyclic lactones (like ivermectin) to provide broad-spectrum coverage against both internal/external nematodes and trematodes.
Mechanism of action
Clorsulon exerts its flukicidal effect by disrupting the parasite's energy metabolism.
- It competitively inhibits two key glycolytic enzymes in susceptible flukes: 3-phosphoglycerate kinase and phosphoglyceromutase.
- This blockade disrupts the Emden-Myerhof glycolytic pathway → depletes the fluke's primary metabolic energy source (ATP) → leads to paralysis and death of the parasite.
- Dose-dependent efficacy: At 7 mg/kg, it kills migrating flukes (8 weeks post-infection); at 2 mg/kg, it only affects adult flukes (14 weeks post-infection).
Safety & warnings
Contraindications
- Female dairy cattle of breeding age
- Dogs (for the ivermectin combination product)
- IV or IM administration (for the injectable product)
Adverse effects
- Local swelling at injection sites (with the injectable combination product)
Precautions
- Dairy Cattle: No milk withdrawal time has been determined; labeled not for use in female dairy cattle of breeding age.
- Administration: The combination injectable product (Ivomec Plus®) must be administered subcutaneously only; do not give IV or IM.
- Species Warning: The manufacturer warns to use the combination product in cattle only, as severe reactions, including fatalities in dogs, may occur.
Monitoring
- Clinical efficacy
Pharmacokinetics
Absorption
After oral administration to cattle, the drug is absorbed rapidly with peak levels occurring in about 4 hours.
Distribution
Approximately 75% of the circulating drug is found in plasma and 25% in erythrocytes. At 8-12 hours after administration, clorsulon levels peak in the fluke.
Overdose
Clorsulon is very safe when administered orally to cattle or sheep. Doses of up to 400 mg/kg have not produced toxicity in sheep. A dose that is toxic in cattle has also not been determined.
Available products
Formulations
- Oral suspension/drench
- Injectable solution (in combination with ivermectin)
Veterinary
- Clorsulon 8.5% (85 mg/mL) Oral Drench (Curatrem®)
- Clorsulon 10% (100 mg/mL) and Ivermectin 1% (10 mg/mL) Injection (Ivomec® Plus, Normectin® Plus)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Unless otherwise instructed by the manufacturer, clorsulon should be stored at room temperature (15-30°C).
Client information
- Administration: If using the oral suspension (Curatrem®), shake the bottle vigorously before use.
- Food Safety: Strict slaughter withdrawal times must be followed: 8 days for the oral suspension and 49 days for the injectable combination.
- Dairy Restrictions: Do not use this medication in female dairy cattle of breeding age to prevent milk contamination.
- Safety: This medication is generally very safe and is considered safe to use in pregnant or breeding animals.
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.