Clorsulon
**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: 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).
Dosing by species
- Fasciola hepatica infections · 7 mg/kg PO · PO · Single dose
- Fasciola hepatica infections · 7 mg/kg PO · PO · Single dose · Deposit suspension over the back of the tongue
- 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 · Combination product with ivermectin
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
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)
Monitoring
- Clinical efficacy
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.
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.