Clorsulon — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Cattle	Oral (drench or in-feed)	7 mg/kg (as a single dose) for mature flukes; 15 mg/kg for immature flukes (when used alone)	Single dose	Duration: One day Notes: Often used in combination with ivermectin (e.g., 1 mg/kg ivermectin + 2 mg/kg clorsulon) for broad-spectrum parasite control. Withdrawal times must be observed.
Sheep	Oral (drench)	7 mg/kg (as a single dose) for mature flukes; 15 mg/kg for immature flukes	Single dose	Duration: One day Notes: Not approved in all countries for sheep; check local regulations. May be used extra-label with veterinary supervision.
Goats	Oral (drench)	7 mg/kg (as a single dose) for mature flukes; 15 mg/kg for immature flukes	Single dose	Duration: One day Notes: Extra-label use; not approved in all regions. Use with caution.

Clinical Indications & Species Uses

General Indications

Treatment of fascioliasis (liver fluke) in ruminants

Cattle (Bovine)

Treatment of fascioliasis (liver fluke) caused by Fasciola hepatica
Control of mature and immature liver flukes

Small Ruminants (Sheep / Goat)

Treatment of fascioliasis (liver fluke) caused by Fasciola hepatica in sheep and goats

Pharmacology & Mechanism of Action

Drug Class: Anthelmintic | Pharmacological Group: Benzenedisulfonamide

Mechanism of Action: Clorsulon is a halogenated sulfonamide anthelmintic that specifically inhibits the glycolytic enzyme phosphoglycerate kinase and phosphoglycerate mutase in the Embden-Meyerhof pathway of the liver fluke Fasciola hepatica. This inhibition disrupts the parasite's energy metabolism, leading to depletion of ATP and eventual death of the fluke. The drug is selectively toxic to the parasite because the fluke relies heavily on anaerobic glycolysis for energy production, whereas the host's metabolism is less dependent on this pathway.

Pharmacodynamics: Clorsulon is highly effective against adult and immature stages of Fasciola hepatica, particularly against mature flukes. It has minimal activity against other nematodes or cestodes. The drug acts systemically after absorption and is distributed to the liver and bile ducts where the flukes reside. Its efficacy is dose-dependent, with higher doses providing better activity against immature flukes. Clorsulon is often combined with ivermectin to provide broad-spectrum antiparasitic coverage in cattle and sheep.

⚡ Pharmacokinetics Summary

Absorption: Clorsulon is well absorbed after oral administration in ruminants. Peak plasma concentrations are reached within 24 hours. In cattle, oral bioavailability is approximately 70-80%.

Distribution: Clorsulon is widely distributed in tissues, with highest concentrations in the liver and bile. It crosses the placenta and is excreted in milk. It is moderately bound to plasma proteins.

Metabolism: Clorsulon undergoes minimal metabolism in the liver. The primary route of elimination is renal excretion of the parent compound and its metabolites.

Excretion: Clorsulon is excreted primarily in urine, with a smaller amount in feces. In cattle, the elimination half-life is approximately 2-3 days.

Half-Life: Cattle: ~2-3 days; Sheep: ~1-2 days

Bioavailability: Oral: ~70-80% in cattle

Protein Binding: Moderate (approximately 60-70% in cattle)

Available Formulations & Strengths

Oral Drench (suspension) 8.5% (85 mg/mL) as a suspension (Oral)

Oral Paste Various concentrations (e.g., 10%) (Oral)

Injectable Solution (combination product) Combination with ivermectin: 1% ivermectin + 10% clorsulon (e.g., 10 mg/mL ivermectin + 100 mg/mL clorsulon) (Subcutaneous)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to clorsulon or any component of the formulation
Do not use in animals with known liver dysfunction (except for fluke treatment)
Do not use in lactating dairy cattle if milk withdrawal time is not observed
Do not use in animals intended for breeding within a certain period (check label)

Warnings & Clinical Precautions:

Use with caution in severely debilitated animals
Do not exceed recommended dosage
Avoid use in animals with severe hepatic impairment
In food animals, observe withdrawal times for meat and milk
Keep out of reach of children
Use protective clothing when handling the drug
Do not use in animals with known sulfonamide sensitivity

Adverse Effects & Reactions

Common:

Mild gastrointestinal upset (e.g., diarrhea, anorexia) in some animals
Local injection site reactions if given subcutaneously

Serious / Severe:

Allergic reactions (rare)
Hepatotoxicity in overdose or in animals with pre-existing liver disease

Rare:

Blood dyscrasias (e.g., anemia, leukopenia) in prolonged use
Neurological signs (e.g., ataxia) in overdose

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Ivermectin	Additive antiparasitic effect; commonly used in combination products. No adverse interactions reported.	Mild
Other fasciolicides (e.g., triclabendazole, albendazole)	Potential additive toxicity or antagonism; use with caution and under veterinary supervision.	Moderate
Sulfonamides	Potential cross-reactivity in hypersensitive animals; avoid concurrent use in animals with sulfonamide sensitivity.	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Salivation
Muscle tremors
Ataxia
Depression
Anorexia
Diarrhea
In severe cases: seizures, respiratory failure

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce emesis if oral overdose is recent (in non-ruminants). Administer activated charcoal to reduce absorption. Provide intravenous fluids, electrolytes, and supportive care. Monitor liver and kidney function. In severe cases, consider anticonvulsants for seizures.

Food Animal Withdrawal Times

🥩 Meat: 28 days🥛 Milk: 0 days

Withdrawal times vary by country and formulation. For cattle, meat withdrawal is typically 28 days; milk withdrawal is zero days for some formulations but may be 7 days for others. Always follow label instructions. For sheep and goats, withdrawal times may be longer; consult local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F), excursions permitted between 15-30°C (59-86°F)

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light. Keep container tightly closed. Avoid freezing. Store in a dry place.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in cattle and sheep in the US (as part of combination products with ivermectin).

Extra-Label (Off-Label) Use: In the US, clorsulon is approved for use in cattle and sheep. Extra-label use in other species or at higher doses requires a valid veterinary-client-patient relationship and must comply with AMDUCA regulations. For food animals, extended withdrawal times may be required.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Clorsulon is a specific fasciolicide used primarily in cattle and sheep for the treatment of liver fluke infections. It is often combined with ivermectin to provide broad-spectrum control of internal and external parasites. The drug is most effective against adult flukes; for immature flukes, higher doses are required. Diagnosis of fascioliasis should be confirmed before treatment. In areas with endemic fascioliasis, strategic deworming programs should be implemented. Clorsulon is generally well tolerated, but withdrawal times must be observed in food animals. It is not recommended for use in non-ruminants due to lack of efficacy and safety data.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)