Clorsulon is a narrow-spectrum antiparasitic active ingredient used in veterinary medicine. It is used in livestock against liver flukes. It is not used against agricultural and household pests. It belongs to the chemical class of the sulphonamides.

Common name:  CLORSULON

Type: veterinary medecine
Chemical class: benzenesulphonamide


Molecular structure of CLORSULON 


Type of action: Flukicide anthelmintic, endoparasiticide
Main veterinary parasites controlled: Liver flukes

Efficacy against a specific parasite depends on the delivery form and on the dose administered. 

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Closulon is a narrow-spectrum anthelmintic effective against some flukes (e.g. Fasciola hepatica). It is not effective against roundworms, tapeworms or external parasites.

It is used moderatly in ruminants mainly as an injectable and very little as a drench, mostly in mixture with ivermectin to add flukicidal activity.

The table below indicates some usual dosing recommendations for clorsulon issued by manufacturers or documented in the scientific literature. They may not be approved in some countries.

Dosing recommendations for CLOSULON
Delivery Parasites Dose (against clorsulon-susceptible parasites)
Oral Fasciola hepatica, Fasciola gigantica 7 mg/kg
Oral Fascioloides magna 21 mg/kg
Subcutaneous Fasciola hepatica 2-8 mg/kg
Oral Fasciola hepatica 7 mg/kg
Subcutaneous Fasciola hepatica 2-4 mg-kg
Oral Fasciola hepatica 7 mg-kg

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Dosing recommendations for antiparasitics depend on national regulations. National regulatory authorities determine whether a product is approved for a given indication, i.e. use on a particular host at a specific dose and against a specific parasite. Check the labels of the products available in your country for specific information on approved indications.


Oral LD50, rat, acute*: >10'000 mg/kg
Dermal LD50, rat, acute*: not found
* These values refer to the active ingredient. Toxicity has to be determined for each formulation as well. Formulations are usually significantly less toxic than the active ingredients.

MRL (maximum residue limit) established for either beef, mutton pork or chicken meat*:

  • CODEX: No
  • EU: Yes
  • USA: Yes
  • AUS: Yes

* This information is an indicator of the acceptance of an active ingredient by the most influential regulatory bodies for use on livestock.

Withholding periods for meat, milk, eggs, etc. depend on delivery form, dose and national regulations. Check the product label in your country.

Learn more about clorsulon safety (poisoning, intoxication, overdose, antidote, symptoms, etc.).

General safety information for antiparasitics is available in specific articles in this site (click to visit):


It is obvious that veterinary products are not intended for and should never be used on humans!!!


Decade of introduction: 1970
Introduced by: MS&D AGVET → MERIAL
Some original brands: CURATREM
Patent: Expired (particular formulations may be still patent-protected)

Use in LIVESTOCK: Yes, moderate in ruminants
Use in DOGS and CATS: No

Main delivery forms: 

Use in human medicine: No
Use in public/domestic hygiene: No
Use in agriculture: No
Generics available:  Yes, a few


In livestock: Yes, a few reports in liver fluke (Fasciola hepatica) on sheep, but seems not to be a widespread problem.

Learn more about parasite resistance and how it develops.


Clorsulon is a specific narrow-spectrum veteran flukicide, moderately used on livestock, mainly ruminants (cattle, sheep and goats). Nowadays it is almost only available in combination with ivermectin, mostly as an injectable but also as a drench.

It is not used on dogs and cats.

Efficacy of clorsulon

Clorsulon is highly effective against adults and late immature stages (>8 weeks) of the common liver fluke (Fasciola hepatica). It is also effective against Fasciola gigantica and Fascioloides magna, two other liver fluke species important for livestock.

It has no efficacy against roundwormstapeworms or any external parasite.

Pharmacokinetics of clorsulon

Ingested clorsulon is quickly absorbed into the bloodstream. Maximum plasma levels are achieved 14 to 24 hours after administration. After subcutaneous injection maximum plasma levels are reached earlier, about 6 hours after treatment. Clorsulon binds strongly (~75%) to plasmatic proteins.

Excretion half-life after oral administration is about 26 hours. 45-50% of the administered dose is excreted unchanged through urine.

Goats have a higher capacity for metabolizing clorsulon than sheep: bioavailability of clorsulon in goats is only 60% of the bioavailability in sheep, which explains its lower efficacy in goats.

Mechanism of action of clorsulon

Clorsulon inhibits various enzymes involved in the glycolytic process of flukes, i.e. it makes it impossible for the flukes to obtain energy from glucose. As a consequence the levels of ATP, the cellular fuel, are depressed.

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