WHO Acute Hazard classification: Not listed.

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.

Acute Toxicity and Tolerance of Clorsulon

  • LD50 acute, rats, p.o. 930 to >10000 mg/kg (depending on the studies)
  • LD50 acute, rats ands mice, i.p. 678 to 938 mg/kg (depending on the studies)
  • Cattle, sheep and goats tolerate clorsulon very well, both after oral and subcutaneous administration.
  • Sheep tolerated single closulon doses of up 200 mg/kg without toxic symptoms (usual therapeutic dose: 4 to 21 mg/kg).
  • Cattle tolerated single closulon doses of up 400 mg/kg without toxic symptoms (usual therapeutic dose: 4 to 21 mg/kg).

Toxic Symptoms caused by Clorsulon Poisoning

  • Information on toxic symptoms caused by closulon alone is rather scarce because it is mostly used in combination with ivermectin.
  • As a general rule, poisoning with clorsulon is quite unusual, due to its low toxicity, the high safety margins and the fact that most species tolerate it very well.

Clorsulon Side Effects, Adverse Drug Reactions (ADRs) and Warnings

  • At therapeutic doses transient swelling at the injection site has been reported.
  • ADRs are quite rare after treatment at the recommended dose.

Antidote and Treatment of Clorsulon Intoxication

  • There is no specific antidote for clorsulon.
  • Treatment consists in supportive and symptomatic measures.

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.

Environmental Toxicity of Clorsulon

  • Clorsulon is hardly toxic to fish and other aquatic organisms.
  • Clorsulon is photodegradable, but quite persistent in the environment. However, it does not bioaccumulate.
  • Studies on its environmental impact when used on in feedlot cattle concluded that the risk of harm to the environment after correct use are negligible.

Additional information

Click here for a list and overview of all safety summaries of antiparasitic active ingredients in this site.

  • Clorsulon belongs to the chemical class of the benzene-sulphonamides.
  • Clorsulon is not used in dogs or cats.
  • Clorsulon is not used in human medicines.
  • Clorsulon is not used in crop pesticides.
  • Clorsulon is not used in public or domestic hygiene as a biocide.
  • Click here for General safety of antiparasitics for domestic animals.
  • Click here for General safety of antiparasitics for humans.
  • Click here for General safety of antiparasitics for the environment.
  • Click here here for technical and commercial information on clorsulon.


If you intend to use a veterinary drug containing this active ingredient you must carefully read and follow the safety instructions in the product label.  Always ask your veterinary doctor, or pharmacist, or contact the manufacturer. Be aware that the safety instructions for the same veterinary medicine may vary from country to country.

The information in this page must not be confused with the Materials and Safety Datasheets (MSDS) officially issued by manufacturers for active ingredients and many other chemicals. MSDSs target safety during manufacturing, transport, storage and handling of such materials. This safety summary is a complement to the information on product labels and MSDS.

The toxicity of an active ingredient must not be confused with the toxicity of finished products, in this case parasiticidal drugs or pesticides. Finished products contain one or more active ingredients, but also other ingredients that can be relevant from the safety point of view.

All information in this site is made available in good faith and following a reasonable effort to ensure its correctness and actuality. Nevertheless, no this regarding guarantee is given, and any liability on its accuracy, integrity, sufficiency, actuality and opportunity is denied. Liability is also denied for any possible damage or harm to persons, animals or any other goods that could follow the transmission or use of the information, data or recommendations in this site by any site visitor or third parties.