WHO Acute Hazard classification: III, slightly hazardous

Mechanism of Action of Cyromazine

The mechanism of action of cyromazine has not been completely elucidated. It is certainly not a Chitin Synthesis Inhibitor like other insect growth regulators such as the benzoylureas. It nevertheless acts upon the molting process, probably interfering with the process of chitin deposition.

Toxicity and Tolerance of Cyromazine

  • LD50 acute, rats, p.o. 3387 - 4460 mg/kg, depending on the studies
  • LD50 acute, rats, dermal, > 3100 mg/kg
  • LD50 acute, rabbits, dermal, > 2010 mg/kg
  • Poultry tolerates orally administered cyromazine very well.
  • Sheep and goats tolerate topically administered cyromazine usually without symptoms.

Toxic Symptoms caused by Cyromazine Poisoning

  • In toxicity studies in mammals (rats, mice, dogs, rabbits) the following symptoms were observed after heavy overdose: ataxia (uncoordinated movements), salivation (drooling), sedation, dispnea (difficult breathing), curved position, exophthalmos (eye bulging out of the orbit). Affected animals recovered 9 to 12 days after treatment.

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

  • As a general rule, intoxications with cyromazine administered at the recommended dose are very rare due to its low toxicity, the high safety margin and the excellent tolerance of sheep, goats and poultry.

Antidote and Treatment of Cyromazine Intoxication

  • There is no antidote for cyromazine poisoning.
  • Treatment consists in supportive and symptomatic measures.

Pharmacokinetics of Cyromazine

  • Topically administered cyromazine is poorly absorbed through the skin of sheep.
  • Cyromazine is quite soluble in water, in contrast with many ectoparasiticides that are lipophilic. After oral administration to poultry 99% of the administered dose is excreted unchanged in the feces. Only about 0.6% is deposited in eggs and very few in chicken tissues.
  • Both in mammals and poultry, most ingested cyromazine is absorbed into blood. A small portion is metabolized in the liver and the largest portion is excreted through urine. Excretion is rather fast: about 95% of the ingested dose is excreted within 24 hours after administration.

Environmental Toxicity of Cyromazine

  • Cyromazine is moderately toxic to birds.
  • Among arthropods (insects, mites, ticks, etc.) cyromazine is quite specific for dipterans and only slightly harmful for many beneficial organisms.
  • Cyromazine is toxic to certain aquatic invertebrates (e.g. mosquito and other Dipteran larvae).
  • Cyromazine is readily soluble in water and breaks down only very slowly, both in soil and water. Consequently it has potential for contaminating groundwater.
  • Correct use on poultry and sheep and for manure and waste treatment is unlikely to be detrimental for the environment, including coprophagous insects.

Additional Information

  • Click here for a list and overview of all safety summaries of antiparasitic active ingredients in this site.
  • Cyromazine is an insect growth regulators (IGR) that belongs to the chemical class of the triazines.
  • Cyromazine is not used in human medicines.
  • Cyromazine is used in crop pesticides.
  • Cyromazine is used in biocides for public or domestic hygiene.
  • 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 for technical and commercial information on cyromazine.


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.