Coumaphos is an antiparasitic active ingredient used in veterinary medicine in dogs and livestock against external parasites (lice, mites, fleas, fliesticks, etc.). It is not used against agricultural pests. It belongs to the chemical class of the organophosphates.

Common name: COUMAPHOS

Other names: COUMAFOS
Type: pesticide
Chemical class: organophosphate


Molecular structure of COUMAPHOS







Type of action: Broad spectrum contact, non systemic ectoparasiticide: insecticide, acaricide, tickicide, louisicide, larvicide
Main veterinary parasites controlled: flies, lice, fleas, mosquitoes, ticks, mites, etc.

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

Click here for general information on features and characteristics of PARASITICIDES.


Click here to view the article in this site with the most common dosing recommendations for coumaphos used in domestic animals.


Oral LD50, rat, acute*: 13 to 41 mg/kg
Dermal LD50, rat, acute*: 860 mg/kg
* 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) set for animal tissues (e.g. beef, mutton pork or chicken)*:

  • CODEX: No
  • EU: No
  • 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. MRL's for animal tissues may be set also for agricultural pesticides that are not approved for use on animals but are used on commodities fed to animals. A MRL may be also set in the form of an IMPORT TOLERANCE for active ingredients not approved in a particular country but approved for imported animal commodities.

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 coumaphos safety (poisoning, intoxication, overdose, antidote, symptoms, etc.).

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


Never use agricultural or hygiene products with this or any other active ingredient on livestock or pets, even if there are veterinary products with this same active ingredient approved for use on animals. The formulations for agricultural or hygiene use are different and may be toxic for livestock or pets.

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


Decade of introduction: 1950
Introduced by: BAYER
Some original brands: ASUNTOL, CO-RAL
Patent: Expired (particular formulations may be still patent-protected)

Use in LIVESTOCK: Yes, abundant, but declining, as all organophosphates
Use in HORSES: Yes, scarce and declining, as all organophosphates
Use in
DOGS and CATS: Yes, abundant, but declining, as all organophosphates

Main delivery forms: 

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


  • In livestock & horses: Yes, as for all organophosphates: very frequent worldwide in such species as cattle ticks (Boophilus spp), horn flies (Haematobia irritans), sheep lice (Damalinia ovis), poultry mites (Dermanyssus gallinae), houseflies (Musca domestica), mosquitoes
    In pets: Yes, quite frequent worldwide in dog and cat fleas (Ctenocephalides spp)

Visit also the section in this site about parasite resistance to antiparasitics and more specifically to coumaphos.


Coumaphos is a classical, veteran parasiticide belonging to the organophosphates. 

Coumaphos has been used a lot in the 1960's to 1990s, both in livestock and pets. For years it has been and still remains the product of choice for the compulsory quanantine dipping of cattle imported to the USA from Mexico in order to control Boophilus microplus  ticks that have been eradicated from the USA.

In livestock it is still used moderately in cattle in concentrates for dipping and spraying, and in dressings mainly in countries where cattle ticks are a problem. Its use as a tickicide declined in the 1980s - 1990's after the introduction of synthetic pyrethroids, which are safer for livestock, operators and wild birds, more effective against biting flies, and easier to handle in plunge dips, because they do not strip. However, after resistance of cattle ticks to synthetic pyrethroids has become a worldwide problem, coumaphos has experienced a slight revival.

In the 1950's to 1970's coumaphos was also used as an oral anthelmintic for ruminants against some roundworms, as well as against cattle grubs on cattle. This usage has disappeared after the introduction of more potent and safer active ingredients (e.g. macrocyclic lactones, benzimidazoles, etc.).

In dogs and cats coumaphos is still used in shampoos, soaps, baths, sprays and the like, but its use has strongly declined after the introduction of more modern and safer flea and tick control spot-ons (= pipettes) and tablets.

Efficacy of coumaphos

As most organophosphates coumaphos is a broad-spectrum insecticide and acaricide. Coumaphos is especially effective against all tick species that affect livestock, both single-host tics (e.g. Boophilus spp.) as well as two-host and multi-host ticks (e.g. Amblyomma spp, Dermacentor spp, Haemaphysalis spp, Hyalomma spp, Rhipicephalus spp, etc.).

However, resistance of important veterinary parasites to all organophosphates, including coumaphos is widespread, especially in cattle ticks (Boophilus spp), horn flies (Haematobia irritans), sheep lice (Damalinia ovis), poultry mites (Dermanyssus gallinae), mosquitoes, dog and cat fleas (Ctenocephalides spp) and houseflies (Musca domestica). As a consequence, products with this active ingredient may not achieve the expected efficacy in many places. The same applies to all other organophosphates. This is also a reason for their progressive replacement with newer active active ingredients with a different mode of action.

Pharmacokinetics of coumaphos

Percutaneous absorption (i.e. through the skin) of topically administered coumaphos depends on the animal species, the administered dose, and the extension of the treated body surface. As a general rule, only a small part of the topically administered dose is absorbed. Treated animals can ingest coumaphos through licking and grooming. Ingested coumaphos absorbed into blood is quickly metabolized and excreted through urine. Several metabolites are substantially more potent acetylcholinesterase inhibitors than coumaphos itself. Part of the ingested coumaphos is excreted unchanged through the feces. After topical administration coumaphos residues are found mainly in meat, fat tissues and milk fat. Tissue residues can be detected up to 30 days after treatment.

Mechanism of action of coumaphos

As all organophosphates insecticides coumaphos acts on the nervous system of the parasites (but also of mammals, birds, fish and many organisms!) as inhibitor of acetylcholinesterase (also known as AchE), an enzyme that hydrolyzes acetylcholine (Ach). Ach is a molecule involved in the transmission of nervous signals from nerves to muscles (so-called neuromuscular junctions) and between neurons in the brain (so-called cholinergic brain synapses).

AchE's role is to terminate the transmission of nervous signals where Ach is the neurotransmitter (there are several other neurotrasmitters). By inhibiting the activity of AchE, carbamates prevent the termination of those nervous signals, i.e. the neurons remain in constant activity and excitation, massively disturbing the normal movements of the parasites. The bottom line for the parasites is that they are paralyzed and die more or less quickly. Organophosphates bind irreversibly to AchE, in contrast with carbamates, another chemical class of parasiticides, which bind reversibly to AchE.

Click here to view the list of all technical summaries of antiparasitic active ingredients in this site.