Malathion is an antiparasitic active ingredient used in veterinary and human medicine. It is used in dogs and livestock against external parasites (lice, mites, fleas, flies, ticks, etc.). It is also used against agricultural, household and public pests. It belongs to the chemical class of the organophosphates.
Other names: MERCAPTOTHION
EFFICACY AGAINST PARASITES
Type of action: Broad spectrum contact, non systemic ectoparasiticide: insecticide, acaricide, tickicide, louisicide, larvicide
Main veterinary parasites controlled: flies, lice, fleas, mosquitoes, ticks, mites, fly maggots (cutaneous myiasis), etc.
Efficacy against a specific parasite depends on the delivery form and on the dose administered. 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.
Click here for general information on features and characteristics of PARASITICIDES.
Oral LD50, rat, acute*: 1375-2800 mg/kg
Dermal LD50, rat, acute*: 4100 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- CODEX: No, withdrawn
- EU: Yes (at or below tht limit of detection, Annex II, IIIA)
- 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.
General safety information for antiparasitics is available in specific articles in this site (click to visit):
- General safety of antiparasitics for domestic animals
- General safety of antiparasitics for humans
- General safety of antiparasitics for the environment
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!!!
MARKETING & USAGE
Decade of introduction: 1950
Introduced by: AMERICAN CYANAMID
Some original brands: NEOMALACID, NEOMUSCARION
Patent: Expired (particular formulations may be still patent-protected)
Use in LIVESTOCK: Yes, very scarce and declining, as all organophosphates
Use in HORSES: Yes, very scarce and declining, as all organophosphates
Use in DOGS and CATS: Yes, very scarce
Main delivery forms:
Use in human medicine: Yes, still approved in a few countries
Use in public/domestic hygiene: Yes, mainly for large-scale mosquito control in public hygiene
Use in agriculture: Yes
Generics available: Yes
In livestock: 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)
Malathion is a classical, veteran parasiticide belonging to the organophosphates. It has never been used a lot on livestock or pets.
Nowadays it is still used in some countries for dusting pig and poultry, alone or in mixtures with other parasiticides.
It is still aproved in some countries as a human medicine against head lice (pediculosis).
Efficacy of malathion
As most organophosphates malathion is a broad-spectrum insecticide, acaricide and larvicide. Malathion is a "generalist" pesticide, with good average efficacy against most external parasites, but not outstanding against a particular one. Malathion is one of the less toxic broad-spectrum organophosphate insecticides. This explains why it is approved for use on human beings in some countries.
However, resistance of important veterinary parasites to all organophosphates, including chlorpyrifos 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 malathion
Percutaneous absorption (i.e. through the skin) of topically administered malathion depends on the animal species, the administered dose, and the extension of the treated body surface. Malathion is readily absorbed through the skin into the bloodstream. Animals treated topically can ingest malathion through licking and grooming. Ingested malathion is quickly absorbed into blood. Malathion is very quickly metabolized to non-toxic metabolites. Excretion half-life is aprox. 8 hours in rats and about 2 days in cows. Excretion is achieved mainly through urine, the rest through feces and exhaled air.
Mechanism of action of malathion
As all organophosphates insecticides malathion 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.
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