Brand: PERMECTRIN ™ Fly & Louse Dust


FORMULATION: ready-to-use dust for treating animals

ACTIVE INGREDIENT(S)Permethrin: 0.25% = 2.5 g/L

CHEMICAL CLASS of the active ingredient(s): synthetic pyrethroid


PARASITES CONTROLLED (spectrum of activity)


Beef & Dairy Cattle

  • Against horn flies, face flies & lice:
    • Place contents of the package in any commercially available dust bag, suspend bags in areas frequented by cattle or in gateways or lanes through which the animals pass daily for water, feed or minerals. Bags may also be suspended in loafing sheds or in front of protected mineral feeders. For lactating dairy cows, bags may be suspended in the exit through which cows leave the milking barn. In all cases, the bags should be adjusted so that the bottom of the bag will hang four to six inches below the topline of the cattle. For reduction of face flies, the bags must be located so the animals will be forced to use them daily and hung at a height to insure that the faces of the cattle will be dusted.
  • Against horn flies & lice:
    • Direct Application: Apply 2.0 ounces of dust per animal by shaker can over the head, neck, shoulders, back and tailhead. Repeat as necessary.


  • Against lice:
    • Direct Application: Apply not more than 1 oz.* (3 level tablespoons) per head as a uniform coat to the head, shoulders and back by use of a shaker can. Repeat as necessary, but not more often than once every ten days. In severe infestations, both individual animals and the bedding may be treated as directed above.


  • Against Northern fowl mites:
    • Direct Application: Apply not more than 1 lb./100 birds, directing dust to thoroughly cover vent area.


  • LD50 (acute oral) in rats: for the a.i. 400 mg/kg (in oil vehicle, 40:60 cis:trans mixture) to 1350 - 4000 mg/kg (in aqueous vehicle, depending on the study)
  • LD50 (acute dermal) in rabbits: for the a.i. 4000 mg/kg
  • Estimated hazard class according to the WHO: U, unlikely to present acute hazard

Suspected poisoning? Read the article on coumaphos safety in this site.

Withholding periods (=withdrawal times) in days for meat & milk (country-specific differences may apply: read the product label)

  • Meat:
    • Cattle: USA NIL
    • Swine: USA 5 days
    • Poultry: USA NIL
  • Milk for human consumption: USA NIL when used according to label.

WARNING !!!: Never use on humans, dogs or cats.

Permethrin and all other 2nd-generation synthetic pyrethroids (e.g. cyhalothrin, cypermethrin, deltamethrin, etc.) are irritant to the eyes and the skin, both of humans and livestock. But irritation is usually worse when using pour-ons than after spraying.

Permethrin and all synthetic pyrethroids (e.g. cyhalothrin, cypermethrin, deltamethrin, etc.) are extremely toxic to fish and aquatic invertebrates Do not apply directly to water, or to areas where surface water is present, or to intertidal areas below the mean high water mark. Do not contaminate water when cleaning equipment or disposing of equipment washwaters.

You may be interested in the following articles in this site dealing with the general safety of veterinary products:


Risk of resistance? YES, resistance of horn flies & poultry mites to synthetic pyrethroids (incl. permethrin) is widespread in the USA and worldwide, and can be very high. 

This means that if this product does not achieve the expected efficacy against the mentioned parasites, it may be due to resistance and not to incorrect use, which is usually the most frequent cause of product failure.

Alternative chemical classes/active ingredients to prevent resistance of external parasites through product rotation:

These alternative products may not be available in all countries, or may not be available for dusting, or may not be effective against all the concerned parasites.

Learn more about resistance and how it develops.


Are the active ingredients of this product ORIGINAL* or GENERICS**?


*Meaning that they are still patent protected and generics are not yet available
**Meaning that they have lost patent protection and may be acquired from manufacturers of generic active ingredients other than the holder of the original patent.

COUNTRIES where this brand/product is marketed: USA
GENERIC BRANDS available? YES. Permectrin Fly & Louse Dust is a brand from BAYER (now ELANCO) containing generic permethrin.

Click here to learn more about GENERIC vs. ORIGINAL drugs.

For an overview on the most used antiparasitic spray, dip & dust BRANDS click here.


This product is one of the various dusts containing synthetic pyrethroids for the control of flies, lice, and mites

Permethrin is a veteran synthetic pyrethroid introduced in the 1970s (by several companies). It is also a broad-spectrum non-systemic insecticide and acaricide massively used in pets, livestock, hygiene and agriculture worldwide. There are thousands of products with permethrin world-wide. It is effective against ticks, flies and certain lice species, but has also a certain repellent effect against mosquitoes, ticks and flies.

Insecticide dusts such as this product are often one of the cheapest options for insect control on animals. However the active ingredients used in such products are mostly rather old (introduced in the 1950s to 1970s) and many pests have developed resistance to them. For cattle, more modern and more effective active ingredients for the control of external parasites are often not available as concentrates but only as ready-to-use pour-ons, injectables, or in the form of insecticide-impregnated ear-tags. They are usually more effective, more convenient and with a longer protection period than dusts and concentrates, but are also more expensive.

All synthetic pyrethroids are veteran pesticides developed in the 1970s-1980s and are basically contact insecticides. This means that when the parasite comes in contact with it (e.g. during the blood meal, after landing on a treated host, etc), the active ingredient that impregnates the host's hair coat penetrates through the cuticle (i.e. the "skin" of insects and other arthropods) into its organism and disturbs essential biological processes in the parasite's body, in this case its nervous system.

After administration to livestock or other animals, synthetic pyrethroids do not have a systemic mode of action, i.e. they are not transmitted to the parasite through the blood or the host. Topically administered synthetic pyrethroids are very poorly absorbed through the skin of the hosts, and what is absorbed is quickly broken down and/or excreted. Consequently the concentration reached in the blood is too low to kill blood-sucking parasites. But this is why they are considered rather safe for mammals, both humans and livestock (cats are an exception: pyrethroids are toxic to them!) and why they leave rather low residues in meat and milk.

Dusting is a delivery form of insecticides that is still often used on poultry wordlwide, due to the fact that tat many bird species have the natural behavior of dusting themselves. Although still popular in the USA, use of dusts in cattle and swine is rather unusual in many other countries (Europe, Latin America, Australia, etc). Dusting for self-treatment of livestock (e.g. using dust bags) has an inherent weakness: Dosing depends on the behavior of the animals. It is unavoidable that some animals get too much product, and other animals not enough. Besides insufficient protection of some animals, this may cause excessive residues in other animals. And it is generally accepted that underdosing of animals favors resistance development. For these reasons parasiticides for dusting are no more allowed in many countries (e.g. the EU). To learn more about dusting animals click here.

Control of susceptible (i.e. non-resistant) horn flies is usually good, because they spend a lot of time on cattle and thus are exposed to the insecticide for a long period of time. Lice are also exposed to insecticides for a long period of time because they never leave the host. Control of face flies is often not as good, due to their different behavior: they do not spend a lot of time on the animals and visit mainly body parts in the face that are humid with body fluids (eyes, nostrils, around the mouth), where the insecticide concentration is diluted by these body fluids. Control of other flies (stable flies, horse fliesblack flies) is insufficient because they may bite the treated animal anywhere in its body and remain attached and thus exposed to the insecticide only during their blood meals that last a few seconds or minutes, which is too short to kill them.


This article IS NOT A PRODUCT LABEL. It offers complementary information that may be useful to veterinary professionals and users that are not familiar with veterinary antiparasitics. 

Information offered in this article has been extracted from publications issued by manufacturers, government agencies (e.g. EMEA, FDA, USDA, etc.) or in the scientific literature. No guarantee is given on its accuracy, integrity, sufficiency, actuality and opportunity, and any liability is denied. Read the site's DISCLAIMER.

In case of doubt contact the manufacturer or a veterinary professional.