Pyriproxyfen is an antiparasitic active ingredient used in veterinary medicine in dogs and cats against fleas. It is also used against agricultural and household pests. It is a so-called Insect Growth Regulator (IGR) belonging to the chemical class of the juvenile-hormone analogues.


Type: pesticide
Other names: NYLAR
Chemical class: juvenile hormone analogue, insect development inhibitor


Molecular structure of PYRIPROXYFEN





Type of action: contact and oral larvicide
Main veterinary parasites controlled: larvae of insects: flies, fleas.

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

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Pyriproxyfen is a contact insect growth regulator used in a few products for flea control in dogs and cats, mainly spot-ons and low-cost sprays, shampoos, soaps, etc. It does not kill fleas, but interrupts their development. For this reason it is mostly used in combination with a flea adulticide (e.g. fipronil, imidacloprid, etc). It has no effect on ticks or mites.

So far it is not used at all in livestock or horses. It is also used against agricultural and household pests.

The table below indicates some usual dosing recommendations for pyriproxyfen issued by manufacturers or documented in the scientific literature. They may not be approved in some countries.

Dosing recommendations for PYRIPROXYFEN
Delivery Parasites Dose (against pyriproxyfen-susceptible parasites)
Topical (spot-on) Fleas 0.5-13.3 mg/kg, dep. on brand and animal weight
Topical (spot-on) Fleas 5-70 mg/kg, dep. on brand and animal weight

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Dosing recommendations for antiparasitics depend on national regulations. 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 parasiteCheck the labels of the products available in your country for specific information on approved indications.


Oral LD50, rat, acute*: >5000 mg/kg
Dermal LD50, rat, acute*: >2000 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): Not applicable: not approved for livestock
Withholding periods for meat, milk, eggs: Not applicable: not approved for livestock

Learn more about pyriproxyfen safety.

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: 1980
Introduced by: SUMITOMO
Some original brands: SUMILARV
Patent: Expired (particular formulations may be still patent-protected)

Use in
DOGS and CATS: Yes, moderate

Main delivery forms: 

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


In livestock: Yes, in houseflies (Musca domestica).
In pets: No


Pyriproxyfen is a Juvenile Hormone Analogue acting as an insect development inhibitor effective against numerous insect species, but with no effect whatsoever on ticks or mites. It only interferes with the molt from pupae to adults, i.e. it does not kill insect larvae and consequently it cannot be used against various myiases.

In dogs and cats it is exclusively used in numerous spot-ons (= squeeze-on = pipettes), as well as in shampoos, soaps, sprays, etc, alone or in combination with flea adulticides, since most flea adulticides have an insufficient impact on the developmental stages in the pets' environment.

In livestock it is not used on-animal but only for premise and environmental treatment against fly larvae.

Pharmacokinetics of pyriproxyfen

After topical administration pyriproxyfen is distributed throughout the hair coat within 24 hours. After treatment at the recommended therapeutic dose (2-5 mg/kg) the highest concentration (~800 mcg/kg) was observerd at the application site and at the back and the flanks (~66 mcg/kg). It remained detectable in the hair coat for about 42 days. It was stored in the hair folicles from where it was continuously released during a period of ~3 months.

Absorption through the skin is very low. Bioavailability reached ~37%, and the highest plasma concentration (2.8 ng/ml) was measured 1-3 days after administration. Half-life was 6 days.

In rats, pyriproxyfen concentrations were found to be highest in the fat, without evidence of accumulation. Pyriproxyfen was highly and rapidly metabolised and excreted into faeces and urine, with the major route of excretion being via the faeces.


Mechanism of action of pyriproxyfen

Pyriproxyfen and other Juvenile Hormone Analogs suppress or stimulate the expression of various genes involved in insect metamorphosis otherwise regulated by natural juvenile hormone. Depending on which gene is affected different biochemical and cellular effects will result. The bottom line is that development is disturbed and interrupted.

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