Pyriproxyfen (Nylar)
Veterinary & Aquatic Services Department, Drs. Foster & Smith


Pyriproxyfen is an insect growth regulator which will inhibit the hatching of flea eggs and the development of flea larvae. It will not kill adult fleas or any stages of a tick. It must be applied to the pet's skin to be effective. It is extremely safe.

Generic Name

Brand Name

Type of Drug
Insect growth regulator

Form and Storage
Topical solution
Store in cool, dry place.

Indication for Use
Treatment and prevention of flea infestation.

General Information
EPA approved for use on the respective species. Available over the counter in many flea and tick products. Once the female flea comes in contact with a dog or cat treated with pyriproxyfen, eggs laid by that female from that point on will not hatch. Flea larvae that come in contact with the treated pet will not develop. This helps prevent a continual flea problem.

Pyroxifen will not kill the adult flea and does not stop the flea from biting and causing flea allergy dermatitis. Pyriproxyfen will not kill any stage of ticks.

Usual Dose and Administration

Follow manufacturer's directions.

Side Effects
May see irritation or redness on the skin. If sensitivity occurs, bathe in mild shampoo and contact your veterinarian.

Do not use on cats hypersensitive (allergic) to it.

Do not get product in pet's eyes or mouth.

Need to treat all pets in the household for fleas or the problem will continue.

Treat year-round for best results or start before warm weather begins each spring in the northern states. .

Drug Interactions
Do not use with other topical pesticides unless directed by your veterinarian.

Unlikely. Because insect growth regulators mimic insect hormones, which are unlike hormones in cats and dogs, they are extremely safe.

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Keep this and all other medications out of the reach of children and pets.

If you think your pet has been poisoned...

Contact your veterinarian or one of the Animal Poison Hotlines (listed below) if you think your pet may have accidentally received or been given an overdose of the medication.

**ASPCA National Animal Poison Control Center

1-888-4ANI-HELP (1-888-426-4435). $65.00 per case, billed to caller's credit card.

Follow-up calls can be made for no additional charge by dialing 888-299-2973.

There is no charge when the call involves a product covered by the Animal Product Safety Service.

**Pet Poison Helpline - 24-hour service available throughout North America for pet owners and veterinary professionals who require assistance with treating a potentially poisoned pet.

1-800-213-6680 ($35.00 per incident). Staffed 24-hours a day.

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