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per-METH-rin - Pronunciation guide

Brand Names

  • Bronco®e Equine Fly Spray Plus
  • Prozap® Final Fly-T Horse Spray and Wipe On Insecticide
  • Flysect® Super-C Repellent Concentrate
  • Ambush™ Insecticide & Repellent
  • Mosquito Halt® Repellent Spray for Horses
  • Durvet Fly Rid Plus
  • Horse Lice Duster III


Permethrin is an insecticide similar in chemical composition to pyrethrin which is derived from the chrysanthemum flower. However, as a synthetic compound, (part of a class known as pyrethroids) permethrin is more stable than pyrethrin and, thus, has a longer shelf life.

Permethrin is used as an external insecticide – either in sprays, wipes, and spot-ons that may be applied directly to the animal, or in more concentrated formulations designed as premises sprays. It is important to read the labels carefully and avoid applying products intended for premises (barn, paddock, etc.) use to the animal.

Permethrin acts upon the insect’s nervous system but is safe in most mammals. Cats are a significant exception to this rule. Permethrin is also toxic to birds, fish, and beneficial insects such as honeybees.


Permethrin is used to control a variety of external parasites, including ticks, lice, gnats, and flies. Products should be applied according to label directions for that specific formulation. Read labels closely!

Dosage and Administration


Method Dosage
(click row for calculator)
Concentration Period Duration
Spray     Treatment NA
Spot-on     Treatment NA
Dust     Treatment NA
Premises     Treatment NA


  • For animal use only.
  • Regulated by the Environmental Protection Agency – Use may be restricted in some states or locations.
  • Label directions should be closely followed. Do NOT use premises sprays on animals.
  • Calculator is for educational purposes only. Follow your veterinarian's instructions regarding use of this, or any, medication.

Side Effects

Skin sensitivity may occur in humans and horses. If signs of sensitivity appear, bathe with mild shampoo and rinse with large amounts of water. Contact your physician or veterinarian if signs persist. Hair discoloration or hair loss may also occur in horses with some concentrated (spot-on) products. Neurotoxicity is seen in cats exposed to permethrin products. Do not use on cats. .


Permethrin is classified as a human carcinogen. Avoid direct contact as much as possible.

Do NOT apply on or near cats.

Avoid contamination of water sources; permethrin is toxic to aquatic organisms.

Permethrin is regulated by the Environmental Protection Agency – Use may be restricted in some states or locations.


None noted.


Signs of overdose would be related to the action of the chemical. Neurotoxicity could be possible at extremely high doses. Skin sensitivity is more likely.


Permethrin 10 Spray ConcentratePermethrin 10 Spray Concentrate

Equi-Spot Spot-On Fly ControlEqui-Spot Spot-On Fly Control



About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.