Pyrethrins, Permethrins, and Pyrethroids
By Dr. Karen Burgess

Pyrethrins, permethrins, and pyrethroids are all are natural products used to repel and kill insects.  While organic in origin, pyrethrins are extremely toxic for cats and fish and lesser so in dogs.

What are pyrethrins?
Pyrethrins are a natural insect repellent and insecticide that tends to break down readily and are derived from the flower of the mum (Chrysanthemum cinerariaefolium).  Over the years pyrethrins have started replacing the more toxic organophosphate products.   Pyrethroids (including permethrin) are synthetic versions of pyrethrins and tend to break down slower in the environment.  The primary action of pyrethrins is on an insect’s nerve center causing almost instantaneous paralysis.  Some insects have developed resistance to natural pyrethrins over the years, thus leading to development of the longer acting pyrethroids.  In some cases additional potentially toxic components (ex. organophosphates) are added to pyrethroids to enhance their efficacy.

What products contain pyrethrins?
Pyrethrins are commonly found in yard treatments, foggers, and dog or cat flea products (shampoos, powders, topical spot ons).

How much pyrethrin exposure is a problem?
For cats or fish, any pyrethrin exposure is a concern.  Remember to keep your dog out of water that may have fish until any topical flea product has completely dried (or 48 hours to be safe).  Products containing pyrethrins have varying percentages of concentration.  If exposure or toxicity is a concern, please contact your veterinarian or animal poison control immediately.

What problems and symptoms do pyrethrins cause?
Symptoms of toxic exposure start shortly after exposure and include drooling/excessive salivation, vomiting, agitation, and gagging.  Some dogs have a skin type of reaction to pyrethrins that may look like excessive itchiness (feeling of pins and needles), restlessness, or whimpering/crying.  Severe exposure may progress to seizures, severe depression/coma, and death.  Cats experience similar but often more severe signs and should be considered an immediate and potentially life threatening emergency.  Often the first sign cat owners notice is trembling or excessive shaking.

What to do if you feel your pet has been exposed to toxic amounts of pyrethrins
Contact your veterinarian, animal emergency hospital, or animal poison control immediately.  If your cat has been exposed to pyrethrins toxicity can be life threatening.  Hospitalization, decontamination (removing product from skin or stomach), muscle relaxants, and supportive care are indicated until no further symptoms are noted.  Prevent exposure by reading product labels carefully (make sure safe to use on cats, correct formula for your pet’s weight) and not allowing cats access to dogs treated with pyrethrins for at least 24 hours.