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A dog acting weird after flea treatment has been applied is simply frightening. That is because no one expects adverse reactions after something as basic as anti-flea product application. However, dog parents complain about such issues. Although not commonly occurring, they are sporadically reported – enough to deserve proper explanation and attention. 

About Topical Flea Treatments for Dogs 

Anti-flea products for dogs are specifically formulated to fight off parasites. Therefore, in order to work well, they need to be strong, and for that purpose, sometimes, they contain pesticides. 

Under normal circumstances, nobody wants their dog anywhere near a pesticide. However, the pesticides' types and doses used in anti-flea products are modified, extensively tested, and generally safe.

The most common active ingredients found in topical anti-flea products for dogs are:

• Pyrethrins and pyrethroids – the first come from the chrysanthemum flower, and the second is synthetic. If ingested, they can affect the central nervous system, especially in young pups, senior dogs, and dogs with severe chronic conditions.

• Organophosphates – derived from phosphoric acid, these are used in many gardening products and extremely dangerous if used in inadequate doses.

• Indoxacarb – a synthetic chemical commonly used in crop chemicals. It fights off flea but not ticks, and therefore, it is often used in combination with other components. If ingested, it causes drooling and fainting.

Alternatively, there are natural anti-flea products formulated for topical use. However, in addition to having a questionable efficacy, they usually contain plant oils which once applied on the skin, cause tingling and burning sensations.

A Natural Dislike 

Before talking about weird behavior post-anti-flea product application, we must mention that some dogs dislike the smell of these products and the sensation the liquid products trigger when applied directly on the skin.

So, it is not uncommon for the dog to engage in several shaking bouts as a way of protesting and an attempt to get rid of the liquid on its back. This behavior should not be confused with adverse reactions.

Why is My Dog Acting Weird After Flea-Treatment?

A dog may obsessively scratch itself after receiving a topical flea treatment. This is because the active component in the products makes the flea a bit hyperactive before actually killing them. 

In simple words, the flea will run around in panic which will irritate the dog and make it scratch itself excessively. This reaction, although perceived as weird, is completely normal.

A dog may also act weird after receiving a topical anti-flea treatment if it associates the application with some traumatic event. For example, if the dog has its topical treatment applied at the vet’s office and it finds vet visit in general to be stressful, it is logical to expect weird behavior after leaving the vet’s.

If a dog acts weird after receiving its usual anti-flea treatment, there are several possible explanations:

  • The active ingredients and components in the anti-flea product have been slightly altered or completely substituted with new ones
  •  The anti-flea product is of low quality
  • The anti-flea product has passed its expiration date
  • The used anti-flea product is not designed for the dog’s size and weight

Adverse Reactions to Flea Products in Dogs 

Finally, the two most serious reasons why a dog may be acting weird after receiving topical anti-flea treatment are allergies and intoxication. Let's take a closer look at both.

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Allergy can take place if the dog is sensitive to the active components used in the product. The active components are absorbed through the skin and once inside the body, they trigger reaction.

Intoxication can happen if a small dog receives a topical anti-flea product designed for larger dogs. The intoxication can occur via two routes – through the skin, when the active components are absorbed and via the mouth, if the dog licks and ingests its topical treatment.

Allergy vs. Intoxication

A dog experiencing an allergic reaction will excessively scratch its body, have watery eyes, sneeze and cough and develop a skin lesion on the back at the same spot where the product was applied.

On the other hand, an intoxicated dog will drool excessively, vomit, have diarrhea, and, more often than not, exhibit neurological signs like loss of coordination, tremors, seizures, and light/noise sensitivity.

What to Do if a Dog Acts Weird After Topical Anti-Flea Treatment?

The first aid for dogs with weird anti-flea medication reactions is bathing with lukewarm water and dishwashing soap.

 Most active ingredients accumulate in the dog’s sebaceous glands, where they are supposed to stay for about a month regardless of the dog’s bathing routine. Therefore, simple bathing of the dog with water or regular dog shampoo will not be able to wash off the product.

 On the other hand, a powerful dishwashing soap will cut through the grease and eliminate the anti-flea product.

Keep in mind that this is just first aid, and its goal is to buy your dog time until reaching the vet’s office. Even if the dog behaves completely normal after the bath, visiting the vet remains of paramount importance.

What Not to Do if a Dog Acts Weird After Topical Anti-Flea Treatment?

Knowing what not to do is equally important as knowing what to do. When dealing with an adverse reaction to topical anti-flea treatments, these are the things you need to avoid:

  •  Do not underestimate the gravity of the situation
  • Unless instructed by your vet, do not induce vomiting
  • Do not discard the product’s package (it would help if the vet knows the active ingredient of the product you used)
  • Never use the same product again.

Concluding Thoughts

Topical flea treatments for dogs, just as the name suggests, are designed specifically for dogs. Before reaching the market, they go through long, detailed, and extensive test phases.

 Therefore, as long as they are used according to the label instructions, most anti-flea treatments are well-tolerated by most dogs.

However, some individual dogs can be overly sensitive, and in these dogs, the skin simply does not agree with the product’s active ingredient. In such cases, it is advisable to search for oral anti-flea alternatives or an anti-flea collar. Keep in mind though that some collars contain the same ingredients as spot-on treatments.

All in all, if your dog had an adverse reaction to the anti-flea treatment you used, consul with your vet and choose a suitable alternative with your trusted vet’s help.

About The Author

Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia.


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