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Activyl for Cats

By | Last Updated : 9th August 2017

What is Activyl

Activyl, by Merck, is a safe spot-on flea treatment for cats. It contains the active ingredient indoxacarb, with isopropyl alcohol as the other component [3].

How does Activyl work in cats

Activyl works in a method known as bioactivation. Certain enzymes in the fleas’ body activate the indoxacarb ingredient of the medication, which then kills the adult fleas, larvae, and eggs, thus interrupting their life-cycle [3]. The medication interferes with their spinal cord and brain, finally causing death [1].

Apart from cats, Indoxacarb is safe for dogs, and also humans [1].

Quick Information

Activyl for Cats

Generic name

Indoxacarb [2]

Brand name

Activyl Spot-On for cats and kittens, Activyl Spot-On for Cats [2, 3]


Flea treatment, antiparasitic agent [1]

Who can take it



Prescription only [1]

Available forms

Topical solution [1]


Do not use Activyl on your cat without first consulting a veterinarian. The medication is available in two variations, Activyl Spot-On for Cats contains 0.03 fl. oz. (1.03 ml) and is meant for larger cats that are over 9 lbs and 8 weeks old. Activyl Spot-On for Cats and Kittens has 0.02 fl. oz. (0.51 ml) and should be given to small cats and kittens weighing between 2 and 9 lbs, but over 8 weeks old. Each pipette must be completely emptied in a single dose [1].

How to apply Activyl Spot-On: Directions for flea treatment

The instructions for administering Activyl on your cat are usually given on the label of the medicine. Here are the basic steps:

  • Hold the applicator upright, away from your face and snap open the tip by bending and folding it back [2].
  • Part the fur at the base of the cat’s skull and put the tip of the applicator on the skin. Applying the solution at this spot will prevent your pet from licking it [2].
  • Squeeze on the applicator and empty all the content on the skin. Make sure not to get any of the product on your skin. Allow it to dry [2].
  • Do this once every 30 days to keep your kitty free from fleas.

Activyl dries fast, although there might be certain oily or wet areas that might take up to 24 hours to dry completely [1].

How long does Activyl take to work

Activyl usually starts working within 8 hours of application [2].

Activyl side-effects

If your cat accidentally ingests the solution, possible adverse reactions like squinting, shaking its head, intermittent over-salivation, and licking its face may occur. These usually go away within a short time. In case these adverse reactions persist, consult a veterinarian immediately [2, 3].


Activyl should not be administered to cats that are allergic to indoxacarb. Inform your vet about all the medications that your cat is taking as some of them may interact with Activyl [1].  Also, refrain from applying it on cats of either sex that are expected to breed, and cats that are pregnant or nursing [2].

Activyl vs. Frontline Plus

Frontline Plus is a topical solution not dissimilar to Activyl. The primary distinguishing feature is that the ingredients of Frontline Plus are fipronil, an insecticide like indoxacarb, and S-methoprene, which kills flea eggs and larvae. While you should not apply Activyl on pregnant and nursing cats, you may do so without any worry in case of Frontline Plus [6].


    1. Indoxacarb (Activyl® Spot-On) for Dogs and Cats – PetPlace.com
    2. Activyl Spot-On for Cats – Drugs.com
    3. Activyl – 1800PetMeds.com
    4. Activyl – US.Activyl.com
    5. ACTIVYL® – MSD-Animal-Health.co.nz
    6. Compare – 1800PetMeds.com

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