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Activyl for Cats

By | Last Updated: 22nd February 2023

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

Proven in a study to be effective in treating fleas, Activyl works in a method known as bioactivation. Certain enzymes in the fleas’ body activate the indoxacarb in the medication, which then interferes with their spinal cord and brain, finally causing death [1]. It also kills the larvae and eggs, thus interrupting their life-cycle [3].

Apart from cats, indoxacarb is also safe for dogs [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]

Type: Flea treatment, antiparasitic agent [1]

Who can take it:  Cats

Availability: 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, containing 0.03 fl. oz. (1.03 ml), is meant for larger cats 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 skull and put the tip of the applicator on the skin. Applying the solution at this spot will prevent the cat from licking it [2].
  • Squeeze on the applicator and empty all the content. 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 cat free from fleas.

Activyl dries fast, although there might be areas that are oily or wet which can 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].

Side-effects: What if your cat licks it

Possible adverse reactions include:

  • Squinting
  • Shaking its head
  • Intermittent over-salivation
  • Licking its face

These usually go away within a short time, otherwise, consult a veterinarian immediately [2, 3].

Contraindications: When should Activyl be avoided

Inform your vet about all the medications that your cat is taking as some of them may interact with indoxacarb [1]. It should not be administered to cats that are:

  • Allergic to indoxacarb
  • Expected to breed
  • Pregnant or nursing [2]

Activyl vs. Frontline Plus

Frontline Plus is a topical solution not dissimilar to Activyl. Studies have shown that Activyl is more efficient in controlling fleas than Frontline Plus. 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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