K9 Advantix II for dogs is one of the most trusted names in flea and tick protection. In addition to treating these common parasites, K9 Advantix II also protects against lice and mosquitoes. Read on to learn more about dosage directions, efficacy, and side effects.


Dogs must be at least 7 weeks old and weigh at least 4 lbs. before using this medication. The dosage strength and application instructions vary depending on your dog’s weight. Here’s a brief overview of the dosage instructions:

  • 4 - 10 lbs. — Apply K9 Advantix in 2 to 3 areas

  • 11 - 20 lbs. — Apply K9 Advantix in 2 to 3 areas

  • 21 - 55 lbs. — Apply K9 Advantix in 4 to 6 areas

  • Over 55 lbs. — Apply K9 Advantix in 4 to 6 areas

Be sure to purchase the correct dosage strength for your dog. Unlike other topical flea treatments, small amounts of K9 Advantix must be applied in 2 to 6 different areas of your dog’s body, depending on their size.

After applying, be sure to wash your hands thoroughly with soap and warm water. Supervise your dog until the medication dries to prevent them from ingesting it. Reapply every 30 days.

Dosage instructions for small dogs under 20 lbs.

Remove the packaging and twist off the cap. Start with your dog standing. Gently part the fur on their back, between the shoulder blades. Apply a small amount directly to the skin. Repeat twice more at the mid-point of the spine and the base of the tail.

Dosage instructions for large dogs 21 lbs. and over

Remove the packaging and twist off the cap. Start with your dog standing. Gently part the fur on their back, between the shoulder blades. Apply a small amount directly to the skin. Repeat up to 5 times more along the spine, with the final application at the base of the tail.


K9 Advantix II starts working within 12 hours to kill existing fleas and remains effective for up to 4 weeks.

Active ingredients in K9 Advantix II

  • Permethrin: 44%

  • Imidacloprid: 8.8%

  • Pyriproxyfen: 0.44%

Permethrin kills fleas, ticks, mosquitoes, and a host of other parasites. It’s a common ingredient in spot flea medications as well as flea collars and similar products.

Imidacloprid is an insecticide that’s also an active ingredient in treatments for roundworms, hookworms, and whipworms. This ingredient is considered safe when used as directed. Currently, no drug interactions have been observed.

Pyriproxyfen is a growth inhibitor. It works by disrupting the reproductive processes of parasites.

Side effects

Possible side effects of K9 Advantix II for dogs include:

  • Vomiting

  • Diarrhea

  • Lethargy

  • Scratching

  • Excessive drooling

  • Burning, numbness, or tingling of the skin

  • Redness or skin irritation at the application site

Most mild symptoms clear up within 48 hours. However, consult your vet immediately if your dog is experiencing more severe symptoms, such as vomiting, diarrhea, and lethargy.


Drug interactions

No drug interactions with K9 Advantix II have been observed. However, if your dog is taking any medications regularly, prescribed or otherwise, consult your veterinarian for advice.

Allergic reactions and sensitivity

Purchasing the correct dosage strength is imperative, as overdose can cause severe symptoms. Cases of allergic reactions and sensitivity to K9 Advantix are rare. However, if your dog develops symptoms that resemble an allergic reaction, contact your veterinarian immediately.

While K9 Advantix II for dogs is safe when used as directed, it can be fatal for cats. Permethrin, one of the active ingredients in K9 Advantix II, is toxic to cats. 

Pet parents of cats and dogs must isolate their cats for at least 24 hours following treatment. Cats can contract permethrin toxicity from grooming or rubbing up against a treated dog. Even sharing furniture can cause poisoning, although this is less likely. When choosing a flea preventative for your cat, be sure to read the product label carefully to ensure it doesn’t contain permethrin.

Frequently asked questions

Do I need a prescription for K9 Advantix II?

No, K9 Advantix II is available over the counter.

Can I use another flea treatment in addition to K9 Advantix II?

That depends on the product and its ingredients. Certain oral medications are safe to combine with K9 Advantix II and other topical flea treatments. Talk to your veterinarian before combining products.

Can I bathe my dog after applying K9 Advantix II?

Wait 24 hours after applying K9 Advantix II before allowing your dog to bathe or swim.

My dog licked some of the medicine. What should I do?

Ingesting a small amount of K9 Advantix shouldn’t cause serious symptoms. You may notice excessive drooling, nausea, or vomiting. According to the Pet Poison Helpline, it’s a good idea to give your dog a tasty treat, like cooked, unseasoned chicken, to remove the bitter taste from their mouth. If symptoms persist, contact your vet, and always supervise your dog until the medication dries.

K9 Advantix II Questions and Advice from Veterinary Professionals

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© 2022 Wag Labs, Inc. All rights reserved.