wagyears

K9 Advantix · Flea & Tick

K9 Advantix II, 21-55 lb

A dog-only household that wants one monthly spot-on against fleas, ticks and mosquitoes

K9 Advantix II, 21-55 lb (4 doses)

K9 Advantix II Flea & Tick Topical for Large Dogs 21–55 lbs., 4ct | Vet-Recommended, 30-Day Protection, Treats & Prevents Fleas, Ticks, Mosquitoes, Biting Flies, and Lice

$57.42 Owner rating 4.4 out of 5 · 44,739 ratingsRepeat purchase

This is something you buy again. We have not worked out a verified monthly cost for this one yet, and would rather say so than divide a pack price by a guess.

The variant we link: 21–55 lbs · 4ctOne Amazon page often holds several sizes; check the selected option before you buy.

Amazon links earn us a commission; it doesn’t change what we recommend. Researched, not tested — how we research.

Buy on Amazon · $57.42

Price checked October 29, 2026; the listing has today's price.

Most owners add · Grooming & Nails

FURminator deShedding Tool

Brushing is the check: it is how a tick gets found before it has been attached a day.

Buy on Amazon · $35.27

Suits these stages

Is the K9 Advantix II, 21-55 lb (4 doses) right for your dog?

Who it’s for
A dog-only household that wants one monthly spot-on against fleas, ticks and mosquitoes.
Who should skip it
There is a cat in the house. The label says do not use on cats, that it may be fatal, and to keep cats away from treated dogs for 24 hours. Also skip if your dog is outside 21-55 lb.

The verdict

The over-the-counter spot-on for an owner who also wants mosquito and biting-fly cover. It is an EPA-registered pesticide (EPA Reg. No. 11556-143 on the box), and Elanco's label says one monthly dose treats and prevents fleas, ticks, mosquitoes, biting flies and lice, kills fleas within 12 hours, repels and kills by contact so parasites do not have to bite, and is waterproof after 24 hours. The label also carries the warning that decides whether it belongs in your house at all: do not use on cats, it may be fatal, and keep cats away from a treated dog for 24 hours. In a mixed household, look at a cat-safe option with your vet instead. This pack is banded for dogs of 21 to 55 pounds; buy the band your dog is in, never a split dose. Which preventive suits your region is a question for your vet.

Drawbacks

  • Dangerous to cats: the label says it may be fatal
  • Monthly application is easy to forget

WagScore

73out of 100
Owner satisfaction
71
Stage fit
80

Owner satisfaction from the product's Amazon star rating and review count; stage fit from our own assessment of how well it suits a dog at puppy, adolescent, adult, senior stage.

How the score is built →

What the listing says

  • Label covers fleas, ticks, mosquitoes, biting flies and lice
  • Kills fleas within 12 hours, per the label
  • Waterproof after 24 hours

Specifications

Protection Duration
1 month per dose (4-dose pack)
Application Method
Topical (spot-on)
Dog Size
21–55 lbs
Water Resistance
Yes (after 24 hrs)
Flea & Tick Kill
Fleas, ticks, mosquitoes, biting flies, lice
EPA Reg. No.
11556-143

From the maker’s listing and Amazon’s product data. Fields the listing doesn’t state are left out, not assumed.

If this one isn’t right

Skip it if: There is a cat in the house. The label says do not use on cats, that it may be fatal, and to keep cats away from treated dogs for 24 hours. Also skip if your dog is outside 21-55 lb.

← Back to the flea & tick comparisonNot sure what stage your dog is in? →

Gear

Pairs with

What tends to be needed alongside flea & tick — hand-picked adjacencies, not "customers also bought".

The rest of this shelf

Everything else we currently recommend on the flea & tick shelf — the same need, Protect.

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