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Capstar vs Comfortis Flea Tabs: Vet Opinion on Which is Best for Your Pet

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By Dr. Joanna Woodnutt

capstar vs comfortis flea tablets

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Dr. Joanna Woodnutt

BVM BVS (Veterinarian)

The information is current and up-to-date in accordance with the latest veterinarian research.

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It can be challenging to choose an appropriate anti-flea product for your pet as there are so many options available. Even as vets, it can be mind-boggling. While the overall goal of all flea treatment is to stop your pet (and you!) being bothered by fleas, there are a few different ways to achieve this, hence the broad range of products available.

Comfortis and Capstar are both effective flea treatments, but they are quite different from one another. In a direct comparison between Capstar and Comfortis, which should you choose?

A quick note on the flea life cycle…

Fleas exist in four life stages – eggs, which hatch to larvae, develop to pupae, then mature into adult fleas. The adult fleas are what you see on your pet, wriggling and leaving little deposits of curly brown poo (flea dirt). Adult fleas feed on your pet but live in, and lay eggs around, your home. The larvae and pupae can also be found around your home. If left untreated, larvae and pupae mature to adult fleas, lay more eggs and your home is infested. 

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Capstar Overview

What is Capstar?

Capstar is a tablet flea treatment for cats and dogs, given by mouth, to kill adult fleas. Capstar can be bought without a veterinary prescription. There are two tablet strengths available:

  • Capstar 11.4 mg – for cats and small dogs, between 2-25 pounds (or 1-11 kg) in body weight.
  • Capstar 57 mg – for larger dogs, from 25-125 pounds (or 11-57 kg) in body weight.

Dogs heavier than 125 pounds need more than one tablet (i.e., a 135-pound dog would have one large and one small tablet). Dogs or cats lighter than 2.2 pounds (1 kg) should not be given Capstar.

Capstar Flea Oral Treatment for Dogs

How does Capstar work?

Capstar is given to your pet by mouth. The ingredient that kills fleas, nitenpyram, is quickly absorbed into your pet’s bloodstream. When the fleas bite, they are exposed to the drug and killed. Fleas start dying from 15 minutes after you pet takes the tablet, and 95% of the fleas exposed to the treatment are dead within 6 hours.

When is Capstar a good choice of flea treatment?

Capstar is your quick-fix flea treatment. It is fast-acting and effective at killing adult fleas, present on your cat or dog at the time of treatment. Pets usually pick-up fleas from the environment, not other animals, so can become infected while exploring outside. If your pet returns home with fleas and your home is otherwise flea-free, give your pet an appropriate dose of Capstar and in 24 hours 100% of the fleas will be dead, job done!

Capstar is also safe for repeated dosing. If you have more of an ongoing problem with fleas, then you can give Capstar everyday, once a day, for as long as you see fleas on your pet. Do not give your pet Capstar more than once per day.

Capstar Flea Oral Treatment for Dogs_blue

Can I use Capstar with other flea products?

If you are seeing fleas on your pet several days in a row, despite treating with Capstar, there is a good chance that other life-cycle stages of fleas are living in your home. Capstar is safe for use alongside other flea products so, to gain control of an infestation, you can use Capstar AND a second product that will kill the other life stages. It is best to seek advice from your veterinarian regarding which flea product is best for your individual situation.

You might already be using a flea prevention treatment, like Comfortis, once a month, but a few pesky fleas can still leap onto your pet. Capstar is safe for use alongside preventative treatments to kill any newly acquired fleas as quickly as possible.

If you see fleas on your pet, you may want to give them a bath. Capstar can be used alongside flea shampoos, although you can wash fleas from your pet’s coat with plain water too.

When is Capstar safe to use?

Capstar is safe for pets as young as 4 weeks, weighing as little as 2lbs. It can be used during pregnancy or while a mother is feeding her young. Capstar can be given with food or without, and as often as every day. Capstar can be used alongside other commonly used drugs, including other flea treatments. Capstar carries minimal risk of side effects. Some pets are itchier for a short while after taking Capstar, due to the increased activity of the fleas as they start to die. In most cases, this effect is mild and quick to resolve.

  • Fast, effective killing of fleas.
  • 100% effective within 24 hours.
  • Cheaper than some other flea products.
  • Can be bought as a single dose.
  • Safe for use in puppies and kittens (>2lbs bodyweight and 4 weeks of age).
  • Safe for use in pregnancy and while nursing young.
  • Safe to use alongside other commonly used drugs, including other flea products.
  • Minimal risk of side effects.
  • Available to buy without a veterinary prescription.
  • Can be given with or without food.
  • Kills adult fleas only – no activity against eggs, larvae or pupae.
  • No residual activity – only kills fleas the day it is given.
  • Can lead to increased itchiness for half an hour after being given.
  • Contains maize starch (corn) so should be used with caution in pets with a known maize allergy.

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Comfortis Overview

What is Comfortis?

Comfortis is a tablet for cats and dogs that kills fleas and helps prevent flea infection. Comfortis must be given with or immediately after food, and only once per month. There are many different strengths of Comfortis available – as Comfortis requires a veterinary prescription, you don’t need to worry about dosing, your vet will prescribe the correct size for your pet.

Comfortis is a great choice for pets that don’t like taking tablets as it is only necessary to dose them once per month. Comfortis tablets are chewable and beef-flavored, to help make them more tempting for pets to eat. The beef flavoring is artificial so, even for pets with a known beef allergy, the risk of an allergic reaction is low.

Comfortis Chewable Tablet for Dogs_orange

How does Comfortis work?

Just like with Capstar, Comfortis is absorbed into the bloodstream of your cat or dog. Fleas are killed quickly by exposure to the active ingredient, spinosad, when they bite your pet. A key difference between Capstar and Comfortis is that Comfortis will keep killing adult fleas that bite your pet for 28days after a single dose.

Comfortis also slows the egg production of fleas so helps to prevent your home becoming infested. The egg-slowing effect lasts for 28 days following a single dose.

When is Comfortis safe to use?

Comfortis is safe for dogs and cats over 14 weeks of age. The safety of Comfortis in pregnant females or those feeding their young has not been assessed so it’s best not to use it. Comfortis should be used with caution in male dogs or cats that are used for breeding. It’s always sensible to discuss flea prevention with your veterinarian, and even more important to do so if your pets are used for breeding.

Comfortis is safe to give once a month, but not more often, because its effects are long-lasting.

Comfortis is safe to use alongside most of the commonly used medications, but not all. Your vet will be aware of this and prescribe accordingly. Comfortis should be used with caution in pets with epilepsy, for example.

Comfortis is best fed to your pet with, or immediately after, food. If fed on an empty stomach its beneficial effects may not last as long.

Comfortis Chewable Tablet for Dogs_green

Does Comfortis cause vomiting?

Some cats and dogs can be sick after dosing with Comfortis. This vomiting is usually mild and requires no treatment. It happens in relatively few animals.

  • Flea treatment and prevention in one tablet, once per month.
  • Fast, effective killing of fleas.
  • 100% effective within 6 hours in terms of killing adult fleas on your pet.
  • Continues killing fleas as they infect your pet for 28 days.
  • Slows flea egg production so reduces chance of flea infestation in your home.
  • Chewable and tasty beef flavor to encourage easy dosing.
  • Can be given with a meal or shortly after eating.
  • Can be bought in handy, six-month blister packs.
  • Safe for use in dogs and cats >14 weeks of age
  • Available only with a veterinary prescription, so you know your veterinarian has reviewed its suitability for you and your pet.
  • Safe for pets with known allergies to beef as flavoring is artificial (please note, any drug can cause an unexpected allergic reaction).
  • Can cause vomiting shortly after dosing in some cases
  • Not suitable for young puppies or kittens
  • Not suitable for breeding pets unless advised otherwise by your veterinarian
  • Should be given with caution in pets with epilepsy

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Capstar or Comfortis? Which Should You Use?

Both Capstar and Comfortis are effective anti-flea products with many benefits, depending on the situation.

Which is best at killing fleas?

Both products start killing fleas within half an hour of being taken. Both products are very effective, killing 100% of fleas on the animal within 24 hours at most.

I have just seen fleas on my pet, which product should I choose?

If you are looking for fast treatment for active adult fleas, Capstar is a great choice.

Take into consideration that, if you see fleas on your pet but they have been there a few days, an infestation might have started in the home. Use Capstar as soon as possible after noticing fleas for maximum benefit.

dog scratching
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What should I use to prevent fleas in my home?

If you are looking to kill adult fleas and prevent breeding of fleas around your home, Comfortis gives you that extra function.

It pays to remember that Comfortis is designed for monthly dosing. Once you choose Comfortis as your monthly flea prevention treatment, keep up regular doses to maintain the beneficial effect. The flea life cycle can be as fast as 12 days in ideal conditions so an infestation can establish very quickly if there’s a gap in treatment.

If deciding between Capstar and Comfortis, which is best?

Essentially, it depends. If you’re treating young puppies and kittens, Capstar is best. If you’re treating breeding adults, Capstar is best. If you want a comparatively cheap, effective way of killing adult fleas, Capstar is best. To give an example, if you are taking in a stray and want to be sure they aren’t bringing in fleas to your free-flea home, Capstar is a great product.

On the other hand, if you have a pet that is terrible at taking tablets, Comfortis is best with its once-monthly regime. If you are using no other flea treatments to control the flea population in your home, Comfortis is best. If you have a pet that is allergic to maize, Comfortis is best.

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As with so many things, which is best is a personal question. The choice between Capstar and Comfortis is no different. It depends on you, your pets and your situation. It is important to treat all cats and dogs in the household at the same time, whichever product you choose.

It is wise to speak with your veterinarian regarding your flea treatment choices. Even if you settle upon a non-prescription product, your veterinarian is best placed to advise you.

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