Capstar(®) is a fast acting insecticide which begins working to kill fleas in as little as 30 minutes. The active ingredient nitenpyram is a synthetic nicotine substance which, once ingested, enters the bloodstream. The drug is then consumed by the parasites feeding on your dog’s blood leading to paralysis and death. Nitenpyram works on “nicotinic acetylcholine receptors”, receptors which are also affected by tobacco.

Because nitenpyram is only dangerous for invertebrates (creatures without a spine) the medicine is not toxic to dogs. It is one of the most effective flea treatments, with some studies showing the medicine killing 99.1% of adult fleas within 3 hours and 100% within 8 hours, a much higher rate than the other drugs tested (cythioate, fipronil, selamectin and imidacloprid).

Does it kill ticks and larvae?

The downside of this drug is that it’s ineffective against ticks, flea eggs/larvae and immature fleas. However it may be effective against fly larvae.

Recommended Dosage

Note: Speak to your vet before administering this medicine.

There are two different boxes of Capstar which are color-coded for dogs of different sizes. The blue box contains tablets suitable for those weighing from 2 to 25 lbs while the green box contains tablets which are suitable for those over 25 lbs. Give one tablet to your dog kill all of the adult fleas on their body.

Weight of dog (lbs)

Colored box to use

2 – 25Blue box (11.4 mg)
Over 25Green box (57 mg)

The tablets can either be placed directly into your dog’s mouth or hidden in their food depending on your preference. If you hid the tablet in food and are not sure if the tablet has been swallowed then you can safely give them a second tablet. But do not exceed this amount.

Note: A dog weighing 20 pounds could be given one tablet from the blue box. If they weighed 30 pounds they could be given one tablet from the green box.

Is It Safe?

The medicine’s active ingredient is a synthetic nicotine which is only toxic to invertebrates, it’s safe to give to dogs.

Treatment is not safe for a dog who is:

  • Under 2 pounds body weight
  • Under 4 weeks old

It is probably safe for pregnant or lactating animals but you should consult with your vet first.

Safety Guidelines

Before administering Capstar you should speak to a vet for guidance and advice. Avoid treating dogs under 2 lbs body weight or under 4 weeks of age, and should not give a dose more than once every 24 hours.

Because of rare reports of seizures it might be best not to give the drug to pets with seizure disorders.

What Is It Used For?

The active ingredient nitenpyram is used to kill mature fleas. Because it is not effective for treating immature fleas or flea eggs it should usually be used in combination with another drug such as lufenuron.

Side Effects

Adverse effects are not expected, but the following are possible:

Most Common

  • Itching (caused by the dying parasites, not the drug)


  • Anxiety
  • Lethargy
  • Diarrhea
  • Vocalization
  • Loss of appetite
  • Loss of coordination
  • Hyperactivity
  • Seizures
  • Trembling
  • Drooling
  • Panting
  • Fever

Overdoses are not usually dangerous, the medicine is tolerated well in higher amounts. However you should always contact a vet or the ASPCA Poison Control Hotline on (888) 426-4435 if an overdose occurs.


Capstar website (defunct)
Dr. P. Connick
Plumb’s Veterinary Drug Handbook (sixth edition)