Capstar Tablet



Active ingredient


Frequency of use

One-off Dose

Minimum age/weight

4 weeks (1kg)
See details below


Fleas (adults)

What is Capstar?

Capstar is a non-prescription oral tablet for dogs and cats. It contains the active ingredient nitenpyram that kills adult fleas. It is usually given as a one-off dose during a visible flea infestation in a pet.
According to the manufacturer (Elanco), Capstar starts to kill adult fleas within ~30 minutes of administration, and kills over 90% of adult fleas in dogs within 4 hours

What does Capstar do?

Capstar is an oral tablet given to your pet. Capstar contains one active ingredient – nitenpyram. Let’s break down how nitenpyram works:

  • Nitenpyram: After your pet has eaten Capstar, nitenpyram is absorbed through the digestive system and enters your pet’s bloodstream. When an adult flea bites your pet and takes a blood meal, nitenpyram interferes with the flea’s nervous system. This paralyses and kills the flea. 
  • Metabolism and Elimination: Nitempyram is rapidly excreted from the body through the urine, in its unchanged form. 
  • Duration of Action: Capstar Although Capstar (Nitenpyram) acts rapidly, it has a short duration of action. Capstar lasts around 24-48 hours, after which fleas can safely feed on your pet again.

What is Capstar for?

Capstar is good for sudden flea problems. It works rapidly, starting to kill adult fleas on your pet within 30 minutes. It’s an excellent choice when you need quick action to tackle fleas that are on an animal. 

However, Capstar doesn’t affect younger stages of fleas. Furthermore, it only treats adult fleas – it does not prevent them. Also, it isn’t useful for long-term use, as daily dosing would be needed. Therefore, Capstar is a short-term solution that doesn’t provide lasting protection. 

Capstar is particularly useful when a pet has caught fleas outside but hasn’t yet brought them into a house which is known to be flea-free. This might be the case if you were bringing in a stray, or if your dog has just been in contact with a flea dog at someone’s house and hasn’t yet come home. It’s also useful in rescue centres, when the other pets in the rescue are flea-free, to prevent new animals from bringing in fleas. If there are fleas in the house, decontamination of the house with another product is necessary to wipe out a flea infestation entirely.

Do note that Capstar only kills adult fleas, and has no effect on other types of parasites (e.g. heartworm, ticks, intestinal worms, mites).

What are the possible side effects with Capstar?

Like all medications, Capstar can have side effects. While these are usually mild or rare, it’s important for pet owners to be informed about these side effects. If your pet experiences side effects, tell your vet – who will then inform the manufacturer. Side effects include:

  • Itching or Scratching: Occasionally, pets may display increased itching or scratching. This often happens within the first hour of your pet taking Capstar. This is  due to the fleas reacting to the medication before they are killed. 
  • Hyperactivity: Some pets may exhibit increased activity or restlessness after taking Capstar. It’s like a burst of energy, and this reaction is usually temporary.
  • Decreased appetite: Some pets may eat less
  • Mild Lethargy: On the flip side, a few pets might experience mild lethargy or tiredness. 
  • Gut upset: Some pets may experience mild gut upset, such as vomiting or diarrhoea. If this persists or is severe, consulting your veterinarian is advisable.
  • Disturbance to pet’s nervous system: This side effect is rare, but very serious. Signs include incoordination, dilated pupils, salivation, trembling and/or even seizures. Contact your vet immediately if you see these signs. A seizure is a life-threatening emergency that requires immediate veterinary attention.
  • Allergic reaction: In rare cases, dogs may experience an allergic reaction, characterised by swelling, itching, or difficulty breathing. Breathing difficulties are life-threatening and require immediate veterinary attention.

It’s important to note that severe adverse reactions to Capstar are rare, and most pets tolerate the medication well. 

If you have any concerns about your pet’s health or notice unusual behavior after administering Capstar, contact your veterinarian. They can provide guidance on whether to continue the treatment and address any potential side effects based on your pet’s specific needs.

How to give Capstar safely

  • Follow instructions carefully: Capstar can be given with or without food. Always use Capstar  exactly as your vet has prescribed, or according to the instructions on the label. This includes the right dose and frequency. You will need to know your pet’s current weight in order to purchase the product with the correct weight range.
  • Never split doses: Always use the right size for your pet. Never try to split a larger dose between several pets. Do not give CAPSTAR (nitenpyram) for large dogs to cats or small dogs, or vice versa.
  • Take care if your dog has a history of seizure: Capstar may reduce the seizure threshold in pets. If your pet has had seizures, check with your vet before giving this drug.
  • Check weight and age: Generally speaking, Capstar 11.4 mg tablets should not be given to cats and dogs less than 4 weeks old or weighing less than 1 kg. Capstar 57 mg tablets should not be used on dogs less than 4 weeks old or weighing less than 11 kg
  • Check with your vet if giving anything else: Your vet should be aware of other drugs your pet is on, but it’s always worth double-checking in case there’s been a miscommunication somewhere.  Your vet is the best person to advise on appropriate preventatives for your pet.
  • Storage and Handling: Store Capstar according to the instructions on the label, usually in a cool and dry place. Make sure it’s out of reach of children and other pets.
  • Report any accidental overdose to your vet immediately: If you have mistakenly given too much Capstar, report it to your vet as soon as you realise the error. They may recommend blood tests, treatment or monitoring, depending on the severity of the overdose.

Capstar FAQs

How quickly does Capstar start working?

Capstar starts working very quickly. It usually starts working around 30 minutes after your pet has taken a dose.

How long does Capstar’s effect last?

Capstar’s effect lasts up to 24-48 hours, after which it is removed from the body and fleas can safely feed again.

Can Capstar be used on puppies and kittens?

Yes, Capstar can be used on puppies and kittens. Capstar 11.4 mg tablets can be used on kittens and puppies that are at least 4 weeks old and weigh at least 1kg. Capstar 57mg tablets can be used on puppies that are at least 4 weeks old and weigh at least 11kg

Can I use Capstar along with other flea prevention products?

You can use Capstar along with some flea prevention products (but not others). Consult your vet on the best flea prevention products to use along with Capstar.

How often can I give my pet Capstar?

Capstar is usually given as a once-off dose. If your pet still has fleas after the first dose, consult your vet. Generally speaking, additional doses may be given – but no more frequently than once a day. Your vet is the best person to advise you on the optimal dose frequency for your pet.

Can Capstar be used for pregnant or nursing pets?

Yes, Capstar can be used for pregnant or nursing pets.

What should I do if my pet vomits after taking Capstar?

If your pet vomits after taking Capstar, contact your vet and report any other signs that your pet may have. Your vet may advise you to monitor your pet closely or bring them in for assessment. You can also ask your vet for alternative flea treatments that do not have to be taken orally (e.g. spot-on flea treatments)

Can I give Capstar to my senior pet?

You can give Capstar to your senior pet after checking with your vet and ensuring that your senior pet does not have any health conditions that would increase the risk of side effects from Capstar.

Capstar Datasheet

All drugs have a manufacturer’s datasheet, which gives information about the drug’s use and possible side effects. There is usually one in your Capstar box, but if you have lost it you can click on the button below to be taken on an online version.

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Please note that the information contained herein is provided for informational purposes only. Although it has been written by a vet, we cannot consider the individual nature of your pet’s problems so it does not constitute veterinary advice. If you have questions about your pet’s medication or their health you should contact a vet, who will be able to help.