Capstar for Cats (Nitenpyram)

PetMD’s medications content was written and reviewed by veterinary professionals to answer your most common questions about how medications function, their side effects, and what species they are prescribed for. This content shouldn’t take the place of advice by your vet.  

What Is Capstar Used for in Cats?

Capstar is a fast-acting oral tablet that begins killing adult fleas on cats and kittens within 30 minutes of administration. One Capstar tablet kills over 90% of fleas within six hours and keeps working for 24 hours. 

Capstar is available without a prescription and is labeled for use in kittens and cats 4 weeks of age or older and weighing at least 2 pounds. 

Fleas are more than a nuisance—they can lead to serious health issues, including:  

• Flea allergy dermatitis, an allergic skin reaction to flea bite saliva 

• Tapeworm infection, which occurs when a cat ingests a flea infected with tapeworm larvae 

Fleas reproduce quickly, making it easy for a small problem to become a large infestation. For example:  

• A single female flea can lay up to 50 eggs a day.  

• One flea may produce up to 2,000 eggs in her lifetime.  

• Eggs hatch into larvae, then develop into pupae and adult fleas. 

Capstar may be given once per day if fleas reappear. If can also be used alongside other flea prevention medications as part of a comprehensive flea control plan, under the guidance of your veterinarian. 

Capstar can be safely used in pregnant and lactating cats. 

How Capstar Works in Cats

Capstar contains nitenpyram, an insecticide that begins working quickly to kill adult fleas on your cat. Once administered, it starts killing fleas within 30 minutes, which helps interrupt the flea life cycle by eliminating adult fleas before they can lay eggs. 

However, Capstar only targets adult fleas—it does not kill flea eggs, larvae, or pupae, and it doesn’t treat fleas in the environment. For this reason, your veterinarian may recommend combining Capstar with a long-term flea preventive to eliminate an active infestation. Additionally, all pets in the household and the household itself should be treated to prevent re-infestation (at the same time).  

How To Give Capstar to Cats

• Follow the directions on the drug label or as provided by your veterinarian. 

• You can give Capstar directly by mouth or hide it in a treat, such as Greenies Feline Pill Pockets. You can also mix it with a small portion of your cat’s food. If administering with food, watch closely to ensure your cat swallows the full tablet. If you’re unsure whether the tablet was ingested, it’s safe to give a second dose.  

• A single dose of Capstar kills adult fleas on your cat. If fleas return, Capstar may be given once per day as needed. 

Possible Side Effects of Capstar in Cats

Capstar is generally well-tolerated in cats. 

Some cats may scratch more than usual after taking Capstar. This is typically due to fleas dying, not a reaction to the medication itself. Other temporary signs you may notice include: 

• Hyperactivity 

• Vocalization 

• Excessive grooming and licking 

Additional reported side effects include: 

• Panting 

• Lethargy 

• Vomiting 

• Fever 

• Decreased appetite 

• Nervousness 

• Diarrhea 

• Difficulty breathing 

• Salivation 

• Loss of balance (ataxia) 

• Seizures 

• Dilated pupils 

• Increased heart rate 

• Trembling 

Human Side Effects 

Capstar is intended for pets only and should never be used by humans. Likewise, pets should not be given medications meant for human use.  

If you accidentally ingest the medication, seek medical attention in person or call Poison Control at 800-222-1222. 

When To Call Your Vet 

Call your veterinarian if you see any of the following, or if you have additional questions or concerns about the use of Capstar for cats: 

• Severe side effects (above) 

• Your pet’s condition worsens or does not improve with treatment 

• You see or suspect an overdose 

Capstar Overdose Concerns in Cats

An overdose of Capstar is unlikely to cause toxicity in cats, as shown in safety studies. 

If you suspect an overdose, immediately seek emergency veterinary care or contact an animal poison control center. Consultation fees often apply. 

• Pet Poison Helpline 855-764-7661  

• ASPCA Animal Poison Control 888-426-4435  

How To Store Capstar for Cats

Keep these storage tips in mind for Capstar: 

• Store at controlled room temperature between 59–77 F (15–25 C). 

• Keep tablets in its original packaging until ready for use. 

• Keep out of reach of children and pets.