By Rania Gollakner, BS, DVM, MPH

What is famciclovir?

Famciclovir (brand name Famvir®) is an anti-viral medication used to treat feline herpesvirus (FHV-1).

Its use in cats is ‘off label’ or ‘extra-label’. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully.

How is famciclovir given?

Famciclovir comes in tablet form; however your veterinarian may compound it into a liquid form. Famciclovir should be given by mouth without food. If your cat vomits or acts sick after receiving the medication, give the next dose with a small amount of food.

What if I miss giving my pet the medication?

If you miss giving your pet a dose, give the next dose as soon as you remember, but if it is close to the next scheduled dose when you remember, skip the dose you missed and give it at the next scheduled time. After that, return to the regular schedule. Never give your pet two doses at once or give extra doses.


Are there any potential side effects?

The usual side effects of famciclovir include decreased appetite and increased amounts of urine. Any side effects should be reported to your veterinarian.

This medication can take a few weeks before full effects are noted, but side effects can occur immediately. Gradual improvements are usually noted after a few days. This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.


Are there any risk factors for this medication?

  • Famciclovir should NOT be used in patients with known hypersensitivity to it or to pencicloir.
  • Caution must be taken when famciclovir is used in patients with a history of kidney disease and in pregnant or nursing animals.

Are there any drug interactions I should be aware of?

Other drugs can interfere with famciclovir, so be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

If your cat needs to be on this medicine for long periods of time, your veterinarian may recommend periodic blood tests to ensure your cat’s body is tolerating the medicine well. Do not miss these important follow-up visits.

How do I store famciclovir?

Store famciclovir tablets in the original prescription bottle at room temperature and protected from light. If your veterinarian has prepared a special liquid formulation, follow the storage recommendations and expiration date on the bottle.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.