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My cat accidentally got a double dose of Famciclovir. Is she okay?

Updated on September 23rd, 2025

Pet's info: Cat | Mixed Breed | Female | spayed | 16 years and 5 months old | 11 lbs

My cat was given a 125 mg dose of Famciclovir at the veterinary clinic at 5:30 pm. I brought this cat home after being boarded overnight and accidentally gave her another 125 mg dose of this medicine at 6:30 pm. She has eaten three small meals since I gave her the additional dose, but has not used the litter box. Have I accidentally harmed her? What should I do? I love her dearly. She seems ok.

3 Answers

Most Helpful Answer

Destini R. Holloway, DVM

Answered By Destini R. Holloway, DVM

Veterinarian

Published on June 19th, 2017

According to the veterinary medicine resource this drug has been tolerated at doses up to 90 mg/kg with mild symptoms (anorexia and excessive drinking) in some cats. Callie would have to have eaten 450 mg of Famciclovir to see these symptoms, so she is well below this amount if she ingested 2-125mg tablets totaling 250mg. She should be fine, however you can also consult with pet poison helpline to talk it over with a certified toxicologist as well. But based on my minimal research she is below the toxic level for ingestion. I hope your sweet girl continues to do well. Take care.
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Related Answers from Veterinarians

  • Answered By Christie Long, DVM

    Veterinarian, Certified Veterinary Acupuncturist

    Knowing Callie's weight would help to determine whether this is a harmful dose. The most commonly followed published dose for famciclovir is 40 milligrams per kilo of body weight every 8 hours. If Callie weighs 10 pounds (average for adult cats) that means that her dose would be around 180 milligrams every 8 hours. If the dose given at the vet clinic was the first of the day, and you gave the second dose (both at 125 mg) I think you have not harmed her. Research shows that at doses of 90 milligrams per kilo, cats showed decreased or absent appetite, and increased thirst. Your dosage wasn't close to that. Monitor, but I suspect she will be fine. You can also call the ASPCA's poison control hotline ((888) 426-4435) for any additional information they may have regarding famciclovir overdoses. There is a fee for their services.

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    1Pet Parents found this answer helpful

  • Answered By Dr. Melanie, BVSc MS

    Veterinarian

    Published on November 9th, 2019

    Thank you for contacting Petco Pet Education Center, formerly Petcoach with your question about Charlie. This may be ok. This can be dosed at 40 to 90mg/kg in cats, and even if he did have 125mg, that is still within the normal dose range. You don't need to do anything. I hope this helps!

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    1Pet Parents found this answer helpful

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