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Famciclovir for Cats

By Evan Ware, DVM

Last reviewed: 7/13/2022

Commonly prescribed for: Feline Herpes Virus and FHV (Feline Viral Rhinotracheitis)

Species: Cats

Therapeutic Class: Antiviral

Basic Information

Famciclovir is an antiviral drug used in veterinary medicine predominantly to treat cats suffering from feline herpes virus and FHV (feline viral rhinotracheitis). Famciclovir itself is not active in either humans or cats; it is metabolized to an active form, penciclovir. Although there is still some debate about how cats absorb and use this drug, there have been some very persuasive studies that show that famciclovir can be useful to treat cats with clinical disease due to FHV-1.

FHV is an upper respiratory infection caused by feline herpesvirus 1. It also is called feline influenza and feline coryza. This is a very serious disease and one that is highly contagious, especially among young kittens. If left untreated, FHV will result in death from pneumonia in most cases.

Veterinary Medicine Uses for Famciclovir

Early onset signs of FHV in cats will typically include loss of appetite, coughing, wheezing, sneezing, nasal discharge, conjunctivitis, and fever. Secondary bacterial infections like sinusitis and empyema can also develop after some time. Ocular problems, such as corneal ulcers, keratitis, and corneal sequestra also can develop.

If a cat becomes infected at an early age, the risk of FHV causing permanent damage to the nasal and sinus tissue is substantially higher. Like many other drugs in veterinary medicine, this drug is not FDA-approved for use in animals and is not available from a veterinary pharmaceutical manufacturer. Instead, it is compounded by a compounding pharmacy.

Potential Side-Effects of Famciclovir

While Famciclovir is appropriate for use in cats, it is a potent drug and some patients can experience side-effects, the most common of which are nausea, vomiting, diarrhea, and low-grade fever. Administering the medication with food can help offset stomach upset.

Be sure to discuss any side effects with your veterinarian immediately.

Famciclovir is a relatively new drug and there is minimal information available about its side effects. This drug was well tolerated by cats in two recent studies.

Drug Interactions with Famciclovir

Probenicid can increase the levels of the active form of famciclovir.

Precautions for Using Famciclovir

Treatment with Famciclovir should be avoided in patients with a known allergy or hypersensitivity to the medication. It also should be avoided in cases in which the patient suffers from acute renal-failure or liver disease.

Since the extent of Famciclovir's excretion into a nursing animal's milk is unknown, use of this drug in pregnant or nursing animals should occur only when the benefits outweigh the risks.

Keep this and all drugs out of the reach of children. Famciclovir is a prescription drug and should be used according to your veterinarian's directions. It should only be given to the animal for which it was prescribed. Do not give this medication to a person.

Different strengths or dosage forms of famciclovir can have different storage requirements. Read the label or ask your pharmacist for the storage requirements of the prescription you receive.

Dosage and Administration of Famciclovir

Famciclovir is administered orally through several formulations including oral tablets, capsules, pastes, and suspensions. This medication is available only with a prescription from a licensed veterinarian.

Due to the intense nature of FHV and feline herpesvirus, it is very important to follow the prescribed directions as precisely as possible. It is equally vital to complete the full course of treatment for the medication to work as intended. Failure to do so will increase the risk of relapse.

Give this medication to your pet exactly as your veterinarian prescribes. If you miss giving your pet a dose of famciclovir, give the next dose as soon as you remember or, if it is close to the next scheduled dose, return to the regular schedule. Do not double dose to catch up. Famciclovir can be given with food. Wash your hands after administering this medication.

If you suspect that your pet or another animal has been accidentally overdosed or has eaten this medication inadvertently, contact your veterinarian or the A.S.P.C.A.'s Animal Poison Control Center at 888.426.4435. Always have the prescription container with you when you take your pet for treatment.

If you or someone else has accidentally ingested this medication call the National Capital Poison Center at 800.222.1222.
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