Cidofovir for Cats

Published Dec. 19, 2023
cat getting a swab at vet exam

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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 Cidofovir for Cats?

Cidofovir is a prescription human antiviral medication that is specially formulated into veterinary eye drops (ophthalmic solution) for the treatment of feline herpesvirus-1 (FHV-1) corneal eye infection (conjunctivitis and keratitis) in cats and sometimes for herpes viral eye infections in horses.

Cidofovir is effective when administered twice daily. It is important to note that cidofovir is not used in dogs for viral eye infections because it causes irritation and possible damage to the eye. Cidofovir is FDA-approved for human use as an intravenous (IV) injection that is given directly into a vein under the skin to treat specific viral infections in immunocompromised individuals.

Cidofovir is currently not FDA-approved as a veterinary medication. However, it is readily utilized in the veterinary field, and veterinarians can legally prescribe certain human drugs in animals in certain circumstances. This is called extra-label or off-label use because this use isn’t described on the drug label.

In certain circumstances, your vet may recommend a compounded formulation of cidofovir. Compounded medications are prescribed if there’s a specific reason your pet’s health can’t be managed by an FDA-approved drug, such as if your pet has trouble taking pills in capsule form, the dosage strength is not commercially available, or the pet is allergic to an ingredient in the FDA-approved medication.

Compounded medications are not FDA-approved. They are created by either a veterinarian or a licensed pharmacist on an individual basis to best suit a patient’s particular needs. You can learn more about compounded medications here.

Cidofovir Considerations for Cats

The IV injectable form of cidofovir is not used in animals, and reproductive and kidney side effects that can occur in humans have not been reported in animals receiving the ophthalmic formulation.

Cidofovir should not be used in cats intended for breeding, in cats that are pregnant or nursing, in cats with kidney disease, or in cats who are hypersensitive to it. Giving cidofovir with other medications that may potentially cause kidney damage (nephrotoxic medications) can result in health risks to your cat, so it is important to discuss your cat’s medications, including vitamins and supplements, and medical conditions with your veterinarian.

How Cidofovir Works in Cats

Cidofovir is classified as an antiviral medication, meaning that it treats viral infections. Cidofovir works by incorporating itself into the DNA strand of a virus, which prevents the virus from making the essential proteins required for its growth and survival. Without these proteins, the virus cannot properly grow or multiply.

Cidofovir Directions for Cats

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

Wear gloves during administration.

Your veterinarian will teach you an effective and minimally stressful way to give eye drops to your cat.

Administer the medication to your cat’s eye in the exact amount that your veterinarian prescribed.

Avoid contamination of the medication. Do not allow the tip of the dropper to touch your cat’s eye or any other surface.

Wait at least five minutes after applying this medication before applying any other medications to the eye. Always consult your veterinarian for the best order in which to give your cat’s eye medications.

If any cidofovir solution remains on your cat’s face after giving the eye drops, gently blot it off with a tissue to prevent exposure to humans and other animals and to prevent your cat from ingesting it.

Missed a Dose?

Speak with your veterinarian about what to do if you forget to give a dose of cidofovir. Generally, they may instruct you to give it when you remember, or if it is almost time for your pet’s next dose, to skip the missed dose and resume your normal dosing schedule. Do not give extra or double doses.

Cidofovir Possible Side Effects in Cats

Cidofovir ophthalmic solution is generally well tolerated in cats. Side effects may include burning or stinging of the eyes after application with stronger concentration solutions.

Human Side Effects

Cidofovir is a medication for humans, frequently with dosages different from those prescribed for your pet by a veterinarian. Due to possible side effects, humans should never use medicine dispensed for their pets and pets should not be given any medicine dispensed for a human’s use.

In humans, IV administration of cidofovir can cause genetic mutations, birth defects, abnormally low volume of semen (hypospermia), and severe kidney toxicity. If you are pregnant, talk to your veterinarian about using another medication.

Your veterinarian and veterinary pharmacist will give you specific instructions including (but not limited to) the following precautions:

  • Ensure that you do not allow this medication to contact your skin, eyes, or gums.

  • Wear disposable gloves while in contact with this medication and wash your hands with soap and water after handling.

  • Cidofovir and its byproducts are found in a treated cat's secretions and bodily waste, including saliva, vomit, urine, stool, and litter. Wear disposable gloves when cleaning up waste and handling the cat litterbox. Do not allow treated cats to lick human skin.

If you accidentally ingest this medication, immediately seek medical attention. If you come into contact with this medication without wearing gloves, immediately wash it off and call your physician or the national Poison Control Center hotline at 800-222-1222.

Call Your Vet If:

  • Severe side effects are seen (see above)

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

  • You see or suspect an overdose

  • You have additional questions or concerns about the use of cidofovir

Cidofovir Overdose Information in Cats

An overdose of cidofovir is unlikely if the eye drops are administered correctly, but toxic effects could occur if your cat ingests the medication.

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

Pet Poison Helpline (855) 764-7661

ASPCA Animal Poison Control (888) 426-4435

Cidofovir Storage for Cats

Always confirm storage requirements by reading the compounding pharmacy’s label, as different strengths or dosage forms of cidofovir may have different storage requirements.

Store this medication in the original prescription bottle in the refrigerator. Do not freeze.

Keep the container tightly closed in order to protect the medication from moisture and light.

Keep out of reach of children and pets.

Cidofovir for Cats FAQs

How much does cidofovir cost for cats?

The cost for a bottle of compounded ophthalmic cidofovir can vary slightly, depending on the veterinary compounding pharmacy's prices and the formulation amount of the medication. Prices can vary depending on the size of the bottle.

Does cidofovir need to be refrigerated?

Yes. Cidofovir ophthalmic solution is typically stored in a refrigerator. Always confirm storage requirements by reading the compounding pharmacy’s label, as different strengths, or dosage forms of cidofovir may have different storage requirements.

How long does it take for cidofovir to work in cats?

Cidofovir usually takes several doses to take effect. You should see a gradual improvement in your cat’s eye symptoms within a few days.

No vet writer or qualified reviewer has received any compensation from the manufacturer of the medication as part of creating this article. All content contained in this article is sourced from public sources or the manufacturer

Featured Image: eclipse_images/ E+ via Getty Images


Meulen K van der, Garre B, Croubels S, Nauwynck H. In vitro comparison of antiviral drugs against feline herpesvirus 1. BMC Veterinary Research. 2006;2:13.

Fontenelle JR, Powell CC, Veir JK, Radecki SV, Lappin MR. Effect of topical ophthalmic application of cidofovir on experimentally induced primary ocular feline herpesvirus-1 infection in cats. American Journal of Veterinary Research. 2008;69:289–293.



Molly Price, DVM


Molly Price, DVM


Dr. Molly Price has practiced small animal medicine for over 20 years and is a graduate of Texas A&M College of Veterinary Medicine. She...

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