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Idoxuridine for Cats

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By Evan Ware, DVM

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Basic Information

Idoxuridine is a topical antiviral cytotoxic agent that is prescribed to treat cats with corneal or conjunctival diseases attributed to feline herpes virus (FHV). FHV can cause several eye problems including corneal ulcers, chronic conjunctivitis, tear duct blockage or infection, keratitis, and inflammation of the anterior chamber of the eye. This drug typically is not used in dogs, as canine herpes virus is not a commonly occurring eye disease.

Veterinary Medicine Uses for Idoxuridine

Idoxuridine was one of the first topical antiviral agents developed. Its primary mechanism of action is to interfere with the DNA production of the virus. The drug effectively stunts the growth of the virus, which prevents the virus from multiplying, while weakening it and making it more susceptible and eventually leading to the death of the virus.

Idoxuridine is very well tolerated, although your cat may need a long course of treatment. Treatment should continue for a week past the resolution of all clinical signs. 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 Idoxuridine

Idoxuridine is used for cats with ophthalmic issues associated with feline herpes virus. However, some cats can experience side effects after receiving treatment. The most-common side effects are sensitivity to light, mild itchiness, swelling, redness, and general irritation. In most cases, these side-effects eventually decrease as the body adjusts to the medication and dosing frequency becomes farther apart.

If the cat experiences symptoms of an allergic reaction, such as difficulty breathing, swelling of the face, lips or tongue, severe itchiness, and skin rash, contact your veterinarian immediately.

Be sure to discuss any side-effects with your veterinarian immediately. Some local irritation of the eye is possible, but rare, with idoxuridine ophthalmic. Systemic side-effects are unlikely.

Drug Interactions with Idoxuridine

Idoxuridine can cause an unwanted reaction when used with other medications. It is very important to discuss your cat's current drug regimen with your veterinarian before treatment begins. Drugs to avoid include certain corticosteroids and topical ointments containing boric acid.

Be sure to review with your veterinarian any medications or supplements your pet may be receiving.

Precautions for Using Idoxuridine

Idoxuridine should not be administered to a veterinary patient that has had an allergic reaction to the drug previously. This medication should also be avoided in pregnant or lactating animals.

Idoxuridine is a powerful antiviral agent and when applied to the eye, it can cause some irritation. In cases that involve physical damage or injury to the eye, caution must be used. Dosing during the first several days of treatment is frequent and requires diligence on the part of the owner. After the initial treatment period, dosing frequency can allow a longer length of time between doses.

Ophthalmic medications are sterile products. It is important to keep the tip of the bottle or ointment tube from contact with yourself or your pet.

Keep this and all drugs out of reach of children. Idoxuridine 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.

Idoxuridine should not be used with topical ophthalmic corticosteroids to treat corneal ulceration. Different strengths or dosage forms of idoxuridine can have different storage requirements. Read the labeling or ask your pharmacist for the storage requirements of the prescription you receive.

Dosage and Administration of Idoxuridine

Idoxuridine is available only with a prescription from a veterinarian. It is compounded in either an ophthalmic ointment or in an ophthalmic solution. Because this medication is sensitive to light and heat, the ophthalmic drops must be stored in a refrigerator when not being administered, though the ointment is not as sensitive to temperature as the solution. Since this medication is fighting an infection in the body, it is very important to complete the entire course of treatment to reduce the risk of a relapse. It is generally continued four to seven days after resolution of symptoms.

If you miss giving your pet a dose of idoxuridine, 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.

When you first begin to treat your cat with idoxuridine, the recommended dose interval can be as frequent as every two to three hours. After a few days, the treatment interval can be stretched to every five to six hours.

Administering eye medications to animals can be a struggle and can require patience and practice. Try not to touch the tube or container tip to your cat's eye or eyelid. It is also important not to contaminate the medication by touching the tip with your fingers or hand. Your veterinarian can help you develop a technique that will be effective and minimally stressful for both you and your cat.

If you are giving your cat more than one eye medication, try to allow at least five minutes between medications. Wash your hands after giving your pet this medication.

If you suspect your pet or another animal was overdosed accidentally 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 bring 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.

About the Author

Dr. Evan Ware

Dr. Evan Ware is a veterinary practitioner in Phoenix, Arizona. He received both his undergraduate degree in microbiology and his Doctorate of Veterinary Medicine from The Ohio State University.

Dr. Ware is currently the Medical Director of University Animal Hospital (VCA) and is also the owner of two other hospitals, including Laveen Veterinary Center and Phoenix Veterinary Center. His areas of expertise include orthopedic medicine and surgery, veterinary oncology and chemotherapy, and general and advanced soft-tissue surgery.