Idoxuridine Ophthalmic

By Rania Gollakner, BS, DVM, MPH

What is idoxuridine?

Idoxuridine (brand names Dendrid®, Herplex®, Stoxil®) is an antiviral topical medication used to treat viral infections of the eye, such as feline herpesvirus-1 (FHV-1) in cats. It may also be useful for treating canine herpesvirus-1 in dogs and equine herpesvirus-2 in horses.

When idoxuridine is prescribed in the treatment of herpesvirus in cats, dogs, and horses, it is referred to as ‘off-label’ use. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully, as their directions may be significantly different from those on the label.

How do I give my pet idoxuridine?

Idoxuridine comes as eye drops or can be compounded by your veterinarian into an eye ointment. Your veterinarian will provide specific instructions for your cat. It is important that you administer this drug to your cat’s eye in the exact amount that it has been prescribed. Drops usually need to be applied every few hours for the first 48 hours, and then several times a day for a week beyond your cat’s clinical signs clearing up. Wait 5-10 minutes before applying any other medications to the eye.

For tips and instructions on administering eye drops and eye ointments, see handouts “Applying Eye Drops to Cats” and “Applying Eye Ointments to Cats”.

It is important to avoid contamination of the eye medication’s applicator tip. Do not touch your cat's eye with the dropper tip and keep a tight lid on the bottle when not in use. Wear disposable gloves when handling this medication. Do not give this medication if the solution becomes cloudy or if it appears to contain particulate matter.

This medication can take up to a few weeks before full effects are noted, but gradual improvements are usually appreciable after a few days.

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 missed dose and give it at the next scheduled time and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Side effects of idoxuridine include eye irritation, such as a burning sensation. The irritation caused by the administration of the drug may be more intense than the inflammation caused by the herpesvirus. Prolonged use can cause other eye conditions. Any side effects or eye changes such as cloudiness, stippling (dotted appearance on the retina), or swelling that you observe should be reported to your veterinarian. Serious side effects may also include weakness, fatigue, mouth sores, or fever.

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?

Idoxuridine should not be used in patients with hypersensitivity to the drug. This medication should be used with caution in animals that are pregnant or nursing. This drug can cause serious adverse effects in people and animals. The drug can be found in the treated cat’s saliva, urine, or feces. Use disposable gloves when handling this medication and when disposing of cat litter. Do not let treated animals lick human skin. Contact your family physician if any exposure to this medication occurs. Pregnant women should NOT handle this medication.

Are there any drug interactions I should be aware of?

Other drugs can interact with this medication, 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?

Your veterinarian may monitor your cat to ensure that the clinical signs have resolved.

How do I store idoxuridine?

In general, this medication is stored in the refrigerator and protected from light and freezing. However, since this medication can be compounded, always follow the storage directions on the medication.

What should I do in case of an emergency?

An overdose of eye medication is unlikely, but side effects or toxic effects could occur if your cat eats the medication. 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.

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