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Interferon (Intron A, Alferon N)

Date Published: 11/12/2007
Date Reviewed/Revised: 11/22/2021

(For veterinary information only)

The size of the tablet/medication is NOT an indication of a proper dose. Never administer any drug without your veterinarian's input. Serious side effects or death can occur if you use drugs on your pet without your veterinarian's advice. 

It is our policy not to give dosing information over the Internet.

Brand Name: Intron A, Alferon N

Available as injectable but commonly diluted into oral liquid


The search for a general stimulant for the immune system has been ongoing, and no single product has emerged as efficacious. Products that are currently employed as immunostimulants include vitamin C, echinacea (an herb), acemannan (an aloe derivative), levamisole (a dewormer), and many others. The interferons are what we call cytokines, meaning they are biochemicals secreted by cells of the immune system to regulate other cells of the immune system. There are several members of the interferon family classified according to the cell receptors to which they bind. Interferons are generally produced in the body in response to viral infections and have antiviral activity as well as immunostimulating properties.

Interferon use in human medicine became much more common after genetic engineering technology enabled the mass production of interferon proteins. Interferon alpha is strongly antiviral in its higher doses and is a more general modulator of the immune response in lower (dilute) doses. That said, proof of effectiveness, especially with the diluted doses, is lacking in veterinary patients, and its use should be considered investigational.

How this Medication is Used

The most common protocols for interferon-alpha use a highly diluted form of the product. A bottle of injectable interferon alpha contains several million units. When this bottle is diluted in saline appropriately to a dose of 30 units per cc, it is easy to see how the original vial can be used to make fairly large quantities of dilute oral solution. This translates into a reasonably priced product. At this time, supplies of interferon alpha 2b are largely limited to compounding pharmacies

The oral preparation of dilute interferon is given once a day. The interferon enters the tonsils and lymph nodes of the throat as it is swallowed and exerts its immunostimulating effect there.

Situations where dilute interferon alpha is commonly prescribed are:

The low dose protocol was originally published with interferon given on alternating weeks (one week on medication and the next week off). This was because there was some concern that bone marrow suppression was possible with interferon, as this had been seen in humans, albeit with higher doses. Since these fears were never realized, daily protocols have become more common. It is important to realize that there is little objective research behind these protocols; use is based on anecdotal impressions of efficacy along with reasonable pricing.

At higher doses (in the 10,000 unit range), interferon alpha is directly antiviral. The higher dose protocols are not commonly used because of expense, side effects potential, and eventual development of antibody production, rendering the drug useless. Situations where these protocols have been used include treatment of:

Interferon has been used topically in cat's eyes for herpes conjunctivitis.

Interferon alpha products should be kept refrigerated and should not be exposed to room temperature for more than 24 hours. If you skip a dose accidentally, simply pick up dosing at the next scheduled time; do not double up on dosing. 

Side Effects

The low-dose interferon protocol has not been associated with side effects, though since the preparation is made in saline, there is an unpleasant salty taste. Giving the liquid mixed in food generally overcomes this issue.

The high-dose protocol may be associated with fever, joint pain, and flu-like symptoms (nausea, diarrhea, dry mouth, dizziness, etc). In humans, bone marrow toxicities have been reported at higher doses. So far, bone marrow issues have not panned out as a problem for pets but this was the origin of the initial alternating week protocols.

Interactions with Other Drugs

Interferon does not interact negatively with other drugs when the low-dose protocol is used and is often combined with antibiotics and even anti-viral drugs.

When the higher dose protocol is used, there can be drug interactions. Concurrent use of colchicine can interfere with the effectiveness of interferon. Concurrent use of interferon with the airway dilator theophylline can boost theophylline blood levels into a toxic range. A similar phenomenon exists with the anti-seizure medication phenobarbital. A neurotoxicity syndrome can result when interferon is combined with vincristine, a chemotherapy drug.

Concerns and Cautions

It is only the higher anti-viral protocols that have potential negative side effects (as noted above).

Commercially available interferons are human recombinant products. This means that as foreign proteins, they stimulate the pet’s immune system to react against them. After 3 to 7 weeks on the high-dose injectable protocols, antibodies against interferon may be produced, rendering them ineffective.

Interferon omega is a feline recombinant product, but it is not available in the U.S. at this time.

Interferon alpha products should not be used in cats with feline infectious peritonitis. 

Vaccination may not be effective in animals on the high-dose protocols.

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