The initial commercial form is the recombinant human interferon alfa-2a (Roferon-A—Hoffman-La Roche). The high potency Roferon-A comes as a 3 million-IU solution in a 1-ml vial. The vial contents are then diluted into 999-ml sterile saline and then divided into 10-ml ampules (3,000 IU/ml) that will remain stable if frozen, according to other veterinary dermatologists. (It has also been described as being further diluted to 1,000 IU/ml.) Once thawed, an ampule should be refrigerated and will remain effective for 30 days. The refrigerated 3,000-IU/ml ampule is used in 0.33-ml (1,000 IU) increments given orally daily. This low-dose oral therapy makes the treatment reasonably priced, as the 3 million-IU vial costs about $40. Instead of the dosage above, some veterinary dermatologists administer 3,000 IU/ml once every three days. The solution is injected into the oral cavity since oromucosal administration induces beneficial systemic effects in animals and people.²⁰ This regimen has been used for canine papillomavirus.²¹ No studies comparing these different protocols exist, and limited information describing Roferon-A's effectiveness in dogs and cats is available.

Human recombinant interferon alpha-2b was evaluated in a pilot study for idiopathic recurrent pyoderma in dogs, and the results suggested only transient benefit at oral dosages of 1,000 IU/ml/day.²² Veterinary dermatologists have also seen feline herpesvirus infection, idiopathic facial dermatitis, and eosinophilic ulcers respond to low-dose oral therapy regimens of interferon alpha-2b.

The use of recombinant feline interferon-omega (Virbagen Omega—Virbac) has been studied for the treatment of several nondermatologic conditions. When administered intravenously at high doses, it improved the clinical signs and reduced the mortality of canine parvoviral infection.^23,24 When administered subcutaneously at high doses, it markedly improved the clinical signs and survival rates of cats infected with feline leukemia virus.²⁵ In addition, it was successfully used to treat chronic gingivostomatitis in a cat when given subcutaneously then orally.²⁶

A recombinant canine interferon-gamma cloned in Japan was shown in a clinical trial to be significantly more effective in treating canine atopic dermatitis than topical diphenhydramine was.²⁹

IMIQUIMOD

We are excited about imiquimod (Aldara—3M Pharmaceuticals) because it is topically applied, has few side effects in people, and appears to stimulate natural immune function, particularly antiviral and antitumor responses. It has been shown to activate intracellular signaling pathways through Toll-like receptor (TLR) 7 and TLR8, resulting in the production of proinflammatory cytokines, in addition to having other undetermined mechanisms of action.³⁰ It is being prescribed for a wide variety of diseases in people including keloids,³¹ virus-induced warts,^32,33 molluscum contagiosum (a human poxvirus infection),³⁴ and epithelial premalignant or neoplastic diseases such as squamous cell carcinoma in situ,³⁵ extramammary Paget's disease,³⁶ actinic keratosis,³⁷ and basal cell carcinoma.³⁸ This drug will undoubtedly find more uses in veterinary medicine; imiquimod may be a valuable therapy for a variety of cutaneous viral lesions and epithelial diseases in cats, particularly actinic keratosis, squamous cell carcinoma, and Bowen's disease. For most conditions in people, it is applied two or three times weekly for various intervals. Burning or irritant reactions are the major side effects. No studies have evaluated the use of this drug in dogs and cats, but one pilot study had positive results treating equine sarcoids with imiquimod.³⁹