Leucogen is primarily used in veterinary medicine as an immunomodulator, especially in the treatment of viral infections in cats. It helps stimulate the production of interferon, enhancing the body's natural defense mechanisms against viruses. It is commonly administered to manage feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV), supporting the immune system during chronic infections. Its ability to boost antiviral responses makes it valuable in improving clinical outcomes and quality of life in infected animals. Leucogen is typically given as a series of injections and is most effective when used in the early stages of disease or during periods of immune suppression.