In the narrow sense, the only synthetic immunomodulator (drug) with proven immunomodulatory and immunopotentiating effects is inosine pranobex. This drug is indicated for the entire spectrum of patients with clinical manifestations of immune deficiency. It has a direct antiviral effect. It modulates the immune system by immunostimulation, or immunooptimization of defensive inflammation [ 6 ] at the cellular level, e.g. by interfering with energy metabolism, cell signaling and proliferation. It modulates components of innate immunity, NK cells and dendritic cells. It suppresses the production of pro-inflammatory cytokines TNF-α and IL-6. It homeostatically and regulatory optimizes the functional polarization of T lymphocyte subsets Th1, Th2, Th17 and Treg. [ 7 ] In clinical studies, isoprinosine normalized impaired cellular immunity by inducing a Th1-type response, which initiates the maturation and differentiation of T lymphocytes. In vivo, it inhibits the synthesis of viral RNA.