The coronavirus disease (COVID-19) pandemic has prompted an accelerated search for drugs and vaccines to reduce morbidity, mortality and contain the spread of infection. In the search for an affordable treatment for COVID‑19, positive experience has been gained with inosine pranobex.
Inosine pranobex is an immunomodulator with a wide range of antiviral properties licensed in some countries for the treatment of various viral infections. Inosine enhances both innate and adaptive immunity, which helps control viral infections, including coronaviruses. The first line of defense against any viral infection are natural killers (NK), which kill infected cells quickly and directly, without waiting for antigen recognition and presentation. Inosine promotes an early and sustained increase in the NK cell pool of circulating lymphocytes, enhances purine nucleotide synthesis, NKG2D ligand expression, and cellular sensitivity to NKG2D-dependent NK cell cytotoxicity in metabolically active cells. In addition, it potentiates chemotaxis and phagocytosis of neutrophils, monocytes and macrophages. Shortly after the onset of a viral infection, the synthesis of cellular RNA and protein is markedly inhibited. Inosine enhances RNA synthesis in human cells while decreasing RNA synthesis. Inosine also modulates adaptive immunity by causing a surge in IgG and complement surface markers. This, in turn, enhances the NK activity of eosinophils.
Given these effects, it has been hypothesized that inosine may be useful in the treatment of COVID‑19. A phase III clinical trial evaluated the efficacy and safety of inosine pranobex when added to standard treatment in symptomatic patients with mild to moderate COVID-19.