“…However, attempts to use the XOR inhibitor allopurinol (Pacher et al, 2006;George and Struthers, 2009) as a therapeutic agent for pneumonia induced by type-A influenza virus in the range of daily doses of 5-50 mg/kg were unsuccessful. Allopurinol had no effect on the course and the outcomes of viral infection (Dolganova and Sharonov, 1997), because the NADH oxidase and nitrite/nitrate reductase activities of XOR, which are realized by the FAD-dependent enzyme site, is not affected when the molybdopterin-containing center of the enzyme is inhibited by allopurinol (Harris and Massey, 1997;Doel et al, 2001;Boueiz et al, 2008). Since there are still no drugs that can inhibit the FAD-dependent activity of XOR, the prescription of heparin, which releases XOP from the connection with glycans and promotes its elimination from the focus of inflammation, is advised in order to prevent pulmonary thromboembolism and to desorb the enzyme from the cytoplasmic membrane of endothelial cells heparin (Povalyaev, 2014;Obi et al, 2019).…”