Inclusion Criteria:  Men and women aged 18 and over at the time of signing the informed consent. The patient is willing and able to give written informed consent to participate in the study and follow the procedures specified in the protocol. Diagnosed with COVID-19, confirmed by a PCR test positive for the SARS-CoV-2 coronavirus in smears from the nasopharynx and oropharynx. Indications for hospitalization for COVID-19 treatment: a moderate condition that does not require oxygen support or low oxygen flow required through a nasal cannula or oxygen mask. A urine test performed during screening, negative for pregnancy in women capable of childbearing.  Exclusion Criteria:  The need for non-invasive ventilation or high oxygen flow, or intubation of the trachea with artificial ventilation, or the use of vasopressors and/or extracorporeal membrane oxygenation at the time of assessment. Decompensation of concomitant pathology, whose severity exceeds the severity of COVID-19 manifestations (for example, acute coronary syndrome, cerebral circulation disorders, acute surgical pathology requiring surgical intervention, bleeding independent of the localization, etc.). Topical or systemic use of Methylene blue for any reasons at the time of evaluation or during the interval of 30 days before hospitalization. Known intolerance or hypersensitivity to Methylene blue (indicated in the medical history of the patient). Patients with a high probability of not surviving within the first 24 h of hospitalization, regardless of the treatment, as defined by the investigator.