This is a pilot study of a single-center, blind, randomized, placebo-controlled, parallel-group study testing for the efficacy and safety of Methylene blue when administered topically as a 0.02% solution for nasopharyngeal and oropharyngeal irrigation in COVID-19 patients requiring hospitalization.

Purpose of the study. To test the hypothesis that the topical application of 0.02% MB solution in the form of repeated nasopharyngeal irrigation will lead to an accelerated recovery compared to placebo, defined by the clinical, laboratory, and radiological improvement with a negative molecular test for SARS-CoV-2 by polymerase chain reaction (PCR). The main objective of the study is to demonstrate the effectiveness of 0.02% MB irrigation of the nasopharynx mucosa over placebo, alongside the standard treatment carried out in accordance with the Temporary Guidelines of "Prevention, Diagnosis, and Treatment of Novel Coronavirus Infection (COVID-19)", version 11 (May 7, 2021). Regarding the recovery of patients with COVID-19, this is defined as a negative PCR test result for the SARS-CoV-2 coronavirus in swabs from the nasopharynx and oropharynx on the 14th and 28th day after initiation of the experimental treatment.

A secondary objective of this study is to evaluate the additional efficacy and overall safety parameters, including saturation dynamics, C-reactive protein, D-dimer, CT signs of lung damage, dynamics of the National Early Warning Score (NEWS) 2 during treatment. Due to the pilot nature of this study, another goal is to calculate the effect based on the number of subjects per group for a future study.

Inclusion Criteria:

1. Men and women aged 18 and over at the time of signing the informed consent.
2. The patient is willing and able to give written informed consent to participate in the study and follow the procedures specified in the protocol.
3. Diagnosed with COVID-19, confirmed by a PCR test positive for the SARS-CoV-2 coronavirus in smears from the nasopharynx and oropharynx.
4. 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.
5. A urine test performed during screening, negative for pregnancy in women capable of childbearing.

Exclusion Criteria:

1. 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.
2. 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.).
3. Topical or systemic use of Methylene blue for any reasons at the time of evaluation or during the interval of 30 days before hospitalization.
4. Known intolerance or hypersensitivity to Methylene blue (indicated in the medical history of the patient).
5. Patients with a high probability of not surviving within the first 24 h of hospitalization, regardless of the treatment, as defined by the investigator.

Randomization by phone