Inclusion Criteria:

1. Signed patient explanation sheet and informed consent for participation in the study.

2. Men and women at the age from 18 through 75 years old.

3. Fibrous changes in the lungs after COVID-19 pneumonia:

1. COVID-19 diagnosis in the past medical history confirmed by positive qualitative
analysis of SARS-CoV-2 RNA by PCR method;

2. The first symptoms of COVID-19 appear no earlier than 2 months before the
screening visit;

3. Fibrous changes in the lungs characteristic for COVID-19 confirmed by the chest
CT scan at screening visit.

4. Negative COVID-19 screening test (confirmed).

5. Severity grade 2 (moderate) or 3 (severe) according to the mMRC Dyspnea Scale at the
screening and randomization visits.

6. Decreased lung function FVC and/or DLCO <80% of the predicted value at the screening
visit.

7. The patient's consent to use adequate contraception methods during the entire study
and within 3 months after its completion. The adequate contraception methods include
the use of the following:

- oral or transdermal contraceptives;

- condom or diaphragm (barrier method) with spermicide;

- intrauterine device.

Exclusion Criteria:

1. Pregnant or breastfeeding women, or women planning pregnancy during the clinical
study; women with childbearing potential (including those who have not been sterilized
by surgery and in the postmenopausal period for less than 2 years) who do not use
adequate contraception methods.

2. The use of invasive artificial lung ventilation (iALV), plasma transfusion (including
plasma of convalescents) and other blood components during therapy against COVID-19.

3. Chronic airway disease in the past medical history, including idiopathic pulmonary
fibrosis (IPF), bronchial asthma, chronic obstructive pulmonary disease (COPD), or
pulmonary hypertension, diagnosed before COVID-19.

4. Significant cardiovascular diseases at present time or during 6 months prior to the
screening, including: chronic heart failure class III or IV (according to the New York
Heart Association classification), clinically significant ventricular arrhythmias
(ventricular tachycardia, ventricular fibrillation), unstable angina, myocardial
infarction, heart and coronary surgery, significant heart valves disease, uncontrolled
hypertension with systolic blood pressure> 180 mm Hg and diastolic blood pressure> 110
mm Hg, thromboembolia of the pulmonary artery or deep vein thrombosis

5. Nephrotic syndrome, moderate to severe chronic renal failure, or significant kidney
disease with a glomerular filtration rate (GFR) <60 ml/min at the screening visit.

6. Cirrhosis of the liver in the past medical history; increase in alanine
aminotransferase (ALT) and/or aspartate aminotransferase (AST) by 3 or more times from
the upper normal level (UNL) at the screening visit; an increase in the total
bilirubin level by 2 or more times from UNL at the screening visit.

7. Hemoglobin level <90 g/L at the screening visit.

8. Severe diseases of the central nervous system, including seizures or conditions in the
past medical history that can cause their development; stroke or transient ischemic
attack within 6 months prior to the screening visit; traumatic brain injury or loss of
consciousness within 6 months prior to the screening visit; a brain tumor.

9. Signs of severe uncontrolled intercurrent disease, such as disorders of the nervous
system, kidney, liver, endocrine system and gastrointestinal tract, which, in the
opinion of the Investigator, could interfere with the patient's participation in the
study.

10. Malignant neoplasms requiring chemotherapy treatment within 6 months prior to the
screening visit.

11. HIV infection in the past-medical history.

12. Prostate cancer or benign prostatic hyperplasia (BPH) with residual urine volume of
more than 100 ml in the past medical history of men.

13. Hypersensitivity or intolerance to any component of the investigated drug.

14. Participation in other clinical studies within 2 months prior to the screening visit.

15. Administration of the following medications: bronchodilators, anticholinergics,
corticosteroids, cytostatics, colchicine, cyclosporin A, interferon-γ-1b, bosentan,
macitentan, etanercept, sildenafil, imatinib, n-acetylcysteine, warfarin, ambrisentan,
nintedanib, pirfenidone 1 month prior to the screening visit.

16. Inability to read or write; unwillingness to understand and follow the procedures of
the study protocol; noncompliance with the drugs administration or procedures
schedule, which according to the researchers may affect the study results or the
patient safety and prevent the further participation of the patient in the study; any
other associated medical or serious mental conditions that make the patient inadequate
for participation in the clinical study and restrict the validity of informed consent
or may affect the patient's ability to participate in the study.