In December 2019 SARS-CoV-2 virus appeared in the world, mainly appearing as an acute infection of the lower respiratory tract. In March 2020, the World Health Organization (WHO) announced a pandemic in relation to the disease caused by the SARS-CoV-2 virus, known as COronaVIrus Disease 2019 (COVID-19). Since then, the efforts of scientists from around the world have focused on finding the right treatment and vaccine for the new disease. COVID-19 has spread rapidly in a few months, affecting patients in all ages. The disease has a varied course, patients can be 80% asymptomatic, but many develop respiratory failure, complicated by sepsis and ultimately death. One of the possible complications associated with COVID-19 lung involvement is pulmonary fibrosis, leading to chronic breathing difficulties and prolonged disability. No specific mechanisms leading to this phenomenon have been identified in COVID-19, but some information is derived from previous studies on the SARS and MERS epidemic. There have been several reports that the use of spironolactone may be important in preventing pulmonary fibrosis.

The aim of the study is to evaluate the effectiveness of intravenous form of mineralocorticoid receptor antagonist canrenoate potassium (an aldosterone antagonist of the spirolactone group) in the treatment of COVID-19-associated pulmonary fibrosis based on the mechanisms of the immune response.

Inclusion Criteria:

1. Patients of both sexes, 18-90 years of age.
2. Patient requiring oxygen therapy, SpO2 <94%.
3. Confirmed COVID-19 infection.
4. At least one risk factor for increased mortality in the course of COVID-19: currently published in the literature e.g. smoking, hypertension, diabetes, cardiovascular disease.
5. Documented informed consent according to ICH-GCP and national regulations.

Exclusion Criteria:

1. Chronic bronchitis, emphysema, interstitial lung disease, or other history of lung disease.
2. Contraindications to the use of spironolactone.
3. Hypersensitivity to spironolactone or any of the excipients.
4. Pregnant patients (pregnancy test will be performed in every patient of reproductive age) and during lactation.
5. Patients with mental illness or dementia who are unable to give informed consent to the examination.
6. ARDS caused by another viral infection (SARS-CoV-2 negative).
7. ARDS from other causes/trauma.
8. Ionic disorders: hyperkalemia, hyponatraemia.
9. Adrenal crisis.
10. Acute and chronic renal failure, creatinine clearance less than 30 ml/min.
11. Anuria.
12. Porphyria.