Inclusion Criteria:  Age 18 - 80 y.o. Since over eighties are very fragile patients, a lot of confounding unpredictable events may interfere with the trial analyses; thus, these patients will be excluded from this exploratory proof-of-concept trial; COVID-19 diagnosis through swab within 14 days from the beginning of symptoms Hospitalization for moderate to severe ARDS (as determined by PaO2/FiO2 ≤300 mmHg at admission) Serum concentration of potassium ≤4.5 mEq/L Consent to participate  Exclusion Criteria:  Invasive mechanical ventilation I.v. hydratation with Darrow's solution or half-strength Darrow's solution underway Acute cardiovascular event (acute myocardial infarction, acute ischaemic stroke) Current malignant disease Creatinine >1.8 mg/dL (for women) and >2.0 mg/dL (for men) or glomerular filtration rate <50 mL/mm Systolic blood pressure <110 mmHg and/or diastolic blood pressure <60 mmHg Known or suspected hypersensitivity to canrenone Hyponatremia Anuria Familial history of porphyria Pregnancy and breastfeeding known or suspected hypersensitivity to canrenone Inclusion in any other pharmacological clinical trials