A Pilot Study of Sildenafil in COVID-19

Inclusion Criteria: 1. Patients diagnosed as COVID-19: 1. mild patient: fever,respiratory and other symptoms, the manifestation of pneumonia can be seen on imaging. 2. severe patients: meet the definition of severe pneumonia(comply with any of the followings): Shortness of breath,RR≥30 bpm;In a resting state:SPO2≤93%;PaO2/FiO2≤300mmHg. 2. Age≥18 years old,unlimited gender. 3. Patients who cannot stop the following drugs during the trial:erythromycin or strong inhibitors of CYP3A4 (such as saquinavir,ketoconazole,itraconazole),nonspecific inhibitors of CYP (such as cimetidine),HIV protease inhibitors (such as ritonavir). 4. Willing to participate in this study,signed Informed Consent and willing to participate in regular follow-up during the study. Exclusion Criteria: 1. Suffer from severe cognitive impairment or mental illness. 2. Pregnant and lactating women. 3. Patients taking nitric oxide drugs and nitrates in any dosage form. 4. Patients with malignant tumors;AMI, stroke or life-threatening arrhythmias within 6 months;hereditary pigmented retinitis;heart failure or unstable angina pectoris of coronary heart disease;patients with severe hypotension and hypertension. 5. Patients who are allergic to the study drug or the researcher believes it is not appropriate. 6. Participate in other clinical studies at the same time.