DYNAMIC Study (DoxycYcliNe AMbulatoIre COVID-19)

Inclusion Criteria: * Man or woman \> 45 years old. * Patient with a positive SARS-CoV-2 PCR * Patient with ENT and / or respiratory symptoms, without hospitalization criteria (no dyspnea, respiratory rate \<22 / min, SaO2 ≥ 94% in ambient air), or digestive signs. * Patient with at least one of the following risk factors for unfavorable outcome: * 70 years, BMI\> 30, cardiovascular history (stroke, coronary artery disease, complicated hypertension, cardiac surgery, NYHA III or IV heart failure), respiratory pathology likely to decompensate during viral infection respiratory failure, unbalanced and / or complicated diabètes, respiratory pathology likely to decompensate in the event of of viral infection, patients with renal insufficiency chronic dialysis, .cancer patients under treatment. Exclusion Criteria: * Lactose-intolerant patients * Patient needing immediate hospitalization for any medical reason * Patient having more than 5 days of clinical symptoms at the inclusion visit * Patients with a history of allergy to tetracyclines * Pregnant or lactating women * Patients participating in another clinical trial * Patients with photosensitive skin pathology * Patients treated with anticoagulant * Patients treated with oral retinoids: isotretinoin, alitretinoin, acitretin * Patients treated with vitamin A Patients treated with systemic antibiotics for the duration of treatment * Patients treated with barbiturates, carbamazepine or phenytoin * Patients with treatment that may have an effect on COVID-19 infection: chloroquine, hydroxychloroquine, remdesivir, ganciclovir, acyclovir, ribavirin, lopinavir-ritonavir * Patients under guardianship or trusteeship or in safeguard of justice