Non-inferiority, multicenter, prospective double-blind, randomized clinical trial of two parallel groups. The randomization between the 2 study groups will be carried out according to a scheme generated by a computer program, in blocks of 6 and stratified by centers. The antibiotic treatment will be evaluated during 5 days compared to the usual antibiotic treatment for more than 7 days in patients with community-acquired pneumonia with a Pneumonia Severity Index IV-V severity score who present an adequate response in the first 4 days of hospital antibiotic treatment.

Inclusion Criteria:

• Patients of both sexes older than 18 years
• Hospitalized patients diagnosed with CAP: appearance of a new radiological infiltrate plus the presence of at least two of the following signs or symptoms: fever (> 38 ° C), cough, expectoration, chest pain, dyspnea or tachypnea, and signs of occupation of the alveolar space.
• That they present a PSI score class IV or V.
• Patients who have received adequate antibiotic treatment according to clinical guidelines (SEPAR, ATS) ((1,8,19)) from the first hour of admission to the emergency room.
• Patients who reach clinical stability: temperature ≤37.2 ºC, heart rate ≤100 beats / min, respiratory rate ≤24 breaths / min, systolic blood pressure> 90 mmHg; oxygen saturation> 90%; or oxygen blood pressure> 60 mmHg (15) before the fourth day.
• Signature of informed consent.

Exclusion Criteria:

• Immunosuppression: Co infection with HIV and presence of AIDS, treatment with neutropenic effect or have received immunosuppressive treatment for any reason. Patients that are in chronic use of corticosteroids as prednisone or its equivalent with > 10 mg / day for 14 days.
• Patients hospitalized in the previous 14 days.
• Patients with pleural effusion
• Suspected multiresistant germs of any cause.
• Hypersensitivity or alterations in the tendons associated with the fuoroquinolones.
• Pregnancy or lactation.

Double blind treatment