Setting: Translacional Surgery Graduation Program - Universidade Federal de São Paulo and Hospital das Clínicas Samuel Libânio - Universidade do Vale do Sapucaí. Background: Breast reduction is one of the most performed plastic surgery procedures. Antibiotics are widely prescribed, on an empirical basis, to prevent surgical site infections. However, there is a lack of evidence to support its use. Objective: To compare the influence of the use of prophylatic antibiotics as a single dose or for 24 hours on surgical site infection rates following reduction mammaplasty. Methods: Randomized trial of non-inferiority, with two parallel groups, double blinded. A total of 146 breast hypertrophy patients, with reduction mammaplasty already scheduled, will be enrolled. Patients will be randomly allocated to group A, that will receive antibiotics only at the anesthesia induction (n=73), or to group B, that will receive antibiotics at the anesthesia induction and for 24 hours (n=73). None of the patients will receive antibiotics after hospital discharge. Patients will be followed-up weekly, for 30 days, regarding surgical site infection. The Centers for Disease Control and Prevention criteria will be applied. A statistical analysis of the data will be performed.

Inclusion Criteria:

• 18 and 60 years of age
• body mass index (BMI) between 19 and 30 kg/m2
• breast hypertrophy according to the criteria of Sacchini et al. and Franco and Rebello

Exclusion Criteria:

• patients who had previously undergone another surgical procedure of the breast
• patients who have been diagnosed with a breast pathology
• smokers
• patients who had a child or breastfed within the last year
• patients with uncontrolled comorbidities, such as arterial hypertension or diabetes
• use of immunosuppressants
• patients who had any infection during the follow-up period, requiring the use of antibiotics
• patients who present any adverse effects due to the antibiotics during the study
• patients who miss follow-up assessments
• patients who withdraw their consent at any time