you are asked to read information about the study and give written consent before any study procedures begin.

the purpose of the study is to compare an antibiotic called cefazolin with a harmless solution (placebo) to see if the antibiotic is needed before breast lumpectomy.

your medical history, current medications, and any allergies are recorded.

basic laboratory tests may be performed to ensure you are fit for surgery.

you are assigned by a computer program to receive either the antibiotic cefazolin or a placebo solution.

the assignment is double‑blind, meaning neither you nor the surgical team knows which product you receive.

within one hour before the start of your lumpectomy, a single dose is given through an intravenous line.

if you are assigned to the antibiotic group, you receive cefazolin 2 g (or 1 g, depending on the study formulation) dissolved for injection and given once.

if you are assigned to the placebo group, you receive 100 ml of sterile sodium chloride solution (0.9 % saline) given once.

the dose is administered only once, immediately before surgery.

the breast‑conserving surgery (lumpectomy) is performed as planned.

the surgical team follows standard procedures for removing the tumor and, if required, a sentinel lymph node sample.

after surgery you remain in the hospital for routine observation.

healthcare staff check the surgical wound regularly for signs of a surgical site infection and monitor for any adverse reactions related to the study medication.

any problems are recorded and managed according to standard medical practice.

you are discharged when the medical team determines it is safe.

scheduled follow‑up appointments are arranged, including a visit around day 30 after surgery to assess the wound for infection.

during the follow‑up you will be asked about any symptoms, additional treatments, or hospital readmissions that may have occurred.

the study ends for you after the day‑30 evaluation, unless a serious complication requires further observation.

all information collected during the trial is entered into the study database, and no further study‑specific procedures are required.