Here is the design of a clinical trial:

Official Title: Surgical Site Infection (SSI) Rates in Patients Undergoing Mastectomy Without Reconstruction, a Comparison Among Those Receiving Preoperative Prophylactic Antibiotics Alone Versus Continued Prophylactic Antibiotics Postoperatively-A Multicenter, Double-blinded Randomized Control Trial.

Included conditions:
- Surgical Site Infection

Study Armgroups:
- {'label': 'Intervention Arm', 'type': 'ACTIVE_COMPARATOR', 'description': 'The intervention arm will be administered, either Cefazolin iv every 8 hours while NPO or cefalexin 500 mg q8 hours per oral if tolerating a diet.', 'interventionNames': ['Drug: Cephalexin 500 MG']}
- {'label': 'Control', 'type': 'PLACEBO_COMPARATOR', 'description': 'Controls will be provided with initially IV placebo while NPO and then with a placebo capsule filled with inert material for the duration of the drains which usually is about 14 days.', 'interventionNames': ['Drug: Placebo']}

Interventions:
- {'type': 'DRUG', 'name': 'Cephalexin 500 MG', 'description': 'Cefalexin 500 mg PO q8 hours will be continued for the duration of the indwelling drains which usually is about 14 days.', 'armGroupLabels': ['Intervention Arm']}
- {'type': 'DRUG', 'name': 'Placebo', 'description': 'A placebo capsule filled with inert material for the duration of the drains which usually is about 14 days.', 'armGroupLabels': ['Control']}

Primary Outcomes:
- {'measure': 'Surgical Site Infection (SSI)', 'description': 'Standard CDC criteria:\n\n1. purulent drainage from the incision or drain site;\n2. organisms isolated from an aseptically obtained culture of fluid or tissue;\n3. deliberate opening of the incision by a surgeon in patients having either tenderness, localized swelling, redness, or warmth; or\n4. diagnosis of SSI by the surgeon or study wound assessor or\n5. prescription of therapeutic antibiotics;\n6. Patients clinically diagnosed and documented to have cellulitis.', 'timeFrame': 'up to 30 days.'}

Please estimate the sample size based on the assumption: 
A 5% level of significance, 80% power, and a 10% inflation for non-response rate.
Sample size calculation
        The sample size was calculated in OpenEpi software V.3.01. The minimum sample size that will be required is 384 patients who have undergone mastectomy with indwelling drains. Of these, 192 patients will be those with a single dose of prophylactic preoperative antibiotic and prolonged use of prophylactic postoperative oral antibiotics (intervention arm), and 192 participants will be those with a single dose of prophylactic preoperative antibiotic with placebo (control arm), with inflation of 10% in both the groups for non-response rate. An anticipated incidence of surgical site infection (SSI) of 3.4% in the intervention arm and 9.2%â14% in the control arm,4 24 with a 5% level of significance and power of 80% to detect a 9% reduction of infection in intervention arm versus the control. Since we will be recruiting participants from three study sites, we applied proportionate sampling to estimate the sample size for each group. In this technique, the sample size of each site is proportionate to the total population size, which was 565. We calculated the per cent (weight) for each group by taking a ratio of the number of individuals in each group and the total population. Hence, we will require a minimum sample of 66 women in the intervention arm and 66 women in the control arm from AKU, 85 women in the intervention arm and 85 women in the control arm from LNH, and 41 women in the intervention arm and 41 women in control arm from DUHS campus.