For most surgeries, when should prophylactic antibiotics be administered relative to skin incision, and what is the main exception?

• A. Within 60 minutes before incision (120 minutes for vancomycin/fluoroquinolones); re-dosing depends on duration and blood loss.
• B. After incision.
• C. 24 hours after.
• D. Only if infection risk high.

Answer: (A)

The key idea is to have adequate antibiotic tissue levels at the moment the skin is opened to prevent surgical site infection. For most surgeries, a prophylactic dose is given within about an hour before the incision so the drug is present in tissues when exposure starts. The main exception involves antibiotics that require longer lead time to complete their infusion; for vancomycin or certain fluoroquinolones, start up to two hours before incision to ensure protective levels are reached by the time the wound is opened. Re-dosing during the operation is guided by how long the procedure lasts and how much blood loss occurs, to keep tissue levels in the protective range. Giving antibiotics after incision or delaying them beyond the preoperative window would fail to provide optimal protection, whereas the timing described above ensures coverage at the critical moment of incision.