When should cephalexin 500 mg three times daily be stopped for a patient who began it on postoperative day [DATE] after an uncomplicated surgery with normal renal function?

Postoperative Antibiotic Duration for Cephalexin 500mg TID

Stop cephalexin after 24 hours postoperatively for uncomplicated clean surgery, as surgical antibiotic prophylaxis should not extend beyond 24 hours and ideally should be limited to a single preoperative dose. 1

Rationale for 24-Hour Maximum Duration

Surgical antibiotic prophylaxis guidelines consistently recommend against extending prophylaxis beyond 24-48 hours postoperatively, with most clean surgeries requiring only a single preoperative dose. 1 The evidence shows:

• For clean surgical procedures (Altemeier class 1), antibiotic prophylaxis should be administered as a single preoperative dose, with intraoperative re-dosing only if the procedure exceeds the drug's half-life interval (for cephalexin/cefazolin: re-dose at 4 hours if surgery continues). 1

• Maximum duration of prophylaxis is 48 hours postoperatively, but this extended duration is reserved only for specific high-risk scenarios (e.g., cardiac surgery with extracorporeal circulation, prosthetic joint implantation). 1

• Prescription of antibiotics beyond the operative period is explicitly not recommended for most surgical procedures. 1

Critical Distinction: Prophylaxis vs. Treatment

The key clinical decision is whether this patient requires:

1. Prophylaxis only (no infection present): Stop at 24 hours maximum
2. Treatment of established infection: Continue for 5-10 days based on infection type

When to Stop at 24 Hours (Prophylaxis)

Stop cephalexin at 24 hours postoperatively if the patient has: 1

• Clean surgical wound (no signs of infection)
• Normal vital signs (no fever, tachycardia)
• Appropriate wound healing
• No purulent drainage
• No expanding erythema or warmth

When to Continue Beyond 24 Hours (Treatment)

Continue cephalexin for 7-10 days if treating an established skin and soft tissue infection: 1, 2

• Documented surgical site infection with purulence
• Cellulitis or erysipelas present
• Positive intraoperative cultures requiring treatment
• Systemic inflammatory response (fever >38°C, HR >90, WBC >12,000 or <4,000) 2

Dosing Correction if Treatment is Indicated

The prescribed dose of 500mg TID (three times daily) is suboptimal. For treatment of methicillin-susceptible Staphylococcus aureus (MSSA) skin and soft tissue infections, the recommended dose is: 1, 2

• Cephalexin 500mg QID (four times daily, every 6 hours) for adults with normal renal function 1, 2
• Duration: 7-10 days depending on clinical response 1, 2

The TID dosing may result in subtherapeutic drug levels, as cephalexin's short half-life requires dosing every 6 hours to maintain consistent tissue concentrations. 2, 3

Common Pitfall to Avoid

Do not confuse surgical prophylaxis with treatment. The most common error is continuing prophylactic antibiotics for 5-7 days postoperatively when no infection exists—this practice:

• Increases antibiotic resistance 1
• Exposes patients to unnecessary adverse effects (diarrhea, C. difficile risk) 1
• Provides no additional benefit for wound healing 1

Specific Stop Date Recommendation

For uncomplicated surgery: Stop cephalexin on postoperative day 1 (24 hours after surgery). 1

If treating documented infection: Continue for 7-10 days total, but correct the dose to 500mg QID. 1, 2