What is the best initial oral antibiotic for a mild superficial postoperative wound infection after coronary artery bypass grafting in an adult without a severe β‑lactam allergy?

Treatment of Mild Postoperative Wound Infection After CABG

For a mild superficial postoperative wound infection after CABG, initiate oral cephalexin or dicloxacillin as first-line therapy, targeting the most common pathogen Staphylococcus aureus, but only after ensuring adequate wound drainage if purulent material is present. 1

Primary Treatment Principle

The cornerstone of managing any surgical site infection is incision and drainage, which must take priority over antibiotic therapy when purulent drainage or fluid collection is present. 2, 1 Antibiotics alone without adequate drainage lead to treatment failure. 1, 3

When Antibiotics Are Indicated

Systemic antibiotics should be prescribed when the patient demonstrates:

• Temperature >38.5°C
• Heart rate >100-110 beats/minute
• Erythema extending >5 cm from the wound edge
• Systemic signs of infection 2, 1, 3

If minimal surrounding cellulitis (<5 cm) and minimal systemic signs are present, antibiotics may be unnecessary after adequate drainage. 2

First-Line Antibiotic Selection

For Clean CABG Wounds (Sternal or Harvest Sites)

Cephalexin or dicloxacillin are the recommended first-line oral agents for clean surgical wounds, providing excellent coverage against methicillin-susceptible Staphylococcus aureus (MSSA), which remains the predominant pathogen in post-CABG infections. 1, 4

The rationale is straightforward: sternal wound infections after CABG are predominantly caused by staphylococci (both S. aureus and S. epidermidis), with leg harvest sites also showing MSSA/MSSE as primary pathogens. 4

MRSA Risk Considerations

If MRSA risk factors are present (prior MRSA colonization, recent hospitalization, failed initial therapy), switch to:

• Trimethoprim-sulfamethoxazole
• Doxycycline, or
• Clindamycin 1, 5

MRSA sternal wound infections carry high mortality and are increasingly common in cardiac surgery populations. 6

Anatomic Location Matters

For leg harvest site infections near the groin/perineum, broader coverage is mandatory due to gram-negative and anaerobic organisms:

• Levofloxacin plus metronidazole, or
• Cephalosporin plus metronidazole 1, 3

This is critical because leg harvest sites show E. coli as a significant pathogen alongside staphylococci. 4

Managing β-Lactam Allergy

For patients with documented penicillin/cephalosporin allergy:

• Clean wounds: Clindamycin, doxycycline, or trimethoprim-sulfamethoxazole 1, 3
• Perineal/leg wounds: Levofloxacin plus metronidazole or moxifloxacin alone 1, 3

Duration of Therapy

Treat for 5-7 days after adequate drainage for superficial SSI with systemic signs. 1, 3 This brief course is sufficient when source control is achieved. Prolonged courses beyond 7 days are unnecessary and promote resistance. 3

Critical Pitfalls to Avoid

• Never rely on antibiotics alone without drainage for purulent infections—this guarantees treatment failure. 1, 3
• Do not prescribe antibiotics for simple seromas without infection signs, as this promotes resistance without benefit. 1, 3
• Avoid using cephalexin/dicloxacillin alone for groin/perineal wounds, as they lack adequate gram-negative and anaerobic coverage. 1
• Obtain wound cultures before starting antibiotics to guide definitive therapy, though empiric treatment should not be delayed. 5

When to Escalate

If the patient fails initial oral therapy with cephalexin, empiric vancomycin is indicated due to high likelihood of MRSA. 5 Consider hospital admission for IV antibiotics if systemic illness develops or if deep tissue involvement is suspected.