What is the recommended treatment and dosing for Septra (trimethoprim/sulfamethoxazole) in a post-operative abdominal wound infection with MRSA?

Septra Dosing for Post-Operative Abdominal MRSA Wound Infection

For a post-operative abdominal wound infection with confirmed MRSA, treat with trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets (160mg/800mg) orally twice daily for 7-14 days, combined with surgical debridement and drainage. 1

Surgical Management First

• Suture removal plus incision and drainage must be performed as the primary intervention for any surgical site infection before or concurrent with antibiotic therapy. 1
• Surgical debridement is the mainstay of therapy and should be performed whenever feasible, as antibiotics alone are insufficient for purulent collections. 2
• Obtain cultures from the wound before starting antibiotics to confirm MRSA and guide definitive therapy. 2, 3

Specific TMP-SMX Dosing Regimen

• Standard dose: TMP-SMX 160mg/800mg (1 double-strength tablet) twice daily is the recommended starting dose for most patients with MRSA skin and soft tissue infections. 1, 2, 4
• High dose: TMP-SMX 320mg/1,600mg (2 double-strength tablets) twice daily can be used for more severe infections, though clinical resolution rates are similar to standard dosing. 5
• The standard dose (1 DS tablet BID) achieves equivalent clinical outcomes to the higher dose in MRSA skin infections (75% vs 73% resolution rates), making it the preferred initial choice. 5

Treatment Duration

• 7-14 days of therapy is recommended for surgical site infections with systemic signs such as erythema extending >5 cm from wound edge, temperature ≥38°C, or WBC >12,000. 1
• For uncomplicated infections without systemic toxicity, 5-10 days may be sufficient. 1, 2
• Extend treatment to the full 14 days if the patient has comorbidities, immunosuppression, or slow clinical response. 2, 4

When to Add or Switch Antibiotics

• TMP-SMX alone does not adequately cover beta-hemolytic streptococci or anaerobes, which are common in abdominal surgical site infections. 2, 4
• For abdominal/perineal surgical site infections, add metronidazole 500mg every 8 hours to cover anaerobic organisms, or use a broader regimen. 1
• If the infection involves the gastrointestinal or genitourinary tract, consider switching to combination therapy: ciprofloxacin 750mg PO every 12 hours plus metronidazole 500mg every 8 hours. 1
• For severe infections with systemic toxicity or sepsis, hospitalize and use IV vancomycin 15-20 mg/kg every 8-12 hours plus piperacillin-tazobactam or a carbapenem. 1, 4

Critical Decision Points

• If MRSA rate is high in your institution (>10-15%), empiric MRSA coverage with TMP-SMX or vancomycin is mandatory while awaiting culture results. 1
• Reassess clinically within 48-72 hours to ensure appropriate response to therapy. 2
• If fever persists beyond 4 days post-operatively with wound erythema >5 cm and systemic illness, begin antibiotics immediately after opening and debriding the wound. 1

Common Pitfalls to Avoid

• Never use TMP-SMX as monotherapy for polymicrobial abdominal wound infections without anaerobic coverage, as this leads to treatment failure. 1, 4
• Do not use rifampin as adjunctive therapy, as it provides no benefit and promotes resistance. 1, 3
• Avoid relying solely on antibiotics without adequate surgical drainage, as this is the most common cause of treatment failure. 2, 4
• TMP-SMX has poor activity against streptococci, so if non-purulent cellulitis develops around the wound, add a beta-lactam or switch to clindamycin. 1, 4