MRSA Coverage for Purulent Skin and Soft‑Tissue Infections in Healthy Adults
Oral Antibiotic Regimens (Outpatient Management)
For otherwise healthy adults with purulent skin or soft‑tissue infection where MRSA is likely, first‑line oral therapy is trimethoprim‑sulfamethoxazole (TMP‑SMX) 1–2 double‑strength tablets twice daily for 5 days, or doxycycline 100 mg twice daily for 5 days. 1, 2
First‑Line Oral Options
TMP‑SMX 1–2 double‑strength tablets (160–320/800–1600 mg) orally twice daily provides excellent MRSA coverage and is the preferred first‑line agent for non‑severe purulent infections. 1, 2
Doxycycline 100 mg orally twice daily is equally effective as TMP‑SMX for purulent cellulitis and represents a co‑first‑line choice. 1, 3, 2
Minocycline 200 mg loading dose, then 100 mg twice daily is another tetracycline option with proven MRSA activity, though doxycycline is more commonly used. 1, 3
Clindamycin 300–450 mg orally every 6–8 hours provides single‑agent coverage for both MRSA and streptococci, but should only be used when local MRSA clindamycin resistance rates are documented to be <10 % due to concerns about inducible resistance. 1, 3, 2
Linezolid 600 mg orally twice daily is highly effective but reserved for complicated cases due to cost and potential hematologic toxicity with prolonged use. 1, 3, 4
Treatment Duration
Treat for exactly 5 days when clinical improvement is evident (reduced warmth, tenderness, erythema; absence of fever); extend to 7–10 days only if symptoms have not improved. 1, 3
High‑quality randomized trial evidence demonstrates that 5‑day courses achieve 98 % clinical resolution with no difference compared to 10‑day regimens for uncomplicated infections. 1
Critical Caveat for Non‑Purulent Cellulitis
TMP‑SMX and tetracyclines (doxycycline/minocycline) lack reliable activity against β‑hemolytic streptococci, which remain the predominant pathogens in typical non‑purulent cellulitis. 1, 2
For non‑purulent cellulitis, initial therapy should be a β‑lactam alone (cephalexin 500 mg four times daily or dicloxacillin 500 mg four times daily); add MRSA coverage only if the patient fails β‑lactam therapy after 48–72 hours or presents with systemic toxicity. 1, 2
When MRSA coverage is needed for non‑purulent cellulitis, combine TMP‑SMX or doxycycline with a β‑lactam to ensure streptococcal coverage. 1
Intravenous Antibiotic Regimens (Inpatient Management)
For hospitalized patients with complicated purulent skin infections requiring MRSA coverage, vancomycin 15–20 mg/kg IV every 8–12 hours (targeting trough levels 15–20 mg/L) is the gold standard first‑line agent. 1, 2
First‑Line IV Options (A‑I Level Evidence)
Vancomycin 15–20 mg/kg IV every 8–12 hours remains the reference standard for severe MRSA infections, with dosing based on actual body weight (not to exceed 2 g per dose). 1, 2
Linezolid 600 mg IV twice daily is equally effective as vancomycin for complicated skin infections, with 79 % cure rates in MRSA skin infections and the advantage of no renal dose adjustment. 1, 3, 5, 6, 4
Daptomycin 4–6 mg/kg IV once daily is bactericidal against MRSA and FDA‑approved for MRSA bacteremia and complicated skin infections; it is particularly useful for persistent MRSA bacteremia or vancomycin treatment failures. 1, 3, 4, 7
Alternative IV Options
Clindamycin 600 mg IV every 8 hours can be used if local MRSA clindamycin resistance is <10 %, offering dual coverage for MRSA and streptococci. 1, 3, 2
Teicoplanin 6–12 mg/kg IV (if available) is a glycopeptide alternative to vancomycin. 3
Ceftaroline 600 mg IV every 12 hours has demonstrated efficacy in complicated MRSA skin infections and represents a newer β‑lactam option with MRSA activity. 3, 4
Tigecycline 100 mg IV loading dose, then 50 mg IV every 12 hours can be considered but may be less effective than other options for serious infections. 3
Tedizolid 200 mg IV once daily is a newer oxazolidinone with MRSA activity. 3, 4
Hospitalization Criteria
Admit patients with purulent cellulitis when any of the following are present:
Systemic inflammatory response syndrome (fever >38 °C, heart rate >90 bpm, respiratory rate >24 breaths/min, leukocytosis). 1, 3
Multiple infection sites or extensive surrounding cellulitis (erythema extending >5 cm from abscess). 1, 3
Rapidly progressive infection or signs of deeper/necrotizing infection. 1, 3
Severe immunocompromise, neutropenia, or significant comorbidities (diabetes, immunosuppression). 1, 3
Infections in difficult‑to‑drain locations (face, hands, genitalia). 1, 3
Failure of outpatient therapy after 24–48 hours. 1
Treatment Duration for Complicated Infections
7–14 days of IV therapy is recommended for complicated skin and soft tissue infections, individualized based on clinical response and adequacy of source control. 1, 3
Transition to oral therapy (TMP‑SMX, doxycycline, clindamycin, or linezolid) once clinical improvement is demonstrated and the patient can tolerate oral medications. 3
Essential Adjunctive Measures
Incision and Drainage
Surgical debridement and drainage of purulent collections is the mainstay of therapy and must be performed whenever feasible; antibiotics alone are insufficient for drainable abscesses. 3
For simple abscesses <5 cm without surrounding cellulitis or systemic features, incision and drainage alone may be adequate without adjunctive antibiotics in immunocompetent patients. 1, 3
Culture and Susceptibility Testing
Obtain cultures from purulent drainage before starting antibiotics to confirm MRSA and guide definitive therapy, particularly in hospitalized patients or those with treatment failure. 3
Bacterial wound cultures are important for characterizing local susceptibility patterns and guiding antibiotic stewardship. 8
Physical Measures
Elevate the affected extremity above heart level for at least 30 minutes three times daily to promote edema drainage. 1
Keep draining wounds covered with clean, dry bandages to prevent transmission and recurrence. 3
Critical Pitfalls to Avoid
Never use β‑lactam antibiotics alone (cephalexin, dicloxacillin, amoxicillin, amoxicillin‑clavulanate) for purulent cellulitis or suspected MRSA infections; they lack activity against methicillin‑resistant organisms due to the mecA gene encoding PBP2a. 3, 2, 9
Do not use TMP‑SMX or doxycycline as monotherapy for typical non‑purulent cellulitis because they do not reliably cover β‑hemolytic streptococci, which cause 85–96 % of non‑purulent cellulitis cases. 1, 2
Do not prescribe antibiotics without performing incision and drainage for drainable abscesses; drainage is the cornerstone of therapy, and antibiotic‑only treatment leads to failure. 3
Avoid clindamycin for serious infections if inducible resistance (D‑test positive) is detected, even if the isolate appears susceptible on routine testing; resistance can emerge during therapy. 1, 2
Never use rifampin as monotherapy or add it routinely to other antibiotics for skin infections; resistance develops rapidly, and there is no evidence of benefit. 1, 2
Do not delay surgical consultation when signs of necrotizing infection develop (severe pain out of proportion, skin anesthesia, rapid progression, "wooden‑hard" tissue, gas or bullae); timely debridement is critical. 1
Reassessment and Treatment Failure
Reassess patients clinically at 48–72 hours after initiating therapy; response to therapy is expected within the first few days. 3, 8
If no improvement after 48–72 hours, consider: inadequate drainage requiring repeat procedure, infection with a resistant organism (obtain cultures if not already done), deeper infection (necrotizing fasciitis, osteomyelitis), or alternative diagnosis. 1, 3
Treatment failure rates of approximately 21 % have been reported with some oral regimens, underscoring the importance of early follow‑up. 1
Special Populations
Pediatric Dosing (Oral)
Clindamycin 10–13 mg/kg per dose (maximum 40 mg/kg/day) every 6–8 hours. 3
TMP‑SMX 4–6 mg/kg per dose (based on TMP component) twice daily. 3
Doxycycline 2 mg/kg per dose twice daily (maximum 100 mg per dose) for children ≥8 years and <45 kg; contraindicated in children <8 years due to tooth discoloration and bone growth effects. 1, 3
Pediatric Dosing (IV)
Vancomycin 15 mg/kg IV every 6 hours is first‑line for hospitalized children with complicated MRSA infections. 3
Clindamycin 10–13 mg/kg IV every 6–8 hours if stable, no bacteremia, and local resistance <10 %. 3
Linezolid 10 mg/kg IV every 8 hours for children <12 years (or 600 mg IV twice daily for children ≥12 years). 3
Renal Impairment
TMP‑SMX requires no dose adjustment at GFR ≥15 mL/min/1.73 m²; adjustments are only needed when GFR is <15 mL/min/1.73 m². 3
Linezolid requires no renal dose adjustment, making it particularly advantageous in chronic kidney disease patients. 3
Daptomycin requires dose adjustment to every 48 hours when CrCl <30 mL/min. 3
Vancomycin dosing must be adjusted based on renal function, with therapeutic drug monitoring targeting trough concentrations of 15–20 mg/L. 1, 2
Prevention of Recurrence
Maintain good personal hygiene with regular handwashing using soap and water or alcohol‑based gel. 3
Avoid sharing personal items (towels, razors, clothing). 3
Consider decolonization with mupirocin (nasal) and chlorhexidine (body) for recurrent MRSA infections. 3
Evaluate and potentially treat household contacts if recurrent infections persist despite appropriate therapy and hygiene measures. 3