What is the next best step for a patient with a breast abscess, initially treated with Keflex (Cephalexin) and then Bactrim (Trimethoprim/Sulfamethoxazole) after incision and drainage (I&D), who now presents with tachycardia and fever?

Hospital Admission for Suspected Systemic MRSA Infection

This patient requires immediate hospital admission for intravenous antibiotics and evaluation for metastatic infection, as fever and tachycardia following failed outpatient management of a breast abscess indicates severe infection with systemic involvement. 1

Immediate Management Steps

Hospitalization Criteria Met

• Fever and elevated heart rate following failed oral antibiotic therapy (Keflex then Bactrim) plus I&D represents severe purulent skin and soft tissue infection requiring IV antibiotics 1
• The presence of systemic signs of infection (fever, tachycardia) after adequate drainage and two courses of oral antibiotics indicates treatment failure and potential for metastatic complications 1, 2
• According to IDSA guidelines, patients with systemic signs (temperature >38.5°C or heart rate >110 beats/minute) require parenteral therapy 1

Diagnostic Workup Required

• Obtain blood cultures immediately (at least 2 sets from separate venipunctures) before starting IV antibiotics 2, 3
• Culture any remaining purulent drainage from the abscess site if accessible 1, 2
• Consider imaging (ultrasound or CT) to evaluate for undrained fluid collections or deeper abscess formation 1
• If bacteremia is confirmed, obtain transthoracic echocardiography to evaluate for endocarditis, as S. aureus bacteremia causes endocarditis in approximately 12% of cases 3

Empiric Antibiotic Therapy

First-Line IV Treatment

Vancomycin 15-20 mg/kg IV every 8-12 hours (not to exceed 2g per dose) is the recommended empiric therapy for severe MRSA skin and soft tissue infections with systemic signs 1, 2

Alternative IV options if vancomycin is contraindicated:

• Daptomycin 4 mg/kg IV every 24 hours 1
• Linezolid 600 mg IV every 12 hours 1
• Ceftaroline 600 mg IV every 12 hours 1

Why Previous Antibiotics Failed

• Keflex (cephalexin) lacks activity against MRSA, which accounts for 87-93% of community-acquired S. aureus skin abscesses 4, 5
• While Bactrim (TMP-SMX) has MRSA activity, oral therapy is insufficient for severe infections with systemic signs 1
• The failure of two oral regimens plus I&D strongly suggests MRSA as the pathogen 2, 5

Source Control Evaluation

Surgical Re-evaluation

• Immediate surgical consultation to assess adequacy of initial drainage and evaluate for undrained collections or necrotizing infection 1
• Breast abscesses may have multiple loculations requiring repeat I&D or placement of drainage catheter 1
• If fever persists >48 hours on appropriate IV antibiotics, inadequate source control is the most likely cause 3, 6

Red Flags for Deeper Infection

Look for signs suggesting necrotizing fasciitis or deeper involvement:

• Skin sloughing, bullae, or crepitus 1
• Pain out of proportion to examination findings 1
• Rapid progression of erythema despite antibiotics 1
• Hypotension or organ dysfunction 1

Duration and De-escalation Strategy

Treatment Duration

• Minimum 7-10 days of IV therapy for complicated skin and soft tissue infection with bacteremia 1
• If blood cultures are positive, duration extends to 14 days minimum (or longer if endocarditis or other metastatic infection identified) 1, 3
• Clinical improvement markers: defervescence, decreasing tachycardia, resolution of erythema 1

Antibiotic Adjustment

• Once culture and susceptibility results return, if MSSA is identified, switch to cefazolin 1-2g IV every 8 hours or nafcillin/oxacillin 1-2g IV every 4-6 hours for superior outcomes 1, 3
• If MRSA is confirmed with vancomycin MIC ≤2 mcg/mL and clinical improvement occurs, continue vancomycin 1
• If no clinical response despite adequate source control, consider alternative agents (daptomycin, ceftaroline, or linezolid) regardless of reported susceptibility 1, 6

Common Pitfalls to Avoid

• Do not continue oral antibiotics in a patient with fever and tachycardia after failed outpatient therapy—this represents severe infection requiring IV treatment 1
• Do not assume adequate drainage from initial I&D; repeat imaging and surgical evaluation are critical 1
• Do not delay blood cultures waiting for imaging results 2, 3
• If bacteremia is documented, do not treat for less than 14 days, as shorter courses are associated with treatment failure and metastatic complications 1, 3