What is the recommended empiric antibiotic therapy for an IV (intravenous) drug user presenting to the Emergency Department (ED) with a skin infection?

Empiric Antibiotic Therapy for IV Drug Users with Skin Infections

For IV drug users presenting to the ED with skin infections, empiric coverage should include vancomycin or another MRSA-active agent plus coverage for gram-negative and anaerobic bacteria with piperacillin-tazobactam, a carbapenem, or ceftriaxone plus metronidazole. 1

Initial Assessment and Classification

• Determine if the infection is purulent (abscess) or non-purulent (cellulitis) as this affects antibiotic choice 1
• Assess for signs of systemic infection (fever >38.5°C, heart rate >110 beats/minute) which necessitates broader coverage 1
• Look for signs of deeper infection suggesting necrotizing fasciitis or myonecrosis requiring immediate surgical consultation 1
• Evaluate for complications common in IV drug users: endocarditis, septic thrombophlebitis, or osteomyelitis 1

Empiric Antibiotic Recommendations

For Mild Infections (outpatient management)

• For purulent infections (abscess) after incision and drainage:

  • Trimethoprim-sulfamethoxazole (TMP-SMX) 160-800 mg twice daily 1, 2
  • Clindamycin 300-450 mg three times daily (if local MRSA resistance is <10%) 1, 2
  • Doxycycline 100 mg twice daily (alternative) 1, 2

• For non-purulent infections (cellulitis):

  • Clindamycin alone (covers both streptococci and CA-MRSA) 1
  • TMP-SMX plus amoxicillin (covers both MRSA and beta-hemolytic streptococci) 1
  • Linezolid alone (covers both organisms but more expensive) 1, 3

For Moderate to Severe Infections (inpatient management)

• Vancomycin 15-20 mg/kg IV every 8-12 hours (for MRSA coverage) 1, 2 PLUS one of the following:
  • Piperacillin-tazobactam 3.375 g IV every 6 hours 1
  • Carbapenem (imipenem, meropenem, or ertapenem) 1
  • Ceftriaxone 1 g IV daily plus metronidazole 500 mg IV every 8 hours 1

Alternative Agents for MRSA Coverage

• Linezolid 600 mg IV/PO twice daily (superior to vancomycin for MRSA skin infections) 1, 3, 4
• Daptomycin 4 mg/kg IV daily 1, 5
• Ceftaroline 600 mg IV every 12 hours 1

Special Considerations for IV Drug Users

• Higher risk of MRSA colonization and infection necessitates empiric MRSA coverage 1
• Consider polymicrobial infections including anaerobes, especially with infections near injection sites 1
• Higher risk of bacteremia and metastatic infections requires thorough evaluation 1
• Injection sites near the groin or axilla may require broader coverage for enteric gram-negatives and anaerobes 1

Duration of Therapy

• 7-14 days is recommended for complicated skin infections 1
• Treatment should be individualized based on clinical response 1
• Longer duration may be needed if bacteremia or deeper infection is present 1

Surgical Management

• Incision and drainage is the primary treatment for abscesses 1
• Prompt surgical consultation for suspected necrotizing infections 1
• Consider imaging (ultrasound, CT, MRI) to evaluate for deeper collections or foreign bodies 1

Monitoring and Follow-up

• Reassess within 48-72 hours to evaluate response to therapy 1
• Consider switching to oral therapy once clinically improving 1, 3
• Screen for other complications common in IV drug users (endocarditis, osteomyelitis) 1

Pitfalls to Avoid

• Failure to consider MRSA as a causative pathogen 1
• Inadequate surgical drainage of abscesses 1
• Missing deeper or necrotizing infections requiring urgent surgical intervention 1
• Overlooking potential bacteremia or endocarditis in febrile patients 1
• Not adjusting antibiotics based on culture results when available 1