What antibiotics are used for bacterial skin infections?

Antibiotics for Bacterial Skin Infections

For bacterial skin infections, first-line treatment should include beta-lactam antibiotics such as penicillins and cephalosporins, with specific choices depending on the type and severity of infection. 1, 2

Types of Skin Infections and First-Line Treatments

Impetigo

• Dicloxacillin 250 mg 4 times per day (adults) or 12 mg/kg/day in 4 divided doses (children) 1
• Cephalexin 250 mg 4 times per day (adults) or 25 mg/kg/day in 4 divided doses (children) 1, 3
• For limited lesions: Mupirocin ointment applied 3 times daily 1

Cellulitis (Non-purulent)

• For mild cases: Antimicrobial agent active against streptococci 1
• For moderate cases without systemic signs: Consider coverage for methicillin-susceptible S. aureus (MSSA) 1
• For severe cases or with MRSA risk factors: Vancomycin or another agent effective against both MRSA and streptococci 1
• A 5-6 day course is sufficient for patients able to self-monitor with close follow-up 1

Purulent Skin Infections (Abscesses)

• Incision and drainage is the primary treatment 1
• For MSSA: Nafcillin 1-2 g every 4 h IV, oxacillin 1-2 g every 4 h IV, or cefazolin 1 g every 8 h IV 1
• For MRSA: Vancomycin 30 mg/kg/day in 2 divided doses IV, linezolid 600 mg every 12 h, or clindamycin 600 mg/kg every 8 h IV 1

Necrotizing Infections

• Urgent surgical exploration and debridement 1
• Broad-spectrum treatment: Vancomycin plus either piperacillin/tazobactam, ampicillin/sulbactam, or a carbapenem 1
• For documented group A streptococcal necrotizing fasciitis: Penicillin plus clindamycin 1

Antibiotic Selection Based on Pathogen

Streptococcal Infections

• Penicillin 2-4 million units every 4-6 h IV plus clindamycin 600-900 mg/kg every 8 h IV 1
• For penicillin-allergic patients: Vancomycin, linezolid, or daptomycin 1

Staphylococcal Infections

• MSSA: Nafcillin 1-2 g every 4 h IV, oxacillin 1-2 g every 4 h IV, or cefazolin 1 g every 8 h IV 1
• MRSA: Vancomycin 30 mg/kg/day in 2 divided doses IV, linezolid 600 mg every 12 h, or clindamycin 300-450 mg 3-4 times per day 1
• For oral therapy of MSSA: Dicloxacillin 500 mg 4 times per day or cephalexin 500 mg 4 times per day 1

Mixed Infections

• Ampicillin-sulbactam 1.5-3.0 g every 6-8 h IV or piperacillin-tazobactam 3.37 g every 6-8 h IV plus clindamycin and ciprofloxacin 1
• Alternative: Imipenem/cilastatin 1 g every 6-8 h IV or meropenem 1 g every 8 h IV 1

Special Considerations

Animal and Human Bites

• Animal bites: Amoxicillin/clavulanate 500/875 mg twice per day (oral) or ampicillin-sulbactam 1.5-3.0 g every 6-8 h (IV) 1
• Human bites: Amoxicillin/clavulanate 875/125 mg twice per day (oral) or ampicillin-sulbactam 1.5-3.0 g every 6 h (IV) 1
• Doxycycline 100 mg twice per day has excellent activity against Pasteurella multocida for animal bites 1

Surgical Site Infections

• For intestinal or genitourinary tract surgery: Piperacillin-tazobactam 3.375 g every 6 h or 4.5 g every 8 h IV, or ertapenem 1 g every 24 h IV 1
• For surgery of trunk or extremity: Oxacillin or nafcillin 2 g every 6 h IV, cefazolin 0.5-1 g every 8 h IV, or cephalexin 500 mg every 6 h orally 1

Duration of Therapy

• For impetigo: 7 days, depending on clinical response 1
• For cellulitis: 5-6 days for uncomplicated cases 1
• For pyomyositis: 2-3 weeks of therapy 1
• For streptococcal pharyngitis: At least 10 days 3

Common Pitfalls and Caveats

• Resistance concerns: Always consider local resistance patterns when selecting empiric therapy 1, 4
• Penicillin allergies: For patients with penicillin allergies, consider cephalosporins (if no immediate hypersensitivity), clindamycin, or fluoroquinolones 1
• MRSA coverage: Include MRSA coverage for patients with risk factors: previous MRSA infection, nasal colonization with MRSA, injection drug use, or systemic inflammatory response syndrome 1
• Tetanus prophylaxis: Administer tetanus toxoid to patients without vaccination within 10 years, especially for contaminated wounds 1
• Cultures: While not routinely recommended for typical cases, obtain cultures for immunocompromised patients, those with malignancy on chemotherapy, neutropenia, severe cell-mediated immunodeficiency, immersion injuries, and animal bites 1

Pediatric Considerations

• Cephalexin dosing for children: 25-50 mg/kg/day in divided doses 3
• Tetracyclines (like doxycycline) are rarely used in children younger than 8 years of age 1
• Fluoroquinolones are contraindicated by the FDA for children and adolescents under 18 years of age 1

By following these evidence-based recommendations for antibiotic selection, clinicians can effectively treat bacterial skin infections while minimizing complications and antibiotic resistance.