What antibiotic treats a skin infection caused by Staphylococcus (Staph) aureus?

Antibiotic Treatment for Staphylococcal Skin Infections

For methicillin-susceptible Staph aureus (MSSA) skin infections, use dicloxacillin or cephalexin for 7 days; for methicillin-resistant Staph aureus (MRSA), use clindamycin, doxycycline, or trimethoprim-sulfamethoxazole (TMP-SMX). 1

Treatment Algorithm Based on Methicillin Susceptibility

For Methicillin-Susceptible Staph Aureus (MSSA)

First-line oral agents:

• Dicloxacillin - penicillinase-resistant penicillin, remains the antibiotic of choice for serious MSSA infections 2
• Cephalexin - first-generation cephalosporin with cure rates of 90% or higher, effective in twice-daily dosing 1, 3

These agents are recommended because most Staph aureus isolates from skin infections like impetigo and ecthyma are methicillin-susceptible 1. Treatment duration should be 7 days 1.

Alternative agents for penicillin-allergic patients:

• Clindamycin - suitable for patients with non-anaphylactic penicillin allergy 1, 4
• Erythromycin - though resistance development is a concern with macrolides 5

Important caveat: Cephalosporins are contraindicated in patients with immediate-type penicillin hypersensitivity (urticaria, angioedema, bronchospasm, or anaphylaxis) 2.

For Methicillin-Resistant Staph Aureus (MRSA)

Oral options for outpatient treatment:

• Clindamycin - FDA-approved for serious skin and soft tissue infections caused by susceptible staphylococci 1, 4
• Trimethoprim-sulfamethoxazole (TMP-SMX) - effective for community-acquired MRSA 1
• Doxycycline or minocycline - tetracyclines are effective alternatives 1
• Linezolid - reserved for more severe cases or treatment failures 1, 6

Treatment duration is typically 5-10 days but should be based on clinical response 1.

Critical distinction: Community-acquired MRSA strains are often non-multiresistant and respond well to clindamycin or TMP-SMX, while hospital-acquired multiresistant MRSA typically requires vancomycin IV 2.

Severity-Based Treatment Approach

Mild Infections (Impetigo, Small Abscesses)

For impetigo:

• Topical mupirocin 2% ointment can be used for localized disease 1, 7
• Oral antibiotics (dicloxacillin or cephalexin for MSSA; clindamycin, TMP-SMX, or doxycycline for MRSA) are preferred for numerous lesions or outbreaks 1

For small abscesses:

• Incision and drainage alone is often adequate for simple abscesses, with cure rates of 85-90% without antibiotics 1
• Add antibiotics if systemic signs present (fever >38°C, tachycardia >90 bpm, tachypnea >24 breaths/min, or abnormal WBC count) 1

Moderate to Severe Infections (Cellulitis, Large Abscesses)

For purulent cellulitis (cellulitis with purulent drainage but no drainable abscess):

• Empirical coverage for MRSA is recommended pending cultures 1
• Use oral agents: clindamycin, TMP-SMX, doxycycline, or linezolid 1

For nonpurulent cellulitis:

• Empirical coverage for β-hemolytic streptococci is primary 1
• Add MRSA coverage only if patient fails β-lactam therapy or has systemic toxicity 1

For hospitalized patients with complicated skin infections:

• IV vancomycin (first-line) 1
• IV linezolid 600 mg twice daily - with cure rates of 79% for MRSA skin infections 1, 6
• IV daptomycin 4 mg/kg once daily 1
• IV clindamycin 600 mg three times daily - if local clindamycin resistance is low (<10%) 1

Treatment duration is 7-14 days based on clinical response 1.

Pediatric Considerations

For children with minor skin infections:

• Mupirocin 2% topical ointment is effective for impetigo and secondarily infected lesions 7
• Avoid tetracyclines in children <8 years of age 1

For hospitalized children with complicated infections:

• Vancomycin is recommended 7
• Clindamycin 10-13 mg/kg/dose IV every 6-8 hours if local resistance is low (<10%) 1, 7
• Linezolid (10 mg/kg every 8 hours for children <12 years; 600 mg twice daily for ≥12 years) 1

Common Pitfalls to Avoid

Do not use rifampin as monotherapy - resistance develops rapidly; it should never be used alone 1.

Do not rely on antibiotics alone for abscesses - incision and drainage is the primary treatment; antibiotics are adjunctive 1.

Do not use mupirocin for extensive infections - it is inappropriate for widespread impetigo, purulent cellulitis, abscesses, or systemic toxicity 7.

Consider local resistance patterns - empiric therapy should be guided by local MRSA prevalence and susceptibility data 1, 8.