What are the treatment options for superficial skin infections with antibiotics?

Treatment of Superficial Skin Infections with Antibiotics

For spreading superficial skin infections like impetigo, erysipelas, and cellulitis, use antibiotics targeting Gram-positive bacteria (particularly streptococci and S. aureus), while simple abscesses require only incision and drainage without antibiotics. 1

Classification and Initial Approach

Superficial skin infections fall into two distinct categories that require fundamentally different management strategies 1, 2:

• Spreading infections (impetigo, erysipelas, cellulitis): Present with erythema, tenderness, and induration; require antibiotic therapy 1
• Well-circumscribed abscesses: Require incision and drainage as primary treatment; antibiotics generally unnecessary 1, 2

Antibiotic Selection for Spreading Infections

First-Line Therapy (Non-MRSA Coverage)

For mild-to-moderate infections without recent antibiotic exposure, target aerobic Gram-positive cocci with oral agents: 1, 2

• Dicloxacillin or cephalexin (500 mg orally 3-4 times daily) 1, 3
• Amoxicillin-clavulanate (500-875 mg twice daily) 1
• Clindamycin (300 mg three times daily) for penicillin-allergic patients 1

These beta-lactams provide excellent coverage against streptococci (the primary cause of erysipelas) and methicillin-susceptible S. aureus 1. Cephalexin is FDA-approved for skin and skin structure infections caused by S. aureus and Streptococcus pyogenes 3.

MRSA Coverage

Add empiric community-acquired MRSA (CA-MRSA) coverage for patients with risk factors or who fail first-line therapy: 1

Risk factors for CA-MRSA include 1:

• Long-stay care facility residence
• Hospitalization within preceding 30 days
• Recent antibiotic exposure (especially beta-lactams, carbapenems, or quinolones)
• Age ≥75 years
• Charlson score >5 points

MRSA-active oral options: 1

• Doxycycline (100 mg twice daily) 1, 4
• Trimethoprim-sulfamethoxazole (160-800 mg twice daily) 1
• Clindamycin (300 mg three times daily) - if local resistance patterns permit 1

MRSA-active parenteral options for severe infections: 1

• Vancomycin (dosed by weight and renal function) 1
• Linezolid (600 mg IV/PO twice daily) - meta-analyses show superior treatment success compared to vancomycin for skin and soft tissue infections (OR 1.40,95% CI 1.01-1.95) 1
• Daptomycin 1

Route of Administration

Use oral antibiotics for mild and many moderate infections; reserve parenteral therapy for severe infections or those with systemic signs: 2

Indications for parenteral therapy include 1:

• Systemic inflammatory response criteria (fever, tachycardia, tachypnea, leukocytosis)
• Signs of organ failure (hypotension, oliguria, altered mental status)
• Immunocompromised state
• Inability to tolerate oral medications

Duration of Therapy

Treat mild infections for 1-2 weeks; moderate-to-severe infections typically require 2-4 weeks depending on response: 2

The duration should be adjusted based on 2:

• Adequacy of source control
• Structures involved
• Wound vascularity
• Clinical response

Management of Simple Abscesses

Incision and drainage alone is sufficient for simple abscesses without antibiotics: 1, 2

A simple abscess is defined as 1:

• Induration and erythema limited to the defined abscess area
• No extension beyond abscess borders
• No extension into deeper tissues
• No multiloculated extension

Drainage technique: 2

• Complete evacuation of all purulent material
• Irrigate wound cavity to remove debris
• Leave wound open to heal by secondary intention
• Apply clean, sterile dressing with daily changes

When to Add Antibiotics to Abscess Drainage

Add antibiotics to incision and drainage only when: 1, 2

• Significant surrounding cellulitis (erythema extending >5 cm beyond wound margins) 2
• Systemic signs of infection present 1
• Immunocompromised patient 1
• Incomplete source control after drainage 1, 2

Special Considerations

Impetigo

Impetigo is caused by β-hemolytic Streptococcus and/or S. aureus, with increasing CA-MRSA prevalence 1. Topical mupirocin 2% ointment applied three times daily for 5-10 days is highly effective (73.7% cure rate, 96.2% cure or marked improvement) 5, 6. Mupirocin shows excellent activity against staphylococci and streptococci with minimal systemic absorption and side effects (<3% local reactions) 7, 5, 6. For widespread impetigo, oral antibiotics (dicloxacillin, cephalexin, or clindamycin) are preferred 1.

Erysipelas

Erysipelas presents as a fiery red, tender plaque with well-demarcated edges, almost always caused by streptococcal species (usually S. pyogenes) 1. Penicillin or amoxicillin remains first-line therapy given the streptococcal etiology 1. S. aureus rarely causes erysipelas, though the role of MRSA remains controversial 1.

Cellulitis

Cellulitis affects the dermis and subcutaneous tissue with warmth, erythema, pain, and often systemic symptoms 1. Begin with beta-lactams (dicloxacillin, cephalexin, or amoxicillin-clavulanate) in areas where CA-MRSA is not prevalent 1. For severe infections or suspected MRSA, use parenteral vancomycin or linezolid 1.

Common Pitfalls to Avoid

• Do not prescribe antibiotics for simple abscesses after adequate drainage - this provides no clinical benefit and promotes resistance 1, 2
• Do not use fluoroquinolones as monotherapy - they have inadequate MRSA coverage despite approval for uncomplicated cellulitis 1
• Do not use topical antibiotics for extensive infections - systemic therapy is required when lesions are widespread 8
• Do not overlook MRSA risk factors - failure to cover MRSA in high-risk patients leads to treatment failure 1

Follow-Up

Reassess within 48-72 hours to evaluate treatment response 2, 9. Patients should return sooner if they develop 2, 9:

• Increasing pain, swelling, or redness
• Fever or systemic symptoms
• No improvement within 48 hours