What oral antibiotics are recommended for a patient with a suspected bacterial skin infection in a setting where oral medication is preferred?

Oral Antibiotics for Suspected Bacterial Skin Infection

For a suspected bacterial skin infection in an outpatient setting, amoxicillin-clavulanate 875/125 mg twice daily is the preferred oral antibiotic, providing coverage against streptococci, methicillin-susceptible Staphylococcus aureus (MSSA), and some anaerobes. 1

Treatment Algorithm Based on Infection Severity and Type

Mild Non-Purulent Infections (cellulitis, erysipelas without systemic symptoms)

• First-line options:
  • Cephalexin 500 mg four times daily 1
  • Amoxicillin 500 mg three times daily 2
  • Penicillin 500 mg four times daily 2
  • Clindamycin 300-450 mg three times daily 1, 3

These infections are typically caused by streptococci, particularly Group A Streptococcus, and MSSA 2. Clindamycin has the advantage of requiring no dose adjustment in renal impairment 3.

Moderate Non-Purulent Infections (cellulitis with systemic symptoms)

• Recommended regimen:
  • Amoxicillin-clavulanate 875/125 mg twice daily 2, 1
  • Alternative: Cephalexin 500 mg four times daily if MRSA is not suspected 1

This provides dual coverage for both streptococci and MSSA 1.

Mild to Moderate Purulent Infections (abscesses, furuncles)

• Primary treatment: Incision and drainage alone may be sufficient without antibiotics 2, 3
• Add antibiotics if:
  • Fever or systemic symptoms present 3
  • Significant surrounding cellulitis (erythema extending beyond abscess borders) 2
  • Immunocompromised patient 2
  • Incomplete source control 3

Antibiotic options when needed:

• Dicloxacillin 500 mg four times daily 1
• Cephalexin 500 mg four times daily 1
• Clindamycin 300-450 mg three times daily 1
• Doxycycline 100 mg twice daily 1
• Trimethoprim-sulfamethoxazole (TMP-SMX) 160-800 mg twice daily 1

TMP-SMX provides excellent MRSA coverage but has limited activity against streptococci, so consider adding a beta-lactam if streptococcal infection is possible 1.

Severe Infections Requiring Hospitalization

These patients need intravenous therapy initially, but linezolid 600 mg every 12 hours orally has 100% bioavailability and can be used for severe MRSA infections if oral route is absolutely necessary 2, 4. However, this scenario typically warrants hospital admission for IV therapy.

Special Clinical Situations

Animal or Human Bites

• First-line: Amoxicillin-clavulanate 875/125 mg twice daily 2
• Alternative if penicillin allergic:
  • Doxycycline 100 mg twice daily PLUS metronidazole 500 mg three times daily 2
  • Moxifloxacin 400 mg daily (monotherapy with anaerobic coverage) 2

Amoxicillin-clavulanate covers Pasteurella multocida (from animal bites) and Eikenella corrodens (from human bites), along with staphylococci, streptococci, and anaerobes 2.

Diabetic Foot Infections (Mild)

• Recommended: Amoxicillin-clavulanate 875/125 mg twice daily 1
• Alternatives: Dicloxacillin, cephalexin, or clindamycin 1

These infections often involve mixed flora including gram-negatives and anaerobes, making amoxicillin-clavulanate particularly appropriate 1.

Recurrent Abscesses

• Obtain cultures to guide targeted therapy 3
• Consider 5-day decolonization regimen:
  • Intranasal mupirocin twice daily 1
  • Chlorhexidine body washes 1

Duration of Therapy

• Standard cellulitis: 5 days, extending if not improved 3
• Abscesses requiring antibiotics: 5-10 days 3
• Animal/human bites: 7-10 days 2
• Erysipeloid: 7-10 days 2

Critical Pitfalls to Avoid

Do not prescribe antibiotics for simple abscesses after adequate drainage unless fever, systemic symptoms, or significant cellulitis is present 3. The drainage itself is curative in most cases 2, 3.

Do not use TMP-SMX as monotherapy for cellulitis without considering streptococcal coverage, as it has poor activity against streptococci despite excellent MRSA coverage 1.

Do not overlook the need for adjunctive measures: elevation of affected limb, examination of interdigital toe spaces for fungal infection that may serve as portal of entry, and addressing underlying predisposing factors like edema 3.

Consider local MRSA prevalence when selecting empiric therapy—in areas with high community-associated MRSA rates, agents with MRSA activity (clindamycin, doxycycline, TMP-SMX) should be prioritized for purulent infections 2, 1.