Oral Antibiotic Protocol for Skin Infections
Initial Assessment and Classification
The treatment protocol depends on whether the infection is purulent (with abscess/pus) or non-purulent (cellulitis/erysipelas), and the severity based on systemic signs of infection. 1, 2
Severity Classification
Assess for systemic inflammatory response syndrome (SIRS) criteria to determine severity 1:
- Temperature >38°C or <36°C
- Tachypnea >24 breaths/minute
- Tachycardia >90 beats/minute
- White blood cell count >12,000 or <4,000 cells/μL
Non-Purulent Infections (Cellulitis/Erysipelas)
Mild to Moderate Severity (No SIRS)
For uncomplicated cellulitis without purulent drainage, use oral antibiotics targeting streptococci and methicillin-susceptible Staphylococcus aureus (MSSA) as first-line therapy. 2
Preferred first-line agents: 1, 2
- Cephalexin 500 mg every 6 hours (or 250 mg four times daily) 1, 3
- Dicloxacillin 250-500 mg every 6 hours 1
Alternative agents for penicillin allergy (non-immediate hypersensitivity): 1
- Cefazolin 1 g every 8 hours IV (if parenteral needed) 1
- Amoxicillin-clavulanate 875/125 mg twice daily 1
Duration: 5 days if clinical improvement occurs; extend if no improvement 2
When to Add MRSA Coverage
Add empiric MRSA-active antibiotics if any of the following are present: 2
- Penetrating trauma or injection drug use
- Purulent drainage despite appearing non-purulent initially
- Evidence of MRSA elsewhere on body
- Nasal MRSA colonization
- Failed initial beta-lactam therapy 1
MRSA-active oral options: 1, 2
- Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily 1, 2
- Doxycycline 100 mg twice daily 1, 2
- Clindamycin 300-450 mg four times daily 1, 2
Important caveat: Clindamycin has potential for cross-resistance and emergence of resistance in erythromycin-resistant strains, with inducible resistance possible in MRSA 1
Purulent Infections (Abscesses, Furuncles, Carbuncles)
Mild Severity
Incision and drainage is the primary treatment for purulent infections, with antibiotics as adjunctive therapy only when indicated. 1, 2
Indications for adding antibiotics after drainage: 2
- Fever or systemic signs present
- Multiple lesions
- Immunocompromised patient
- Drainage alone has failed
- Severe local symptoms or rapid progression 1
When antibiotics are indicated, use MRSA-active agents: 1, 2
- Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily
- Doxycycline 100 mg twice daily
- Clindamycin 300-450 mg four times daily
Duration: 5 days if clinical improvement occurs 2
Moderate to Severe Purulent Infections
For patients with SIRS criteria, failed initial treatment, or markedly impaired host defenses, use MRSA-active antibiotics empirically. 1
Same MRSA-active oral agents as above, or consider IV therapy if meeting criteria for severe infection 1, 2
Special Situations
Impetigo and Ecthyma
Use a 7-day oral regimen with an agent active against S. aureus unless cultures yield streptococci alone (when penicillin is recommended). 1
For methicillin-susceptible infections: 1
- Dicloxacillin 250 mg four times daily
- Cephalexin 250 mg four times daily
- Amoxicillin-clavulanate 875/125 mg twice daily
When MRSA is suspected or confirmed: 1
- Doxycycline 100 mg twice daily
- Clindamycin 300-400 mg four times daily
- Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily
For limited lesions, topical therapy may suffice: 1
- Mupirocin ointment applied twice daily
- Retapamulin ointment applied twice daily
Bite Wounds (Animal or Human)
Amoxicillin-clavulanate is the antibiotic of choice for bite wounds due to coverage of both aerobic and anaerobic pathogens. 1, 2
Dosing: 875/125 mg twice daily 1
Alternative for penicillin allergy: 1
- Moxifloxacin 400 mg daily (covers anaerobes as monotherapy)
- Ciprofloxacin 500-750 mg twice daily OR levofloxacin 750 mg daily PLUS metronidazole 250-500 mg three times daily
Important: Administer tetanus toxoid if not vaccinated within 10 years (or 5 years for dirty wounds); Tdap preferred if not previously given 1
Recurrent Infections
For recurrent skin infections, implement a comprehensive approach: 2
- Drain and culture early lesions
- Treat with 5-10 day course based on culture results
- Consider decolonization regimens: intranasal mupirocin twice daily for 5 days, daily chlorhexidine washes, daily decontamination of personal items 2
Criteria for IV Therapy/Hospitalization
Severe infections require IV therapy when any of the following are present: 2
- Systemic inflammatory response syndrome (SIRS)
- Hemodynamic instability or hypotension 1
- Altered mental status
- Concern for necrotizing infection
- Severely immunocompromised status
- Failed oral antibiotic treatment 1
IV regimens for severe infections: 2
- Vancomycin 15-20 mg/kg every 8-12 hours (for MRSA coverage)
- Cefazolin 1 g every 8 hours (for streptococcal/MSSA coverage)
- Vancomycin PLUS piperacillin-tazobactam or carbapenem for broad polymicrobial coverage
Key Clinical Pearls
Common pitfalls to avoid:
- Do not use first-generation cephalosporins, macrolides, clindamycin, or aminoglycosides for human bite wounds due to Eikenella corrodens resistance 1
- Trimethoprim-sulfamethoxazole has poor activity against anaerobes; avoid as monotherapy for bite wounds 1
- Cephalosporins are contraindicated in patients with immediate penicillin hypersensitivity (urticaria, angioedema, bronchospasm, anaphylaxis) 4
- Most S. aureus strains are now penicillin-resistant; penicillin G is not appropriate for staphylococcal infections 4, 5
Twice-daily dosing enhances compliance: Cephalexin can be given as 500 mg every 12 hours for streptococcal pharyngitis, skin infections, and uncomplicated cystitis, improving medication adherence 3, 6, 5