What is the recommended initial antibiotic dose for cellulitis?

Initial Antibiotic Dosing for Cellulitis

For uncomplicated cellulitis, the recommended initial antibiotic regimens are cephalexin 500 mg orally 3-4 times daily, clindamycin 300-450 mg orally three times daily, or amoxicillin-clavulanate 875/125 mg orally twice daily for 5-6 days. 1

First-Line Treatment Options

Oral Therapy for Uncomplicated Cellulitis

• Cephalexin: 500 mg orally 3-4 times daily for 5-6 days 1
• Clindamycin: 300-450 mg orally three times daily for 5-6 days 1
• Amoxicillin-clavulanate: 875/125 mg orally twice daily for 5-6 days 1

Intravenous Therapy for More Severe Cases

• Cefazolin: 1-2g IV every 8 hours (with or without metronidazole) 1
• Metronidazole: 500mg IV/oral every 8 hours (when anaerobic coverage is needed) 1

Treatment Considerations Based on Patient Factors

MRSA Risk Assessment

For patients with risk factors for MRSA (athletes, children, men who have sex with men, prisoners, military recruits, residents of long-term care facilities, prior MRSA exposure, IV drug users), consider:

• TMP-SMX: 1-2 double-strength tablets twice daily 1, 2
• Doxycycline: 100 mg twice daily (not for children under 8 years) 1
• Linezolid: 600 mg twice daily (for severe cases) 1
• Daptomycin: 4 mg/kg IV once daily (for severe cases) 1

Treatment Duration

Standard duration is 5-6 days for uncomplicated cellulitis, which has been shown to be as effective as longer courses 1, 3. Treatment should be extended if:

• Infection has not improved within 5-7 days
• Patient has complicating factors (elderly, diabetes, bacteremia)

Monitoring Response

• Clinical improvement should be assessed within 72 hours of starting therapy 1
• If no improvement is seen, consider:
  • Resistant organisms
  • Secondary conditions mimicking cellulitis
  • Underlying complications (immunosuppression, liver disease, kidney disease)

Common Pitfalls to Avoid

1. Inadequate MRSA coverage in high-risk patients 1
2. Using TMP-SMX alone for streptococcal infections (poor activity against streptococci) 1
3. Prescribing fluoroquinolones to children under 18 years (contraindicated) 1
4. Not adjusting therapy when clinical improvement is not seen within 72 hours 1
5. Failing to recognize when hospitalization is needed (deeper infection, poor adherence, immunocompromised, failing outpatient treatment) 1

Special Considerations

• Local resistance patterns should guide empiric therapy choices 1
• Surgical drainage is essential if an abscess develops 1
• Blood cultures should be obtained in patients with severe infection or systemic symptoms 1

In areas with high MRSA prevalence, antibiotics with activity against community-associated MRSA (such as TMP-SMX and clindamycin) may have higher success rates than cephalexin 4, but for standard uncomplicated cellulitis without purulence, beta-lactams targeting streptococci remain first-line therapy 1, 5.