What is the recommended dosage and frequency of oral antibiotics, such as cephalexin (Cephalexin) or dicloxacillin (Dicloxacillin), for a 17-year-old with cellulitis?

Antibiotic Treatment for Cellulitis in a 17-Year-Old

For a 17-year-old with cellulitis, cephalexin should be administered at a dosage of 500 mg orally every 6 hours (2 g daily) for 5-10 days, with treatment individualized based on clinical response. 1

Recommended First-Line Treatment

Cephalexin (First-Line Option)

• Dosage: 500 mg orally every 6 hours (2 g daily)
• Alternative dosing: 500 mg every 12 hours for uncomplicated cellulitis 1
• Duration: 5-10 days (5 days may be sufficient for uncomplicated cases) 2
• Rationale: Targets typical Gram-positive pathogens including beta-hemolytic streptococci and methicillin-sensitive Staphylococcus aureus, which are the predominant causes of non-purulent cellulitis 3

Dicloxacillin (Alternative Option)

• Dosage: 250 mg orally every 6 hours (1 g daily) 4
• Duration: 5-10 days, continuing at least 48 hours after the patient becomes afebrile and asymptomatic 4
• Administration: Best absorbed when taken on an empty stomach (1 hour before or 2 hours after meals) with at least 120 mL of water 4

Treatment Considerations

Assessment for MRSA Risk

• For standard non-purulent cellulitis, MRSA coverage is generally not necessary 3
• If purulent drainage is present or MRSA is suspected:
  • Consider adding TMP-SMX to cephalexin OR
  • Switch to clindamycin 600 mg orally three times daily 2

Severity Assessment

• Mild to moderate cellulitis: Oral therapy as outlined above
• Severe cellulitis: Consider hospitalization and parenteral antibiotics if:
  • Rapid progression
  • Systemic symptoms (fever, tachycardia)
  • Immunocompromised state
  • Failed outpatient therapy

Duration of Treatment

• Standard duration: 5-10 days 2
• Continue until:
  • At least 48 hours after becoming afebrile and asymptomatic 4
  • Resolution of erythema, swelling, and tenderness 5
• Recent evidence suggests 5 days may be as effective as 10 days for uncomplicated cases 2

Monitoring and Follow-up

• Evaluate response within 48-72 hours
• Treatment failure signs include:
  • Fever
  • Increase in erythema (>25%), swelling, or tenderness after 3-4 days
  • No decrease in symptoms after 3-4 days 5

Clinical Pearls and Pitfalls

• Pitfall: Unnecessarily adding MRSA coverage for non-purulent cellulitis. Studies show that cephalexin alone is generally sufficient for typical non-purulent cellulitis 6, 5.

• Pitfall: Inadequate dosing. For a 17-year-old (adult-sized patient), use adult dosing rather than pediatric weight-based dosing to ensure adequate coverage 1.

• Pearl: Consider obtaining cultures from any purulent drainage to guide therapy if initial empiric treatment fails 2.

• Pearl: Elevating the affected area can help reduce edema and speed resolution of symptoms 2.