What is the recommended dose of Keflex (cefalexin) for a 49-pound child with cellulitis?

Cephalexin Dosing for Cellulitis in a 49-Pound Child

For a 49-pound (22.3 kg) child with cellulitis, administer cephalexin 25-50 mg/kg/day divided into 3-4 doses, which translates to 560-1,115 mg per day or approximately 140-280 mg per dose four times daily (using 250 mg/5 mL suspension: 2.8-5.6 mL four times daily). 1, 2

Weight-Based Calculation

• Patient weight: 49 pounds = 22.3 kg 2
• Standard dosing range: 25-50 mg/kg/day for cellulitis 1, 2
• Daily dose calculation:
  • Lower range: 22.3 kg × 25 mg/kg = 558 mg/day
  • Upper range: 22.3 kg × 50 mg/kg = 1,115 mg/day 2
• Per-dose calculation (four times daily):
  • Lower range: 140 mg per dose
  • Upper range: 280 mg per dose 2

Practical Dosing Recommendations

For non-purulent cellulitis (most common presentation), start with the standard dose of 25-50 mg/kg/day divided four times daily. 3, 1 The FDA label provides specific guidance for a 20 kg (44 lb) patient: 1-2 teaspoons of 250 mg/5 mL suspension four times daily, which corresponds to 250-500 mg per dose. 2 For your 22.3 kg patient, this translates to approximately 1-2 teaspoons (250-500 mg) four times daily. 2

Alternative twice-daily dosing: For improved adherence, the Infectious Diseases Society of America supports dividing the total daily dose into twice-daily administration for skin and skin structure infections in patients over 1 year of age. 1, 2 This would be 280-560 mg twice daily (approximately 1.5-2.5 teaspoons of 250 mg/5 mL suspension twice daily). 1, 2

Critical Clinical Context

Cephalexin is ONLY appropriate for non-purulent cellulitis where β-hemolytic streptococci are the primary concern. 3, 1 Do NOT use cephalexin if:

• The cellulitis is purulent (has associated abscess or drainage) - requires MRSA coverage with clindamycin or TMP-SMX 3, 1
• The patient has systemic toxicity or rapid progression - requires intravenous therapy 3
• There is concern for community-acquired MRSA based on local epidemiology 3, 1
• The patient has failed β-lactam therapy previously 3, 1

Treatment Duration and Monitoring

• Duration: 5-10 days, individualized based on clinical response 1
• Critical monitoring point: Assess for treatment failure at 48-72 hours 1
• If no improvement by 48-72 hours: Switch to empirical MRSA coverage (clindamycin 10-13 mg/kg/dose three times daily, maximum 40 mg/kg/day) 3, 1

Dosing Frequency Considerations

While four times daily dosing is FDA-approved and traditional, recent evidence supports less frequent dosing for improved adherence:

• Three times daily: 45 mg/kg/dose (maximum 1.5 g) three times daily has demonstrated 99% cure rates in pediatric bone and joint infections with excellent tolerability 4
• Twice daily: The FDA label explicitly permits twice-daily dosing for skin and skin structure infections in children over 1 year of age 2

For this 22.3 kg patient, practical twice-daily dosing would be 500 mg (2 teaspoons of 250 mg/5 mL) twice daily, which provides 45 mg/kg/day and falls within the recommended 25-50 mg/kg/day range. 1, 2

Common Pitfalls to Avoid

• Do not use cephalexin for purulent cellulitis - this is the most common error, as purulent infections require MRSA coverage 3, 1
• Do not continue cephalexin beyond 48-72 hours without clinical improvement - this indicates likely MRSA or need for alternative therapy 1
• Do not use cephalexin if erythema migrans (Lyme disease) cannot be excluded - first-generation cephalosporins are ineffective for Lyme disease 1
• Ensure adequate hydration and monitor for gastrointestinal symptoms, which are the most common adverse effects 4