Cephalexin Dosing for Pediatric Cellulitis
For pediatric cellulitis, cephalexin (Keflex) should be dosed at 25-50 mg/kg/day divided into 3-4 doses, with consideration for higher dosing (75-100 mg/kg/day) in severe infections. 1
Standard Dosing Recommendations
FDA-Approved Dosing
The FDA label for Keflex specifies 1:
- Standard dose: 25-50 mg/kg/day divided into 3-4 doses
- Skin and soft tissue infections: May be divided and administered every 12 hours
- Severe infections: Dosage may be doubled
Guideline-Based Dosing for Staphylococcal Infections
For methicillin-susceptible Staphylococcus aureus (MSSA) skin and soft tissue infections, the IDSA guidelines recommend 2, 3:
- Oral cephalexin: 75-100 mg/kg/day divided into 3 or 4 doses
- This represents the preferred oral agent for MSSA cellulitis in children
Practical Dosing Strategies
Frequency Options
Three times daily dosing is increasingly supported as an alternative to four times daily:
- Recent pharmacokinetic modeling supports 45 mg/kg/dose (maximum 1.5 g) three times daily 4, 5
- This achieves the same pharmacodynamic target (free drug concentration above MIC for ≥40% of dosing interval) as traditional four times daily dosing 6
- A retrospective study of 149 children with bone and joint infections showed 99% cure rate with this regimen 4
Twice daily dosing may be considered for less severe infections:
- The FDA label permits every 12-hour dosing for skin and soft tissue infections 1
- Pharmacokinetic studies suggest 22-45 mg/kg/dose twice daily for MSSA with MIC ≤2 mg/L 6
High-Dose Regimens for Moderate Cellulitis
A recent study evaluated high-dose oral cephalexin for moderate cellulitis treated as outpatients 7:
- Success rate of 89.7% (105/117 children)
- Only 10.3% treatment failure requiring admission or IV antibiotics
- No severe complications reported
- This approach potentially reduces hospitalization rates
Dosing by Severity
Mild to Moderate Cellulitis (Outpatient)
- 25-50 mg/kg/day divided into 3-4 doses
- Alternative: 45 mg/kg/dose three times daily (maximum 1.5 g/dose)
- Consider twice daily dosing for improved adherence in mild cases
Severe Cellulitis
- 75-100 mg/kg/day divided into 3-4 doses 2, 3
- Maximum daily dose should not exceed 4 grams 1
- If doses >4 g/day are required, consider parenteral cephalosporins
Important Clinical Considerations
MRSA Coverage
Cephalexin does NOT cover MRSA. If MRSA is suspected (purulent cellulitis, abscess, treatment failure, or local high MRSA prevalence), alternative agents are required 2, 3:
- Clindamycin: 30-40 mg/kg/day in 3-4 divided doses (oral)
- Trimethoprim-sulfamethoxazole: 8-12 mg/kg/day based on TMP component
Duration of Therapy
- Typical duration: 7-10 days for uncomplicated cellulitis
- For streptococcal infections: minimum 10 days 1
Common Pitfalls
- Underdosing: Using 25 mg/kg/day for moderate-severe infections when 50-100 mg/kg/day is indicated
- Assuming MRSA coverage: Cephalexin is only effective for MSSA and streptococcal cellulitis
- Poor adherence with QID dosing: Consider TID or BID regimens when appropriate to improve compliance
- Ignoring treatment failure: If no improvement in 48-72 hours, reassess for MRSA, abscess, or alternative diagnosis
Safety Profile
Cephalexin is generally well-tolerated in children 7, 4:
- Mild gastrointestinal symptoms most common
- Rare neutropenia (usually mild and self-limited)
- Safe in children >1 year of age for skin infections