Pediatric Cephalexin Dosing for Cellulitis
For uncomplicated cellulitis in children, prescribe cephalexin 25–50 mg/kg/day divided into 4 doses (every 6 hours) for 7 days, with a maximum daily dose of 4 grams. 1
Standard Weight-Based Dosing
The Infectious Diseases Society of America recommends cephalexin 25–50 mg/kg/day divided into 3–4 doses for pediatric skin and soft tissue infections caused by methicillin-susceptible Staphylococcus aureus (MSSA) and Streptococcus species. 1
The traditional dosing interval is every 6 hours (four times daily), though recent pharmacokinetic data support three-times-daily dosing at higher individual doses (up to 45 mg/kg per dose, maximum 1.5 g) for bone and joint infections. 2, 3
For cellulitis specifically, the four-times-daily regimen remains the guideline-recommended standard because it maintains consistent bactericidal concentrations against common skin pathogens. 1
Maximum Daily Dose and Duration
The maximum daily dose is 4 grams per day, regardless of weight. 1
Treatment duration should be 7 days for uncomplicated cellulitis, with clinical improvement expected within 48–72 hours. 1, 4
If no improvement occurs by 48–72 hours, reassess for abscess formation requiring drainage, consider MRSA coverage (clindamycin or trimethoprim-sulfamethoxazole), or escalate to parenteral therapy. 1
Adjustments for Infants Younger Than Two Months
Cephalexin dosing listed in the IDSA guidelines is not appropriate for neonates; refer to the American Academy of Pediatrics Red Book for neonatal-specific dosing. 1
Infants under 3 months with cellulitis should generally be hospitalized for parenteral therapy (cefazolin 50 mg/kg/day divided every 8 hours or nafcillin 100–150 mg/kg/day divided every 6 hours) due to the risk of serious bacterial infection and the need for close monitoring. 1
Renal Impairment Adjustments
Cephalexin is renally cleared, and patients with creatinine clearance < 30 mL/min require dose reduction proportional to the degree of renal dysfunction. 5
For children with significant renal impairment, consult pediatric nephrology or infectious disease specialists to adjust the dosing interval (e.g., every 8–12 hours instead of every 6 hours) while maintaining therapeutic serum concentrations. 5
Severe Cephalosporin Allergy
For children with documented severe (anaphylactic) cephalosporin or penicillin allergy, clindamycin 30–40 mg/kg/day divided into 3–4 doses orally is the preferred alternative for uncomplicated cellulitis. 1, 6
Clindamycin provides excellent coverage against both β-hemolytic streptococci and community-acquired MRSA, making it ideal for empiric therapy in penicillin-allergic patients. 1, 6
The cross-reactivity risk between penicillins and cephalosporins is approximately 1–3% for non-anaphylactic reactions, so cephalexin may be cautiously used under medical supervision in patients with non-severe penicillin allergy (e.g., rash without angioedema or bronchospasm). 7
Alternative Therapy for MRSA
If community-acquired MRSA is suspected (purulent drainage, abscess, failure of β-lactam therapy, or local MRSA prevalence > 10%), switch to clindamycin 30–40 mg/kg/day divided into 3–4 doses orally or trimethoprim-sulfamethoxazole 8–12 mg/kg/day (based on trimethoprim component) divided into 2 doses. 1, 6
Clindamycin should only be used empirically when local MRSA clindamycin resistance rates are < 10%; perform D-zone testing on erythromycin-resistant MRSA isolates to detect inducible clindamycin resistance. 1, 6
For severe cellulitis with systemic toxicity requiring hospitalization, vancomycin 40–60 mg/kg/day divided every 6–8 hours intravenously is the parenteral drug of choice for MRSA. 1
Clinical Monitoring and Common Pitfalls
Expect clinical improvement (reduced erythema, warmth, swelling, and fever) within 48–72 hours; lack of improvement warrants reassessment for abscess, deeper infection, or resistant organisms. 1, 4
Underdosing cephalexin (using < 25 mg/kg/day) is a common error that risks treatment failure, especially in regions with intermediate penicillin-resistant S. aureus. 1
Failure to consider MRSA in patients with purulent cellulitis, recent antibiotic exposure, or known MRSA colonization is a critical pitfall; these patients require MRSA-active therapy from the outset. 1, 6
Do not use cephalexin for cellulitis with systemic signs of toxicity (hypotension, tachycardia, altered mental status) or concern for necrotizing fasciitis; these patients require immediate hospitalization, broad-spectrum IV antibiotics (e.g., vancomycin plus piperacillin-tazobactam), and surgical consultation. 1