Cephalexin Dosing for Pediatric Group A Streptococcal Infections
For a child with confirmed or presumed Group A Streptococcus pharyngitis or skin infection who cannot receive penicillin or amoxicillin, prescribe cephalexin at 20 mg/kg per dose twice daily (maximum 500 mg per dose) for a full 10 days. 1, 2
Critical Allergy Assessment First
Before prescribing cephalexin, you must determine the type of penicillin allergy:
Non-immediate (delayed) reactions such as mild rash occurring hours to days after penicillin exposure carry only a 0.1% cross-reactivity risk with first-generation cephalosporins, making cephalexin safe and the preferred first-line alternative. 1, 2
Immediate/anaphylactic reactions including anaphylaxis, angioedema, respiratory distress, or urticaria within 1 hour of penicillin administration carry up to a 10% cross-reactivity risk with all cephalosporins—these patients must avoid cephalexin entirely and receive clindamycin instead. 1, 2
Specific Dosing Regimen
Cephalexin 20 mg/kg per dose orally twice daily (maximum 500 mg per dose) for 10 days is the recommended regimen for children with non-immediate penicillin allergy and Group A Streptococcal pharyngitis or skin infections. 1, 2, 3
The FDA label confirms that for streptococcal pharyngitis in pediatric patients over 1 year of age and for skin and skin structure infections, the total daily dose may be divided and administered every 12 hours. 3
The usual pediatric dosage ranges from 25 to 50 mg/kg/day in divided doses, with the twice-daily regimen (20 mg/kg per dose) falling within this range and providing adequate coverage. 3
Why This Specific Dose
The 20 mg/kg twice-daily dosing achieves therapeutic plasma levels and has been demonstrated in clinical trials to be equally effective as four-times-daily regimens for Group A Streptococcal pharyngitis. 4
Twice-daily dosing significantly improves adherence compared to more frequent regimens, which is critical since non-compliance is a primary cause of treatment failure. 5
First-generation cephalosporins have strong, high-quality evidence supporting their efficacy as preferred alternatives for penicillin-allergic patients without immediate hypersensitivity, with superior bacterial eradication rates compared to penicillin in some studies. 1, 2, 6
Mandatory 10-Day Course
All antibiotics except azithromycin require a full 10-day course to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever. 1, 7, 2
Shortening the course by even a few days results in appreciable increases in treatment failure rates and raises the risk of acute rheumatic fever, even if symptoms resolve within 3–4 days. 1, 7
The FDA label specifically states that "in the treatment of β-hemolytic streptococcal infections, a therapeutic dosage of cephalexin should be administered for at least 10 days." 3
Alternative Options When Cephalexin Cannot Be Used
If the child has an immediate/anaphylactic penicillin allergy:
Clindamycin 7 mg/kg per dose three times daily (maximum 300 mg per dose) for 10 days is the preferred alternative, with only ~1% resistance among Group A Streptococcus in the United States. 1, 7, 2
Azithromycin 12 mg/kg once daily (maximum 500 mg) for 5 days is an acceptable alternative, though macrolide resistance rates are 5–8% in the United States and vary geographically. 1, 7, 2
Clarithromycin 7.5 mg/kg per dose twice daily (maximum 250 mg per dose) for 10 days is also an option but carries similar resistance concerns as azithromycin. 1, 2
Common Pitfalls to Avoid
Never prescribe cephalexin to a child who had anaphylaxis, angioedema, or immediate urticaria to penicillin—the 10% cross-reactivity risk makes this unsafe. 1, 2
Do not shorten the course below 10 days despite clinical improvement, as this dramatically increases treatment failure and rheumatic fever risk. 1, 7
Avoid broad-spectrum cephalosporins (cefdinir, cefuroxime, cefpodoxime) when narrow-spectrum cephalexin is appropriate—they are more expensive and promote resistant flora. 1, 7
Ensure the full 20 mg/kg per dose is prescribed—underdosing may compromise treatment effectiveness, particularly for resistant strains. 1