Is cephalexin a suitable treatment option for a 5-year-old child, weighing 68.9 pounds and 49 inches tall, with strep throat, particularly if they have failed penicillin therapy?

Cephalexin Use in a 5-Year-Old with Strep Throat After Penicillin Failure

Cephalexin is an appropriate and effective treatment option for this 5-year-old child (68.9 pounds/31.3 kg) with strep throat, particularly after penicillin failure, and should be dosed at 25-50 mg/kg/day divided into 2-4 doses for 10 days. 1

FDA-Approved Indication and Safety

• Cephalexin is FDA-approved for respiratory tract infections caused by Streptococcus pyogenes (the causative organism of strep throat), though the FDA notes that penicillin remains the usual drug of choice for streptococcal infections 1
• The safety and effectiveness of cephalexin in pediatric patients has been established in clinical trials, and this 5-year-old patient falls well within the approved age range 1
• Cephalexin capsules should only be used if the child can swallow capsules; otherwise, the oral suspension formulation is recommended 1

Superior Efficacy After Penicillin Failure

• Cephalosporins, including cephalexin, demonstrate superior bacteriologic eradication rates compared to penicillin for Group A streptococcal pharyngitis, with combined failure rates of 11% versus 23% respectively (P < 0.001) 2
• Penicillin failure rates for streptococcal pharyngitis have increased from 2-10% historically to approximately 30% in recent decades, making alternative antibiotics increasingly important 3
• The mechanisms of penicillin failure include lack of compliance, copathogenicity with beta-lactamase producing organisms, and penicillin tolerance—factors that cephalosporins may overcome more effectively 3

Specific Dosing for This Patient

• For this 31.3 kg (68.9 pound) child, the recommended dose is 25-50 mg/kg/day divided into 2-4 doses 1, 4
• A practical regimen would be 500 mg twice daily (approximately 32 mg/kg/day) or 250 mg four times daily, both falling within the recommended range 4
• The suspension formulation is well-accepted by young children and enhances compliance, particularly important given that non-compliance is a major cause of penicillin treatment failure 5, 3
• Treatment duration should be 10 days to ensure adequate eradication and prevent rheumatic fever, though the FDA notes that data establishing cephalexin's efficacy in preventing rheumatic fever are limited 1

Clinical Effectiveness Evidence

• Cephalexin achieves cure rates of 90% or higher for streptococcal infections, with 12+ years of clinical experience demonstrating sustained efficacy 5
• In pharyngitis and tonsillitis due to beta-hemolytic streptococci, cephalexin is comparable to penicillin in clinical response and bacteriological cure rate 4
• The twice-daily dosing option enhances medication compliance compared to penicillin's more frequent dosing requirements 5

Important Clinical Considerations

• Culture and susceptibility testing should be performed to confirm Group A streptococcus and guide therapy 1
• Adverse effects are generally mild and infrequent, primarily consisting of gastrointestinal upset, rash, and urticaria, and rarely require discontinuation 4
• The drug is substantially excreted by the kidney, though dose adjustment is typically not needed in children with normal renal function 1
• Patients should complete the full 10-day course even if symptoms improve early, as incomplete treatment may promote bacterial resistance 1

When Cephalexin May Not Be Optimal

• If Haemophilus influenzae is suspected (more relevant for otitis media than pharyngitis), cephalexin has a 50% failure rate and should not be used 4
• For strep throat specifically, this is not a concern as S. pyogenes is uniformly susceptible 1, 4