Can Keflex (cephalexin) treat streptococcal infections?

Can Keflex Treat Strep?

Yes, Keflex (cephalexin) is effective for treating streptococcal infections, including Group A streptococcal pharyngitis (strep throat) and streptococcal skin infections, and is specifically recommended as a first-line alternative for patients with non-immediate penicillin allergies. 1, 2

When Cephalexin Should Be Used for Strep

For strep throat in penicillin-allergic patients (non-anaphylactic):

• Cephalexin is the preferred first-line alternative when patients have non-immediate penicillin allergies (no history of anaphylaxis, angioedema, or urticaria to penicillins) 1, 2
• The IDSA and WHO Working Group selected cephalexin based on lower relapse rates, good tolerability, and narrow spectrum compared to macrolides 1

For streptococcal skin infections:

• The FDA specifically approves cephalexin for skin and skin structure infections caused by Staphylococcus aureus and/or Streptococcus pyogenes 3
• Clinical studies demonstrate cure rates of 90% or higher for streptococcal and staphylococcal skin infections 4

Critical Dosing Requirements

Adults:

• 500 mg every 12 hours for streptococcal pharyngitis 3
• Alternative: 250 mg every 6 hours for less severe infections 3
• Must complete full 10-day course to prevent acute rheumatic fever 1, 2

Pediatric patients:

• 20 mg/kg per dose twice daily (maximum 500 mg per dose) for 10 days 1, 2
• For β-hemolytic streptococcal infections specifically, therapeutic dosage must be administered for at least 10 days 3

When Cephalexin Should NOT Be Used

Absolute contraindications:

• Patients with immediate/anaphylactic penicillin reactions (history of anaphylaxis, angioedema, or urticaria) should avoid cephalexin due to up to 10% cross-reactivity risk 5, 2
• These patients should receive clindamycin or azithromycin instead 2

Important Resistance Considerations

Viridans streptococci (relevant for endocarditis prophylaxis):

• Cephalexin shows 96% resistance among viridans group streptococci blood culture isolates, making it the least active cephalosporin tested 5
• For endocarditis prophylaxis in penicillin-allergic patients, cephalexin is listed as an option but cefazolin or ceftriaxone are 2-4 times more active 5

Group A streptococcus (strep throat):

• Cephalexin remains highly effective for Group A streptococcal pharyngitis with strong evidence supporting its use 1, 2
• Clinical studies show comparable efficacy to penicillin for pharyngitis and tonsillitis 6

Common Pitfalls to Avoid

• Do not prescribe shorter courses than 10 days (except azithromycin's 5-day regimen) - even though symptoms resolve in 3-4 days, full course completion is essential for preventing acute rheumatic fever 2
• Do not assume all penicillin-allergic patients can receive cephalexin - only those with non-immediate reactions; patients with anaphylaxis, angioedema, or urticaria must avoid all beta-lactams 5, 1
• Do not use cephalexin for endocarditis prophylaxis when better cephalosporin options exist - cefazolin or ceftriaxone are significantly more active against viridans streptococci 5
• Penicillin remains the drug of choice for streptococcal infections in patients without penicillin allergy 3, 4

Efficacy Evidence

• Twice-daily and four-times-daily cephalexin regimens are equally effective, with failure rates of 7.3% and 5.3% respectively in GAS pharyngitis 7
• Cephalexin is generally effective in eradicating streptococci from the nasopharynx, though substantial data for preventing rheumatic fever are limited compared to penicillin 3
• Adverse effects (mostly gastrointestinal upsets, rash, urticaria) are relatively infrequent and rarely require discontinuation 6