Is cephalexin effective in treating bacterial pharyngitis?

Does Cephalexin Treat Pharyngitis?

Yes, cephalexin effectively treats bacterial pharyngitis caused by Group A Streptococcus, but it should be reserved as a second-line option for patients with non-anaphylactic penicillin allergy, not used as first-line therapy. 1, 2

First-Line Treatment Remains Penicillin or Amoxicillin

• Penicillin or amoxicillin is the treatment of choice for Group A Streptococcus (GAS) pharyngitis due to proven efficacy, safety, narrow spectrum, and low cost 1, 3, 4
• Penicillin-resistant GAS has never been documented anywhere in the world, making penicillin highly reliable 3
• The FDA label for cephalexin explicitly states: "Penicillin is the usual drug of choice in the treatment and prevention of streptococcal infections, including the prophylaxis of rheumatic fever" 4

When Cephalexin Is Appropriate

Cephalexin should be used specifically for patients with non-immediate (non-anaphylactic) penicillin allergy. 2, 5

• First-generation cephalosporins like cephalexin are the preferred alternative for penicillin-allergic patients without immediate hypersensitivity 2, 5
• Dosing: 500 mg orally every 12 hours for adults (or 20 mg/kg per dose twice daily in children, maximum 500 mg/dose) for a full 10 days 2
• The 10-day course is essential to achieve maximal pharyngeal eradication of GAS and prevent acute rheumatic fever 2

Critical Safety Consideration: Cross-Reactivity

• Up to 10% of patients with immediate/anaphylactic penicillin reactions have cross-reactivity with cephalosporins 2, 5
• Immediate reactions include anaphylaxis, angioedema, respiratory distress, or urticaria occurring within 1 hour of penicillin administration 2
• All beta-lactams, including cephalexin, must be avoided in patients with immediate hypersensitivity to penicillin 2, 5
• For patients with non-severe, delayed penicillin reactions, the cross-reactivity risk drops to only 0.1% 2

Evidence of Efficacy

• Cephalexin demonstrates comparable or superior bacteriologic cure rates to penicillin in streptococcal pharyngitis 6, 7
• One randomized, double-blind study showed combined treatment failure rates of 10% with cephalexin versus 19% with penicillin 7
• The FDA label confirms cephalexin is "generally effective in the eradication of streptococci from the nasopharynx" 4
• However, the FDA notes that "substantial data establishing the efficacy of cephalexin in the subsequent prevention of rheumatic fever are not available at present" 4

Why Not First-Line?

• Cephalexin has a broader antimicrobial spectrum than needed for streptococcal pharyngitis, which increases selection pressure for antibiotic-resistant flora 5, 3
• Narrow-spectrum first-generation cephalosporins like cephalexin are preferred over broad-spectrum cephalosporins (cefuroxime, cefixime, cefdinir), but penicillin remains narrower still 5
• Cephalexin is more expensive than penicillin or amoxicillin 3

Alternative Options for True Penicillin Allergy

For patients with immediate/anaphylactic penicillin allergy who cannot use any cephalosporins:

• Clindamycin is the preferred choice: 300 mg orally three times daily for 10 days in adults (or 7 mg/kg per dose three times daily in children, maximum 300 mg/dose) 2
• Clindamycin has approximately 1% resistance rate among GAS in the United States 2
• Clindamycin demonstrates high efficacy even in chronic streptococcal carriers 2

Macrolides are acceptable but less reliable:

• Azithromycin: 500 mg once daily for 5 days (or 12 mg/kg once daily in children, maximum 500 mg) 2
• Clarithromycin: 250 mg twice daily for 10 days (or 7.5 mg/kg per dose twice daily in children, maximum 250 mg/dose) 2
• Macrolide resistance rates are 5-8% in the United States and vary geographically 2

Common Pitfalls to Avoid

• Never use cephalexin in patients with anaphylaxis, angioedema, or immediate urticaria to penicillin due to the 10% cross-reactivity risk 2, 5
• Never shorten the course below 10 days despite clinical improvement, as this increases treatment failure rates and risk of acute rheumatic fever 2
• Do not prescribe cephalexin as first-line therapy when penicillin or amoxicillin can be used, as this unnecessarily broadens antibiotic spectrum and increases cost 3
• Assuming all penicillin-allergic patients cannot receive cephalosporins is incorrect—only those with immediate/anaphylactic reactions should avoid them 2