What alternative antibiotics can be given to a patient with pharyngitis who is allergic to amoxicillin?

Treatment of Pharyngitis in Amoxicillin-Allergic Patients

For patients with pharyngitis allergic to amoxicillin, use first-generation cephalosporins (cephalexin 500 mg twice daily for 10 days) if the allergy was non-immediate, or clindamycin (300 mg three times daily for 10 days) if the allergy was anaphylactic. 1

Critical First Step: Determine the Type of Allergy

The type of amoxicillin allergy dictates which alternatives are safe:

• Non-immediate reactions (delayed rash, mild symptoms occurring >1 hour after administration): Cross-reactivity risk with cephalosporins is only 0.1%, making them safe and preferred 2
• Immediate/anaphylactic reactions (anaphylaxis, angioedema, respiratory distress, urticaria within 1 hour): Must avoid ALL beta-lactam antibiotics including cephalosporins due to up to 10% cross-reactivity risk 1, 3

Treatment Algorithm Based on Allergy Type

For Non-Immediate Amoxicillin Allergy

First-generation cephalosporins are the preferred choice with strong, high-quality evidence supporting their efficacy, narrow spectrum, and low cost 1:

• Cephalexin: 500 mg orally every 12 hours for 10 days (adults) or 20 mg/kg per dose twice daily (maximum 500 mg/dose) for 10 days (children) 1, 2
• Cefadroxil: 30 mg/kg once daily (maximum 1 gram) for 10 days 1

These agents have proven efficacy comparable to penicillin and are significantly less expensive than broader-spectrum alternatives 1

For Immediate/Anaphylactic Amoxicillin Allergy

Clindamycin is the preferred first-line alternative with strong, moderate-quality evidence 3:

• Clindamycin: 300 mg orally three times daily for 10 days (adults) or 7 mg/kg per dose three times daily (maximum 300 mg/dose) for 10 days (children) 1, 3
• Demonstrates high efficacy in eradicating streptococci, even in chronic carriers 1
• Only ~1% resistance rate among Group A Streptococcus in the United States 1, 3

Acceptable alternatives include:

• Azithromycin: 500 mg once daily for 5 days (adults) or 12 mg/kg once daily (maximum 500 mg) for 5 days (children) 1, 3

  • Only antibiotic requiring just 5 days due to prolonged tissue half-life 1
  • However, macrolide resistance is 5-8% in the United States and varies geographically 1, 3

• Clarithromycin: 250 mg twice daily for 10 days (adults) or 7.5 mg/kg per dose twice daily (maximum 250 mg/dose) for 10 days (children) 1

  • Similar resistance concerns as azithromycin 1

Critical Treatment Duration Requirements

A full 10-day course is mandatory for all antibiotics except azithromycin to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever 1, 2, 3. Shortening the course by even a few days results in appreciable increases in treatment failure rates 1. Azithromycin requires only 5 days due to its unique pharmacokinetics 1, 3.

Common Pitfalls to Avoid

• Do not use cephalosporins in patients with immediate/anaphylactic reactions to amoxicillin—the 10% cross-reactivity risk makes this dangerous 1, 3
• Do not assume all penicillin-allergic patients cannot receive cephalosporins—only those with immediate/anaphylactic reactions should avoid them 1
• Do not shorten treatment courses below 10 days (except azithromycin's 5-day regimen) as this dramatically increases treatment failure and rheumatic fever risk 1, 2
• Be aware of local macrolide resistance patterns before prescribing azithromycin or clarithromycin, as resistance varies geographically and can lead to treatment failure 1, 3
• Do not use trimethoprim-sulfamethoxazole for strep throat—it has high resistance rates and is not recommended for Group A Streptococcus 1

Adjunctive Therapy

• Acetaminophen or NSAIDs (ibuprofen) should be considered for moderate to severe symptoms or high fever 1, 3
• Avoid aspirin in children due to risk of Reye syndrome 1, 3
• Corticosteroids are not recommended as adjunctive therapy 1, 3