What is the antibiotic of choice for a patient with bacterial tonsillitis who is allergic to penicillin (PCN)?

Antibiotic Treatment for Bacterial Tonsillitis in Penicillin-Allergic Patients

For patients with bacterial tonsillitis who are allergic to penicillin, cephalexin is the preferred first-line antibiotic, with clarithromycin or azithromycin as alternatives when cephalosporin use is contraindicated due to severe penicillin allergy. 1, 2

Antibiotic Selection Algorithm Based on Allergy Type

Non-Anaphylactic Penicillin Allergy (e.g., rash):

1. First choice: Cephalexin

   • Dosage: 20 mg/kg per dose twice daily (maximum = 500 mg per dose) for 10 days 2
   • Rationale: Lower rate of clinical relapse compared to penicillin while maintaining good tolerability and narrow spectrum 1

2. Alternative: Cefadroxil

   • Dosage: 30 mg/kg once daily (maximum = 1 g) for 10 days 2
   • Note: Only for non-immediate/non-anaphylactic penicillin allergies

Severe/Anaphylactic Penicillin Allergy:

1. First choice: Clarithromycin

   • Dosage: 7.5 mg/kg twice daily (maximum 250 mg per dose) for 10 days 2
   • Rationale: Recommended by WHO for pharyngitis where there is severe allergy to penicillin 1

2. Alternative: Azithromycin

   • Dosage: 12 mg/kg once daily (maximum = 500 mg) for 5 days 2, 3
   • Rationale: Convenient once-daily dosing and shorter treatment duration (5 days vs 10 days) 4
   • Clinical efficacy: Demonstrated 95% bacteriologic eradication rate for Group A Streptococcus 3

3. Alternative for areas with high macrolide resistance: Clindamycin

   • Recommended for 10 days of therapy 2
   • Particularly appropriate when S. pneumoniae is identified as a pathogen 1

Important Clinical Considerations

Efficacy Concerns

• Macrolides (clarithromycin, azithromycin) have approximately 5-8% resistance rates among Group A Streptococcal isolates in the US 2
• Clindamycin resistance remains low at approximately 1% among Group A Streptococcal isolates 2
• TMP/SMX, tetracyclines, and sulfonamides should NOT be used due to high prevalence of resistant strains 2

Treatment Monitoring

• Clinical improvement should be expected within 24-48 hours of starting appropriate antibiotic therapy 2
• Persistent symptoms beyond 48-72 hours may indicate treatment failure or resistance 2
• Complete the full course of antibiotics (5 days for azithromycin, 10 days for others) to prevent complications and ensure eradication 2, 3

Common Pitfalls to Avoid

1. Misclassifying penicillin allergy severity:

   • Assess the nature of previous reactions carefully
   • Cephalosporins can be safely used in patients with non-anaphylactic reactions to penicillin 5
   • For true anaphylactic reactions, avoid all beta-lactams including cephalosporins 5

2. Inadequate treatment duration:

   • Ensure patients complete the full course of antibiotics
   • Azithromycin: 5 days
   • Other antibiotics: 10 days

3. Overlooking local resistance patterns:

   • In areas with high macrolide resistance, clindamycin may be preferable for penicillin-allergic patients 2

4. Unnecessary broad-spectrum coverage:

   • Fluoroquinolones have limited activity against GAS and are not recommended due to their broad spectrum and high cost 2

By following this algorithm, clinicians can effectively treat bacterial tonsillitis in penicillin-allergic patients while minimizing treatment failures and adverse effects.