What antibiotic can be used to treat tonsillitis and urinary tract infection (UTI) in a patient with an allergy to amoxicillin (amoxicillin)?

Antibiotic Options for Tonsillitis and UTI in Amoxicillin-Allergic Patients

For patients with both tonsillitis and urinary tract infection who have an amoxicillin allergy, clindamycin is the most appropriate antibiotic choice for tonsillitis, while ciprofloxacin is recommended for the UTI component. 1

First-Line Treatment Approach

For Tonsillitis:

• Clindamycin: 7 mg/kg per dose three times daily (maximum 300-450 mg per dose) for 10 days 1
  • Excellent coverage against Group A Streptococcus
  • Recommended by IDSA guidelines specifically for penicillin-allergic patients
  • Superior efficacy in patients with recurrent tonsillitis compared to penicillin 2

For UTI:

• Ciprofloxacin: 500 mg twice daily for 7 days (for uncomplicated UTI) or 7-14 days (for complicated UTI) 1, 3
  • Provides excellent coverage against common uropathogens including E. coli, Klebsiella, and Proteus
  • First choice for pyelonephritis and upper UTIs in penicillin-allergic patients 1

Alternative Options Based on Allergy Severity

If patient has non-anaphylactic reaction to amoxicillin:

• Cephalosporins may be considered:
  • Cefuroxime: 250-500 mg twice daily for 10 days (tonsillitis) and 7-14 days (UTI) 1
  • Cefpodoxime: 100-200 mg twice daily for 5-10 days 1
  • Note: 10% cross-reactivity risk between penicillins and cephalosporins

If patient has severe/anaphylactic penicillin allergy:

For Tonsillitis:

• Macrolides:
  • Azithromycin: 500 mg on day 1, then 250 mg daily for 4 days 1, 4
  • Clarithromycin: 250 mg twice daily for 10 days 1, 4
  • Caution: Local resistance patterns should be considered as macrolide resistance can be as high as 25% 5

For UTI:

• Trimethoprim-sulfamethoxazole: 160/800 mg twice daily for 3 days (uncomplicated) or 7-14 days (complicated) 1
  • Consider only if local resistance rates are <20%

Important Clinical Considerations

1. Verify the nature of the amoxicillin allergy:

   • True anaphylaxis vs. rash or GI intolerance
   • This will determine if cephalosporins are a viable option

2. Diagnostic confirmation:

   • For tonsillitis: Rapid antigen detection test and/or throat culture to confirm Group A Streptococcus 1
   • For UTI: Urine culture before initiating antibiotics when possible 1

3. Treatment duration:

   • Tonsillitis requires full 10-day course (except azithromycin) to prevent rheumatic fever 1
   • UTI duration depends on severity: 3-7 days for uncomplicated, 7-14 days for complicated or upper UTI 1

4. Monitoring:

   • Assess clinical response within 48-72 hours
   • If no improvement, reevaluate diagnosis and consider alternative antibiotics

Special Situations

• Recurrent tonsillitis: Clindamycin has shown superior efficacy in preventing recurrence 2
• Complicated UTI: Consider parenteral therapy initially with ceftriaxone if available 1
• Pediatric patients: Adjust dosing by weight and consider taste preferences for oral formulations

Common Pitfalls to Avoid

1. Using fluoroquinolones for uncomplicated infections in young patients due to risk of tendon damage
2. Short-course therapy for streptococcal tonsillitis (except azithromycin)
3. Assuming all beta-lactam allergies are true anaphylactic reactions
4. Not considering local resistance patterns, especially for macrolides and TMP-SMX
5. Treating presumed viral pharyngitis with antibiotics

Remember that clindamycin for tonsillitis and ciprofloxacin for UTI provides the most reliable coverage for both infections in patients with amoxicillin allergy, while minimizing the risk of treatment failure due to resistance.