What antibiotic can be prescribed for an adult with an ear infection who is allergic to penicillin (PCN)?

Antibiotic Selection for Adult Ear Infection with Penicillin Allergy

For an adult with an ear infection (acute otitis media) who is allergic to penicillin, prescribe either a second- or third-generation cephalosporin (cefdinir, cefuroxime, or cefpodoxime) if the allergy is non-Type I hypersensitivity, or alternatively use doxycycline, a respiratory fluoroquinolone (levofloxacin or moxifloxacin), or azithromycin/clarithromycin if the allergy is severe (Type I hypersensitivity). 1

Type of Penicillin Allergy Determines Antibiotic Choice

The critical first step is determining the type of penicillin allergy:

Non-Type I Hypersensitivity (e.g., rash without anaphylaxis)

• Cephalosporins are safe and preferred 1
• Second- and third-generation cephalosporins (cefdinir, cefuroxime, cefpodoxime, ceftriaxone) have negligible cross-reactivity with penicillin due to distinct chemical structures 1
• Cross-reactivity risk is only 0.1% in patients without severe/recent penicillin reactions 1
• Cefdinir is preferred among oral options for better patient acceptance 1
• Ceftriaxone 50 mg IM/IV daily for 1-3 days is an alternative parenteral option 1

Type I Hypersensitivity (immediate reactions: anaphylaxis, angioedema, urticaria)

Avoid all beta-lactams including cephalosporins. Use these alternatives: 1

• Doxycycline 100 mg twice daily 1
• Respiratory fluoroquinolones: levofloxacin or moxifloxacin 1
• Macrolides: azithromycin 500 mg daily for 5 days or clarithromycin 250 mg twice daily for 10 days 1

Important Caveats About Macrolides

Macrolides have significant limitations that make them less ideal choices: 1

• High resistance rates: >40% of Streptococcus pneumoniae in the US is macrolide-resistant 1
• Should be reserved for true Type I penicillin allergy when fluoroquinolones or doxycycline cannot be used 1
• Despite resistance concerns, azithromycin and clarithromycin remain acceptable alternatives for penicillin-allergic patients 1

Treatment Duration

• Standard duration: 10 days for most oral antibiotics 1
• Azithromycin exception: 5 days due to prolonged tissue half-life 1, 2
• Shorter courses (5-7 days) may be considered for uncomplicated cases 1

Clinical Pitfalls to Avoid

• Do not use trimethoprim-sulfamethoxazole: High resistance rates (50% for S. pneumoniae, 27% for H. influenzae) make this a poor choice 1
• Avoid first-generation cephalosporins (cephalexin, cefazolin) in patients with any penicillin allergy history, as cross-reactivity is higher than with second/third-generation agents 1
• Fluoroquinolones should not be first-line in non-allergic patients due to comparable outcomes but higher adverse event rates compared to amoxicillin-clavulanate 1

Reassessment Strategy

If no clinical improvement after 48-72 hours, consider: 1

• Switching to a different antibiotic class
• Possibility of viral co-infection or non-bacterial etiology
• Need for tympanocentesis if available, especially for recurrent or severe cases 1