In a 68-year-old woman with an acute upper respiratory infection who is allergic to penicillins, methocarbamol (Robaxin), and intravenous contrast, what first‑line oral antibiotic should be prescribed?

Antibiotic Selection for Upper Respiratory Infection in Penicillin-Allergic Patient

For this 68-year-old woman with an upper respiratory infection and penicillin allergy, a respiratory fluoroquinolone (levofloxacin or moxifloxacin) should be prescribed if bacterial infection is suspected and antibiotics are warranted. 1

Initial Assessment: Does This Patient Need Antibiotics?

Most upper respiratory infections are viral and do not require antibiotics. 2, 3 You should only prescribe antibiotics if:

• Symptoms persist ≥10 days without improvement, suggesting acute bacterial rhinosinusitis (ABRS) 4
• Symptoms worsen within 10 days after initial improvement (double worsening pattern) 4
• Severe illness is present (moderate-to-severe pain or fever ≥38.3°C/101°F) 4

If symptoms are present <10 days without worsening, observation with symptomatic treatment is appropriate. 4

First-Line Antibiotic Choice for Penicillin Allergy

Respiratory fluoroquinolones (levofloxacin or moxifloxacin) are the preferred first-line agents for penicillin-allergic patients with bacterial respiratory infections. 1 This recommendation is based on:

• Superior coverage against respiratory pathogens including S. pneumoniae and H. influenzae 1
• Appropriate for patients with true β-lactam allergy 1
• Recommended by multiple guidelines for penicillin-allergic patients with ABRS 4, 1

Alternative Options (Lower Efficacy)

If fluoroquinolones are contraindicated or unavailable:

• Trimethoprim-sulfamethoxazole is a cost-effective alternative for ABRS in penicillin-allergic patients 4

• Macrolides (azithromycin or clarithromycin) may be used, but have significantly reduced efficacy 4, 1

  • Clinical efficacy only 78% for macrolides versus 91-92% for β-lactams 1
  • High and rising resistance rates among S. pneumoniae and H. influenzae 5
  • Should be considered second-tier options 5, 6

• Doxycycline is another alternative, though less preferred 4, 1

Critical Clinical Pitfalls

If the patient fails to improve after 72 hours of antibiotic therapy, you must reassess for complications, consider switching antibiotic classes, or obtain imaging/cultures. 1 Do not simply extend the same antibiotic. 1

Prior antibiotic use within 4-6 weeks is a major risk factor for resistant organisms. 1 In this scenario, respiratory fluoroquinolones become even more important as first-line therapy, and you should avoid using the same antibiotic class previously prescribed. 1

Practical Prescribing

• Levofloxacin 750 mg once daily or moxifloxacin 400 mg once daily for 5-7 days 1
• Counsel the patient on medication adherence, potential adverse effects (tendon rupture risk, QT prolongation), and the importance of completing the full course 4
• Emphasize supportive care: hydration, analgesics for pain, and decongestants as needed 4

Note: The allergies to Robaxin (methocarbamol) and IV contrast are not relevant to antibiotic selection and do not contraindicate any of the recommended respiratory antibiotics. 4