What first‑line antibiotic regimen should be used for an otherwise healthy adult with acute otitis media, acute bacterial sinusitis, and group A streptococcal pharyngitis, assuming no penicillin allergy?

First-Line Antibiotic for Ear Infection, Sinus Infection, and Strep Throat

For an otherwise healthy adult with acute otitis media, acute bacterial sinusitis, and group A streptococcal pharyngitis without penicillin allergy, prescribe amoxicillin-clavulanate (Augmentin) 875 mg orally twice daily for 10 days. This single agent covers all three infections simultaneously and is the preferred first-line therapy recommended by major guidelines 1, 2.

Why Amoxicillin-Clavulanate Is the Optimal Choice

Amoxicillin-clavulanate is specifically recommended as the preferred agent for acute bacterial rhinosinusitis by the 2012 IDSA guidelines 1. This recommendation is based on concern for ampicillin-resistant Haemophilus influenzae and Moraxella catarrhalis, which are common pathogens in both sinusitis and otitis media 1, 2.

• The clavulanate component inhibits β-lactamases produced by H. influenzae and M. catarrhalis, which are responsible for approximately 30-40% of acute otitis media and sinusitis cases 2, 3.
• For streptococcal pharyngitis, the amoxicillin component provides complete coverage against Group A Streptococcus, which has zero documented resistance to penicillins worldwide 1.
• This single regimen eliminates the need for multiple antibiotics and simplifies adherence 2.

Required Treatment Duration

A full 10-day course is mandatory for several critical reasons:

• For streptococcal pharyngitis: 10 days is essential to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever 1, 4.
• For acute bacterial sinusitis: Most guidelines recommend 10 days for uncomplicated cases 1.
• For acute otitis media: Standard duration is 10 days in adults 1, 2.

Shortening the course increases treatment failure rates and, for strep throat specifically, raises the risk of acute rheumatic fever 1, 4.

Alternative Regimens If Amoxicillin-Clavulanate Cannot Be Used

For Non-Immediate (Delayed) Penicillin Allergy

• First-generation cephalosporins (e.g., cephalexin 500 mg twice daily for 10 days) can be used safely, as the cross-reactivity risk is only 0.1% with delayed reactions 4.
• However, cephalexin alone may not adequately cover β-lactamase-producing organisms in sinusitis and otitis media 2.

For Immediate/Anaphylactic Penicillin Allergy

• Respiratory fluoroquinolone (e.g., levofloxacin 500 mg daily or moxifloxacin 400 mg daily) for 7-10 days covers all three infections 1.
• Clindamycin 300 mg three times daily for 10 days covers strep throat (with only 1% resistance) but does not cover H. influenzae, requiring a separate agent for sinusitis/otitis media 1, 4.
• Doxycycline may be considered for sinusitis but is contraindicated for streptococcal pharyngitis as it fails to eradicate Group A Streptococcus and does not prevent rheumatic fever 4.

When to Suspect Bacterial Infection Requiring Antibiotics

Acute Bacterial Rhinosinusitis

Reserve antibiotics for patients with 1:

• Persistent symptoms for more than 10 days without improvement
• Severe symptoms (fever >39°C, purulent nasal discharge, or facial pain) lasting ≥3 consecutive days
• Double sickening (worsening after initial improvement following a typical viral URI)

Acute Otitis Media

• Diagnosis requires purulent or mucopurulent middle ear fluid with a red, retracted tympanic membrane 1.
• In adults, AOM is rare but requires the same treatment as in children 1.

Streptococcal Pharyngitis

• Confirm with rapid antigen detection test (RADT) or throat culture before prescribing antibiotics 1, 4.
• Clinical features alone cannot reliably distinguish bacterial from viral pharyngitis 4.

Critical Pitfalls to Avoid

• Do not prescribe trimethoprim-sulfamethoxazole (Bactrim) for any of these infections—it fails to eradicate Group A Streptococcus in 20-25% of cases and has poor activity against pneumococci 1, 4.
• Do not use cefixime or older fluoroquinolones (ciprofloxacin, ofloxacin) as they have poor activity against S. pneumoniae 1, 4.
• Do not shorten the antibiotic course below 10 days based on clinical improvement, as this dramatically increases treatment failure and rheumatic fever risk 1, 4.
• Do not prescribe antibiotics for viral upper respiratory infections masquerading as these conditions—confirm bacterial etiology first 1, 2.

Adjunctive Symptomatic Management

• Acetaminophen or ibuprofen for fever, sore throat, ear pain, and facial pain 4.
• Intranasal saline irrigation for sinusitis symptoms 1.
• Intranasal corticosteroids may alleviate sinusitis symptoms and potentially decrease antibiotic use 1.
• Avoid aspirin in children due to Reye syndrome risk 4.
• Corticosteroids are not recommended as adjunctive therapy for streptococcal pharyngitis 4.

When to Refer or Reassess

• Patients who are seriously ill, deteriorate despite antibiotic therapy, or have recurrent episodes should be referred to a specialist (otolaryngologist, infectious disease specialist, or allergist) 1.
• Reassess within 48-72 hours if no clinical improvement occurs 4.