What is the best antibiotic for a typical adult patient with an uncomplicated sinus infection and no known allergies or significant medical history?

Best Antibiotic for Sinus Infection

For an adult with uncomplicated acute bacterial sinusitis and no allergies, amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days is the preferred first-line antibiotic. 1, 2

First Confirm This Is Actually Bacterial Sinusitis

Most sinus infections (98-99.5%) are viral and resolve spontaneously within 7-10 days without antibiotics. 1 Reserve antibiotics only for patients meeting one of three specific criteria: 1

• Persistent symptoms ≥10 days without clinical improvement
• Severe symptoms (fever ≥39°C with purulent nasal discharge or facial pain) for ≥3 consecutive days
• "Double sickening" - worsening symptoms after initial improvement from a viral URI lasting at least 5 days

The number needed to treat with antibiotics is 18 for one additional rapid cure, but the number needed to harm from adverse effects is only 8. 1 This means most patients experience more harm than benefit from antibiotics. 1

First-Line Antibiotic Choice

Amoxicillin-Clavulanate (Preferred)

Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days is the preferred first-line agent according to the 2012 IDSA guidelines. 1, 2 This recommendation is based on concern for ampicillin-resistant Haemophilus influenzae and Moraxella catarrhalis, though no direct evidence proves it superior to plain amoxicillin. 1

The clavulanate component provides coverage against β-lactamase-producing organisms, which account for nearly 50% of H. influenzae strains and 90-100% of M. catarrhalis. 2

Use high-dose amoxicillin-clavulanate (2 g/125 mg twice daily) for patients with: 2

• Recent antibiotic use within the past month
• Age >65 years
• Moderate-to-severe symptoms
• Comorbid conditions or immunocompromised state

Plain Amoxicillin (Alternative First-Line)

Some professional societies, including the American Academy of Allergy, Asthma & Immunology and the American Academy of Family Physicians, recommend plain amoxicillin 500 mg twice daily (mild disease) or 875 mg twice daily (moderate disease) as the preferred first-line agent. 1, 2 This is appropriate for uncomplicated cases without recent antibiotic exposure. 2

Important Nuance: Watchful Waiting

The American Academy of Otolaryngology-Head and Neck Surgery emphasizes watchful waiting without immediate antibiotics as initial management for all patients with uncomplicated acute bacterial sinusitis, regardless of severity. 1 This approach is appropriate when reliable follow-up can be assured, with antibiotics started only if no improvement occurs by 7 days or symptoms worsen at any time. 2

For Penicillin-Allergic Patients

Non-Severe Allergy (Rash, Delayed Reaction)

Second- or third-generation cephalosporins are safe and preferred: 1, 2

• Cefuroxime (second-generation)
• Cefpodoxime (third-generation, superior activity against H. influenzae)
• Cefdinir (third-generation)

The risk of cross-reactivity between penicillins and second/third-generation cephalosporins is negligible. 2

Severe Allergy (Anaphylaxis/Type I Hypersensitivity)

Respiratory fluoroquinolones are the first-line choice: 1, 2

• Levofloxacin 500 mg once daily for 10-14 days 2, 3
• Moxifloxacin 400 mg once daily for 10 days 2

These provide 90-92% predicted clinical efficacy against drug-resistant S. pneumoniae and β-lactamase-producing H. influenzae. 2, 3

Doxycycline 100 mg once daily for 10 days is an acceptable alternative but has lower efficacy (77-81% vs 90-92%) due to limited activity against H. influenzae. 1, 4

What NOT to Use

Avoid these antibiotics due to high resistance rates: 2

• Azithromycin and macrolides - 20-25% resistance for S. pneumoniae and H. influenzae 2
• Trimethoprim-sulfamethoxazole - 50% resistance for S. pneumoniae, 27% for H. influenzae 2
• First-generation cephalosporins (cephalexin) - inadequate coverage against H. influenzae 2

Treatment Duration

Standard duration is 5-10 days, with most guidelines recommending treatment until symptom-free for 7 days (typically 10-14 days total). 1, 2 Recent evidence supports 5-7 day courses for uncomplicated cases with comparable efficacy and fewer adverse effects. 2, 5

When to Switch Antibiotics (Treatment Failure)

Reassess at 3-5 days. 2 If no improvement, switch to: 1, 2

• High-dose amoxicillin-clavulanate (if not already used)
• Respiratory fluoroquinolone (levofloxacin or moxifloxacin)
• Third-generation cephalosporin (cefpodoxime or cefdinir)

Essential Adjunctive Therapies

These improve outcomes regardless of antibiotic choice: 1, 2

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide twice daily) - reduce mucosal inflammation and potentially decrease antibiotic use 1, 2
• Saline nasal irrigation - provides symptomatic relief 1, 2
• Analgesics (acetaminophen, NSAIDs) for pain 1, 2
• Decongestants (systemic or topical) as needed 1, 2

Critical Pitfalls to Avoid

• Don't prescribe antibiotics for symptoms <10 days unless severe symptoms are present (fever ≥39°C with purulent discharge for ≥3 consecutive days). 1, 2
• Don't use fluoroquinolones as first-line in patients without documented β-lactam allergies - this promotes antimicrobial resistance. 2
• Don't continue ineffective therapy beyond 3-5 days - reassess and switch antibiotics if no improvement. 2
• Don't use mucus color alone to determine antibiotic need - color reflects neutrophils, not bacteria. 2

When to Refer to a Specialist

Refer to otolaryngology, infectious disease, or allergy/immunology for: 1, 2

• Symptoms refractory to two courses of appropriate antibiotics
• Recurrent sinusitis (≥3 episodes per year)
• Suspected complications (orbital cellulitis, meningitis, brain abscess)
• Seriously ill patients who deteriorate despite therapy