What medication is recommended for acute bacterial sinusitis in an otherwise healthy adult?

First-Line Antibiotic for Acute Bacterial Sinusitis

For an otherwise healthy adult with acute bacterial sinusitis, prescribe amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days as first-line therapy. 1, 2, 3, 4

Confirm the Diagnosis Before Prescribing

Before starting antibiotics, verify the patient meets at least one of three diagnostic criteria for bacterial (not viral) sinusitis 1, 2, 3:

• Persistent symptoms ≥10 days without clinical improvement (purulent nasal discharge with nasal obstruction or facial pain/pressure) 1, 2
• Severe symptoms for ≥3-4 consecutive days: fever ≥39°C (102°F) with purulent nasal discharge 1, 2
• "Double sickening": worsening symptoms after initial improvement from a viral upper respiratory infection 1, 2

Critical context: 98-99.5% of acute rhinosinusitis is viral and resolves spontaneously within 7-10 days without antibiotics. 1, 2 Do not prescribe antibiotics for symptoms lasting <10 days unless severe features are present. 1, 2

Why Amoxicillin-Clavulanate Over Plain Amoxicillin

The clavulanate component is essential because 30-40% of Haemophilus influenzae and nearly all Moraxella catarrhalis isolates produce β-lactamase, rendering plain amoxicillin ineffective. 2, 3, 4 Amoxicillin-clavulanate achieves 90-92% predicted clinical efficacy against the major sinusitis pathogens (Streptococcus pneumoniae, H. influenzae, M. catarrhalis). 2, 4

Treatment Duration: 5-10 Days

Treat for 5-10 days or until symptom-free for 7 consecutive days (typically 10-14 days total). 1, 2, 3 Recent evidence shows that shorter 5-7 day courses provide comparable efficacy with fewer adverse effects compared to traditional 10-day regimens. 1, 2

When to Use High-Dose Amoxicillin-Clavulanate

Escalate to high-dose amoxicillin-clavulanate 2 g/125 mg twice daily for patients with 1, 2:

• Recent antibiotic use within the past month
• Age >65 years
• Moderate-to-severe symptoms
• Comorbid conditions (diabetes, chronic cardiac/hepatic/renal disease)
• Immunocompromised state

High-dose therapy provides enhanced coverage against penicillin-resistant S. pneumoniae. 1

Alternatives for Penicillin-Allergic Patients

Non-Severe (Non-Type I) Penicillin Allergy

For patients with a history of rash or mild reactions (not anaphylaxis), use second- or third-generation cephalosporins 1, 2, 3, 4:

• Cefuroxime-axetil (second-generation) 1, 2
• Cefpodoxime-proxetil (third-generation, superior activity against H. influenzae) 1, 2
• Cefdinir (third-generation) 1, 2

The risk of serious cross-reactivity between penicillins and second/third-generation cephalosporins is negligible. 2, 4

Severe (Type I/Anaphylactic) Penicillin Allergy

For documented anaphylaxis or severe reactions, use respiratory fluoroquinolones 1, 2, 3:

• Levofloxacin 500 mg once daily for 10-14 days 1, 2, 5
• Moxifloxacin 400 mg once daily for 10 days 1, 2

Fluoroquinolones achieve 90-92% predicted clinical efficacy and provide excellent coverage against multidrug-resistant S. pneumoniae. 2, 5 However, reserve fluoroquinolones for patients with documented severe β-lactam allergies or treatment failures to prevent resistance development. 1, 2

Doxycycline 100 mg once daily for 10 days is an acceptable but suboptimal alternative, with only 77-81% predicted efficacy and limited activity against H. influenzae. 2

Watchful Waiting: An Equally Valid Initial Strategy

For uncomplicated acute bacterial sinusitis, watchful waiting without immediate antibiotics is appropriate when reliable follow-up can be ensured. 1, 2, 3 Give the patient a prescription but instruct them to fill it only if there is no improvement by 7 days or if symptoms worsen at any time. 1 The number needed to treat with antibiotics to achieve one additional cure is 10-15 over 7-15 days, reflecting the high rate of spontaneous recovery. 1, 2

Essential Adjunctive Therapies (Add to All Patients)

Intranasal Corticosteroids (Strongly Recommended)

Prescribe intranasal corticosteroids (mometasone, fluticasone, or budesonide) twice daily to reduce mucosal inflammation and improve symptom resolution. 1, 2, 3, 4 Multiple randomized controlled trials provide strong evidence that intranasal steroids accelerate recovery when added to antibiotic therapy. 2

Supportive Measures

• Saline nasal irrigation 2-3 times daily for symptomatic relief and mucus clearance 1, 2
• Analgesics (acetaminophen or ibuprofen) for pain and fever 1, 2
• Adequate hydration 2

Reassessment and Treatment Failure Protocol

Reassess at 3-5 Days

If there is no improvement after 3-5 days, switch to 1, 2, 3:

• High-dose amoxicillin-clavulanate (if not already prescribed), OR
• Respiratory fluoroquinolone (levofloxacin or moxifloxacin)

Reassess at 7 Days

If symptoms persist or worsen at 7 days 1, 2:

• Reconfirm the diagnosis of acute bacterial sinusitis
• Exclude complications (orbital cellulitis, meningitis, brain abscess)
• Consider imaging (CT scan) only if complications are suspected
• Switch to second-line therapy if not already done

When to Refer to Otolaryngology

Refer patients with 1, 2, 3:

• No improvement after 7 days of appropriate second-line antibiotic therapy
• Worsening symptoms at any time
• Suspected complications (severe headache, visual changes, periorbital swelling, altered mental status)
• Recurrent sinusitis (≥3 episodes per year), requiring evaluation for underlying allergic rhinitis, immunodeficiency, or anatomic abnormalities

Antibiotics to Avoid as First-Line Therapy

Azithromycin and Other Macrolides

Do not use azithromycin or clarithromycin due to resistance rates of 20-25% for both S. pneumoniae and H. influenzae. 1, 2, 3, 4 Azithromycin is the antibiotic most likely to be used inappropriately for sinusitis. 2

Trimethoprim-Sulfamethoxazole (Bactrim/Septra)

Do not use trimethoprim-sulfamethoxazole due to 50% resistance in S. pneumoniae and 27% resistance in H. influenzae. 2

First-Generation Cephalosporins

Do not use cephalexin or cefadroxil due to inadequate coverage against H. influenzae (≈50% of strains produce β-lactamase). 2

Common Pitfalls to Avoid

• Prescribing antibiotics for viral rhinosinusitis: Wait at least 10 days unless severe symptoms are present. 1, 2
• Using fluoroquinolones as first-line therapy in non-allergic patients: This promotes antimicrobial resistance. 1, 2
• Inadequate treatment duration: Ensure minimum 5 days for adults to prevent relapse. 1, 2
• Failing to reassess at 3-5 days: Early identification of treatment failure prevents prolonged illness and complications. 1, 2
• Relying on mucus color alone: Purulent (colored) discharge reflects neutrophils, not necessarily bacteria. 2
• Obtaining routine imaging: Reserve CT scans for suspected complications or alternative diagnoses. 1, 2

Expected Timeline for Improvement

Most patients should experience noticeable improvement within 3-5 days of starting appropriate antibiotic therapy. 2 By 7 days, approximately 73-85% of patients show clinical improvement, and by 10-14 days, 86-91% achieve cure or improvement. 2 If there is no improvement by 3-5 days, this constitutes treatment failure and requires switching antibiotics. 2