When should antibiotics (abx) be prescribed for patients with acute bacterial sinusitis, considering factors such as disease severity, allergy to penicillin, and underlying health conditions like diabetes or immunocompromised states?

When to Prescribe Antibiotics for Sinusitis

Prescribe antibiotics for acute bacterial sinusitis only when patients meet one of three specific diagnostic criteria: persistent symptoms ≥10 days without improvement, severe symptoms (fever ≥39°C with purulent nasal discharge) for ≥3 consecutive days, or "double sickening" (worsening after initial improvement from a viral URI). 1

Diagnostic Criteria Before Prescribing

Most acute rhinosinusitis (98-99.5%) is viral and resolves spontaneously within 7-10 days without antibiotics 1. You must confirm one of these three patterns before prescribing:

• Persistent symptoms: Nasal discharge (purulent or non-purulent) OR nasal obstruction/congestion lasting ≥10 days without clinical improvement 1
• Severe onset: High fever (≥39°C/102.2°F) AND purulent nasal discharge for at least 3-4 consecutive days at illness onset 1, 2
• Double sickening: Initial viral URI symptoms that improve, then worsen within 10 days with new fever, headache, or increased nasal discharge 1, 2

Watchful waiting without immediate antibiotics is appropriate for uncomplicated cases when reliable follow-up can be assured, with antibiotics started only if no improvement by 7 days or worsening at any time 1, 3.

First-Line Antibiotic Selection

For Most Adults Without Penicillin Allergy

Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days is the preferred first-line antibiotic for acute bacterial sinusitis in adults 1, 3. The clavulanate component provides essential coverage against β-lactamase-producing Haemophilus influenzae and Moraxella catarrhalis, which have become increasingly prevalent 3, 4.

Plain amoxicillin 500 mg twice daily (mild disease) or 875 mg twice daily (moderate disease) remains acceptable for uncomplicated cases without recent antibiotic exposure 1, 3.

High-Risk Patients Requiring High-Dose Therapy

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

• Recent antibiotic use within the past month 3
• Age >65 years 3
• Moderate-to-severe symptoms 3
• Comorbid conditions (diabetes, immunocompromised states) 3
• Areas with high prevalence of drug-resistant Streptococcus pneumoniae 3, 4

For Penicillin-Allergic Patients

Non-Anaphylactic Penicillin Allergy (Rash, Mild Reactions)

Second- or third-generation cephalosporins are safe and appropriate, as the risk of serious cross-reactivity is negligible 5, 6:

• Cefuroxime-axetil (second-generation) 3, 5, 6
• Cefpodoxime-proxetil (third-generation, superior H. influenzae coverage) 3, 5, 6
• Cefdinir (third-generation) 3, 5, 6

True Penicillin Allergy (Anaphylaxis/Type I Hypersensitivity)

Respiratory fluoroquinolones are the first-line choice:

• Levofloxacin 500 mg once daily for 10-14 days 3, 5, 6, 7
• Moxifloxacin 400 mg once daily for 10 days 3, 5, 6

These provide 90-92% predicted clinical efficacy against drug-resistant S. pneumoniae and β-lactamase-producing organisms 3, 7.

Doxycycline 100 mg once daily for 10 days is an acceptable alternative for mild disease, though it has a 20-25% predicted bacteriologic failure rate and limited H. influenzae activity 3, 6, 8.

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, 3. Shorter 5-7 day courses have comparable efficacy with fewer adverse effects 1, 3, 9.

When to Reassess and Switch Antibiotics

Reassess at 3-5 days: If no improvement, confirm the diagnosis meets bacterial criteria and consider switching to second-line therapy 1, 3.

At 7 days: If symptoms persist or worsen, reconfirm diagnosis and switch to broader-spectrum antibiotics 1, 3:

• High-dose amoxicillin-clavulanate (if not already used) 3
• Respiratory fluoroquinolones (levofloxacin or moxifloxacin) 3, 5, 6
• Third-generation cephalosporins (cefpodoxime or cefdinir) 3, 5

Critical Antibiotics to AVOID

Never use these as first-line therapy due to high resistance rates:

• Azithromycin and macrolides: 20-40% resistance for S. pneumoniae and H. influenzae 3, 5, 6, 10
• Trimethoprim-sulfamethoxazole: 50% resistance for S. pneumoniae, 27% for H. influenzae 3, 5, 6
• First-generation cephalosporins (cephalexin): Inadequate H. influenzae coverage 3

Essential Adjunctive Therapies

Prescribe these regardless of antibiotic choice to improve outcomes:

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide twice daily) reduce mucosal inflammation 1, 3
• Saline nasal irrigation for symptomatic relief 1, 3
• Analgesics (acetaminophen or NSAIDs) for pain and fever 1, 3
• Decongestants (oral or topical for ≤3 days) 1

Special Considerations

Diabetes and Immunocompromised States

Use high-dose amoxicillin-clavulanate (2 g/125 mg twice daily) as first-line therapy for these high-risk patients 3. Consider earlier reassessment at 3 days and lower threshold for switching to fluoroquinolones if no improvement 3.

Pediatric Patients

• Standard dose: Amoxicillin 45 mg/kg/day in 2 divided doses 3
• High-dose: Amoxicillin 80-90 mg/kg/day in 2 divided doses for age <2 years, daycare attendance, or recent antibiotic use 3
• Amoxicillin-clavulanate: 80-90 mg/kg/day of amoxicillin component with 6.4 mg/kg/day clavulanate in 2 divided doses for high-risk children 3

Common Pitfalls to Avoid

• Do not prescribe antibiotics for symptoms <10 days unless severe symptoms are present (fever ≥39°C with purulent discharge for ≥3 days) 1, 3
• Do not use fluoroquinolones as first-line therapy in patients without documented β-lactam allergies—this promotes antimicrobial resistance 3, 5, 6
• Do not continue ineffective therapy beyond 3-5 days—early reassessment prevents treatment failure 1, 3
• Do not use mucus color alone to determine antibiotic need, as color reflects neutrophils, not bacteria 3

Expected Timeline for Improvement

Most patients should show noticeable improvement within 3-5 days of starting appropriate antibiotic therapy 3. By 7 days, approximately 73-85% show clinical improvement 3. Complete resolution typically occurs by 10-14 days or when symptom-free for 7 consecutive days 1, 3. If worsening at any time, immediately reassess for complications (orbital cellulitis, meningitis, brain abscess) and switch antibiotics 3.