What is the best antibiotic for acute bacterial sinusitis?

Best Antibiotic for Acute Bacterial Sinusitis

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, 2

First-Line Treatment

Amoxicillin-clavulanate is superior to plain amoxicillin due to the increasing prevalence (20-30%) of β-lactamase-producing organisms (Haemophilus influenzae and Moraxella catarrhalis) that render plain amoxicillin ineffective 1, 2. The combination achieves 90-92% predicted clinical efficacy against the major pathogens: Streptococcus pneumoniae, H. influenzae, and M. catarrhalis 1.

Standard Dosing

• Adults: Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days 1, 2
• Children: High-dose amoxicillin-clavulanate 80-90 mg/kg/day (of amoxicillin component) with 6.4 mg/kg/day clavulanate divided twice daily for 10-14 days 1, 3

High-Dose Regimen for High-Risk Patients

Use high-dose amoxicillin-clavulanate (2 g amoxicillin/125 mg clavulanate twice daily) for patients with 1:

• Recent antibiotic use within the past 4-6 weeks
• Age >65 years
• Moderate-to-severe symptoms
• Comorbid conditions or immunocompromised state

Confirm the Diagnosis First

Do not prescribe antibiotics unless the patient meets one of three diagnostic criteria 1, 2:

1. Persistent symptoms ≥10 days without clinical improvement
2. Severe symptoms (fever ≥39°C with purulent nasal discharge) for ≥3-4 consecutive days
3. "Double sickening": worsening symptoms after initial improvement from a viral upper respiratory infection

Most acute rhinosinusitis (98-99.5%) is viral and resolves spontaneously within 7-10 days without antibiotics 1. Prescribing antibiotics for viral rhinosinusitis contributes to antimicrobial resistance without clinical benefit 1.

Treatment Duration

Shorter courses (5-7 days) have comparable efficacy to traditional 10-day regimens with fewer adverse effects 1, 2. However, treatment should continue until symptom-free for 7 days, which typically results in a 10-14 day total course 1.

For children, the minimum duration is 10-14 days 3.

Penicillin-Allergic Patients

Non-Severe Allergy (Rash, Delayed Reaction)

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

• Cefuroxime-axetil (second-generation)
• Cefpodoxime-proxetil or cefdinir (third-generation)

The risk of cross-reactivity between penicillins and second/third-generation cephalosporins is negligible 1.

Severe Type I Hypersensitivity (Anaphylaxis)

Respiratory fluoroquinolones are the treatment of choice 1, 2:

• Levofloxacin 500 mg once daily for 10-14 days 1, 4
• Moxifloxacin 400 mg once daily for 10 days 1

These achieve 90-92% predicted clinical efficacy and provide excellent coverage against drug-resistant S. pneumoniae and β-lactamase-producing organisms 1, 4.

What NOT to Use as First-Line Therapy

Avoid these antibiotics due to high resistance rates 1, 2:

• Azithromycin and other macrolides: 20-25% resistance for both S. pneumoniae and H. influenzae 1, 5
• Trimethoprim-sulfamethoxazole: 50% resistance for S. pneumoniae, 27% for H. influenzae 1
• First-generation cephalosporins (cephalexin): Inadequate coverage against H. influenzae 1
• Doxycycline: 20-25% predicted bacteriologic failure rate 1

Second-Line Treatment for Treatment Failure

If no improvement occurs within 3-5 days, switch to 1, 2:

• High-dose amoxicillin-clavulanate (if not already used)
• Respiratory fluoroquinolones (levofloxacin 500-750 mg once daily or moxifloxacin 400 mg once daily) for 10-14 days

Reassess at 3-5 days (adults) or 72 hours (children) 1, 3. If symptoms worsen or fail to improve, this constitutes treatment failure and requires switching antibiotics immediately 1, 3.

Essential Adjunctive Therapies

Add these to antibiotic therapy in all patients to improve outcomes 1, 2:

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide twice daily): Reduce mucosal inflammation and improve symptom resolution 1
• Saline nasal irrigation: Provides symptomatic relief and removes mucus 1
• Analgesics (acetaminophen or ibuprofen): For pain and fever management 1

Watchful Waiting Option

For adults with uncomplicated acute bacterial sinusitis, watchful waiting without immediate antibiotics is equally appropriate when reliable follow-up can be assured 1, 2. Start antibiotics only if no improvement by 7 days or symptoms worsen at any time 1.

Critical Pitfalls to Avoid

• Do not prescribe antibiotics for symptoms <10 days unless severe features are present (fever ≥39°C with purulent discharge for ≥3 consecutive days) 1, 2
• Do not use plain amoxicillin as first-line therapy given the high prevalence (20-30%) of β-lactamase-producing organisms 2
• Do not continue ineffective antibiotics beyond 3-5 days—failure to reassess and switch therapy leads to prolonged illness and potential complications 1, 2
• Do not use fluoroquinolones as first-line therapy in patients without documented β-lactam allergies to prevent resistance development 1, 2
• Ensure adequate treatment duration: Minimum 5 days for adults, 10 days for children 1, 3

Pediatric-Specific Considerations

For children failing initial amoxicillin therapy at 72 hours, switch to high-dose amoxicillin-clavulanate 80-90 mg/kg/day (of amoxicillin component) with 6.4 mg/kg/day clavulanate divided twice daily 3. Alternative second-line options include ceftriaxone 50 mg/kg IM/IV once daily 3.

Red flags requiring immediate imaging and specialist consultation include periorbital or orbital swelling, impaired extraocular muscle function, impaired visual acuity, severe headache, altered mental status, seizures, or focal neurologic findings 3.