What is the recommended antibiotic treatment for an adult patient with acute sinusitis and no underlying health conditions or allergies to penicillin?

Antibiotic Treatment for Acute Sinusitis in Adults

First-Line Recommendation

Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days is the preferred first-line antibiotic for acute bacterial sinusitis in adults without penicillin allergy. 1

This recommendation prioritizes coverage against β-lactamase-producing organisms (Haemophilus influenzae and Moraxella catarrhalis), which have become increasingly prevalent, achieving 90-92% predicted clinical efficacy. 1

Confirming Bacterial Sinusitis Before Prescribing

Before prescribing antibiotics, verify the patient meets one of three diagnostic criteria for bacterial sinusitis: 1

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

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

Alternative First-Line Option: Watchful Waiting

Watchful waiting without immediate antibiotics is equally 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. 1 This approach recognizes that even bacterial sinusitis shows 73% spontaneous improvement by 7-12 days without antibiotics. 1

Plain Amoxicillin as an Alternative

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 However, amoxicillin-clavulanate is preferred due to increasing prevalence of β-lactamase-producing organisms. 1

High-Dose Amoxicillin-Clavulanate 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 month
• Age >65 years
• Moderate-to-severe symptoms
• Comorbid conditions or immunocompromised state

Important evidence note: Two recent randomized trials 2, 3 showed conflicting results on high-dose versus standard-dose amoxicillin-clavulanate. The 2021 trial found no benefit from high-dose therapy 2, while the 2018 trial found benefit only with immediate-release (not extended-release) high-dose formulation, but with increased severe diarrhea (15.8% vs 4.8%). 3 Given this mixed evidence and increased adverse effects, reserve high-dose therapy for the specific high-risk scenarios listed above.

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 Recent evidence supports shorter 5-7 day courses with comparable efficacy and fewer adverse effects. 1, 4

When to Reassess and Switch Antibiotics

Reassess at 3-5 days: If no improvement, switch to second-line therapy immediately. 1 Only 30-41% of patients improve by days 3-5, so lack of complete resolution does not necessarily indicate failure. 1

Reassess at 7 days: If symptoms persist or worsen, reconfirm diagnosis and switch to second-line therapy. 1 By 7 days, 73-85% of patients show clinical improvement even with placebo. 1

If worsening at any time: Immediately reassess for complications (orbital cellulitis, meningitis, brain abscess) and switch antibiotics. 1

Second-Line Treatment Options

If no improvement after 3-5 days of amoxicillin-clavulanate, switch to: 1

• Respiratory fluoroquinolones: Levofloxacin 500 mg once daily or moxifloxacin 400 mg once daily for 10 days (90-92% predicted efficacy against drug-resistant S. pneumoniae and β-lactamase-producing organisms) 1
• Third-generation cephalosporins: Cefpodoxime or cefdinir (superior activity against H. influenzae) 1

Essential Adjunctive Therapies

Add these to antibiotic therapy to improve outcomes: 1

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide twice daily) - reduces mucosal inflammation with strong evidence from multiple RCTs
• Saline nasal irrigation - provides symptomatic relief and removes mucus
• Analgesics (acetaminophen or ibuprofen) - relieves pain and fever

Antibiotics to Avoid

Never use these as first-line therapy: 1

• Azithromycin and macrolides - resistance rates exceed 20-25% for both S. pneumoniae and H. influenzae 1, 5
• Trimethoprim-sulfamethoxazole - 50% resistance rate for S. pneumoniae, 27% for H. influenzae 1
• First-generation cephalosporins (cephalexin) - inadequate coverage against H. influenzae 1

Common Pitfalls to Avoid

• Prescribing antibiotics for viral rhinosinusitis lasting <10 days promotes antimicrobial resistance without clinical benefit 1
• Using fluoroquinolones as first-line therapy in patients without β-lactam allergies promotes resistance 1
• Inadequate treatment duration can lead to relapse - ensure minimum 5 days, typically 7-10 days 1
• Waiting beyond 7 days to change therapy in non-responders delays effective treatment 1
• Expecting rapid improvement - most patients show noticeable improvement within 3-5 days, with complete resolution by 10-14 days 1

Expected Timeline for Improvement

• By 3-5 days: Reduction in fever, facial pain, and purulent nasal discharge expected 1
• By 7 days: 73-85% of patients show clinical improvement 1
• By 10-14 days: Complete resolution typically occurs 1

When to Refer to a Specialist

Refer to otolaryngology if: 1

• No improvement after 7 days of appropriate second-line antibiotic therapy
• Worsening symptoms at any time
• Suspected complications (orbital cellulitis, meningitis, brain abscess)
• Recurrent sinusitis (≥3 episodes per year)
• Sinusitis refractory to two courses of appropriate antibiotics