How should I treat an otherwise healthy adult with an acute lower respiratory tract infection and fever, assuming no drug allergies, severe comorbidities, or immunosuppression?

Treatment of Chest Infection with Fever

For an otherwise healthy adult with a lower respiratory tract infection and fever, prescribe amoxicillin 500-1000 mg three times daily for 5-7 days as first-line therapy. 1, 2

Initial Assessment and Risk Stratification

Before prescribing antibiotics, determine whether this is pneumonia versus acute bronchitis, as this fundamentally changes management:

Suspect Pneumonia When:

• New focal chest signs on examination 1
• Fever lasting >4 days 1
• Dyspnea or tachypnea (respiratory rate ≥30) 1
• Pulse rate >100 beats/min 1

Use C-Reactive Protein (CRP) Testing:

• **CRP <20 mg/L** with symptoms >24 hours makes pneumonia highly unlikely 1
• CRP >100 mg/L makes pneumonia likely 1
• If doubt persists after CRP testing, obtain a chest X-ray to confirm or exclude pneumonia 1

Antibiotic Selection

First-Line Treatment:

Amoxicillin 500-1000 mg every 8 hours is the preferred first-choice antibiotic based on least chance of harm and wide clinical experience 1, 2

Alternative first-line option: Tetracycline (doxycycline 100 mg twice daily) 1, 2

For Penicillin Allergy:

• Macrolides (azithromycin 500 mg daily, clarithromycin 250-500 mg twice daily, or erythromycin) in countries with low pneumococcal macrolide resistance 1, 2
• Tetracyclines (doxycycline 100 mg twice daily) 1, 2

Reserve Fluoroquinolones:

Levofloxacin or moxifloxacin should only be used when there are clinically relevant bacterial resistance rates against all first-choice agents, or for treatment failures 1, 2

Treatment Duration and Monitoring

Standard Duration:

5-7 days for uncomplicated LRTI managed at home 2

Expected Clinical Response:

• Clinical improvement should occur within 3 days of starting antibiotics 1
• Instruct patients to contact you if no noticeable effect within 3 days 1
• Advise patients to return if symptoms persist beyond 3 weeks 1

Red Flags Requiring Immediate Re-evaluation:

• Fever exceeding 4 days 1
• Worsening dyspnea 1
• Patient stops drinking 1
• Decreasing consciousness 1

Hospital Referral Criteria

Consider immediate hospital referral for:

• Severe illness signs: tachypnea, tachycardia, hypotension, confusion 1, 2
• Temperature <35°C or ≥40°C 2
• Heart rate ≥125 beats/min 2
• Blood pressure <90/60 mmHg 1, 2
• Cyanosis 2
• Elderly patients with relevant comorbidities (diabetes, heart failure, moderate-severe COPD, liver disease, renal disease, malignant disease) 1
• Failure to respond to initial antibiotic treatment 1

Critical Pitfalls to Avoid

Do NOT Order Routine Microbiological Tests:

Cultures and gram stains are not recommended in primary care for LRTI 1

Do NOT Prescribe Symptomatic Treatments:

Cough suppressants, expectorants, mucolytics, antihistamines, inhaled corticosteroids, and bronchodilators should not be prescribed for acute LRTI in primary care 1

Avoid Fluoroquinolone Overuse:

Overuse drives resistance; reserve for documented failures or when first-line agents have clinically relevant resistance rates 1, 2

Consider Local Resistance Patterns:

National/local resistance rates should guide antibiotic selection, particularly for macrolides where pneumococcal resistance may compromise efficacy 1

Set Realistic Expectations:

Many LRTIs are viral and self-limiting; cough may persist longer than the antibiotic treatment duration 2. Recent evidence shows antibiotics have no measurable impact on severity or duration of cough in many acute LRTIs 3, though they remain indicated when bacterial pneumonia is suspected based on clinical criteria.