In a patient presenting to the emergency department with suspected community‑acquired pneumonia, what investigations and laboratory tests should be obtained, and what is the recommended empiric treatment regimen (including drug choices, dosages, order of administration, and duration)?

Emergency Department and Hospital Management of Suspected Community-Acquired Pneumonia

Immediate Investigations Upon Presentation

All hospitalized patients with suspected pneumonia require a chest radiograph, complete blood count with differential, comprehensive metabolic panel (including electrolytes, glucose, liver and renal function), and oxygen saturation assessment immediately upon arrival. 1

Essential Laboratory Work:

• Complete blood count with differential - assess for leukocytosis (>10,000/μL) or leukopenia (<4,000/μL) 2
• Comprehensive metabolic panel including:
  • Serum sodium, glucose 1
  • Liver function tests (AST, ALT) 1
  • Renal function (BUN, creatinine) 1
  • Electrolytes 1
• C-reactive protein (CRP) when available - levels >100 mg/L strongly suggest bacterial infection 1, 3
• Oxygen saturation by pulse oximetry - mandatory for all patients 1
• Arterial blood gas - obtain in any patient with severe illness, chronic lung disease, or oxygen saturation concerns to assess oxygenation and CO2 retention 1

Radiographic Studies:

• Chest X-ray (posteroanterior and lateral) - required to confirm air space density consistent with pneumonia 1, 2

Microbiological Testing:

• Blood cultures (two sets) - obtain before antibiotics in all hospitalized patients 1
• Sputum Gram stain and culture - collect before antibiotics if patient can produce adequate sample (>25 neutrophils and <10 squamous epithelial cells per low-power field), particularly if drug-resistant pathogens or organisms not covered by usual empiric therapy are suspected 1
• COVID-19 and influenza testing - mandatory when these viruses are circulating in the community, as results affect treatment and infection control 2

Common pitfall: Do not delay antibiotic administration to obtain sputum cultures; collect specimens rapidly but prioritize immediate antibiotic therapy 1

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Empiric Antibiotic Treatment Regimen

Timing of Administration:

Antibiotics must be administered immediately after diagnosis is established, without delay. 1 In patients with septic shock, delay must not exceed 1 hour after diagnosis. 1

Non-Severe Pneumonia (Medical Ward):

First-line therapy for hospitalized patients without ICU needs is intravenous ceftriaxone 1 gram every 24 hours PLUS azithromycin 500 mg daily (or erythromycin 1 gram every 8 hours). 1, 2

Alternative regimens (in order of preference):

• IV cefotaxime 1 gram every 8 hours PLUS macrolide 1
• IV cefuroxime 750-1500 mg every 8 hours PLUS macrolide 1
• IV amoxicillin 1 gram every 6 hours PLUS macrolide (only in areas with low beta-lactamase-producing H. influenzae) 1
• Respiratory fluoroquinolone monotherapy (levofloxacin or moxifloxacin) - acceptable alternative 1

Rationale: Combination beta-lactam/macrolide therapy accounts for atypical pathogen coinfection (present in significant proportion of cases) and has demonstrated superior outcomes compared to monotherapy in hospitalized patients, particularly those with moderate-to-severe disease. 1

Severe Pneumonia (ICU):

For ICU-admitted patients, use IV ceftriaxone 1 gram every 24 hours (or cefotaxime 1 gram every 8 hours) PLUS IV azithromycin 500 mg daily (or erythromycin 1 gram every 6 hours). 1, 2

Alternative for severe cases:

• Second-generation fluoroquinolone (levofloxacin or ciprofloxacin) PLUS macrolide 1
• Consider adding rifampicin 600 mg every 12 hours if Legionella suspected or patient not responding 1

Special Circumstances:

For suspected aspiration or cavitated pneumonia:

• IV amoxicillin-clavulanate 2 grams every 6 hours 1
• Alternative: Second or third-generation cephalosporin PLUS clindamycin 600 mg every 8 hours 1

Penicillin allergy:

• Respiratory fluoroquinolone monotherapy (levofloxacin or moxifloxacin) 1

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Treatment Duration

Minimum treatment duration is 3 days for hospitalized patients responding to therapy. 2

Standard durations by severity:

• Non-severe, uncomplicated pneumonia: 7 days of appropriate antibiotics 4
• Severe microbiologically undefined pneumonia: 10 days 4
• Legionella, staphylococcal, or Gram-negative enteric bacilli pneumonia: 14-21 days 4

Switching from IV to oral therapy: Transition when patient is clinically stable (afebrile for 24 hours, hemodynamically stable, improving respiratory symptoms, able to take oral medications). 1 Use the same antibiotic class when possible. 1

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Supportive Care and Monitoring

Oxygen Therapy:

• Target oxygen saturation >92% and PaO2 >8 kPa 1
• High-concentration oxygen can be safely administered in uncomplicated pneumonia 1
• In COPD patients with ventilatory failure, titrate oxygen carefully with repeated arterial blood gas measurements 1

Fluid Management:

• Assess for volume depletion and administer IV fluids as needed 1, 4

Vital Sign Monitoring:

Monitor and record at least twice daily (more frequently in severe cases): 1, 4

• Temperature
• Respiratory rate
• Heart rate
• Blood pressure
• Mental status
• Oxygen saturation
• Inspired oxygen concentration

Laboratory Reassessment:

• Remeasure CRP and repeat chest X-ray in patients not progressing satisfactorily by day 2-3 1, 4
• Assess clinical stability markers daily: fever resolution, respiratory rate normalization, hemodynamic stability 5

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Failure to Improve

If patient fails to improve within 48-72 hours, do NOT change antibiotics immediately unless marked clinical deterioration or bacteriologic data necessitates change. 1, 5

Reassessment includes:

• Repeat chest radiograph to evaluate for complications (pleural effusion, empyema, abscess) 5, 4
• Repeat CRP and white blood cell count 4
• Consider thoracentesis if moderate or large pleural effusion identified 5
• Bronchoscopy may be indicated for persistent symptoms at 6 weeks or earlier if severe non-response 1, 4

Antibiotic Modification (if needed):

• Non-severe pneumonia on amoxicillin: Add or substitute macrolide 4
• Non-severe on combination therapy: Switch to respiratory fluoroquinolone 4
• Severe pneumonia not responding: Consider adding rifampicin 600 mg every 12 hours 4

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Follow-Up Planning

Arrange clinical review at 6 weeks with repeat chest radiograph for patients with persistent symptoms, physical signs, or high risk for malignancy (smokers, age >50 years). 1, 4 Chest X-ray need not be repeated before hospital discharge in patients with satisfactory clinical recovery. 1