1. Key Definitions

1.1 Pneumonia

• Definition: An infectious process involving the lung parenchyma (alveoli, interstitium), leading to consolidation or infiltrates on imaging.
• Common Pathogens:
  • Typical: Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus.
  • Atypical: Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella spp.
  • Viral: Influenza, SARS-CoV-2 (COVID-19), RSV, etc.

1.2 Pneumonitis

• Definition: A non-infectious inflammation of the lung tissue, often from inhaled chemical irritants, radiation, drugs, or hypersensitivity (allergic) reactions.
• Causes:
  • Chemical/Radiation: Radiation therapy to the chest, inhalation of toxic gases.
  • Drug-induced: Methotrexate, amiodarone, nitrofurantoin, certain chemotherapy agents.
  • Hypersensitivity Pneumonitis: Exposure to molds, bird proteins (“bird fancier’s lung”), occupational allergens.

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2. Clinical Presentation and Lab Findings

2.1 Pneumonia

1. Symptoms:
   • Productive cough (purulent sputum)
   • Fever, chills
   • Dyspnea, tachypnea
   • Pleuritic chest pain
2. Physical Exam:
   • Dullness to percussion
   • Increased tactile fremitus
   • Bronchial (tubular) breath sounds over consolidated area
   • Inspiratory crackles (rales)
3. Labs & Imaging:
   • Elevated WBC (leukocytosis with left shift)
   • Elevated inflammatory markers (CRP, ESR)
   • Chest X-ray: Lobar consolidation (typical) or patchy infiltrates (atypical)

2.2 Pneumonitis

1. Symptoms:
   • Dry cough
   • Dyspnea (progressive)
   • Fatigue
   • Fever (less common or low-grade)
2. Physical Exam:
   • Fine crackles
   • May have normal percussion/fremitus if the process is more interstitial
3. Labs & Imaging:
   • Mild or no leukocytosis (unless secondary infection)
   • Chest X-ray/High-Resolution CT (HRCT): Ground-glass or interstitial patterns
   • Possibly elevated inflammatory markers, but not as pronounced as bacterial infection

3. Risk of Sepsis

• Pneumonia: High risk for sepsis due to the infectious nature; pathogens can invade the bloodstream leading to systemic inflammatory response.
• Pneumonitis: Generally low risk of sepsis unless there is superimposed infection (e.g., aspiration leading to bacterial pneumonia).

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4. Management of Pneumonia

4.1 Determining Outpatient vs. Inpatient

• Severity Scores:
  • CURB-65 (Confusion, Urea > 7 mmol/L, Respiratory rate ≥ 30/min, low Blood pressure, age ≥ 65).
  • Pneumonia Severity Index (PSI).
• Comorbidities: COPD, CHF, CKD, diabetes, immunosuppression → higher risk → often require hospital admission.
• Clinical Judgment: Vital signs, mental status, ability to comply with therapy, social circumstances.

4.2 Outpatient (OPD) Management of Community-Acquired Pneumonia (CAP)

> For otherwise healthy adults, with no recent antibiotic use or comorbidities:

1. Azithromycin (Macrolide)
   • Dose: 500 mg PO on day 1, followed by 250 mg PO once daily on days 2–5 (typical “Z-Pak” regimen)
   • Alternative daily regimen: 500 mg PO once daily for 3 days
2. Doxycycline
   • Dose: 100 mg PO twice daily for 5–7 days

> If comorbidities or recent antibiotic use (risk of drug-resistant S. pneumoniae):

1. Beta-lactam + Macrolide
   • Example: High-dose amoxicillin (1 g PO TID) or amoxicillin-clavulanate (2 g PO BID) PLUS azithromycin 500 mg PO day 1, then 250 mg PO daily
   • Duration: ~5–7 days (tailored to clinical response)
   OR
2. Respiratory Fluoroquinolone (Monotherapy)
   • Levofloxacin 750 mg PO once daily or
   • Moxifloxacin 400 mg PO once daily
   • Duration: ~5 days (with levofloxacin 750 mg daily) to 7 days (with standard dosing)

4.3 Inpatient (IPD) Management of CAP

Empiric Regimens typically cover both typical and atypical pathogens:

1. IV Beta-lactam + Macrolide
   • Ceftriaxone 1–2 g IV once daily (commonly 2 g IV once daily in many hospitals for severe pneumonia)
   • Azithromycin 500 mg IV once daily
   • Switch to oral equivalents once the patient is stable and improving (e.g., ceftriaxone → amoxicillin-clavulanate, IV azithromycin → oral azithromycin).
2. IV Respiratory Fluoroquinolone (Monotherapy)
   • Levofloxacin 750 mg IV once daily OR
   • Moxifloxacin 400 mg IV once daily
   • Typically used if there is a contraindication to beta-lactams or macrolides, or patient has penicillin allergy, etc.
3. Duration: Usually 5–7 days, ensuring the patient is afebrile for at least 48 hours and clinically stable. Severe cases, complications, or Pseudomonas coverage might prolong the course.

4.4 Additional Supportive Care for Pneumonia

• Oxygen supplementation for hypoxia (target SpO₂ ≥ 92–94%).
• Fluids for hydration and hemodynamic support if needed.
• Antipyretics (e.g., acetaminophen) for fever.
• Monitor for sepsis and follow sepsis protocol if signs of shock or organ dysfunction appear.

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5. Management of Pneumonitis

5.1 Non-Infectious Pneumonitis

1. Identify and Remove the Inciting Cause:
   • Discontinue offending drug (e.g., methotrexate, nitrofurantoin).
   • Limit exposure to allergens (e.g., molds, bird proteins).
   • Minimize/complete radiation therapy if radiation-induced.
2. Corticosteroids:
   • Indicated if there is significant respiratory compromise or persistent inflammation.
   • Typical regimen for moderate-severe cases: Prednisone 0.5–1 mg/kg/day for 1–2 weeks, then taper over several weeks to months depending on clinical/radiological response.
3. Supportive Therapy:
   • Oxygen if hypoxic.
   • Adequate hydration.
   • Pulmonary rehabilitation if chronic.

5.2 Aspiration Pneumonitis vs. Pneumonia

• Aspiration Pneumonitis: Primarily chemical lung injury from acidic gastric contents. Antibiotics may not be necessary initially if pure chemical insult and no clear bacterial infection.
• Aspiration Pneumonia: Bacterial infection (often anaerobes) superimposed after aspiration event. Requires antibiotic coverage for anaerobes:
  • e.g., Ampicillin-sulbactam 1.5–3 g IV q6h or
  • Clindamycin 600 mg IV q8h, or
  • Piperacillin-tazobactam 3.375 g IV q6h (in more severe hospital settings).

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6. Monitoring & Prevention of Sepsis

• Watch for Signs of Sepsis: Tachycardia, hypotension, altered mental status, elevated lactate.
• Sepsis Protocol:
  • Early goal-directed therapy: IV fluids (initial bolus ~30 mL/kg for hypotension), vasopressors if persistent hypotension, broad-spectrum antibiotics if bacterial infection is suspected.
  • Frequent reassessments, serum lactate monitoring, source control.

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7. Practical Pearls for Medical Students

1. Assess Severity: Use CURB-65 or PSI to guide outpatient vs. inpatient decision.
2. Choose Empiric Antibiotics Wisely: Balance coverage of typical and atypical organisms in pneumonia; adapt to local resistance patterns.
3. Dose Appropriately:
   • Ceftriaxone 1–2 g IV once daily
   • Azithromycin 500 mg IV or PO once daily (or a loading dose of 500 mg then 250 mg daily if outpatient)
   • Levofloxacin 750 mg IV/PO once daily (or 500 mg once daily for longer duration)
4. De-escalate Therapy: Once cultures or PCR identify the pathogen, narrow antibiotic coverage to reduce resistance and toxicity.
5. Steroids:
   • Generally not recommended for routine bacterial pneumonia, unless there is another indication (e.g., refractory septic shock, certain viral pneumonias, or COPD exacerbation overlap).
   • First-line in non-infectious pneumonitis with significant inflammation.
6. Duration of Treatment: Typically 5–7 days for uncomplicated pneumonia, but can be extended if complications arise (empyema, lung abscess, etc.).
7. Follow-Up: Reassess clinically and radiologically (e.g., repeat chest X-ray in 4–6 weeks if needed for high-risk patients).

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Summary

• Pneumonia: Infectious, higher risk of sepsis. Common inpatient regimen is ceftriaxone 2 g IV once daily + azithromycin 500 mg IV once daily or a respiratory fluoroquinolone alone. Outpatient regimens vary with comorbidities and resistance risk (e.g., macrolide alone or beta-lactam + macrolide or fluoroquinolone monotherapy).
• Pneumonitis: Non-infectious inflammatory lung disease; managed by removing the offending agent and possibly using steroids (e.g., prednisone). Sepsis risk is low unless a secondary bacterial infection ensues.