What are the treatment guidelines for community-acquired pneumonia (CAP)?

Community-Acquired Pneumonia Treatment Guidelines

For outpatient CAP without comorbidities, use amoxicillin 1g every 8 hours or doxycycline 100mg twice daily; for patients with comorbidities or recent antibiotic use, use a respiratory fluoroquinolone (levofloxacin 750mg daily, moxifloxacin 400mg daily) or combination therapy with an advanced macrolide plus high-dose amoxicillin. 1

Initial Assessment and Site-of-Care Decision

• Severity assessment determines treatment location using a 3-step process: evaluate preexisting conditions compromising home safety, calculate the Pneumonia Severity Index (PSI) with home care recommended for risk classes I-III, and apply clinical judgment 1, 2
• CURB-65 scoring helps identify patients suitable for outpatient management 2
• For hospitalized patients, administer the first antibiotic dose in the emergency department to minimize time to treatment 2
• Empiric therapy should be initiated regardless of initial procalcitonin level in patients with clinically suspected and radiographically confirmed CAP 2

Outpatient Treatment Regimens

Previously Healthy Patients (No Recent Antibiotics)

• First-line options: Amoxicillin 1g every 8 hours OR doxycycline 100mg twice daily 1
• Alternative: A macrolide (azithromycin 500mg day 1, then 250mg daily; or clarithromycin 500mg twice daily) 1
• The amoxicillin recommendation is based on proven efficacy in inpatient CAP despite lack of atypical coverage, with an excellent safety profile 1
• Doxycycline provides broad-spectrum coverage including common pathogens and atypicals, though clinical trial data are limited 1

Patients with Comorbidities or Recent Antibiotic Use

• Comorbidities include: COPD, diabetes, renal failure, heart failure, or malignancy 1
• Preferred regimens: Respiratory fluoroquinolone alone (levofloxacin 750mg daily, moxifloxacin 400mg daily, or gemifloxacin 320mg daily) 1, 3
• Alternative: Advanced macrolide (azithromycin or clarithromycin) plus high-dose amoxicillin or amoxicillin-clavulanate 1
• Fluoroquinolones are justified despite safety concerns due to their performance in numerous outpatient CAP studies and coverage of resistant organisms 1

Special Situations

• Suspected aspiration: Amoxicillin-clavulanate or clindamycin 1, 2
• Influenza with bacterial superinfection: β-lactam or respiratory fluoroquinolone 1

Inpatient Non-ICU Treatment

Medical Ward Patients

• Standard regimen: Respiratory fluoroquinolone alone OR advanced macrolide plus β-lactam 1, 2
• Specific combinations: Amoxicillin plus macrolide (azithromycin or clarithromycin) for combined oral therapy 2, 4
• Most non-severe inpatients can be treated with oral antibiotics 2
• When oral therapy is contraindicated, use IV ampicillin or benzylpenicillin plus IV erythromycin or clarithromycin 2

Recent Antibiotic Exposure

• Select regimen based on the nature of recent antibiotic therapy: advanced macrolide plus β-lactam OR respiratory fluoroquinolone alone 1

ICU/Severe CAP Treatment

Standard Severe CAP (No Pseudomonas Risk)

• Mandatory combination therapy: β-lactam (ceftriaxone, cefotaxime, or ampicillin-sulbactam) PLUS either advanced macrolide OR respiratory fluoroquinolone 1, 2
• Parenteral antibiotics should be administered immediately after diagnosis 2
• This combination provides coverage for typical bacteria, atypicals, and Legionella 1

β-Lactam Allergy (No Pseudomonas Risk)

• Respiratory fluoroquinolone with or without clindamycin 1

Pseudomonas Risk Factors Present

• Risk factors include: structural lung disease, bronchiectasis, recent hospitalization, or recent broad-spectrum antibiotic use 1
• Regimen 1: Antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) PLUS ciprofloxacin or levofloxacin 750mg 1, 4
• Regimen 2: Antipseudomonal β-lactam PLUS aminoglycoside PLUS respiratory fluoroquinolone or macrolide 1
• Combination therapy with an antipseudomonal β-lactam is mandatory when Pseudomonas is documented or presumed 3

MRSA Risk

• Add vancomycin or linezolid to the regimen when community-acquired MRSA is suspected 4

Duration of Therapy

• Minimum duration: 5 days for clinically stable patients 2, 4, 5
• 3-day treatment: Acceptable for non-severe or moderate CAP stabilized at day 3 5
• 5-day treatment: When clinical stability achieved by day 5 5
• 7-day treatment: For other uncomplicated CAP cases 5
• Extended duration (14-21 days): Required for Legionella, staphylococcal, or gram-negative enteric bacilli infections 2
• Patients must be afebrile for 48-72 hours with no more than one CAP-associated sign of clinical instability before discontinuation 2, 4
• Longer therapy needed if initial treatment was inactive against the identified pathogen or if extrapulmonary complications exist 4

Switching from IV to Oral Therapy

• Switch criteria: Hemodynamic stability, clinical improvement, afebrile status, decreasing white blood cell count, functioning GI tract with adequate oral intake 2, 4
• Improvement in cough and dyspnea should be documented 2
• Most patients can be switched within 72 hours of admission 6

Treatment Failure Management

• Reassess at 48-72 hours if no clinical improvement 2
• Perform careful review of clinical history, examination, prescription chart, and all investigations 2
• Obtain repeat chest radiograph, CRP, white cell count, and additional microbiological testing 2
• Consider alternative diagnoses, resistant organisms, or complications such as empyema or abscess 2

Follow-Up

• Clinical review at 6 weeks with general practitioner or hospital clinic 2, 4
• Repeat chest radiograph indicated for: persistent symptoms, persistent physical signs, or high risk for underlying malignancy (especially smokers over 50 years) 2, 4

Important Caveats

• Multidrug-resistant S. pneumoniae (MDRSP): Defined as resistance to ≥2 of the following: penicillin (MIC ≥2 mcg/mL), 2nd generation cephalosporins, macrolides, tetracyclines, or trimethoprim-sulfamethoxazole 3
• Levofloxacin demonstrates 95% clinical and bacteriologic success against MDRSP 3
• Fluoroquinolone resistance: Some Pseudomonas isolates develop resistance rapidly during treatment; periodic culture and susceptibility testing recommended 3
• Antibiotic stewardship: Rising multidrug resistance rates, particularly in hospital-acquired pathogens causing CAP, necessitate careful antibiotic selection and duration optimization 7
• Azithromycin-containing regimens show lower rates of treatment failure in some studies 7