What is the recommended dosage of azithromycin (Zithromax) for pneumonia?

Azithromycin Dosage for Pneumonia

For community-acquired pneumonia in adults, azithromycin is dosed at 500 mg on day 1, followed by 250 mg once daily on days 2-5 (total 1.5 g over 5 days), but should NOT be used as monotherapy in hospitalized patients or those with comorbidities—these patients require combination therapy with a beta-lactam antibiotic. 1, 2, 3

Adult Dosing by Clinical Context

Outpatient Adults WITHOUT Comorbidities

• Standard regimen: 500 mg orally on day 1, then 250 mg once daily on days 2-5 1, 3
• Alternative 3-day regimen: 500 mg once daily for 3 days (also totaling 1.5 g) 3
• Critical restriction: Use azithromycin monotherapy ONLY in areas where pneumococcal macrolide resistance is <25% 1, 4
• Azithromycin provides excellent coverage for atypical pathogens (Mycoplasma pneumoniae, Chlamydia pneumoniae, Legionella species) 2

Outpatient Adults WITH Comorbidities

Azithromycin monotherapy is contraindicated in patients with: 1, 4

• Chronic heart, lung, liver, or renal disease
• Diabetes mellitus
• Alcoholism
• Malignancy or asplenia
• Age >65 years
• Recent antibiotic use (within 3 months)
• Immunosuppression

Mandatory combination therapy: 1, 4

• Amoxicillin 1 g three times daily OR amoxicillin-clavulanate 875/125 mg twice daily (or 2000/125 mg twice daily)
• PLUS azithromycin 500 mg on day 1, then 250 mg daily on days 2-5

Hospitalized Adults (All Severity Levels)

Azithromycin monotherapy is absolutely contraindicated in hospitalized patients 4

Required combination therapy: 1, 2

• Beta-lactam (ampicillin-sulbactam, ceftriaxone 1-2 g IV q12h, or cefotaxime 1-2 g IV q8h)
• PLUS azithromycin 500 mg IV or PO daily
• Duration: 7-10 days total 2

For severe pneumonia with Legionella species, azithromycin is an alternative at 1000 mg IV on day 1, then 500 mg IV/PO daily, though fluoroquinolones are preferred 1

Pathogen-Specific Dosing

Mycoplasma pneumoniae

• Alternative regimen (doxycycline preferred): 500 mg PO on day 1, then 250 mg PO daily for 4 days 1
• Duration: 7-14 days for severe cases 1

Chlamydophila pneumoniae

• Preferred regimen: 500 mg PO on day 1, then 250 mg PO daily for 4 days 1
• This is first-line therapy for this pathogen 1

Legionella species

• Alternative regimen: 1000 mg IV on day 1, then 500 mg IV/PO daily 1
• Fluoroquinolones (levofloxacin 750 mg or moxifloxacin 400 mg) are preferred 1

Pediatric Dosing (≥6 months)

Community-Acquired Pneumonia

• Standard 5-day regimen: 10 mg/kg (maximum 500 mg) as single dose on day 1, followed by 5 mg/kg (maximum 250 mg) once daily on days 2-5 1, 3
• Total course: 1.5 g over 5 days 4

Atypical Pneumonia in Children

• Same dosing as CAP: 10 mg/kg (max 500 mg) day 1, then 5 mg/kg (max 250 mg) daily days 2-5 1, 4
• Alternative for children >7 years: Doxycycline 100 mg twice daily 1

Acute Otitis Media (Alternative Indication)

• 3-day regimen: 10 mg/kg once daily for 3 days 3
• 1-day regimen: 30 mg/kg as single dose 3

Critical Safety Considerations

Cardiac Monitoring

• Obtain baseline ECG in patients with cardiac risk factors before initiating therapy 4
• Contraindicate if QTc >450 ms (men) or >470 ms (women) 4
• Azithromycin prolongs QT interval; avoid concurrent use with other QT-prolonging medications 2

Drug Interactions

• Separate from antacids: Aluminum- or magnesium-containing antacids reduce absorption; separate administration times 2
• Monitor when used with cytochrome P450-metabolized drugs 2

Renal Impairment

• No dose adjustment needed for GFR 10-80 mL/min 3
• Exercise caution with GFR <10 mL/min (AUC increases 35%) 3

Common Pitfalls to Avoid

1. Never use azithromycin monotherapy in hospitalized patients—this is associated with treatment failure and increased mortality 4

2. Do not use as monotherapy in patients who received antibiotics in the past 3 months—risk of resistant organisms 4

3. Avoid in areas with macrolide resistance ≥25%—treatment failure rates are unacceptably high 1, 4

4. Do not use monotherapy in elderly patients (>65 years) or those with comorbidities—these patients require combination therapy with beta-lactams 1, 4

5. Ensure clinical improvement within 48-72 hours—if no improvement, investigate for resistant organisms or alternative diagnoses 1, 4

Treatment Duration and Response

• Minimum duration: 5 days for standard regimen 1, 3
• Extended duration: 7-14 days may be needed for atypical pathogens or severe cases 1, 4
• Expected response: Patients should become afebrile within 48 hours and show clinical improvement within 48-72 hours 1, 5
• Radiographic clearance: Typically occurs within 8-9 days 6