Azithromycin Dosing for Acute Bronchitis
Azithromycin is not recommended for acute bronchitis in otherwise healthy adults, as it provides no clinical benefit over placebo and contributes to antimicrobial resistance. 1
Evidence Against Azithromycin Use in Acute Bronchitis
A randomized, double-blind, controlled trial of 220 adults with acute bronchitis found no difference in health-related quality of life at 7 days between azithromycin (1.5g total over 5 days) and vitamin C placebo (difference 0.03,95% CI -0.20 to 0.26, p=0.8) 1
Return to usual activities by day 7 was identical in both groups: 89% with azithromycin versus 89% with vitamin C (difference 0.5%, p>0.9) 1
The study was stopped early by the data-monitoring committee after 220 patients due to clear lack of efficacy 1
When Azithromycin May Be Appropriate: Acute Exacerbations of Chronic Bronchitis (AECB)
If the patient has underlying chronic bronchitis with acute exacerbation (increased cough, sputum production, dyspnea, and purulent sputum), then azithromycin 500 mg once daily for 3 days is an appropriate regimen. 2, 3, 4
Standard Dosing for AECB
Azithromycin 500 mg orally once daily for 3 days (total dose 1.5 grams) 2, 3, 4
This 3-day regimen achieves clinical cure rates of 85-96% at day 21-24, equivalent to 10-day courses of clarithromycin or amoxicillin/clavulanate 3, 4
Clinical success rates at day 10-12 are 93% with the 3-day azithromycin regimen 3
Microbiological Efficacy in AECB
Bacteriologic cure rates at test of cure for common pathogens: Streptococcus pneumoniae 90.6%, Haemophilus influenzae 71.4-85.7%, Moraxella catarrhalis 91.7-100% 3, 4
Pathogen eradication occurs in 89-100% of microbiologically-assessable patients 2, 5, 4
Critical Distinction: Acute Bronchitis vs. AECB
Acute bronchitis = new-onset cough in a patient WITHOUT underlying chronic lung disease → No antibiotics indicated 1
AECB = worsening symptoms (increased cough, sputum volume/purulence, dyspnea) in a patient WITH chronic bronchitis → Antibiotics may be appropriate 2, 3
Safety Profile
Treatment-related adverse events occur in 20.9-25% of patients, primarily gastrointestinal (diarrhea 4.4-6.4%, nausea 4.4%, abdominal pain 6.3%) 3, 4
Discontinuation due to adverse events is rare (0-3% of patients) 1, 3, 4
Azithromycin has fewer gastrointestinal side effects than amoxicillin/clavulanate (31% vs 51% overall adverse events) 6
Common Pitfalls to Avoid
Do not prescribe azithromycin for uncomplicated acute bronchitis in healthy adults, as this provides no benefit and promotes antimicrobial resistance 1
Do not use the "Z-Pak" 5-day regimen (500mg day 1, then 250mg days 2-5) for bronchitis, as the evidence supports either no antibiotics for acute bronchitis or a 3-day course (500mg daily x 3 days) for AECB 2, 3, 4
Do not confuse acute bronchitis with community-acquired pneumonia, which requires different treatment algorithms and longer durations 7, 8
Verify the patient has chronic underlying lung disease before prescribing antibiotics for bronchitis symptoms 2, 3