Azithromycin Dosing for Acute Chest Infections
For acute community-acquired pneumonia and lower respiratory tract infections in adults, use azithromycin 500 mg on day 1, followed by 250 mg once daily on days 2-5 (total 5-day course). 1
Standard Acute Treatment Regimen
The FDA-approved dosing for community-acquired pneumonia is:
- Day 1: 500 mg as a single dose
- Days 2-5: 250 mg once daily 1
An alternative 3-day regimen (500 mg daily for 3 consecutive days) is also FDA-approved for acute bacterial exacerbations of COPD and acute bacterial sinusitis, though the 5-day regimen provides higher total drug exposure. 1
Clinical Pharmacology Supporting Short-Course Therapy
Azithromycin's unique pharmacokinetics justify these abbreviated treatment courses:
- Tissue concentrations exceed serum levels by 100-fold and remain elevated for 7-10 days after the last dose 2, 3
- The terminal elimination half-life extends up to 5 days, maintaining therapeutic tissue levels well beyond the dosing period 4, 3
- Concentrations in respiratory tissues (tonsil, lung) continuously exceed MICs for key pathogens (S. pneumoniae, H. influenzae, S. aureus) for up to 10 days following a 5-day course 5
Important Safety Considerations
Before initiating therapy, obtain an ECG to assess QTc interval. Do not use azithromycin if QTc >450 ms (men) or >470 ms (women) due to risk of serious cardiac arrhythmias. 6, 7
Additional precautions:
- Avoid concurrent use with aluminum- or magnesium-containing antacids (reduces absorption by 24%) 7, 8
- Take with or without food, though large meals may reduce absorption by up to 50% 4
- Monitor for gastrointestinal side effects (nausea, diarrhea, abdominal pain), which are dose-related but generally better tolerated than erythromycin 4
When NOT to Use These Regimens
The dosing above applies to acute infections only. Do not confuse with long-term prophylactic regimens for chronic conditions:
- For bronchiectasis with ≥3 exacerbations/year: use azithromycin 500 mg three times weekly OR 250 mg daily for minimum 6 months 6
- For COPD exacerbation prevention: use azithromycin 250 mg three times weekly 6
Pediatric Dosing
For children ≥6 months with community-acquired pneumonia:
- Day 1: 10 mg/kg as single dose
- Days 2-5: 5 mg/kg once daily 1