Azithromycin Dosing for Bacterial Infections
The typical adult dose of azithromycin is 500 mg on day 1, followed by 250 mg once daily on days 2-5 (the "Z-pack" regimen) for most respiratory tract infections, or a single 1 gram dose for chlamydial urethritis/cervicitis. 1, 2
Adult Dosing by Indication
Respiratory Tract Infections
- Community-acquired pneumonia (outpatient): 500 mg on day 1, then 250 mg daily for days 2-5 (total 5 days) 1, 3
- Severe CAP (hospitalized, non-ICU): 500 mg IV daily for 2-5 days, followed by oral 500 mg daily to complete 7-10 days total 4
- Bronchiectasis with ≥3 exacerbations/year: 500 mg three times weekly for at least 6 months (strongest evidence for long-term prophylaxis) 2
- Alternative: 250 mg daily also has strong supportive evidence 2
Sexually Transmitted Infections
- Non-gonococcal urethritis/cervicitis (Chlamydia): Single 1 gram dose orally 1, 2, 5
- Persistent urethritis after doxycycline failure: 500 mg day 1, then 250 mg daily for 4 days (extended regimen) 1, 2
- Important caveat: Never use azithromycin as monotherapy for gonorrhea due to widespread resistance; combine with ceftriaxone if gonococcal infection suspected 1, 2
Other Infections
- Travelers' diarrhea/dysentery: Either single 1 gram dose OR 500 mg daily for 3 days 1
- Legionnaires' disease (hospitalized): 500 mg IV daily for 2-7 days, then oral to complete 7-10 days total 1
- Legionnaires' disease (outpatient): 500 mg day 1, then 250 mg daily for 4 days 1
- Cat scratch disease: 500 mg day 1, then 250 mg for 4 additional days (patients >45 kg) 2
- Disseminated MAC in AIDS: 250 mg daily with ethambutol 2
- MAC prophylaxis in AIDS (CD4 <50): 1,200 mg once weekly 2
Pediatric Dosing
Standard Regimens (Age ≥6 months)
- Community-acquired pneumonia: 10 mg/kg day 1 (max 500 mg), then 5 mg/kg once daily days 2-5 (max 250 mg/day) 1, 7, 3, 8
- Acute otitis media: Three options per FDA label 3:
- 30 mg/kg as single dose, OR
- 10 mg/kg once daily for 3 days, OR
- 10 mg/kg day 1, then 5 mg/kg days 2-5
- Acute bacterial sinusitis: 10 mg/kg once daily for 3 days 3
- Pharyngitis/tonsillitis (age ≥2 years): 12 mg/kg once daily for 5 days 3, 8
Special Pediatric Populations
- Pertussis (infants <6 months): 10 mg/kg per day for 5 days 2
- Pertussis (≥6 months): 10 mg/kg day 1 (max 500 mg), then 5 mg/kg days 2-5 (max 250 mg) 2
- Chlamydial conjunctivitis (neonates): 20 mg/kg once daily for 3 days 2
Administration Considerations
Timing and Food
- Can be taken with or without food 1, 3
- Avoid concurrent antacids: Aluminum- or magnesium-containing antacids reduce absorption by up to 50%; separate by at least 2 hours 1, 9
Liquid Formulation Pitfalls
- Critical: Verify the mg/mL concentration on the bottle label before calculating dose 1
- Common concentrations are 100 mg/5 mL (20 mg/mL) or 200 mg/5 mL (40 mg/mL) 1
- For 1 gram single dose: 50 mL if using 200 mg/5 mL concentration OR 25 mL if using 100 mg/5 mL concentration 1
Safety Monitoring for Long-Term Therapy
Before initiating long-term azithromycin (e.g., for bronchiectasis):
- Obtain baseline ECG to assess QTc interval 2
- Measure baseline liver function tests 2
- Avoid in patients taking other QT-prolonging medications without careful risk assessment 2
Common Adverse Effects
- Gastrointestinal symptoms (abdominal pain, diarrhea, nausea, vomiting) are most common but generally mild to moderate 1, 2, 8
- Better GI tolerance than erythromycin 8, 9
- Headache and dizziness may occur 1, 2
Pregnancy and Infants
- FDA Pregnancy Category B: Considered safe and effective in pregnancy 2, 7
- Preferred over erythromycin in infants <1 month due to lower risk of infantile hypertrophic pyloric stenosis 1, 2
Resistance and Stewardship Considerations
- Long-term macrolide use increases antimicrobial resistance, though clinical impact remains uncertain 2
- For Mycoplasma genitalium with macrolide resistance, switch to moxifloxacin 400 mg daily for 7-14 days 1
- Patients treated for STIs should abstain from sexual intercourse for 7 days after completing therapy 2