Azithromycin Dosing and Frequency
Azithromycin dosing varies significantly by indication, but the most common adult regimen is 500 mg on day 1 followed by 250 mg daily for days 2-5, while pediatric dosing is typically 10 mg/kg on day 1 followed by 5 mg/kg daily for days 2-5.
Adult Dosing Regimens
Respiratory Tract Infections
- Community-acquired pneumonia (atypical pathogens): 10 mg/kg IV on days 1-2, then transition to oral therapy; or oral azithromycin 10 mg/kg on day 1 followed by 5 mg/kg daily on days 2-5 1
- Legionnaires' disease (hospitalized): 500 mg IV daily for 2-7 days, then oral to complete 7-10 days total 2, 3
- Legionnaires' disease (outpatient): 500 mg on day 1, followed by 250 mg daily for 4 days 2, 3
- Bronchiectasis prophylaxis: 500 mg three times weekly or 250 mg daily 1
Skin and Soft Tissue Infections
- Cat scratch disease (>45 kg): 500 mg on day 1 followed by 250 mg for 4 additional days 1, 4
- Acute skin infections: 500 mg once daily for 3 days 5
Sexually Transmitted Infections
- Non-gonococcal urethritis/cervicitis (Chlamydia): Single 1 gram dose 2, 4
- Mycoplasma genitalium: 500 mg on day 1, then 250 mg daily for 4 additional days 2
- Note: Azithromycin should NOT be used as monotherapy for gonococcal infections due to resistance; combine with ceftriaxone 2
Other Infections
- Travelers' diarrhea/dysentery: Single 1 gram dose or 500 mg daily for 3 days 2
- Babesiosis (with atovaquone): 500-1000 mg on day 1, then 250 mg once daily thereafter 4
- Disseminated MAC in AIDS: 250 mg daily with ethambutol 4
- MAC prophylaxis in AIDS (CD4 <50): 1200 mg once weekly 4
Pediatric Dosing Regimens
Standard Respiratory Infections
- Community-acquired pneumonia: 10 mg/kg on day 1 (maximum 500 mg), followed by 5 mg/kg once daily on days 2-5 (maximum 250 mg/day) 1, 6
- Acute otitis media: Three options available 6:
- 5-day regimen: 10 mg/kg on day 1, then 5 mg/kg daily for days 2-5
- 3-day regimen: 10 mg/kg once daily for 3 days
- 1-day regimen: 30 mg/kg as a single dose
- Acute bacterial sinusitis: 10 mg/kg once daily for 3 days 6
Pharyngitis/Tonsillitis
- Streptococcal pharyngitis: 12 mg/kg once daily for 5 days (age ≥2 years) 6
- This higher dose is necessary due to higher recurrence rates with standard dosing compared to penicillin 7
Other Pediatric Indications
- Cat scratch disease (<45 kg): 10 mg/kg on day 1, then 5 mg/kg for 4 more days 1, 4
- Pertussis (<6 months): 10 mg/kg per day for 5 days 4
- Pertussis (≥6 months): 10 mg/kg (max 500 mg) on day 1, then 5 mg/kg (max 250 mg) daily for days 2-5 4
- Chlamydial conjunctivitis (neonates): 20 mg/kg once daily for 3 days 4
Administration Considerations
Timing and Food
- Can be taken with or without food 6
- Avoid concurrent antacids: Aluminum- or magnesium-containing antacids reduce absorption by up to 50%; separate by at least 2 hours 2, 4
- Large meals may reduce absorption by up to 50% 8
Liquid Formulation Calculations
- Verify concentration on bottle label before calculating dose—formulations vary (100 mg/5 mL vs 200 mg/5 mL) 2
- For 200 mg/5 mL concentration: 12.5 mL on day 1 and 6.25 mL on days 2-5 for standard dosing 2
- For 100 mg/5 mL concentration: 25 mL on day 1 and 12.5 mL on days 2-5 for standard dosing 2
Special Populations
- Pregnancy: FDA Category B; considered safe and preferred over erythromycin 4
- Infants <1 month: Preferred over erythromycin due to lower risk of infantile hypertrophic pyloric stenosis 4
- Immunocompromised (babesiosis): Higher doses of 600-1000 mg daily may be used 2
Key Clinical Pearls
Advantages
- Once-daily dosing significantly improves adherence compared to alternatives like doxycycline 4
- Short treatment courses (3-5 days) due to prolonged tissue half-life 9, 8
- Single-dose regimens allow for directly observed therapy, particularly valuable for STIs 4
- Better GI tolerance than erythromycin 7, 9
Common Pitfalls
- Low serum concentrations: Tissue concentrations are therapeutic, but serum levels are low; breakthrough bacteremia may occur in severely ill patients 9
- H. influenzae in chronic bronchitis: Some patients may be refractory to azithromycin therapy; monitor closely 9
- Macrolide resistance: Erythromycin-resistant organisms are also resistant to azithromycin 9
- Streptococcal pharyngitis: Higher recurrence rates than penicillin; requires 12 mg/kg/day dosing in children 7
- Re-dosing after vomiting: Safety of re-dosing the 30 mg/kg single-dose regimen in children who vomit within 30 minutes has not been established 6
Adverse Effects
- Most common: Gastrointestinal symptoms (nausea, diarrhea, abdominal pain, vomiting), headache, dizziness 4, 8
- Generally mild to moderate in severity 4, 7
- Better tolerated than amoxicillin/clavulanic acid in children 7