Azithromycin Oral Dosing
The standard adult dose of azithromycin is 500 mg on day 1, followed by 250 mg once daily on days 2-5 for most respiratory infections, or a single 1 gram dose for sexually transmitted infections like chlamydia. 1
Adult Dosing Regimens
Respiratory Tract Infections
- Community-acquired pneumonia, pharyngitis/tonsillitis, and uncomplicated skin infections: 500 mg as a single dose on day 1, followed by 250 mg once daily on days 2-5 (total 5-day course) 1
- Acute bacterial exacerbations of COPD: Either 500 mg once daily for 3 days OR the standard 5-day regimen (500 mg day 1, then 250 mg daily for days 2-5) 1
- Acute bacterial sinusitis: 500 mg once daily for 3 days 1
Sexually Transmitted Infections
- Non-gonococcal urethritis and cervicitis (chlamydia): Single 1 gram oral dose 1, 2
- Gonococcal urethritis and cervicitis: Single 2 gram oral dose 1
- Critical caveat: Azithromycin should NOT be used as monotherapy for gonorrhea due to resistance concerns; always combine with ceftriaxone 3
- Genital ulcer disease (chancroid): Single 1 gram oral dose 1
Key Administration Points
- Azithromycin can be taken with or without food 1
- Avoid concurrent antacids: Do not administer simultaneously with aluminum- or magnesium-containing antacids, as they reduce absorption by up to 50%; separate by at least 2 hours 3, 4
- For sexually transmitted infections, patients should abstain from sexual intercourse for 7 days after completing therapy 2
Pediatric Dosing Regimens
Acute Otitis Media (≥6 months)
- 5-day regimen: 10 mg/kg as a single dose on day 1, followed by 5 mg/kg once daily on days 2-5 1
- 3-day regimen: 10 mg/kg once daily for 3 days 1
- 1-day regimen: 30 mg/kg as a single dose 1
Community-Acquired Pneumonia (≥6 months)
- 10 mg/kg as a single dose on day 1, followed by 5 mg/kg once daily on days 2-5 1
Acute Bacterial Sinusitis (≥6 months)
- 10 mg/kg once daily for 3 days 1
Pharyngitis/Tonsillitis (≥2 years)
- 12 mg/kg once daily for 5 days 1
Pertussis
- Infants <6 months: 10 mg/kg per day for 5 days 2
- Infants and children ≥6 months: 10 mg/kg (maximum 500 mg) on day 1, followed by 5 mg/kg per day (maximum 250 mg) on days 2-5 2
Chlamydial Conjunctivitis in Neonates
- 20 mg/kg body weight per day orally once daily for 3 days 5
Special Populations
Pregnancy
- Azithromycin is FDA Pregnancy Category B and is considered safe 2
- Preferred over erythromycin in infants <1 month due to lower risk of infantile hypertrophic pyloric stenosis 2, 5
- For chlamydial infections in pregnancy: Single 1 gram dose is an alternative regimen 5
Renal Impairment
- No dosage adjustment needed for GFR 10-80 mL/min 1
- Exercise caution in severe renal impairment (GFR <10 mL/min), as AUC increases by 35% 1
Hepatic Impairment
- Pharmacokinetics not established; no specific dosage adjustment recommendations available 1
Clinical Pharmacology Pearls
- Prolonged tissue half-life: Azithromycin maintains therapeutic tissue concentrations for approximately 10 days after a single 1 gram dose, with a terminal elimination half-life of up to 5 days 2, 6
- Extensive tissue distribution: Tissue concentrations exceed serum concentrations by up to 100-fold, with high concentrations in tonsils, lungs, prostate, lymph nodes, and liver 6
- Intracellular accumulation: Concentrated within phagocytes, monocytes, and macrophages, enhancing activity against intracellular pathogens 7, 6
Common Adverse Effects
- Gastrointestinal symptoms are most common: abdominal pain (6%), diarrhea (4-5%), nausea (4%), and vomiting 1, 8
- These occur less frequently than with erythromycin 7, 8
- Other reported effects include headache and dizziness 2
Compliance Advantages
- Single-dose regimens (1 gram for STIs) provide the advantage of directly observed therapy and eliminate compliance concerns 2
- Short duration (3-5 days) and once-daily dosing significantly improve adherence compared to alternatives like doxycycline 2
- Dispense medication on-site when possible to maximize adherence 2