Azithromycin Dosing
For adults with community-acquired infections, azithromycin is dosed as 500 mg on day 1 followed by 250 mg daily on days 2-5, or alternatively 500 mg daily for 3 days depending on the indication. 1
Adult Dosing by Indication
Standard Regimens
Community-acquired pneumonia (mild), pharyngitis/tonsillitis, uncomplicated skin infections: 500 mg single dose on Day 1, then 250 mg once daily Days 2-5 1
Acute bacterial exacerbations of COPD: Either 500 mg daily for 3 days OR 500 mg Day 1, then 250 mg daily Days 2-5 1
Acute bacterial sinusitis: 500 mg daily for 3 days 1
Chlamydial infections (non-gonococcal urethritis/cervicitis): 1 gram single dose 2, 1
Gonococcal urethritis/cervicitis: 2 gram single dose (though CDC does not recommend widespread use due to resistance concerns) 2, 3, 1
Chancroid (genital ulcer disease): 1 gram single dose 1
Azithromycin can be taken with or without food. 1
Pediatric Dosing
By Indication and Age/Weight
For chlamydial conjunctivitis:
- Children <45 kg: Erythromycin base or ethylsuccinate 50 mg/kg/day divided into 4 doses for 14 days 2
- Children ≥45 kg but <8 years: Azithromycin 1 gram orally, single dose 2, 3
- Children ≥8 years: Azithromycin 1 gram single dose OR doxycycline 100 mg twice daily for 7 days 2, 3
For acute otitis media, acute bacterial sinusitis, and community-acquired pneumonia:
5-Day Regimen (otitis media and pneumonia): 10 mg/kg Day 1, then 5 mg/kg Days 2-5 1
3-Day Regimen (otitis media and sinusitis): 10 mg/kg daily for 3 days 1
1-Day Regimen (otitis media only): 30 mg/kg as single dose 1
Practical Pediatric Dosing Table
For a child weighing 20 kg using the 5-day regimen:
- Day 1: 5 mL of 200 mg/5 mL suspension (200 mg)
- Days 2-5: 2.5 mL daily (100 mg)
- Total course: 15 mL (600 mg total) 1
Important caveat: The 30 mg/kg single-dose regimen for otitis media has not been studied for safety if the child vomits within 30 minutes and requires re-dosing. 1
Neonates
For chlamydial pneumonia or conjunctivitis: Erythromycin base or ethylsuccinate 50 mg/kg/day divided into 4 doses for 14 days 2, 3
Alternative for neonates: Azithromycin suspension 20 mg/kg/day once daily for 3 days 2
Critical warning: Erythromycin in infants <6 weeks has been associated with infantile hypertrophic pyloric stenosis; monitor closely for symptoms. 2, 3
Renal Impairment
No dosage adjustment is required for mild to moderate renal impairment (GFR 10-80 mL/min). 1, 4
For severe renal impairment (GFR <10 mL/min), the AUC increases by 35% and Cmax by 61% compared to normal function. Exercise caution in severe renal impairment, though no specific dose reduction is mandated by the FDA label. 1, 4 The pharmacokinetic study showed that neither AUC nor distribution volume were significantly affected across the spectrum of renal function, and nonrenal clearance remains intact. 4
Hepatic Impairment
No dosage adjustment is recommended for mild to moderate hepatic impairment (Child-Pugh Class A or B). 1, 5
Pharmacokinetic studies in cirrhotic patients showed that while Cmax was slightly higher in Class B cirrhosis (0.51 mg/L vs 0.29 mg/L in controls) and elimination half-life was modestly prolonged (68.1 hours vs 53.5 hours), the AUC, volume of distribution, total clearance, and renal clearance were similar across groups. 5 The FDA label states that pharmacokinetics have not been established in hepatic impairment and no specific recommendations can be made, but the research evidence supports no adjustment for mild-moderate disease. 1, 5
Macrolide Allergy
If there is a true macrolide allergy, azithromycin cannot be used. For chlamydial infections in children with β-lactam allergies, alternatives include:
- Erythromycin (if macrolide allergy is specifically to azithromycin only)
- For children ≥8 years: Doxycycline 100 mg twice daily for 7 days 2, 3
For gonococcal infections with severe cephalosporin allergy, consult infectious disease specialists as alternative regimens have limited data. 2, 3
Key Clinical Considerations
Gastrointestinal side effects are the most common adverse events, occurring in 4-5% with diarrhea/loose stools, 3% with nausea, and 2-3% with abdominal pain on standard multi-dose regimens. 1 The single 2-gram dose has higher GI side effect rates (18% nausea, 14% diarrhea). 1
Discontinuation rates due to treatment-related side effects are low: 0.7% in adults on 5-day regimens and 0.6% on 3-day regimens. 1
Tissue distribution is extensive with a volume of distribution of 31.1 L/kg, resulting in tissue concentrations far exceeding plasma levels (e.g., lung tissue >100-fold higher than plasma). 1 This extensive distribution explains the prolonged terminal half-life of 68 hours despite low plasma concentrations. 1
Body weight is the primary determinant of azithromycin clearance across all age groups, with apparent clearance values of 0.187 L/h/kg in preterm neonates, 1.28 L/h/kg in children, and 1.66 L/h/kg in adults. 6 In children, age and liver function also influence clearance. 6