What is the recommended dose of Azithromycin (macrolide antibiotic) for pediatric patients, considering age, weight, and medical history, including those with impaired renal (kidney) or hepatic (liver) function?

Azithromycin Pediatric Dosing

For most pediatric infections, administer azithromycin 10 mg/kg (maximum 500 mg) on day 1, followed by 5 mg/kg (maximum 250 mg) daily for days 2-5. 1

Standard Dosing Regimens by Indication

Community-Acquired Pneumonia and Atypical Pneumonia

• Use the 5-day regimen: 10 mg/kg (max 500 mg) on day 1, then 5 mg/kg (max 250 mg) daily for days 2-5 for pneumonia caused by Mycoplasma pneumoniae, Chlamydia pneumoniae, or Chlamydia trachomatis 1
• This regimen is recommended by both the American Academy of Pediatrics and the Infectious Diseases Society of America for children ≥6 months 1
• Important caveat: Azithromycin is NOT first-line for typical bacterial pneumonia caused by S. pneumoniae or H. influenzae—amoxicillin remains the preferred agent for these pathogens 1

Pertussis Treatment and Prophylaxis

• Infants <6 months: 10 mg/kg once daily for 5 days 1
• Children ≥6 months: 10 mg/kg (max 500 mg) on day 1, then 5 mg/kg (max 250 mg) daily for days 2-5 1
• Azithromycin is preferred over erythromycin in young infants due to better safety profile and lower risk of gastrointestinal side effects 1

Streptococcal Pharyngitis (Strep Throat)

• Critical point: Azithromycin is SECOND-LINE therapy only; penicillin or amoxicillin remain first-line 1
• If azithromycin must be used: 12 mg/kg once daily for 5 days (maximum 500 mg/day) 1
• The higher dose (12 mg/kg vs. standard 10 mg/kg) is necessary because standard dosing results in high recurrence rates 1, 2
• Studies show the 10 mg/kg regimen has a 40.5% bacteriologic relapse rate at 1 month, compared to only 13-15% with higher dosing or penicillin 2

Chlamydial Infections in Adolescents

• Uncomplicated urethritis or cervicitis: Single 1 gram oral dose 1

MAC Prophylaxis in HIV-Infected Children

• 20 mg/kg body weight (maximum 1,200 mg) by mouth weekly 1

Weight-Based Dosing Alternative

For children who cannot be dosed by mg/kg calculation, use these weight-based doses for once-daily administration 1:

• 15-25 kg: 200 mg once daily
• 26-35 kg: 300 mg once daily
• 36-45 kg: 400 mg once daily
• ≥46 kg: 500 mg once daily

Intravenous Dosing

When parenteral therapy is required for atypical pneumonia, give 10 mg/kg IV once daily (max 500 mg) on days 1-2, then transition to oral therapy as soon as clinically feasible 1

Common pitfall to avoid: Do not continue IV therapy beyond 2 days when oral therapy is tolerated 1. Remember that IV azithromycin is specifically for atypical pathogens—typical bacterial pneumonia requires beta-lactam antibiotics as first-line 1

Special Populations

Infants <1 Month

• Azithromycin is the preferred macrolide for pertussis treatment: 10 mg/kg once daily for 5 days 1
• Monitor for infantile hypertrophic pyloric stenosis (IHPS), though azithromycin has not been strongly associated with this condition 1
• The benefits of treating severe pertussis outweigh potential risks in this age group 1

Renal and Hepatic Impairment

• No specific dose adjustments are provided in the guideline evidence for pediatric patients with renal or hepatic impairment
• Use clinical judgment and monitor closely, as azithromycin undergoes hepatic metabolism and has minimal renal excretion (approximately 9% urinary excretion) 3

Alternative Macrolides for Allergic Patients

If the patient is allergic to azithromycin 1, 4:

• Clarithromycin: 15 mg/kg/day divided into 2 doses (better tolerated, preferred)
• Erythromycin: 40 mg/kg/day divided into 4 doses
• Doxycycline: Only for children >7 years old (avoid in younger children due to dental staining)

Important Drug Interactions and Administration Considerations

• Do not administer with aluminum- or magnesium-containing antacids, as they significantly reduce absorption 1
• Space antacids at least 2 hours before or after azithromycin
• Monitor for QT interval prolongation when used with other QT-prolonging medications 1
• Monitor when used with drugs metabolized by cytochrome P450 enzyme system 1

Safety Profile

• Azithromycin has fewer gastrointestinal side effects compared to erythromycin 1
• Common adverse effects include abdominal discomfort, diarrhea, nausea, vomiting, headache, and dizziness 1
• Treatment-related adverse events occur in approximately 9% of patients and are typically mild to moderate 5
• Higher doses (20 mg/kg/day) are associated with more adverse effects (23%) compared to standard doses (18%), but still generally well-tolerated 2
• FDA Pregnancy Category B 1

Maximum Dosing Rule

Never exceed adult doses regardless of weight: maximum 500 mg on day 1 and 250 mg daily for the standard 5-day respiratory regimen 1