What is the recommended dosing of azithromycin (macrolide antibiotic) for a 13-year-old?

Azithromycin Dosing for a 13-Year-Old

For a 13-year-old, azithromycin dosing depends on the indication: for respiratory tract infections like community-acquired pneumonia or atypical pneumonia, use 10 mg/kg (maximum 500 mg) on day 1, then 5 mg/kg (maximum 250 mg) once daily for days 2-5; for uncomplicated chlamydial infection, use a single 1 gram oral dose. 1, 2

Standard Respiratory Tract Infection Dosing

The 5-day regimen is the preferred approach for most respiratory indications in adolescents:

• Day 1: 10 mg/kg orally (maximum 500 mg) 1, 2
• Days 2-5: 5 mg/kg orally once daily (maximum 250 mg) 1, 2

This regimen applies to community-acquired pneumonia, atypical pneumonia caused by Mycoplasma pneumoniae or Chlamydia pneumoniae, and acute bacterial sinusitis. 1, 3

Weight-Based Dosing Considerations

For a typical 13-year-old weighing 46 kg or more, the practical dosing translates to:

• Day 1: 500 mg orally 1
• Days 2-5: 250 mg orally once daily 1

If the adolescent weighs 36-45 kg, use 400 mg on day 1, then 200 mg daily for days 2-5. 1

Indication-Specific Dosing

Streptococcal Pharyngitis (Second-Line Only)

Azithromycin is NOT first-line for strep throat—penicillin or amoxicillin remain preferred. 1 If azithromycin must be used due to penicillin allergy:

• 12 mg/kg once daily for 5 days (maximum 500 mg/day) 1, 2
• The higher dose is necessary because standard dosing has high recurrence rates for streptococcal pharyngitis 1

Chlamydial Infections

For uncomplicated urethritis or cervicitis caused by Chlamydia trachomatis:

• Single 1 gram oral dose 4, 1

This is the CDC-recommended treatment for adolescents with genital chlamydial infections. 1

Important Clinical Caveats

When Azithromycin is NOT Appropriate

Azithromycin is specifically indicated for atypical pathogens, NOT typical bacterial pneumonia. 3 For typical bacterial pneumonia caused by Streptococcus pneumoniae or Haemophilus influenzae, amoxicillin remains the first-line agent at 90 mg/kg/day in 2 divided doses (maximum 4 g/day). 3

Hospitalized Patients Requiring IV Therapy

If the adolescent requires hospitalization and parenteral therapy for atypical pneumonia:

• 10 mg/kg IV once daily (maximum 500 mg) on days 1 and 2 1, 3
• Transition to oral therapy as soon as clinically feasible 1
• Avoid prolonged IV therapy beyond 2 days when oral therapy is tolerated 1

Maximum Dose Limits

Oral doses should 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

Administration and Drug Interactions

• Azithromycin can be taken with or without food, though administration with meals may improve gastrointestinal tolerability 2, 5
• Avoid concurrent administration with aluminum- or magnesium-containing antacids, as they reduce absorption 1
• Monitor for QT interval prolongation when used with other medications that affect cardiac conduction 1

Common Adverse Effects

The most frequent side effects are gastrointestinal: abdominal discomfort, diarrhea, nausea, vomiting, headache, and dizziness. 1 These are typically mild to moderate and rarely necessitate treatment discontinuation. 6 Azithromycin has fewer gastrointestinal side effects compared to erythromycin. 1