What is the weight-based dosing regimen for Azithromycin (generic name) in pediatric and adult patients with varying degrees of renal function?

Azithromycin Weight-Based Dosing

For pediatric patients, administer azithromycin 10 mg/kg (maximum 500 mg) on day 1, followed by 5 mg/kg (maximum 250 mg) once daily for days 2-5, with no dose adjustment required for renal impairment in either children or adults. 1, 2

Pediatric Dosing by Indication

Community-Acquired Pneumonia and Atypical Respiratory Infections

• Standard 5-day regimen: 10 mg/kg (max 500 mg) on day 1, then 5 mg/kg (max 250 mg) daily for days 2-5 1, 2
• This regimen is specifically indicated for atypical pathogens including Mycoplasma pneumoniae, Chlamydia pneumoniae, and Chlamydia trachomatis 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

Streptococcal Pharyngitis

• Higher dose required: 12 mg/kg once daily for 5 days (maximum 500 mg/day) 1
• This higher dose is necessary because the standard 10 mg/kg regimen results in high recurrence rates 1
• Azithromycin is second-line therapy only; penicillin or amoxicillin remain first-line 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 the preferred macrolide for infants under 1 month due to better safety profile compared to erythromycin 1

MAC Prophylaxis in HIV-Infected Children

• Weekly dosing: 20 mg/kg (maximum 1,200 mg) once weekly 1

Weight-Based Dosing Table for Children

For children requiring single daily dosing (alternative to mg/kg calculation): 1

Weight Range	Daily Dose
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

Adolescent Dosing

Respiratory Tract Infections

• Use the standard pediatric regimen: 10 mg/kg (max 500 mg) day 1, then 5 mg/kg (max 250 mg) days 2-5 1
• Oral doses should never exceed adult maximums regardless of weight 1

Uncomplicated Chlamydial Infections

• Single-dose regimen: 1 gram orally as a single dose 1

Intravenous Dosing for Pediatric Patients

• Standard IV regimen: 10 mg/kg once daily (maximum 500 mg per dose) on days 1-2 1
• Transition to oral therapy as soon as clinically feasible 1
• Infusion guidelines: Administer at 1 mg/mL concentration over 3 hours OR 2 mg/mL concentration over 1 hour 3
• Common pitfall: Avoid prolonged IV therapy beyond 2 days when oral therapy is feasible 1

Renal Function Considerations

Pediatric and Adult Patients with Renal Impairment

• No dose adjustment required for mild to moderate renal impairment (GFR 10-80 mL/min) 2, 4
• For severe renal impairment (GFR <10 mL/min), mean Cmax and AUC increase by 61% and 35% respectively, but no formal dose adjustment is recommended 2
• Azithromycin undergoes primarily biliary excretion (approximately 6% appears unchanged in urine), making renal impairment less clinically significant 2, 4
• Use with caution in patients with hepatic impairment, as biliary excretion is the main route of elimination 3

Administration Guidelines

Oral Formulations

• Timing: Administer 1 hour before or 2 hours after meals 3, 1
• Antacid interaction: Do not administer simultaneously with aluminum- or magnesium-containing antacids; separate by at least 2 hours 3, 1
• Pediatric suspension: Specifically designed to be reconstituted with water before administration; preferred for children who cannot swallow tablets 1

Important Drug Interactions

• Monitor when used with drugs metabolized by cytochrome P450 enzyme system 1
• Monitor for QT interval prolongation when co-administered with other QT-prolonging medications 1

Common Pitfalls to Avoid

1. Underdosing for strep throat: Using the standard 10 mg/kg regimen instead of the required 12 mg/kg for streptococcal pharyngitis leads to high recurrence rates 1

2. Inappropriate first-line use: Prescribing azithromycin for typical bacterial pneumonia when amoxicillin should be first-line 1

3. Exceeding maximum doses: Always cap pediatric doses at adult maximums (500 mg day 1,250 mg days 2-5 for respiratory infections) 1, 2

4. Antacid co-administration: Simultaneous administration with aluminum/magnesium antacids significantly reduces absorption 3, 1

5. Prolonged IV therapy: Continuing IV azithromycin beyond 2 days when oral therapy is feasible 1

Expected Clinical Response

• Children on adequate azithromycin therapy should demonstrate clinical improvement within 48-72 hours 1
• If no improvement or deterioration occurs within this timeframe, further investigation is warranted, including assessment for complications such as parapneumonic effusion 1

Safety Considerations

• Common adverse effects: Gastrointestinal disturbances (abdominal discomfort, diarrhea, nausea, vomiting), dizziness, headache 3, 1
• Rare but serious: Acute interstitial nephritis, allergic reactions/anaphylaxis, pseudomembranous colitis 3
• Azithromycin has fewer gastrointestinal side effects compared to erythromycin 1
• FDA Pregnancy Category B 1