What is the recommended dosage of azithromycin (Zithromax) for a 5-year-old child weighing 65 pounds with suspected atypical pneumonia?

Azithromycin Dosing for a 65-Pound Child with Suspected Atypical Pneumonia

For a 5-year-old child weighing 65 pounds (approximately 29.5 kg) with suspected atypical pneumonia, administer azithromycin 10 mg/kg (300 mg) on day 1, followed by 5 mg/kg (150 mg) once daily on days 2 through 5. 1, 2

Weight-Based Dosing Calculation

• Child's weight: 65 pounds = 29.5 kg 1
• Day 1 dose: 10 mg/kg = 295 mg (round to 300 mg maximum for practical dosing) 1, 2
• Days 2-5 dose: 5 mg/kg = 147.5 mg (round to 150 mg for practical dosing) 1, 2

Practical Administration Using Oral Suspension

Using the 200 mg/5 mL suspension formulation (most appropriate for this weight range): 2

• Day 1: 7.5 mL (1½ teaspoons) = 300 mg 2
• Days 2-5: 3.75 mL (¾ teaspoon) = 150 mg daily 2
• Total course: 22.5 mL suspension delivering 900 mg total over 5 days 2

Clinical Context and Rationale

Azithromycin is the preferred macrolide for atypical pneumonia caused by Mycoplasma pneumoniae, Chlamydophila pneumoniae, or Chlamydia trachomatis in children. 3, 1, 4

• The 5-day regimen (10 mg/kg day 1, then 5 mg/kg days 2-5) is specifically recommended by both the Infectious Diseases Society of America and the Pediatric Infectious Diseases Society for atypical pathogens 3, 1, 4
• This dosing achieves sustained tissue concentrations due to azithromycin's long half-life and extensive tissue distribution 5, 6

Important Clinical Considerations

Expect clinical improvement within 48-72 hours of initiating therapy. 1, 4

• If no improvement occurs within this timeframe, reevaluation is necessary to assess for complications or alternative diagnoses 1, 4
• Children with atypical pneumonia treated with azithromycin demonstrate earlier cessation of cough compared to erythromycin (3.6 vs 5.5 days) 7

Critical caveat: If typical bacterial pneumonia (particularly Streptococcus pneumoniae) cannot be excluded, consider adding high-dose amoxicillin 90 mg/kg/day in 2 divided doses, as azithromycin alone is NOT first-line for typical bacterial pathogens 3, 4

• Beta-lactam antibiotics remain the cornerstone for pneumococcal pneumonia 3, 4
• For hospitalized children where both typical and atypical pathogens are considerations, empiric combination therapy with a beta-lactam plus azithromycin is recommended 3

Administration Guidelines

Azithromycin can be taken with or without food. 2

• Do NOT administer simultaneously with aluminum- or magnesium-containing antacids, as these reduce drug absorption; separate by at least 2 hours 1, 2
• The pediatric oral suspension must be reconstituted with water before administration 1
• Administer 1 hour before or 2 hours after meals for optimal absorption 1

Safety Monitoring

Common adverse effects include gastrointestinal symptoms (abdominal discomfort, diarrhea, nausea, vomiting), which are generally mild to moderate. 1, 5

• Azithromycin has fewer gastrointestinal side effects compared to erythromycin 1, 7
• Monitor for potential QT interval prolongation, particularly if the child is on other medications that affect cardiac conduction 1
• Exercise caution in patients with hepatic impairment, as azithromycin undergoes primarily biliary excretion 1

Alternative Considerations

If the child cannot tolerate azithromycin or has a documented allergy: 1

• Clarithromycin 15 mg/kg/day in 2 divided doses for 10 days 1
• Erythromycin 40 mg/kg/day in 4 divided doses for 10-14 days (though less well tolerated) 1
• Avoid doxycycline in children under 8 years due to risk of permanent tooth discoloration 4

Follow-Up

Complete the full 5-day course even if symptoms improve earlier. 1, 4

• Schedule follow-up within 48-72 hours to assess clinical response 1, 4
• Chest X-ray normalization typically occurs by day 7-14 in children with atypical pneumonia treated with azithromycin 7
• If deterioration occurs or no improvement is seen within 48-72 hours, investigate for complications such as parapneumonic effusion or consider alternative diagnoses 1