What is the appropriate dose of Azithromycin (generic name) for a child weighing 125 pounds with a Body Mass Index (BMI) of 22.88?

Azithromycin Dosing for a 125-Pound Child

For a child weighing 125 pounds (56.7 kg) with a BMI of 22.88, prescribe azithromycin 500 mg once daily, as this weight falls into the "46 kg and above" category per British Thoracic Society guidelines. 1

Weight-Based Dosing Algorithm

This child's weight of 125 pounds converts to approximately 56.7 kg, which clearly exceeds the 46 kg threshold for adult-equivalent dosing. 1

The specific dosing tiers are:

• Children 15-25 kg: 200 mg once daily 1, 2
• Children 26-35 kg: 300 mg once daily 1, 2
• Children 36-45 kg: 400 mg once daily 1, 2
• Children 46 kg and above: 500 mg once daily 1, 2

Indication-Specific Considerations

The 500 mg daily dose applies to most common pediatric indications at this weight. 1

For respiratory tract infections (community-acquired pneumonia, acute bacterial sinusitis):

• Standard regimen: 500 mg on day 1, then 250 mg daily for days 2-5 2, 3
• Alternative 3-day regimen: 500 mg once daily for 3 days 3

For streptococcal pharyngitis (second-line only):

• Higher dose required: 12 mg/kg once daily for 5 days (approximately 680 mg for this patient, though maximum adult dose of 500 mg typically applies) 2, 3
• Note: Penicillin or amoxicillin remains first-line; azithromycin has higher recurrence rates 2

For acute otitis media:

• Single-dose option: 30 mg/kg as a single dose (not to exceed 1500 mg) 3
• Standard 5-day regimen: 500 mg day 1, then 250 mg days 2-5 3

Critical Safety Monitoring

Obtain baseline ECG before initiating therapy and repeat at 2 weeks, as azithromycin can prolong QT interval. 1

Key drug interactions to avoid:

• Antacids containing aluminum or magnesium (separate by 2 hours) 1
• QT-prolonging medications (amiodarone, metoclopramide, domperidone, disopyramide, methadone) 1
• Monitor digoxin levels if coadministered 1
• Monitor for colchicine toxicity if used together 1

Monitor intermittently throughout treatment:

• Liver function tests 1
• Renal function 1
• Complete blood count 1
• Audiometry if symptoms develop 1

Common Pitfalls to Avoid

Do not underdose based on age alone. This child's weight clearly qualifies for the maximum pediatric dose of 500 mg daily, equivalent to adult dosing. 1, 2

Do not use azithromycin as first-line for typical bacterial pneumonia caused by S. pneumoniae or H. influenzae—amoxicillin remains preferred for these pathogens. 2 Azithromycin is specifically indicated for atypical pathogens (Mycoplasma, Chlamydia). 2

Do not prescribe azithromycin as first-line for strep throat—penicillin or amoxicillin is preferred, and azithromycin has higher recurrence rates requiring a higher dose (12 mg/kg daily). 2

Ensure compliance with the full course. The convenience of once-daily dosing and short duration (3-5 days) should optimize adherence, but emphasize completion even if symptoms improve. 4, 5

Formulation Selection

At this weight, tablets are more practical than suspension. 3 The 500 mg tablet strength allows for straightforward once-daily administration without the need for measuring liquid formulations. 3

If suspension is required, the 200 mg/5 mL concentration would necessitate 12.5 mL (2.5 teaspoons) for a 500 mg dose. 3