What is the appropriate dose of azithromycin for a 160-pound child?

Azithromycin Dosing for a 160-Pound Child

For a 160-pound (approximately 73 kg) child, prescribe azithromycin 500 mg on day 1, followed by 250 mg once daily on days 2-5 for most indications. 1, 2

Weight-Based Dosing Threshold

A 160-pound child weighs approximately 73 kg, which places them in the "46 kg and above" category where adult dosing applies. 1

• Children ≥46 kg receive the standard adult dose of 500 mg once daily according to weight-based pediatric guidelines 1
• The FDA label confirms this approach, stating that pediatric patients above 50 kg (110 lbs) receive 500 mg on day 1, followed by 250 mg daily for days 2-5 for most respiratory infections 2
• At 160 pounds, this child has clearly exceeded the weight threshold where pediatric weight-based calculations (mg/kg) transition to fixed adult dosing 1, 2

Standard 5-Day Regimen

The recommended regimen is:

• Day 1: 500 mg as a single dose 1, 2
• Days 2-5: 250 mg once daily 1, 2

This 5-day course is appropriate for:

• Community-acquired pneumonia 1, 3, 2
• Pharyngitis/tonsillitis (as second-line therapy) 2
• Skin and soft tissue infections 2
• Acute bacterial sinusitis 2

Alternative Dosing for Specific Indications

For pharyngitis/tonsillitis specifically, consider the higher dose regimen:

• 12 mg/kg once daily for 5 days (approximately 876 mg daily for a 73 kg patient, though practically this would be 500 mg daily) provides better eradication rates for Group A Streptococcus 4
• However, the FDA label lists pharyngitis as second-line therapy with the standard 500/250 mg regimen 2

For acute bacterial exacerbations of COPD or sinusitis, a 3-day course is an option:

• 500 mg once daily for 3 days 2

Important Clinical Considerations

Administration:

• Azithromycin can be taken with or without food 2
• Avoid concurrent administration with aluminum- or magnesium-containing antacids, as they reduce absorption by up to 50% 3, 5

Common Pitfalls to Avoid:

• Do not underdose by using 250 mg on day 1—the loading dose of 500 mg is critical for achieving adequate tissue concentrations 1, 2
• Do not prescribe weight-based mg/kg dosing for children this size; they receive adult fixed dosing 1, 2
• Monitor for QT prolongation if the patient is on other QT-prolonging medications 1, 3

Tolerability:

• Gastrointestinal adverse effects (nausea, diarrhea, abdominal pain) occur in approximately 9% of patients but are generally mild to moderate 6
• Azithromycin has better gastrointestinal tolerance than erythromycin 3, 5