What is the recommended dose of azithromycin (Zithromax) for a 3-year-old child weighing 27 pounds?

Azithromycin Dosing for a 3-Year-Old Weighing 27 Pounds

For a 3-year-old child weighing 27 pounds (12.3 kg), the recommended azithromycin dose is 10 mg/kg (approximately 125 mg) on day 1, followed by 5 mg/kg (approximately 62.5 mg) once daily on days 2 through 5 for most respiratory tract infections. 1, 2, 3

Standard Dosing Regimen

The FDA-approved dosing for pediatric patients is based on the specific indication 3:

For Community-Acquired Pneumonia (Atypical Pathogens)

• Day 1: 10 mg/kg as a single dose (maximum 500 mg) = approximately 125 mg for this child 1, 2, 3
• Days 2-5: 5 mg/kg once daily (maximum 250 mg) = approximately 62.5 mg for this child 1, 2, 3
• This 5-day regimen is specifically indicated for atypical pneumonia caused by Mycoplasma pneumoniae, Chlamydia pneumoniae, or Chlamydia trachomatis 1, 2

For Acute Otitis Media or Acute Bacterial Sinusitis

• Alternative 3-day regimen: 10 mg/kg once daily for 3 days = approximately 125 mg daily 3
• Alternative 1-day regimen (otitis media only): 30 mg/kg as a single dose = approximately 375 mg 3

For Pharyngitis/Tonsillitis (Second-Line Only)

• Higher dose required: 12 mg/kg once daily for 5 days = approximately 150 mg daily 4, 1, 3
• This higher dose is necessary because standard dosing results in high recurrence rates for streptococcal pharyngitis 1

Practical Administration Using Oral Suspension

Using the 200 mg/5 mL suspension strength 3:

For the standard 5-day regimen (10 mg/kg day 1, then 5 mg/kg days 2-5):

• Day 1: 3.75 mL (approximately 150 mg) 3
• Days 2-5: 1.875 mL (approximately 75 mg) 3
• Total volume: 11.25 mL over 5 days 3

For pharyngitis/tonsillitis (12 mg/kg daily for 5 days):

• Days 1-5: 3.75 mL daily (approximately 150 mg) 3

Critical Clinical Considerations

When Azithromycin Is Appropriate

• First-line for atypical pneumonia caused by Mycoplasma, Chlamydia, or Legionella 1, 2
• Second-line for streptococcal pharyngitis when penicillin or amoxicillin cannot be used 4, 1
• Alternative for acute otitis media when beta-lactams are contraindicated 3

When Azithromycin Is NOT Appropriate

• Not first-line for typical bacterial pneumonia caused by Streptococcus pneumoniae or Haemophilus influenzae—amoxicillin remains the preferred agent 1, 2, 5
• Not first-line for streptococcal pharyngitis—penicillin or amoxicillin should be used first 4, 1

Common Pitfalls to Avoid

Underdosing

• Always calculate the dose based on actual body weight in kilograms (27 lbs = 12.3 kg) 1, 2
• For pharyngitis/tonsillitis, the standard 10 mg/kg dose is insufficient; use 12 mg/kg to prevent recurrence 1, 3

Drug Interactions

• Do not administer simultaneously with aluminum- or magnesium-containing antacids, as they reduce absorption by up to 50% 1, 2, 6
• Separate administration by at least 2 hours 2

Inappropriate Indication Selection

• Azithromycin should not be used as empiric first-line therapy for presumed bacterial pneumonia in this age group 1, 2, 5
• Beta-lactam antibiotics (amoxicillin at 90 mg/kg/day) remain first-line for typical bacterial pneumonia 5

Administration and Tolerability

• Azithromycin can be taken with or without food 3
• Gastrointestinal side effects (nausea, diarrhea, abdominal pain) are common but generally mild to moderate 1, 7
• Azithromycin has fewer gastrointestinal side effects than erythromycin, improving compliance 1, 7, 8
• Once-daily dosing after day 1 improves compliance compared to multiple daily dosing regimens 7, 8

Safety Monitoring

• Monitor for QT prolongation if used with other QT-prolonging medications 2
• If the child vomits within 30 minutes of the first dose, re-dosing at the same total dose is reasonable, though safety data are limited 3
• Reassess within 48-72 hours if symptoms do not improve 5