Azithromycin Dosing for a 20-Pound Baby
For a 20-pound (approximately 9 kg) baby aged 6 months or older, administer azithromycin 90 mg (4.5 mL of 200 mg/5 mL suspension) on day 1, followed by 45 mg (2.25 mL) once daily on days 2 through 5. 1
Weight-Based Calculation
- A 20-pound baby weighs approximately 9 kg 1
- The standard FDA-approved pediatric dosing for most indications (community-acquired pneumonia, otitis media, sinusitis) in children ≥6 months is 10 mg/kg on day 1, then 5 mg/kg daily on days 2-5 1
- This translates to 90 mg on day 1 and 45 mg on days 2-5 for this weight 1
Indication-Specific Considerations
For Pertussis in Infants <6 Months
- If this baby is under 6 months old and being treated for pertussis, the dosing differs: give 10 mg/kg once daily for 5 consecutive days (90 mg daily for all 5 days) 2, 3
- The CDC recommends azithromycin as the preferred macrolide for pertussis treatment and prophylaxis in infants under 1 month, as it has not been associated with infantile hypertrophic pyloric stenosis (IHPS) unlike erythromycin 2, 3
- Monitor infants <1 month receiving any macrolide for IHPS and other serious adverse events 2, 3
For Pharyngitis/Tonsillitis
- If treating streptococcal pharyngitis/tonsillitis in a child ≥2 years, use 12 mg/kg once daily for 5 days (approximately 108 mg daily for 5 days) 1, 4
- This higher dose (total 60 mg/kg over 5 days) provides better GABHS eradication rates than lower doses 4
For Acute Otitis Media Alternative Regimens
- A single 30 mg/kg dose (270 mg) can be used for acute otitis media, though the standard 5-day regimen is more commonly prescribed 1
- A 3-day regimen of 10 mg/kg daily (90 mg daily for 3 days) is also FDA-approved for otitis media 1
Practical Administration
- Use the 200 mg/5 mL suspension concentration for easier dosing at this weight 1
- Azithromycin can be taken with or without food 1
- Do not administer simultaneously with aluminum- or magnesium-containing antacids, as they reduce absorption 2, 3, 5
Common Pitfalls to Avoid
- Do not underdose: Ensure the full 10 mg/kg is given on day 1, as subtherapeutic dosing may lead to treatment failure 3
- Age matters for pertussis: Infants <6 months require 10 mg/kg daily for all 5 days, not the step-down regimen 2, 3
- Pharyngitis requires higher dosing: The standard 5-day regimen has higher recurrence rates for streptococcal pharyngitis; use 12 mg/kg daily for 5 days instead 4
- Monitor for vomiting: If the child vomits within 30 minutes of a single-dose regimen, re-dosing may be considered, though safety data is limited 1
Safety Profile
- Azithromycin is generally well-tolerated in children, with adverse events occurring in approximately 9% of patients 6
- Most common side effects are mild-to-moderate gastrointestinal complaints (abdominal discomfort, diarrhea, nausea, vomiting) 2, 6
- Treatment discontinuation due to adverse effects is rare (0.3% in one large study) 7
- Azithromycin has fewer gastrointestinal side effects compared to erythromycin 3, 6