Azithromycin Dosing for 25 kg Female with Upper Respiratory Tract Infection
For a 25 kg female pediatric patient with an upper respiratory tract infection, administer azithromycin 250 mg (10 mg/kg) on day 1, followed by 125 mg (5 mg/kg) once daily on days 2 through 5, for a total 5-day course.
Dosing Rationale
The standard pediatric dosing for azithromycin in respiratory tract infections follows a weight-based calculation of 10 mg/kg (maximum 500 mg) on day 1, then 5 mg/kg (maximum 250 mg) daily for days 2-5 1, 2, 3. For this 25 kg patient:
- Day 1: 10 mg/kg × 25 kg = 250 mg
- Days 2-5: 5 mg/kg × 25 kg = 125 mg daily
An alternative weight-based guideline from Thorax specifically recommends 200 mg once daily for children weighing 15-25 kg 2. However, the IDSA/PIDS and FDA-approved dosing using the 10 mg/kg on day 1 followed by 5 mg/kg regimen is more widely endorsed and provides higher initial loading 1, 3.
Clinical Context and Indications
Azithromycin is specifically indicated for atypical pathogens causing upper respiratory infections, including Mycoplasma pneumoniae, Chlamydia pneumoniae, and Chlamydia trachomatis 1, 2.
Critical Caveat
If this is typical bacterial pharyngitis (strep throat) or pneumonia caused by Streptococcus pneumoniae or Haemophilus influenzae, amoxicillin remains the first-line agent, not azithromycin 1, 2. Azithromycin should only be used when:
- Atypical pathogens are suspected or confirmed
- The patient has a documented penicillin allergy
- There is clinical failure with beta-lactam therapy
For streptococcal pharyngitis specifically, if azithromycin must be used, a higher dose of 12 mg/kg once daily for 5 days (maximum 500 mg/day) is necessary due to high recurrence rates with standard dosing 2.
Administration Guidelines
- Azithromycin can be taken with or without food 3
- The oral suspension formulation is well-tolerated and palatable for children 4, 5
- Using the 200 mg/5 mL suspension concentration for a 25 kg child:
- Day 1: 6.25 mL (1¼ teaspoons)
- Days 2-5: 3.125 mL (approximately ⅝ teaspoon) 3
Expected Clinical Response
Children on adequate therapy should demonstrate clinical improvement within 48-72 hours 1. If the patient deteriorates or shows no improvement within this timeframe, further investigation is warranted, including:
- Re-evaluation for bacterial superinfection requiring beta-lactam coverage
- Consideration of resistant organisms
- Assessment for complications such as parapneumonic effusion 1
Safety Considerations
Azithromycin is generally well-tolerated in children, with adverse events occurring in approximately 9% of patients 5. Common side effects include:
- Gastrointestinal complaints (abdominal discomfort, diarrhea, nausea, vomiting)
- Headache and dizziness 2
Important drug interactions: Avoid concurrent administration with aluminum- or magnesium-containing antacids, as they reduce absorption 2. Monitor for QT interval prolongation when used with other QT-prolonging medications 2.