Azithromycin Dosing for Strep Throat in a 12-Year-Old
For a 12-year-old child weighing 111 pounds (50.4 kg) with strep throat, prescribe azithromycin 12 mg/kg once daily for 5 days, which equals 600 mg (15 mL of 200 mg/5 mL suspension) once daily for 5 days, for a total treatment course of 3000 mg. 1, 2
Weight-Based Calculation
- Patient weight: 111 pounds = 50.4 kg
- Recommended dose: 12 mg/kg/day × 50.4 kg = 604.8 mg/day (round to 600 mg) 1, 2
- Using 200 mg/5 mL suspension: 600 mg ÷ 200 mg = 3, then 3 × 5 mL = 15 mL once daily 1
- Duration: 5 days 1, 2
- Total course: 3000 mg over 5 days 1
Rationale for 12 mg/kg Dosing
The higher dose of 12 mg/kg/day for 5 days (total 60 mg/kg) is specifically required for strep throat to achieve adequate bacterial eradication rates. 2 The standard 10 mg/kg regimen used for other respiratory infections results in inferior bacteriologic eradication rates of only 65% compared to 82% with penicillin, making it inadequate for Group A Streptococcus pharyngitis. 3 Research demonstrates that a total dose of 60 mg/kg azithromycin provides optimal GABHS eradication rates comparable to standard penicillin therapy. 2
Alternative Dosing Regimen
- A 3-day regimen at 20 mg/kg/day (1000 mg daily for 3 days) achieves the same total 60 mg/kg dose and equivalent eradication rates 2
- However, the FDA-approved dosing for pharyngitis/tonsillitis is specifically the 5-day regimen at 12 mg/kg/day 1
Critical Prescribing Details
Write the prescription as:
- Azithromycin 200 mg/5 mL oral suspension
- Dispense: 75 mL (one bottle)
- Sig: Give 15 mL (3 teaspoons) by mouth once daily for 5 days
- Total dose per treatment course: 3000 mg 1
Common Pitfall to Avoid
Do not use the standard 10 mg/kg dosing regimen for strep throat. 3 The lower dose (10 mg/kg/day for 3 days, total 30 mg/kg) is FDA-approved for otitis media, sinusitis, and community-acquired pneumonia but results in bacteriologic failure rates of 35% for streptococcal pharyngitis. 1, 3 This inadequate dosing leads to treatment failures, persistent carriage, and potential complications including rheumatic fever. 2
Tolerability and Monitoring
- Azithromycin is well-tolerated in children, with primarily mild-to-moderate gastrointestinal adverse effects occurring in approximately 11% of patients 4
- The once-daily dosing for 5 days offers superior adherence compared to penicillin V's three-times-daily dosing for 10 days 2
- Clinical improvement should be evident within 24-48 hours of initiating therapy 2