Amoxicillin Dosing for Strep Pharyngitis in an 11-Year-Old, 32kg Patient
For this 11-year-old patient weighing 32kg with possible strep throat, give amoxicillin 1000 mg once daily for 10 days. 1, 2
Recommended Dosing Regimen
The FDA-approved dosing for streptococcal pharyngitis in pediatric patients weighing less than 40kg is 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours for severe infections. 1 However, once-daily dosing at 50 mg/kg (approximately 1000-1500 mg for this patient) has been proven equally effective and is now recommended by the American Heart Association to improve compliance. 2
Specific Dosing Options for This Patient:
Once-daily dosing: 1000 mg (50 mg/kg) once daily for 10 days - This is the preferred regimen for improved compliance with equivalent efficacy to multiple daily dosing 2, 3
Twice-daily dosing: 750 mg (approximately 45 mg/kg/day) every 12 hours for 10 days - This is FDA-approved and has strong evidence supporting equivalent efficacy to more frequent dosing 1, 3
Three-times-daily dosing: 500 mg every 8 hours for 10 days - This is the traditional FDA-approved regimen but offers no advantage over simpler schedules 1
Critical Duration Requirement
A full 10-day course is absolutely essential to prevent acute rheumatic fever, regardless of clinical improvement. 1, 4 The FDA label explicitly states: "It is recommended that there be at least 10 days' treatment for any infection caused by Streptococcus pyogenes to prevent the occurrence of acute rheumatic fever." 1
Why Once-Daily Dosing is Optimal
Once-daily amoxicillin significantly improves compliance compared to multiple daily dosing, with no disadvantage in clinical or bacteriologic outcomes. 2
Meta-analysis demonstrates that once-daily amoxicillin (but NOT once-daily penicillin) achieves cure rates equivalent to more frequent dosing schedules. 3
Amoxicillin is ideal for once-daily dosing due to its pharmacokinetics and low cost compared to other once-daily alternatives like azithromycin or extended-release formulations. 2
Administration Instructions
Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance. 1
Treatment should continue for the full 10 days even if the patient becomes asymptomatic after 48-72 hours. 1
Common Pitfalls to Avoid
Do NOT shorten the course below 10 days - Even a few days' reduction dramatically increases treatment failure rates and risk of acute rheumatic fever 4, 1
Do NOT use once-daily penicillin V - Unlike amoxicillin, once-daily penicillin is associated with 12 percentage points lower cure rate and should not be used 3
Do NOT substitute two 250mg tablets for one 500mg tablet if using combination products - This results in excessive clavulanate dosing, though this is not relevant for plain amoxicillin 5
Alternative Regimens if Penicillin Allergy is Discovered
If the patient has a non-immediate penicillin allergy, use cephalexin 20 mg/kg/dose (approximately 640 mg) twice daily for 10 days 4
If the patient has an immediate/anaphylactic penicillin allergy, use clindamycin 7 mg/kg/dose (approximately 224 mg, round to 225 mg) three times daily for 10 days 4