What is the appropriate amoxicillin dose for my 2‑year‑old, 13‑kg child; is 4 mL of a 458 mg/5 mL suspension correct?

The Dose You Gave Is Too High and Potentially Dangerous

You administered approximately 367 mg of amoxicillin (4 mL × 458 mg/5 mL = 366.4 mg), which equals 28.2 mg/kg for your 13 kg child—this is below the recommended therapeutic dose but the concentration (458 mg/5 mL) appears incorrect and needs immediate verification with your pharmacist.

Critical Safety Issue: Verify the Concentration

The concentration you stated (458 mg/5 mL) is not a standard amoxicillin formulation. Standard amoxicillin suspensions come in:

• 125 mg/5 mL
• 250 mg/5 mL
• 400 mg/5 mL (less common)

You must immediately check the bottle label to confirm the actual concentration. If you truly have a 458 mg/5 mL concentration (which would be unusual), this represents a dosing error risk.

What the Correct Dose Should Be

For a 13 kg, 2-year-old child, the recommended amoxicillin dosing depends on the infection severity 1, 2:

Standard Dosing (Mild-Moderate Infections)

• 45 mg/kg/day divided every 12 hours = 292.5 mg twice daily
• Using 250 mg/5 mL suspension: 5.85 mL (approximately 6 mL) twice daily

High-Dose Regimen (Severe Infections or High Resistance Risk)

• 80-90 mg/kg/day divided every 12 hours = 520-585 mg twice daily
• Using 250 mg/5 mL suspension: 10.4-11.7 mL twice daily

High-dose amoxicillin is specifically recommended for children under 2 years, those in daycare, or those who received antibiotics in the past 30 days 1.

Why Your Child Needs High-Dose Amoxicillin

Your 2-year-old falls into the high-risk category for antibiotic-resistant bacteria 1. The guideline explicitly states:

"Patients presenting with moderate to severe illness as well as those younger than 2 years, attending child care, or who have recently been treated with an antimicrobial may receive high-dose amoxicillin-clavulanate (80–90 mg/kg per day of the amoxicillin component with 6.4 mg/kg per day of clavulanate in 2 divided doses with a maximum of 2 g per dose)" 1.

For uncomplicated infections without these risk factors, standard dosing of 45 mg/kg/day is acceptable 1, 2.

Immediate Action Steps

1. Contact your pharmacist immediately to verify the actual concentration on your bottle
2. Do not give another dose until you confirm the correct concentration and dosing
3. Calculate the correct dose based on verified concentration:
   • For standard-dose: 292.5 mg (45 mg/kg/day ÷ 2)
   • For high-dose: 520-585 mg (80-90 mg/kg/day ÷ 2)
4. Administer doses every 12 hours (twice daily) 2

Common Pitfalls to Avoid

Weight-based dosing errors are extremely common in pediatrics 3. Research shows that larger children systematically receive lower mg/kg doses than recommended, while prescribers often hesitate when calculated doses approach adult maximums 3, 4. For your 13 kg child, even the high-dose regimen (585 mg twice daily = 1170 mg/day total) is well below the adult maximum of 1500-1750 mg/day and is both safe and necessary 2.

The FDA label clearly states that for severe infections or lower respiratory tract infections in children weighing less than 40 kg, the dose should be "45 mg/kg/day in divided doses every 12 hours or 40 mg/kg/day in divided doses every 8 hours" 2.

Duration of Treatment

Continue treatment for a minimum of 48-72 hours beyond symptom resolution 2. For streptococcal infections, treat for at least 10 days to prevent rheumatic fever 2.