Amoxicillin Dosing for an 18.6 kg Child
For a child weighing 18.6 kg, the recommended dose of amoxicillin is 45 mg/kg/day divided into two doses (approximately 418 mg twice daily) or 40 mg/kg/day divided into three doses (approximately 248 mg three times daily), depending on the severity and type of infection being treated. 1, 2
Dosing Guidelines Based on Infection Type
Mild to Moderate Infections
- Ear/Nose/Throat, Skin/Skin Structure, Genitourinary Tract:
- 25 mg/kg/day divided every 12 hours (465 mg/day ≈ 233 mg twice daily)
- OR 20 mg/kg/day divided every 8 hours (372 mg/day ≈ 124 mg three times daily) 2
Severe Infections or Lower Respiratory Tract Infections
- 45 mg/kg/day divided every 12 hours (837 mg/day ≈ 418 mg twice daily)
- OR 40 mg/kg/day divided every 8 hours (744 mg/day ≈ 248 mg three times daily) 1, 2
Specific Pathogen-Based Dosing
For Streptococcus pneumoniae with penicillin MICs <2.0 μg/mL:
- 90 mg/kg/day in 2 doses (1,674 mg/day ≈ 837 mg twice daily)
- OR 45 mg/kg/day in 3 doses (837 mg/day ≈ 279 mg three times daily) 1
For Group A Streptococcus:
- 50-75 mg/kg/day in 2 doses (930-1,395 mg/day ≈ 465-698 mg twice daily) 1
For Haemophilus influenzae (β-lactamase negative):
- 75-100 mg/kg/day in 3 doses (1,395-1,860 mg/day ≈ 465-620 mg three times daily) 1
Administration Considerations
- Timing: Give at the start of a meal to minimize gastrointestinal intolerance 2
- Duration: Continue treatment for a minimum of 48-72 hours beyond symptom resolution 2
- For Streptococcal infections: Minimum 10 days of treatment to prevent acute rheumatic fever 2
Important Clinical Considerations
- Amoxicillin is well-absorbed orally, producing serum concentrations twice as high as similar doses of ampicillin 3
- For children under 40 kg, weight-based dosing is critical to ensure therapeutic efficacy while minimizing adverse effects 2
- The absorption of amoxicillin is not significantly affected by food intake 3
Potential Pitfalls and Caveats
- Avoid the 875 mg dose in patients with severe renal impairment (GFR <30 mL/min) 2
- Be aware of potential allergic reactions, especially in patients with history of penicillin allergy
- For suspected β-lactamase-producing organisms, consider amoxicillin-clavulanate instead of amoxicillin alone 4
- Reconstituted oral suspension must be shaken well before use and discarded after 14 days 2
By following these dosing guidelines for an 18.6 kg child, you can provide effective antimicrobial therapy while minimizing the risk of adverse effects and antimicrobial resistance.