What is the appropriate dose of amoxicillin (amoxicillin) for a 13-year-old female patient weighing 123.83 kg?

Amoxicillin Dosing for a 13-Year-Old Female Weighing 123.83 kg

For a 13-year-old female patient weighing 123.83 kg, the appropriate amoxicillin dose is 75 mg twice daily (adult dosing), as the patient weighs >40 kg.

Dosing Rationale

The FDA-approved amoxicillin dosing for children is weight-based until they reach 40 kg, after which adult dosing is used. Since this patient weighs significantly more than 40 kg (123.83 kg), adult dosing should be applied.

Weight-Based Dosing Thresholds

For children weighing >40 kg, the recommended dosage is:

• 75 mg twice daily for standard treatment 1
• For more severe infections: 875 mg every 12 hours or 500 mg every 8 hours 1

Infection-Specific Considerations

The specific infection being treated will influence the final dosage:

• Ear/Nose/Throat, Skin/Skin Structure, Genitourinary Tract infections:

  • Mild/Moderate: 500 mg every 12 hours or 250 mg every 8 hours
  • Severe: 875 mg every 12 hours or 500 mg every 8 hours

• Lower Respiratory Tract infections:

  • Mild/Moderate or Severe: 875 mg every 12 hours or 500 mg every 8 hours

Duration of Treatment

• Treatment should continue for a minimum of 48 to 72 hours beyond symptom resolution
• For Streptococcus pyogenes infections, a minimum of 10 days of treatment is recommended to prevent acute rheumatic fever 1

Special Considerations

Renal Function

• For patients with impaired renal function (GFR 10-30 mL/min): 500 mg or 250 mg every 12 hours
• For severe renal impairment (GFR <10 mL/min): 500 mg or 250 mg every 24 hours 1

Administration

• Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance 1
• For suspension formulations, shake well before using

Common Pitfalls to Avoid

1. Underdosing: Despite the patient's young age, adult dosing is appropriate due to her weight exceeding 40 kg. Using pediatric dosing calculations would be incorrect.

2. Failure to adjust for infection severity: Ensure the dose is appropriate for the specific infection being treated.

3. Inadequate duration: Particularly for streptococcal infections, ensure a full 10-day course is completed.

4. Not considering drug interactions: Be aware of potential interactions with other medications the patient may be taking.

5. Ignoring patient tolerance: Monitor for adverse effects, particularly gastrointestinal symptoms, and advise taking with food.