What is the recommended dosage of amoxicillin for a patient with moderate renal impairment (GFR of 43) and a urinary tract infection?

Amoxicillin Dosing for Urinary Tract Infection in Moderate Renal Impairment (GFR 43)

For a patient with moderate renal impairment (GFR 43 mL/min/1.73m²) and a urinary tract infection, the recommended dosage of amoxicillin is 500 mg every 8 hours or 875 mg every 12 hours. 1

Dosing Rationale

According to the FDA drug label for amoxicillin, patients with moderate renal impairment (GFR between 30-50 mL/min) do not generally require a reduction in dose. Only patients with severe renal impairment (GFR <30 mL/min) require dosage adjustment 1.

The standard dosing regimen for urinary tract infections with amoxicillin is:

• 500 mg every 8 hours OR
• 875 mg every 12 hours

Dosing Algorithm Based on GFR:

1. GFR >30 mL/min: Standard dosing (no adjustment required)

   • 500 mg every 8 hours OR 875 mg every 12 hours

2. GFR 10-30 mL/min: Reduced dosing

   • 500 mg or 250 mg every 12 hours (depending on infection severity)

3. GFR <10 mL/min: Significantly reduced dosing

   • 500 mg or 250 mg every 24 hours (depending on infection severity)

4. Hemodialysis patients:

   • 500 mg or 250 mg every 24 hours
   • Additional dose both during and at the end of dialysis

Clinical Considerations

Monitoring Requirements

• Renal function should be monitored during treatment, especially if the patient's condition changes or if they experience intercurrent illness
• Monitor for clinical response within 48-72 hours of initiating therapy

Duration of Treatment

• UTI treatment should continue for a minimum of 48-72 hours beyond the time the patient becomes asymptomatic
• For uncomplicated UTIs, a 7-day course is typically sufficient

Administration

• Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance 1

Important Precautions

• If the patient develops acute illness, temporary discontinuation of amoxicillin may be warranted to prevent potential nephrotoxicity 2
• Ensure adequate hydration during treatment to prevent crystalluria, particularly in patients with compromised renal function
• Be aware that the patient's GFR may fluctuate, requiring reassessment of dosing if clinical status changes

Common Pitfalls to Avoid

1. Underdosing: Insufficient dosing can lead to treatment failure and development of resistant organisms
2. Overdosing: Excessive dosing in renal impairment can lead to drug accumulation and toxicity
3. Failure to adjust for body size: Remember that standard GFR is normalized to body surface area; for patients significantly larger or smaller than average, consider calculating absolute clearance
4. Not considering drug interactions: Be aware of other medications that might affect renal function or interact with amoxicillin

By following these guidelines, you can optimize treatment efficacy while minimizing the risk of adverse effects in patients with moderate renal impairment.