Amoxicillin Dosing for eGFR 27 mL/min/1.73 m²
For a patient with an eGFR of 27 mL/min/1.73 m², amoxicillin should be dosed at 500 mg or 250 mg every 12 hours, depending on infection severity, as this falls within the severe renal impairment category (eGFR 10-30 mL/min). 1
Dosing Algorithm Based on Renal Function
With an eGFR of 27 mL/min/1.73 m², this patient has severe renal impairment requiring significant dose adjustment 1:
- Standard dose reduction: 500 mg every 12 hours for moderate-to-severe infections 1
- Alternative reduced dose: 250 mg every 12 hours for mild infections 1
- Critical restriction: The 875 mg dose formulation should NOT be used in patients with eGFR <30 mL/min 1
Infection Severity Considerations
The choice between 500 mg vs 250 mg every 12 hours depends on:
- Moderate-to-severe infections (pneumonia, complicated UTI, severe skin infections): Use 500 mg every 12 hours 1
- Mild infections (uncomplicated UTI, minor skin infections): Use 250 mg every 12 hours 1
- UTI-specific guidance: For stage 4 CKD (eGFR 15-29 mL/min), amoxicillin-clavulanate 500 mg every 12 hours or 250 mg every 8 hours is recommended depending on severity 2
Critical Monitoring Requirements
Renal function monitoring is essential because:
- Drug accumulation occurs with any degree of renal insufficiency 3
- Renal function should be reassessed within 48-72 hours of starting antibiotics to detect further deterioration 2
- Close monitoring for adverse effects is warranted as amoxicillin clearance is highly correlated with creatinine clearance 4
Important Clinical Caveats
Avoid common dosing errors:
- Do NOT use standard dosing (500 mg every 8 hours or 875 mg every 12 hours) as this leads to drug accumulation 1
- Recent evidence suggests that recommended dose reductions may lead to subtherapeutic concentrations for less susceptible pathogens (MIC >2 mg/L), though adequate coverage is maintained for highly susceptible organisms (MIC ≤2 mg/L) 5
- For borderline renal function, consider 24-hour urine collection to accurately define the degree of impairment before finalizing the regimen 3
Special Circumstances
If the patient progresses to hemodialysis (eGFR <10 mL/min):
- Reduce to 500 mg or 250 mg every 24 hours 1
- Administer an additional dose both during and at the end of each dialysis session 1
- Always give the dose AFTER dialysis, never before, to ensure optimal drug levels 3
- Hemodialysis significantly clears amoxicillin with an average half-life of 2.3-3.6 hours during dialysis 4, 6
Pharmacokinetic Rationale
The dose reduction is necessary because:
- Amoxicillin is 68% renally excreted in patients with normal kidney function 4
- Serum half-life increases from 71 minutes (normal function) to approximately 16 hours in anephric patients 4
- At eGFR 27 mL/min, the half-life is significantly prolonged, requiring dose reduction by approximately 50% or doubling the dosing interval 3, 7