Amoxicillin Dosing for an 84-Year-Old Patient with EGFR of 22
For an 84-year-old patient with an eGFR of 22 mL/min/1.73m², the appropriate amoxicillin dose is 250-500 mg every 24 hours, depending on the severity of the infection. 1
Dosing Considerations in Renal Impairment
- Patients with severe renal impairment (GFR 10-30 mL/min) should receive 250-500 mg every 12 hours, depending on the severity of the infection 1
- Patients with very severe renal impairment (GFR less than 10 mL/min) should receive 250-500 mg every 24 hours, depending on the severity of the infection 1
- With an eGFR of 22 mL/min, this patient falls in the severe renal impairment category, but close to the very severe threshold, warranting careful dosing consideration 1
- The 875 mg dose of amoxicillin should NOT be used in patients with a glomerular filtration rate less than 30 mL/min 1
Clinical Reasoning for Dose Selection
- Amoxicillin is primarily eliminated by the kidneys, and reduced renal function significantly decreases drug clearance 2
- There is a linear relationship between amoxicillin elimination rate and creatinine clearance, necessitating dosage adjustments in renal impairment 2
- Recent research suggests that standard dose reductions in renal impairment may lead to subtherapeutic concentrations, especially when targeting less susceptible pathogens 3
- For infections with highly susceptible organisms (MICs ≤2 mg/L), reduced doses still achieve >90% probability of target attainment even in severe renal impairment 3
Important Administration Guidelines
- Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance 1
- Treatment should be continued for a minimum of 48-72 hours beyond symptom resolution 1
- For Streptococcus pyogenes infections, treatment should continue for at least 10 days to prevent acute rheumatic fever 1
- For this elderly patient with severe renal impairment, close monitoring for adverse effects and clinical response is essential 4
Special Considerations for Elderly Patients with Renal Impairment
- Older patients with renal impairment have increased risk of UTI-related hospitalization and death, suggesting a need for careful monitoring 5
- Non-adherence to renal dosing guidelines is common (46% in severe renal impairment) and may cause moderate to severe harm in over 70% of cases 6
- Reporting the eGFR alongside medication orders has been shown to improve adherence to renal dosing guidelines 6
- For elderly patients on dialysis, an additional dose should be administered both during and at the end of dialysis 1
Common Pitfalls to Avoid
- Avoid using the 875 mg dose in this patient, as it is contraindicated in patients with eGFR <30 mL/min 1
- Be cautious about excessive dose reduction that could lead to treatment failure, especially for less susceptible pathogens 3
- Remember that the pharmacokinetics of amoxicillin are altered in renal impairment, with decreased clearance and prolonged half-life 2
- Consider consulting with a nephrologist or clinical pharmacist for complex cases, especially when treating serious infections in patients with severe renal impairment 4