Renal Dose Adjustment for Amoxicillin and Azithromycin at eGFR 28
Amoxicillin requires dose adjustment at eGFR 28, while azithromycin does not require any dose modification.
Amoxicillin Dosing with eGFR 28
Amoxicillin must be adjusted in severe renal impairment (eGFR <30 mL/min). 1
The FDA label explicitly states that "amoxicillin is primarily eliminated by the kidney and dosage adjustment is usually required in patients with severe renal impairment (GFR less than 30 mL/min)." 1
With an eGFR of 28, this patient falls into the severe renal impairment category requiring modification. 1
Research confirms a significant decrease in amoxicillin clearance and elimination rate in renal failure, with a linear relationship between the drug's elimination half-life and creatinine clearance. 2
High blood levels occur more readily in patients with impaired renal function because of decreased renal clearance, increasing the risk of toxic reactions. 1
Specific Adjustment Strategy
Extend the dosing interval rather than reducing individual doses to maintain therapeutic peak concentrations while preventing accumulation. 3
For eGFR <30 mL/min, consider three-times-weekly dosing instead of daily administration, though specific amoxicillin intervals are not standardized in guidelines. 3
Monitor closely for adverse effects and clinical response, particularly in elderly patients where this level of renal impairment is common. 4
Consult nephrology or clinical pharmacy for complex infections requiring higher doses in this renal function range. 4
Azithromycin Dosing with eGFR 28
No dose adjustment is required for azithromycin at any level of renal impairment, including eGFR 28. 5
The FDA label clearly states: "No dosage adjustment is recommended for subjects with renal impairment (GFR ≤80 mL/min)." 5
The mean drug exposure (AUC) was similar in subjects with GFR 10-80 mL/min compared to normal renal function. 5
Research demonstrates that neither the area under the curve, distribution volume, nor maximal plasma concentration are significantly affected by renal insufficiency. 6
The dosage regimen of azithromycin in renal impairment should be the same as in patients with normal renal function. 6
Important Caveat for Severe Renal Impairment
While no dose adjustment is needed, the FDA label notes that AUC increased 35% in subjects with GFR <10 mL/min, and "caution should be exercised when azithromycin is administered to subjects with severe renal impairment." 5
At eGFR 28, this patient is above the GFR <10 threshold, so standard dosing applies without special precautions beyond routine monitoring. 5
Key Clinical Pitfalls to Avoid
Do not reduce amoxicillin dose per administration—instead extend the interval to maintain adequate peak concentrations for bacterial killing. 3
Avoid assuming all beta-lactams behave identically in renal failure; amoxicillin requires adjustment while some others may not. 7
Do not unnecessarily adjust azithromycin dosing based on renal function, as this may lead to subtherapeutic levels without providing safety benefit. 6
Remember that elderly patients often have reduced renal function despite normal serum creatinine due to decreased muscle mass, making eGFR calculation essential. 3
Consider that amoxicillin can be removed by hemodialysis, requiring post-dialysis supplementation if the patient progresses to dialysis. 1