Medication Dosing in Renal Impairment

Introduction to Renal Impairment Considerations

The American Thoracic Society/CDC/Infectious Diseases Society of America guidelines recommend using creatinine clearance rather than just serum creatinine for dosing adjustments in patients with impaired renal function 1
Creatinine clearance directly measures the kidney's ability to filter substances, which is crucial for determining appropriate medication dosages in renal impairment 1

For patients with creatinine clearance <30 mL/min and those receiving hemodialysis, dosing intervals should be increased rather than simply reducing doses 1
For medications like ethambutol that are 80% cleared by the kidneys, dosing frequency should be changed from daily to three times weekly when creatinine clearance is <30 mL/min 2
Antiviral medications like oseltamivir require dosage reduction to 75 mg once daily for patients with creatinine clearance <30 mL/min 3, 4, 5

Tuberculosis medications like ethambutol require interval adjustments rather than dose reductions when creatinine clearance is <30 mL/min 1, 2
For patients on hemodialysis, medications should generally be administered after dialysis sessions to avoid premature clearance of the drug 1, 2
Some medications (like rifampin and isoniazid) are primarily metabolized by the liver and may not require dosage adjustments in renal impairment 1

Decreasing the dose of medications rather than increasing the dosing interval may lead to subtherapeutic peak concentrations and treatment failure 1, 2
Failing to consider the impact of hemodialysis on drug clearance can lead to inadequate dosing 1, 2

The Kidney Disease: Improving Global Outcomes (KDIGO) guidelines acknowledge that while eGFR equations have been validated for assessing renal function, pharmacokinetic studies historically used the Cockcroft-Gault equation for drug dosing recommendations 6

eGFR equations report values normalized to body surface area, while drug dosing requires absolute clearance in ml/min, and using eGFR for drug dosing without de-normalizing for body surface area may lead to underdosing larger patients and overdosing smaller patients 6
When absolute clearances calculated from MDRD Study equation estimates were compared with measured GFR and Cockcroft-Gault calculations, concordance was only 75% to 78%, indicating potential for dosing discrepancies 6

For medications requiring precise dosing due to narrow therapeutic or toxic ranges, cystatin C-based methods or direct measurement of GFR may be more appropriate 6, 7

Failing to convert eGFR values to absolute clearance when using for medication dosing can lead to inappropriate dosing 6
Not considering that different laboratory methods for measuring serum creatinine can affect the accuracy of both CrCl and eGFR calculations 8