Medicines and renal impairment

fe is the abbreviation for fraction of drug excreted unchanged in the urine.

For predominantly renally cleared drugs (fe > 0.5), dose adjustment should be considered in relation to impairment of renal function (creatinine clearance/eGFR).

 

General Advice

• Assess renal function using estimated glomerular filtration rate (eGFR) or creatinine clearance (CrCl).
• Consider reducing doses of drugs that are predominantly renally cleared (those with fe > 0.5) in relation to impairment of renal function.
• When renal function is < 30 mL/min preferentially use metabolised drugs over renally cleared drugs.

 

Pharmacokinetic Considerations

For drugs that are renally cleared i.e. fe > 0.5.

1. Choose the dose rate i.e. dose and frequency that you would use in this patient if renal function was normal (CrCl 100 mL/min).
2. Calculate the patient’s creatinine clearance (CrCl) using the Cockcroft and Gault calculator. 
   • Alternatively the estimated glomerular filtration rate (eGFR) supplied by the laboratories can be used for patients whose BSA is close to 1.73m². Use this method to adjust the eGFR for body surface area.
   • Interpretation is dependent on the clinical condition of the patient. If renal function is changing (e.g: acute kidney injury), these estimates are not reliable and dosing should take this into account.
3. Calculate dose rate:
   • In patients with renal dysfunction, it is essential to adjust the dose for some medicines. Dose adjustment to reduce side effects should be considered for other medicines.
   • For drugs with fe ≥ 0.9, use this equation(assume normal CrCl of 100 mL/min):
   • For drugs with fe < 0.9, use this equation:

 

Pharmacodynamic Considerations

• Water and electrolyte handling may be significantly altered (e.g. increasing the likelihood of oedema, hyponatraemia, and hyperkalaemia).
• Nephrotoxic drugs (e.g. non-steroidal anti-inflammatory drugs) may aggravate already impaired kidneys.