Prescribing medicines (drugs) in chronic kidney disease (CKD) - using the appropriate estimate of renal function to avoid the risk of adverse drug reactions

Prescribing medicines in renal impairment: using the appropriate estimate of renal function to avoid the risk of adverse drug reactions

For most patients and most medicines, estimated Glomerular Filtration Rate (eGFR) is an appropriate measure of renal function for determining dosage adjustments in renal impairment; however, in some circumstances, the Cockcroft-Gault formula should be used to calculate creatinine clearance (CrCl).

Advice for healthcare professionals (1):

• MHRA has received reports and queries related to the choice of renal function estimate used when prescribing medicines for patients with renal impairment
  
  
• for most drugs and for most adult patients of average build and height, estimated Glomerular Filtration Rate (eGFR) should be used to determine dosage adjustments
  
  
• creatinine clearance (CrCl) should be calculated using the Cockcroft-Gault formula to determine dosage adjustments for:
  • direct-acting oral anticoagulants (DOACs) patients taking nephrotoxic drugs (examples include vancomycin and amphotericin B)
  • elderly patients (aged 75 years and older)
  • patients at extremes of muscle mass (BMI <18 kg/m2 or >40 kg/m2)
  • patients taking medicines that are largely renally excreted and have a narrow therapeutic index, such as digoxin and sotalol
    
    
• when dose adjustment based on CrCl is important and no advice is provided in the relevant BNF monograph, consult the Summary of Product Characteristics
  
  
• reassess renal function and drug dosing in situations where eGFR and/or CrCl change rapidly, such as in patients with acute kidney injury (AKI)

Cockcroft-Gault equation is often used as a method of estimating GFR (although it was developed as a method of predicting creatinine clearance) from knowledge of serum creatinine, age and weight:

• creatinine clearance = (((140 - age in years) x (wt in kg)) x 1.23) / (serum creatinine in micromol/l)

For women multiply the result of calculation by 0.85.The calculation is unreliable if the patient has unstable renal function, is very obese, or is oedematous.

Click here for calculator for Cockcroft-Gault formula

Reference:

• MHRA. Drug Safety Update volume 13, issue 3: October 2019: 3.