The Medicines and Healthcare products Regulatory Agency (MHRA) has issued guidance on when to use estimated glomerular filtration rate (eGFR) or the Cockcroft-Gault formula to measure renal impairment before prescribing different drug classes.
The agency advises that for most patients and most medicines, 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).
For most drugs and for most adult patients of average build and height, eGFR should be used to determine dosage adjustments. The Cockcroft-Gault formula should be used to determine adjustments for the following:
- direct-acting oral anticoagulants (DOACs);
- nephrotoxic drugs (including vancomycin and amphotericin B);
- elderly patients (age, ≥75 years);
- patients at extremes of muscle mass (BMI, 2 or >40 kg/m2); and
- medicines that are largely renally excreted and have a narrow therapeutic index (e.g. digoxin and sotalol).
When dose adjustment based on CrCl is important and no advice is provided in the relevant BNF monograph, prescribers are advised to consult the Summary of Product Characteristics.
Renal function and drug dosing should be reassessed in situations where eGFR and/or CrCl change rapidly, such as in patients with acute kidney injury, the MHRA says.
The advice has been issued following a number of reports and queries related to the choice of renal function estimate used when prescribing medicines for patients with renal impairment.
A recent cross-sectional study of data from 80 general practices in the UK found that prescribing of drugs outside recommendations for use in patients with reduced kidney function was widespread for the eight drugs analysed. The prescribed dose was too high for kidney function in up to 40 per cent of people aged ≥65 years and up to 80 per cent of people aged ≥85 years.