For many years the Cockcroft-Gault equation has been the gold standard for estimating creatinine clearance, which is used as a surrogate marker for glomerular filtration rate (GFR) and hence to estimate renal function. Although Cockcroft-Gault is routinely used to ‘calculate’ GFR in order to identify required modifications of drug doses, there is some debate over whether it’s more appropriate to use ideal or actual body weight, particularly in cancer patients where capping of body surface area (BSA) for dose calculations is no longer recommended.
When dosing carboplatin, which is 100% renally cleared, the recommendation from COSA and other bodies is to undertake actual measurement of GFR by nuclear medicine scan, as dosing according to Cockcroft-Gault GFR may underestimate dosing in some patient populations and overdose in others. However, NM GFR incurs a cost, and may not always be accessible in a timely fashion.
Newer formulae are available, including Modified Diet in Renal Disease (MDRD) and Chronic Kidney Disease-Epidemiology (CKD-EPI). These were originally designed to alert physicians to gradual changes in kidney functionality, therefore have not been validated in acute renal impairment or for use in drug dosing, and do not necessarily take into account the patient’s BSA. This presentation will discuss what it means when an eGFR, or estimated glomerular filtration rate, is reported by a pathology system, and what its utility is when calculating doses of renally cleared cancer therapies, plus those which have the potential to be nephrotoxic, e.g. cisplatin.