Evaluation of Cockcroft-Gault (CG) and abbreviated modified diet in renal disease (MDRD) formulae in dosing of cancer drugs other than carboplatin

Abstract

2522 Background: Glomerular filtration rate (GFR) is often used to determine initial dosing of renally-excreted cancer drugs. Estimated GFR (eGFR) can be calculated using serum creatinine (SrCr) -based formulae such as CG and MDRD. MDRD is more accurate in non-cancer patients, does not require patient weight, and is reported automatically by all laboratories in British Columbia (BC). We previously showed that CG and MDRD have similar accuracy for carboplatin dosing in patients with gynecological malignancies. We now examine dosing of all renally-excreted cancer drugs in the general cancer population. Since this setting does not include routine measurement of GFR, we report the concordance of eGFR derived from CG and MDRD. Methods: Patient data were collected retrospectively at the BC Cancer Agency. The primary outcome was concordance of eGFR derived from CG and MDRD, using the method of Bland and Altman. A difference of ≥ 30% was assumed to be clinically significant because this difference would usually lead to dose adjustment based on reclassification of renal function. The secondary outcome was the proportion of patients who would have received a different initial dose due to difference in eGFR. Each patient’s dose was determined from dose adjustment tables stated in specific treatment protocols. Results: 313 patients were evaluated: 40% male, median 56y, 67.5kg, 166cm, SrCr 74micromol/L. Median eGFR derived from CG and MDRD were 86.8mL/min and 87.6mL/min, respectively. A difference of ≥ 30% in eGFR was found in 17.9% (56/313) of patients. 8.6% (27/313) of patients would have received a different dose due to difference in eGFR; of these, 67% (18/27) would have received a higher dose. Conclusions: There is good concordance of eGFR derived from CG and MDRD for most cancer patients, with less than 10% of patients expected to receive a different initial dose of chemotherapy. MDRD may be a reasonable alternative to CG for dosing of any renally-excreted cancer drug. No significant financial relationships to disclose.