Objective: Although the Calvert formula is the standard method to calculate the dose of carboplatin, there is no consensus how to determine the glomerular filtration rate (GFR) without using [51Cr]-ethylenediamine tetraacetic acid (51Cr-EDTA). Creatinine clearance (Ccr), calculated using the Cockroft-Gault, Jelliffe, Modified-Jelliffe or Wright formulae, has been used as a substitute for the GFR. In addition to these four formulae, the Chatelut formula has been proposed as a way to calculate carboplatin clearance. Among these formulae, Jelliffe formula does not include body surface area (BSA) or body weight to adjust the body size and thus may have greater bias than the other four formulae in estimating carboplatin clearance. The purpose of this study is to evaluate if these five formulae could equally estimate the carboplatin clearance.
Methods: : Carboplatin clearance was estimated in 253 patients with gynecologic cancer who received carboplatin-based chemotherapy between January 1996 and August 2004. Ccr was estimated using the Cockroft-Gault, Jelliffe, Modified-Jelliffe or Wright formulae. Carboplatin clearance was also calculated directly by using the Chatelut formula. The five estimations of carboplatin clearance were compared with each other using the post-hoc Wilcoxon signed rank test. The median percent error (MPE) and the median absolute percent error (MAPE) were evaluated by comparing carboplatin clearance. The relationships between BSA and ratios of estimated carboplatin clearance (Jelliffe/Cockroft-Gault, Jelliffe/Modified-Jelliffe, Jelliffe/Wright, Jelliffe/Chatelut) were evaluated by using simple regression.
Results: : The estimated carboplatin clearances were: Cockroft-Gault formula, 109.8 +/- 28.4; Jelliffe formula, 128.5 +/- 28.2; Modified-Jelliffe formula, 110.8 +/- 25.7; Wright formula, 112.2 +/- 24.3; Chatelut formula, 114.1 +/- 33.0. A statistically significant difference was observed between carboplatin clearance calculated using Jelliffe formula and that given by each of the other four formulae. Comparing the results of the Cockroft-Gault formula with the Jellife, Modified-Jelliffe, Wright and Chatelut formulae yielded MPEs of +19%, +2%, +3% and +3% and MAPEs of 27%, 5%, 6% and 6%, respectively. There was a significant correlation between BSA and ratio of estimated carboplatin clearance (Jelliffe/Cockroft-Gault, Jelliffe/Modified-Jelliffe, Jelliffe/Wright, Jelliffe/Chatelut), with Pearson correlation coefficients of 0.928, 0.847, 0.965 and 0.839 respectively. As the BSA of patient became smaller, the differences between the carboplatin clearance calculated by the Jelliffe formula from other four formulas became larger.
Conclusions: : Estimates of carboplatin clearance calculated by the Jelliffe formula tend to have greater positive bias compared to the other four formulae, particularly when the BSA of the patient is small. In order to conduct collaborative international studies, it may be necessary to standardize the formula used to estimate carboplatin clearance to perform international collaboration studies.