Carboplatin dosage formulae can generate inaccurate predictions of carboplatin exposure in carboplatin/paclitaxel combination regimens

Carboplatin is a frequently used antitumour agent recommended to be administered according to the Calvert formula: dose = AUC x (GFR+25), where GFR is the glomerular filtration rate as measured by Cr-51-EDTA clearance and AUC is the targeted area under the carboplatin concentration versus time curve. In several modified Calvert formulae, the GFR is estimated on the basis of serum creatinine levels. We compared AUCs of carboplatin that were predicted by modified Calvert formulae with actual measured AUCs in 75 courses in patients with non-small cell lung cancer or ovarian cancer who were treated with the combination of carboplatin-paclitaxel. Predictions were made using two modified Calvert formulae, in which the GFR was calculated by serum creatinine level-based equations, according to Jelliffe (Eq. 1) and Cockroft-Gault (Eq. 2). We also studied the performance of a formula for the clearance of carboplatin, as proposed by Chatelut (Eq. 3). The actual measured mean AUC was 4.6 mg/ml.min (range 1.9 to 10.4 mg/ml min, SD 1.7). Equation 1 overestimated the AUC by 32.9% with an imprecision of 43.0%, and equation 2 overestimated the AUC by 27.6% with an imprecision of 33.4%. For equation 3, an AUC overestimation of only 10.2%, but with an imprecision of 25.3%, was observed. In conclusion, all three equations overestimated the carboplatin AUCs and had poor precisions. We concluded that the real carboplatin AUCs were lower than calculated, using the three tested formulae. This may have important consequences for ongoing and future phase II and III studies with carboplatin-paclitaxel combinations, utilising these formulae to calculate the carboplatin dose. Thus far, the original Calvert dosage formula remains the 'golden standard'.