Pharmacokinetic and Pharmacogenetic Study of Etoposide in High-Dose Protocol (TI-CE) for Advanced Germ Cell Tumors.

BACKGROUND: Etoposide dosing is based on body surface area. We evaluated if further dose individualization would be required for high dose (HD) etoposide within the TI-CE (taxol, ifosfamide, carboplatin, and etoposide) protocol. METHODS: Eighty-eight patients received 400 mg/m2/day of etoposide as a 1-hour IV infusion on 3 consecutive days over 3 cycles as part of a phase II trial evaluating efficacy of therapeutic drug monitoring (TDM) of carboplatin in the TI-CE HD protocol. Pharmacokinetic (PK) data were analyzed using population PK model on NONMEM to quantify inter- and intra-individual variabilities. Relationship between etoposide exposure and pharmacodynamic (PD) endpoints, and between selected genetic polymorphisms and tumor response or toxicity were evaluated. RESULTS: The inter-patient, inter- and intra-cycle variabilities of clearance were 16%, 9% and 0.1%, respectively. The PK-PD relationship was not significant despite a trend toward higher etoposide exposure in patients responding to treatment. A significant correlation was found between exposure and extended neutropenia at cycle 3. A significant association between UGT1A1*28 polymorphism and late neutropenia was observed but needs further evaluation. CONCLUSIONS: The present study suggests that neither a priori dose individualization nor dose adaptation using TDM is required validating body surface area dosing of etoposide in the TI-CE protocol.

Estimation of Unbound Carboplatin Clearance From Total Plasma Concentrations as a Means of Facilitating Therapeutic Drug Monitoring.

BACKGROUND: Therapeutic drug monitoring of carboplatin is based on its unbound clearance (CLU) determined by Bayesian analysis on unbound (U) concentrations. However, the ultrafiltration of plasma samples presents technical and time constraints. Therefore, this study aims to estimate CLU using total plasma (P) concentrations. METHODS: U and P concentration data of 407 patients were obtained from 2 clinical studies in which actual CLU had been determined for each patient. The patients were then split into development (277 patients) and prospective data sets (130 patients). Two approaches were evaluated. PK-model-only approach: a 3-compartment pharmacokinetic (PK) model based on U and P concentrations and taking into account the protein binding process was developed. The model with patient covariates was also evaluated. Linear regression approach: an equation (CLU = aCLP + b) was obtained by linear regression analysis between actual CLU and CLP, which is the total plasma clearance obtained by analyzing P concentrations according to a 2-compartment PK model. Predictive performance was then assessed within the prospective data set by estimating CLU from P concentrations using each approach and computing the relative percentage error (PE) between estimated CLU and actual CLU. RESULTS: The linear regression equation was CLU (L/h) = 1.15 CLP (L/h) + 0.13. The mean PE (MPE) between CLU (estimated using the equation) and the actual CLU was +1.2% (ranging from -31% to +33%) and the mean absolute PE (MAPE) was 9.7%. With the 3-compartment PK model, the MPE was +2.3% (ranging from -41% to +31%) and the MAPE was 11.1%. Inclusion of covariates in the 3-compartment model did not improve the estimation of CLU [MPE = +6.3% (from -33% to +37%); MAPE = 11.4%]. CONCLUSIONS: The linear equation gives a relatively good estimation of CLU based on P concentrations, making PK-based carboplatin dose adaptation possible for centers without ultrafiltration facilities.

Therapeutic Drug Monitoring of Carboplatin in High-Dose Protocol (TI-CE) for Advanced Germ Cell Tumors: Pharmacokinetic Results of a Phase II Multicenter Study.

Purpose: We aimed to evaluate the performance of therapeutic drug monitoring (TDM) approach in controlling interpatient variability of carboplatin exposure (AUC) in patients treated with TI-CE high-dose chemotherapy for advanced germ cell tumors and to assess the possibility of using a formula-based dosing method as a possible alternative.Experimental Design: Eighty-nine patients receiving carboplatin for 3 consecutive days during 3 cycles were evaluable for pharmacokinetic study. Blood samples were taken on day 1 to determine the carboplatin clearance using a Bayesian approach (NONMEM 7.2) and to adjust the dose on day 3 to reach the target AUC of 24 mg.min/mL over 3 days. On days 2 and 3, samples were taken for retrospective assessment of the actual AUC. A population pharmacokinetic analysis was also performed on 58 patients using NONMEM to develop a covariate equation for carboplatin clearance prediction adapted for future TI-CE patients, and its performance was prospectively evaluated on the other 29 patients along with different methods of carboplatin clearance prediction.Results: The mean actual AUC was 24.4 mg.min/mL per cycle (22.4 and 26.8 for 10th and 90th percentiles, respectively). The new covariate equation [CL (mL/min) = 130.7 × (Scr/83)-0.826 × (BW/76)+0.907 × (Age/36)-0.223 with Scr in µmol/L, BW in kilograms, age in years] allows unbiased and more accurate prediction of carboplatin clearance compared with other equations.Conclusions: TDM allows controlling and reaching the target AUC. Alternatively, the new equation of carboplatin clearance prediction, better adapted to these young male patients, could be used if TDM cannot be implemented. Clin Cancer Res; 23(23); 7171-9. ©2017 AACR.