Phase-I study of a new schedule based on increasing days of topotecan administration associated with dose individualisation.

BACKGROUND: The most commonly prescribed schedule of topotecan administration is daily for five days, every 21 days. Both pre-clinical and clinical studies suggest that a more protracted schedule may increase its therapeutic index. The current study was undertaken to determine the maximum tolerated number of days with 30-minute i.v. infusion of topotecan daily at fixed area under the plasma concentration-time curve (AUC) (i.e., 35 microg/Lxh). PATIENTS AND METHODS: Topotecan was administered i.v. over 30 min. The planned levels of number of days of administration were: 7, 10, 13, 15 and 17. The dose was individualized according to the patient's individual topotecan clearance observed after the first infusion of each cycle. RESULTS: Twenty-three patients were enrolled and received 71 cycles of therapy. The 13-day level was defined as the maximum number of days of administration. The main side effects were thrombocytopenia and anaemia, whereas neutropenia was infrequent. The mean (coefficient of variation) observed AUC was 34.6 (21%), and 33.4 (19%) microg/Lxh, for the last day of cycle 1, and of cycle 2, respectively. Confirmed partial responses were observed in one patient with metastatic desmoplastic tumour and in two patients with small round metastatic endocrine carcinoma. CONCLUSION: The recommended number of topotecan administration is 10 days. Beyond the potential clinical interest of topotecan administered for a 10-day period, this is the first trial showing the feasibility of a phase-I study exploring a number of administrations of daily AUC rather than a total dose in mg/m(2).

Mechanism-based models for topotecan-induced neutropenia.

OBJECTIVE: A semiphysiologic pharmacokinetic-pharmacodynamic model was applied to describe topotecan-induced neutropenia, to quantify interindividual and intraindividual pharmacodynamic variability, and to study the effect of covariates on the model. METHODS: Data were obtained from patients treated with topotecan given either orally (118 patients) or intravenously (71 patients), according to different schedules (5 to 21 consecutive days), with or without cisplatin. The model mimics the maturation chain of neutrophils. Topotecan concentration-time profiles affected the proliferation of neutrophil precursors (sensitive cells) through an inhibitory linear model (topotecan is assumed to induce cell loss by a function, E drug, proportional to the topotecan concentration in the central compartment: E drug = Slope . Concentration). The topotecan plasma concentration versus time profile was generated for each patient by modeling the data according to a 2-compartment pharmacokinetic model and first-order absorption for oral administration by use of NONMEM. RESULTS: The model described the time course of neutrophil values well. Topotecan neutropenic effect exhibited a large interpatient variability (coefficient of variation of 82% for the slope values). The oral route was associated with a 43% lower value for slope, corresponding to a lower toxicity. The combination with cisplatin increased the neutropenic effect compared with topotecan alone by a factor 3.5. The intrapatient variability between cycle 1 and cycle 2 on slope was lower for the intravenous administration than for the oral administration. By application of the model to a new weekly schedule of topotecan, neutrophil values at the nadir were consistent with those observed during a phase I study of this regimen. CONCLUSION: This model can be used to describe both the duration and intensity of neutropenia; the area between the curve of neutrophil count versus time and a critical neutrophil count (such as 0.500 x 10(3) /mm 3 ) would be a better toxic endpoint than the unique observed value of neutrophil at nadir. The model may be used to predict neutropenia corresponding to regimens of topotecan not yet explored.

Maximum a posteriori Bayesian estimation of oral cyclosporin pharmacokinetics in patients with stable renal transplants.

OBJECTIVE: To develop a maximum a posteriori probability (MAP) Bayesian estimator for the pharmacokinetics of oral cyclosporin, based on only three timepoints, and evaluate its performance with respect to a full-profile nonlinear regression approach. PATIENTS: 20 adult patients with stable renal transplants given orally administered microemulsified cyclosporin and mycophenolate. METHODS: Cyclosporin was assayed by liquid chromatography-mass spectrometry. Nonlinear regression and MAP Bayesian estimation were performed using a home-made program and a previously designed pharmacokinetic model including an S-shaped absorption profile described by a gamma distribution. OUTCOME MEASURES AND RESULTS: MAP Bayesian estimation using the best limited sampling strategy (before administration, and 1 and 3 hours after administration) was compared with nonlinear regression (taken as the reference method) for the prediction of the different pharmacokinetic parameters and exposure indices. Median relative prediction error was -0.49 and -3.42% for area under the concentration-time curve over the administration interval of 12 hours (AUC12) and estimated peak drug concentration (Cmax), respectively (nonsignificant). Relative precision was 2.00 and 4.32%, and correlation coefficient (r) was 0.985 and 0.955, for AUC12 and Cmax, respectively. CONCLUSION: This paper reports preliminary results in a stable renal transplant patient population, showing that MAP Bayesian estimation can allow accurate prediction of AUC12 and Cmax with only three samples (0, 1 and 3 hours). Although these results require confirmation by further studies in other clinical settings, using other drug combinations, other analytical methods and commercially available pharmacokinetic software, the method seems promising as a tool for the therapeutic drug monitoring of cyclosporin in clinical practice or for exposure-controlled studies.

Estimation of glomerular filtration rate in children.

The aim of this study was to develop a method to predict the glomerular filtration rate (GFR) in children by using the population pharmacokinetic approach. This powerful approach is widely used for drug development in order to study relationships between patients' characteristics (demographic, morphological, biological covariates) and pharmacokinetic parameters. For the first time, (51)Cr-EDTA plasma concentrations from 64 children (development data set) were analyzed using the Non-linear Mixed Effects Model (NONMEM) program to determine the most appropriate equation to relate (51)Cr-EDTA clearance (as a measurement of GFR) and patient characteristics. The most predictive equation was based on body weight, square height, and plasma creatinine (PCr, determined by the Jaffé method). This equation was then validated using the data from a further 33 patients. This equation produced estimates of GFR that were less biased and more precise than those obtained using the widely used Schwartz formula. The coefficient of correlation between estimated and actual GFR was 0.83, and the 10th to 90th percentiles for percentage errors were -20% to +30%. Finally, analysis of the whole data set (97 patients) led to an equation (i.e., GFR (ml/min)=[56.7 x Body weight (kg)+0.142 x Length(2)(cm)]/PCr ( microM)) very similar to that obtained from the development data set. This equation would be useful for estimating GFR in children when isotopic determination of the (51)Cr-EDTA clearance cannot be performed.