Bruno Reigner

Preferential activation of capecitabine in tumor following oral administration to colorectal cancer patients.

Purpose: Capecitabine (Xeloda) is a novel fluoropyrimidine carbamate rationally designed to generate 5-fluorouracil (5-FU) preferentially in tumors. The purpose of this study was to demonstrate the preferential activation of capecitabine, after oral administration, in tumor in colorectal cancer patients, by the comparison of 5-FU concentrations in tumor tissues, healthy tissues and plasma. Methods: Nineteen patients requiring surgical resection of primary tumor and/or liver metastases received 1,255 mg/m2 of capecitabine twice daily p.o. for 5–7 days prior to surgery. On the day of surgery, samples of tumor tissue, adjacent healthy tissue and blood samples were collected simultaneously from each patient, 2 to 12 h after the last dose of capecitabine had been administered. Concentrations of 5-FU in various tissues and plasma were determined by HPLC. The activities of the enzymes (CD, TP and DPD) involved in the formation and catabolism of 5-FU were measured in tissue homogenates, by catabolic assays. Results: The ratio of 5-FU concentrations in tumor to adjacent healthy tissue (T/H) was used as the primary marker for the preferential activation of capecitabine in tumor. In primary colorectal tumors, the concentration of 5-FU was on average 3.2 times higher than in adjacent healthy tissue (P=0.002). The mean liver metastasis/healthy tissue 5-FU concentration ratio was 1.4 (P=0.49, not statistically different). The mean tissue/plasma 5-FU concentration ratios exceeded 20 for colorectal tumor and ranged from 8 to 10 for other tissues. Conclusions: The results demonstrated the preferential activation of capecitabine to 5-FU in colorectal tumor, after oral administration to patients. This is explained to a great extent by the activity of TP in colorectal tumor tissue, (the enzyme responsible for the conversion of 5′-DFUR to 5-FU), which is approximately four times that in adjacent healthy tissue. In the liver, TP activity is approximately equal in metastatic and healthy tissue, which explains the lack of preferential activation of capecitabine in these tissues.

Clinical Pharmacokinetics of Capecitabine

Capecitabine is a novel oral fluoropyrimidine carbamate that is preferentially converted to the cytotoxic moiety fluorouracil (5-fluorouracil; 5-FU) in target tumour tissue through a series of 3 metabolic steps. After oral administration of 1250 mg/m2, capecitabine is rapidly and extensively absorbed from the gastrointestinal tract [with a time to reach peak concentration (tmax) of 2 hours and peak plasma drug concentration (Cmax) of 3 to 4 mg/L] and has a relatively short elimination half-life (t1/2) [0.55 to 0.89h]. Recovery of drug-related material in urine and faeces is nearly 100%.Plasma concentrations of the cytotoxic moiety fluorouracil are very low [with a Cmax of 0.22 to 0.31 mg/L and area under the concentration-time curve (AUC) of 0.461 to 0.698 mg · h/L]. The apparent t1/2 of fluorouracil after capecitabine administration is similar to that of the parent compound.Comparison of fluorouracil concentrations in primary colorectal tumour and adjacent healthy tissues after capecitabine administration demonstrates that capecitabine is preferentially activated to fluorouracil in colorectal tumour, with the average concentration of fluorouracil being 3.2-fold higher than in adjacent healthy tissue (p = 0.002). This tissue concentration differential does not hold for liver metastasis, although concentrations of fluorouracil in liver metastases are sufficient for antitumour activity to occur. The tumour-preferential activation of capecitabine to fluorouracil is explained by tissue differences in the activity of cytidine deaminase and thymidine Phosphorylase, key enzymes in the conversion process.As with other cytotoxic drugs, the interpatient variability of the pharmacokinetic parameters of capecitabine and its metabolites, 5′-deoxy-5-fluorocytidine and fluorouracil, is high (27 to 89%) and is likely to be primarily due to variability in the activity of the enzymes involved in capecitabine metabolism. Capecitabine and the fluorouracil precursors 5′-deoxy-5-fluorocytidine and 5′-deoxy-5-fluorouridine do not accumulate significantly in plasma after repeated administration. Plasma concentrations of fluorouracil increase by 10 to 60% during long term administration, but this time-dependency is assumed to be not clinically relevant.A potential drug interaction of capecitabine with warfarin has been observed. There is no evidence of pharmacokinetic interactions between capecitabine and leucovorin, docetaxel or paclitaxel.

Pharmacokinetics and Pharmacodynamics of Intravenous and Subcutaneous Continuous Erythropoietin Receptor Activator (C.E.R.A.) in Patients with Chronic Kidney Disease

Continuous Erythropoietin Receptor Activator (C.E.R.A.) is a new agent that is in development for the treatment of anemia with extended administration intervals in patients who have chronic kidney disease (CKD), both those on and those not on dialysis. This was an open-label, randomized, multicenter, two-period, crossover study in erythropoiesis-stimulating agentnaïve patients who had CKD and anemia and were receiving peritoneal dialysis. After a 1-wk run-in period, 16 patients were randomly assigned to receive a single administration of intravenous C.E.R.A. 0.4 microg/kg (n = 8) or subcutaneous C.E.R.A. 0.8 microg/kg (n = 8). Six weeks after the first administration of C.E.R.A. (4-wk assessment, 2-wk washout), the route of administration was switched so that all patients received single administrations of both intravenous C.E.R.A. 0.4 microg/kg and subcutaneous C.E.R.A. 0.8 microg/kg. C.E.R.A. had a prolonged and comparable half-life after intravenous (mean 134 h) and subcutaneous (mean 139 h) administration. Reticulocyte counts peaked at a median of 8 d after intravenous and subcutaneous administration with no difference in the time course between administration routes. This resulted in similar mean values for the area under the reticulocyte count-time curve (1191 x 10(9) and 1193 x 10(9).d per L, respectively) and the maximum absolute increase in reticulocyte counts (36 x 10(9) and 41 x 10(9)/L, respectively). C.E.R.A. has a prolonged and comparable half-life after intravenous or subcutaneous injection, suggesting that extended administration intervals may be feasible in patients with CKD.

Prediction of Hepatic Metabolic Clearance Based on Interspecies Allometric Scaling Techniques and In Vitro-In Vivo Correlations

This article reviews the methods available for predicting hepatic metabolic clearance in humans, and discusses their application to the processes of drug discovery and development. The application of these techniques has increased markedly during the past few years because of the improved availability of human liver samples, which has increased the opportunities to use in vitro studies to predict human clearance. The techniques available involve both empirical and physiologically based approaches. Allometric scaling using in vitro data from animals and humans combines certain aspects of both approaches.An evaluation of data retrieved from the literature indicates that, together with in vitro human data, allometric scaling based on a combination of in vitro and in vivo preclinical data can accurately predict clearance in humans. With this approach, 80% of the predictions were within a 2-fold factor of actual human clearance values, with an overall accuracy of 1.6-fold.The uncertainties and inaccuracies in predicting human clearance are related to: (i) the specific method that is used to make the prediction; (ii) the experimental design and the model used to determine the in vitro clearance; (iii) protein binding within the in vitro test system; and (iv) various in vivo factors such as the involvement of extrahepatic metabolism and active transport processes, interindividual variability and nonlinearity in pharmacokinetics.In contrast to purely empirical approaches, the physiological approach to predicting clearance gives an opportunity to integrate some of these complexities and, therefore, should provide more confidence in the prediction of clearance in humans.

An Evaluation of the Integration of Pharmacokinetic and Pharmacodynamic Principles in Clinical Drug Development Experience within Hoffmann La Roche

SummaryThe integration of pharmacokinetic and pharmacodynamic principles into drug development has been proposed as a way of making it more rational and efficient. The use of these principles in drug development to make scientific and strategic decisions is defined as the ‘pharmacokinetic-pharmacodynamic guided approach to drug development’.The objectives of this survey were: (i) to assess the extent the pharmacokinetic-pharmacodynamic guided approach to drug development has been used in a large multinational pharmaceutical company: (ii) to evaluate the impact of pharmacokinetic and/or pharmacodynamic results on clinical drug development; and (iii) to identify factors which prevented the full application of the pharmacokinetic-pharmacodynamic guided approach.This was done by looking at 18 projects in the current development portfolio at Hoffman La Roche and evaluating the use of this approach by interviewing the responsible clinical pharmacologist using a standardised questionnaire.(i) Benefits from using the pharmacokinetic-pharmacodynamic guided approach were reported in every project, independent of development phase and therapeutic area. This approach was more extensively used in the recent projects. The selection of dosages in clinical studies was found to be the most important application of pharmacokinetic-pharmacodynamic results in terms of an impact on drug development, (ii) Time savings, up to several months, could be quantified in 8 projects during the entry-into-man studies and in 6 projects during the phase II or III studies. In 4 projects, 1 clinical study was avoided. (iii) The most important scientific factor preventing the full application of the approach was the lack of knowledge on the predictive value of the pharmacodynamic or surrogate marker for effect (6 projects).The results of the survey have shown that the use of the pharmacokinetic-pharmacodynamic guided approach has contributed to making clinical drug development more rational and more efficient. Opportunities to apply the pharmacokinetic-pharmacodynamic approach should be identified in each project and a project specific strategy for the pharmacokinetic-pharmacodynamic guided approach should be defined during phase 0 of drug development.

A human capecitabine excretion balance and pharmacokinetic study after administration of a single oral dose of 14C-labelled drug.

An excretion balance and pharmacokinetic study was conducted in cancer patients with solid tumors who received a single oral dose of capecitabine of 2000 mg including 50 μ Ci of 14C-radiolabelled capecitabine. Blood, urine and fecal samples were collected until radioactive counts had fallen to below 50 dpm/mL in urine, and levels of intact drug and its metabolites were measured in plasma and urine by LC/MS-MS (mass spectrometry) and 19F-NMR (nuclear magnetic resonance) respectively. Based on the results of the 6 eligible patients enrolled, the dose was almost completely recovered in the urine (mean 95.5%, range 86–104% based on radioactivity measurements) over a period of 7 days after drug administration. Of this, 84% (range 71–95) was recovered in the first 12 hours. Over this time period, 2.64% (0.69–7.0) was collected in the feces. Over a collection period of 24–48h, a total of 84.2% (range 80–95) was recovered in the urine as the sum of the parent drug and measured metabolites (5′-DFCR, 5′-DFUR, 5-FU, FUH2, FUPA, FBAL). Based on the radioactivity measurements of drug-related material, absorption is rapid (tmax 0.25–1.5 hours) followed by a rapid biphasic decline. The parent drug is rapidly converted to 5-FU, which is present in low levels due to the rapid metabolism to FBAL, which has the longest half-life. There is a good correlation between the levels of radioactivity in the plasma and the levels of intact drug and the metabolites, suggesting that these represent the most abundant metabolites of capecitabine. The absorption of capecitabine is rapid and almost complete. The excretion of the intact drug and its metabolites is rapid and almost exclusively in the urine.

Phase I and Pharmacokinetic Study of the Oral Fluoropyrimidine Capecitabine in Combination With Paclitaxel in Patients With Advanced Solid Malignancies

PURPOSE To evaluate the feasibility of administering the oral fluoropyrimidine capecitabine in combination with paclitaxel, to characterize the principal toxicities of the combination, to recommend doses for subsequent disease-directed studies, and to determine whether significant pharmacokinetic interactions occur between these agents when combined. PATIENTS AND METHODS Sixty-six courses of capecitabine and paclitaxel were administered to 17 patients in a two-stage dose-escalation study. Paclitaxel was administered as a 3-hour intravenous (IV) infusion every 3 weeks, and capecitabine was administered continuously as two divided daily doses. During stage I, capecitabine was escalated to a target dose of 1,657 mg/m(2)/d, whereas the paclitaxel dose was fixed at 135 mg/m(2). In stage II, paclitaxel was increased to a target dose of 175 mg/m(2), and the capecitabine dose was the maximum established in stage I. Pharmacokinetics were characterized for each drug when given alone and concurrently. RESULTS Myelosuppression, predominately neutropenia, was the principal dose-limiting toxicity (DLT). Other toxicities included hand-foot syndrome, diarrhea, hyperbilirubinemia, skin rash, myalgia, and arthralgia. Two patients treated with capecitabine 1,657 mg/m(2)/d and paclitaxel 175 mg/m(2) developed DLTs, whereas none of six patients treated with capecitabine 1,331 mg/m(2)/d and paclitaxel 175 mg/m(2) developed DLTs during course 1. Pharmacokinetic studies indicated that capecitabine and paclitaxel did not affect the pharmacokinetic behavior of each other. No major antitumor responses were noted. CONCLUSION Recommended combination doses of continuous capecitabine and paclitaxel are capecitabine 1,331 mg/m(2)/d and paclitaxel 175 mg/m(2)/d IV every 3 weeks. Favorable preclinical mechanistic interactions between capecitabine and paclitaxel, as well as an acceptable toxicity profile without clinically relevant pharmacokinetic interactions, support the performance of disease-directed evaluations of this combination.

Significant Effect of Capecitabine on the Pharmacokinetics and Pharmacodynamics of Warfarin in Patients With Cancer

PURPOSE Clinical cases of capecitabine and other fluorouracil-based chemotherapies potentiating the effects of coumarin derivatives have been reported. This study assessed the influence of capecitabine on the pharmacokinetics (PK) and pharmacodynamics (PD) of warfarin. PATIENTS AND METHODS Four patients with advanced/metastatic cancer completed the study, receiving a single oral dose of 20 mg warfarin before the start of standard capecitabine treatment (day 1), and again during the third cycle of capecitabine (day 61). PK parameters of warfarin and capecitabine and PD parameters of warfarin were assessed on days 1 and 61. RESULTS During capecitabine treatment, the area under the plasma concentration time curve from 0 to infinity (AUC(0-infinity)) of S-warfarin increased by 57% (90% CI, 32% to 88%) with a 51% prolongation of the elimination half-life (t(1/2); 90% CI, 32% to 74%). Exposure to R-warfarin was not significantly affected. Plasma concentrations of capecitabine and its metabolites were not influenced by warfarin. During capecitabine treatment, the effect of warfarin on the baseline corrected AUC of the International Normalized Ratio (INR) increased by 2.8 times (90% CI, 1.33 to 5.70), with the maximum observed INR value almost doubling. Because of the administration of vitamin K to some patients with elevated INRs, these figures are likely to underestimate the true PD effect. Mean baseline factor VII levels dropped while on capecitabine therapy, potentially contributing to the observed PD interaction, though this effect did not reach statistical significance. CONCLUSION There is a significant pharmacokinetic interaction between capecitabine and S-warfarin, resulting in exaggerated anticoagulant activity. Patients receiving warfarin anticoagulant therapy concomitantly with capecitabine should have their INR closely monitored and warfarin doses adjusted accordingly.

Influence of the antacid Maalox on the pharmacokinetics of capecitabine in cancer patients

Purpose: In the present study the possible influence of the antacid Maalox on the pharmacokinetics of capecitabine (Xeloda) and its metabolites was investigated in cancer patients. Methods: A total of 12 patients with solid, predominantly metastatic tumors of various origin received a single oral dose of 1250 mg/m2 of capecitabine (treatment A), a single oral dose of 1250 mg/m2 of capecitabine followed immediately by 20 ml of Maalox (treatment B), and a single oral dose of 1250 mg/m2 of capecitabine followed 2 h later by 20 ml of Maalox (treatment C) in an open, randomized, three-way cross over fashion. Serial blood and urine samples were collected for up to 24 h after each administration. Unchanged capecitabine and its metabolites were analyzed in plasma using liquid chromatography/mass spectrometry and in urine using nuclear magnetic resonance spectroscopy. Results: Administration of Maalox either concomitantly with capecitabine or delayed by 2 h did not influence the time to peak plasma concentrations (Cmax) or the elimination half-lives of capecitabine and its metabolites. Unexpectedly, moderate increases in the Cmax and AUC0–∞ values obtained for capecitabine and 5′-deoxy-5-fluorocytidine were observed when Maalox was given together with capecitabine. However, these increases, which ranged between 10% and 31%, were not statistically significant (P > 0.05) and are not of clinical significance. There was no indication of consistent changes in the plasma concentrations of the other metabolites 5′-deoxy-5′-fluorouridine (5′-DFUR), 5-fluorouracil, and α-fluoro-β-alanine. The Cmax and AUC0–∞ values recorded for these three metabolites increased and decreased in a stochastic manner. The magnitude of these changes was low (<13%) and not statistically significant. The primary statistical analysis of the AUC0–∞obtained for 5′-DFUR provided a P value of 0.4524 and clearly indicated no significant difference between the treatments. The addition of Maalox had no influence on the overall urinary recovery or the proportion of the dose recovered as capecitabine or its metabolites from urine. Conclusion: At the dose used in this study, the effect of concomitantly delivered Maalox on the extent and rate of gastrointestinal absorption of capecitabine is not clinically significant. Therefore, there is no need to adjust the dose or timing of capecitabine administration in patients treated with Maalox.

Clinical pharmacokinetic/pharmacodynamic and physiologically based pharmacokinetic modeling in new drug development: The capecitabine experience

Preclinical studies, along with Phase I, II, and III clinical trials demonstrate the pharmacokinetics, pharmacodynamics, safety and efficacy of a new drug under well controlled circumstances in relatively homogeneous populations. However, these types of studies generally do not answer important questions about variability in specific factors that predict pharmacokinetic and pharmacodynamic (PKPD) activity, in turn affecting safety and efficacy. Semi-physiological and clinical PKPD modeling and simulation offer the possibility of utilizing data obtained in the laboratory and the clinic to make accurate characterizations and predictions of PKPD activity in the target population, based on variability in predictive factors. Capecitabine is an orally administered pro-drug of 5-fluorouracil (5-FU), designed to exploit tissue-specific differences in metabolic enzyme activities in order to enhance efficacy and safety. It undergoes extensive metabolism in multiple physiologic compartments, and presents particular challenges for predicting pharmacokinetic and pharmacodynamic activity in humans. Clinical and physiologically based pharmacokinetic (PBPK) and pharmacodynamic models were developed to characterize the activity of capecitabine and its metabolites, and the clinical consequences under varying physiological conditions such as creatinine clearance or activity of key metabolic enzymes. The results of the modeling investigations were consistent with capecitabines rational design as a triple pro-drug of 5-FU. This paper reviews and discusses the PKPD and PBPK modeling approaches used in capecitabine development to provide a more thorough understanding of what the key predictors of its PBPK activity are, and how variability in these predictors may affect its PKPD, and ultimately, clinical outcomes.