Isabelle Lochon

Population pharmacokinetics of total and unbound etoposide.

Abstract A population pharmacokinetics study using the NONMEM program was undertaken to determine the effects of different covariates on the pharmacokinetic parameters of etoposide. A total of 1,044 plasma etoposide concentrations were determined by high-performance liquid chromatography (HPLC) in 100 patients (pts; 75 men and 25 women aged 25–85 years) treated for various tumor types with i.v. (57 pts) or oral (43 pts) etoposide. For 67 pts, etoposide plasma protein binding was determined by equilibrium dialysis; the unbound fraction ranged from 4% to 24%. A linear two-compartment model with first-order absorption (for oral dosing) accurately described the concentration versus time data. The central and peripheral volumes of distribution were significantly correlated with the body surface area [Vc (L) = 5.5 × BSA (m2) and Vp = 4.1 × BSA], but even after BSA had been taken into account, the interindividual variability of the two volumes remained high (34% and 57%, respectively). The clearance (CL) was not correlated with the following covariates: age, BSA, sex, height, and levels of serum bilirubin and liver enzymes. The final regression model for CL was CL (ml/min) = 49.8 × (1 − 0.009 × PRO) × WT/Scr + 33.8 × (1 − 0.29 × META) × (1− (1 − 0.012 × ALB), where ALB, PRO, WT,and Scr, respectively, were albuminemia, proteinemia (g/l), weight (kg), and serum creatinine (μM ) and META = 1 if the patient had liver metastases (otherwise, META = 0). The interindividual variability in CL (mean value 30 ml/min) decreased only from 32% to 26% when these covariates were taken into account. The mean oral bioavailability was 66%, showing an interindividual variability of 37%. The plasma clearance of the unbound fraction was strongly and negatively correlated with Scr but was not dependent on either PRO or ALB. These data show that modifications in PRO levels do not directly affect plasma exposure to unbound etoposide. This analysis makes possible the rational consideration of modifications of covariates such as Scr in etoposide dosing. This population data base will constitute the prerequisite for adaptative control with feedback dosing for continuous oral administration of etoposide.

Comparison of the pharmacokinetics and efficacy of irinotecan after administration by the intravenous versus intraperitoneal route in mice

Abstract Irinotecan (CPT-11) is a new drug active in colorectal cancer. A comparison was made of the efficacy and pharmacokinetics of CPT-11 after i.p. versus i.v. administration to mice. We found that i.p. administration of CPT-11 to mice bearing C26 colon cancer was more efficient and less toxic than i.v. administration; a 100-mg i.p. dose induced an increase in life span equivalent to that produced by a 300-mg i.v. dose, and toxic deaths appeared after doses of 400 mg/kg given i.v. and 800 mg/kg given i.p. Pharmacokinetic parameters of CPT-11 and SN-38 were compared after i.v. or i.p. administration in mice bearing P388 leukemia ascites. Peritoneal CPT-11 and SN-38 AUC values were higher after i.p. administration than after i.v. injection. Plasmatic AUC values remained equivalent. Moreover, peritoneal CPT-11 clearance was 10-fold lower after i.p. versus i.v. administration. If the survival and pharmacologic advantage of i.p. CPT-11 in the murine model considered can be translated to a safe and practical mode of therapy in patients and if local toxicity does not prove to be a major adverse effect, then a potentially useful agent could be added to the drugs known to be active when given by the i.p. route for adjuvant therapy in colon cancer.

A universal formula based on cystatin C to perform individual dosing of carboplatin in normal weight, underweight, and obese patients.

Purpose: It has recently been shown that it is possible to improve the prediction of carboplatin clearance by adding plasma cystatin C level (cysC), an endogenous marker of glomerular filtration rate, to the other patient characteristics routinely used for carboplatin individual dosing, namely serum creatinine (Scr), actual body weight (ABW), age, and sex. This multicenter pharmacokinetic study was done to evaluate prospectively the benefit of using cysC for carboplatin individual dosing. Experimental Design: The 357 patients included in the study were receiving carboplatin as part of established protocols. A population pharmacokinetic analysis was done using NONMEM program. Seven covariates studied were as follows: Scr, cysC, age, sex, ABW, ideal body weight, and lean body mass. Results: The best covariate equation was as follows: carboplatin clearance (mL/min) = 117.8. (Scr/75)−0.450. (cysC/1,00)−0.385. (ABW/65)+0.504. (age/56)−0.366. 0.847sex, with Scr in μmol/L, cysC in mg/L, ABW in kilograms, age in years, and sex = 0 for male. Using an alternative weight descriptor (ideal body weight or lean body mass) did not improve the prediction. This final covariate model was validated by bootstrap analysis. The bias (mean percentage error) and imprecision (mean absolute percentage error) were +1% and 15%, respectively, on the total population, and were of a similar magnitude in each of the three subgroups of patients defined according to their body mass index. Conclusion: For the first time, a unique formula is proposed for carboplatin individual dosing to patients, which is shown to be equally valid for underweight, normal weight, and obese patients.

A limited-sampling strategy for estimation of etoposide pharmacokinetics in cancer patients.

Abstract Etoposide (VP16), a widely used anticancer drug, is a topoisomerase II inhibitor. A number of studies have highlighted a correlation between hematologic toxicity and pharmacokinetic or physiological parameters. Other studies have also suggested that the anti-tumor response could be related to the plasma etoposide concentration. Therefore, it would seem of interest to individualize VP16 dose regimens on the basis of pharmacokinetic parameters. The aim of this study was to develop and validate a limited-sampling strategy allowing VP16 pharmacokinetic evaluation with minimal disturbance to the patient. A total of 34 patients (54 kinetics) received VP16 at various dose regimens, with doses ranging between 30 and 200 mg and infusion times varying between 0.5 and 2 h. The statistical characteristics of the pharmacokinetic parameters were assessed from the first courses of treatment performed in 23/34 patients; then the following three-sample protocol was designed: the end of the infusion and 5 and 24 h after the start of the infusion. For validation of the model the main pharmacokinetic parameters (clearance, half-lives, volume of distribution) were estimated in the 11 remaining patients by maximum-likelihood estimation (ML) and by Bayesian estimation (BE) using the three sampling times designed. Statistical comparison showed a good concordance between ML and BE estimates (the bias for clearance was –1.72%). The limited-sampling strategy presented herein can thus be used for accurate estimation of VP16 pharmacokinetic parameters.

Dihydropyrimidine dehydrogenase activity in normal, inflammatory and tumour tissues of colon and liver in humans

Background/Purpose: Dihydropyridmidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5FU). Although this catabolism is likely to occur in the liver in humans, there may be a local inactivation in tumours, modifying the efficacy of 5FU. The aim of this study was to examine the DPD activity in normal, inflammatory and malignant tissues from both the colon and the liver to assess the modifications of DPD activity in the process of tumourigenesis. Methods: DPD activity was evaluated in 107 patients, corresponding to 194 samples (70 colorectal tumour and normal colon, nine metastases secondary to a colon cancer, ten inflammatory colon, 20 samples of normal liver, seven from primary liver cancer, and eight from inflammatory liver). DPD activity was determined using an enzymatic reaction followed by analysis of 5FU and its catabolite dihydro-5FU by high-performance liquid chromatograph. Results were expressed as pmol of 5FU catabolized/min · mg protein. Results: DPD was highly variable in tumour and normal tissues, both from colon and liver. In colon, the correlation between DPD activity in tumour and normal mucosa was weak, even if it was statistically significant due to the higher number of samples. In inflammatory colon tissue (ulcerative colitis or Crohns disease), DPD activity was significantly higher than in normal tissue (P=0.006). In liver metastases from colon cancer, DPD activity was not significantly different from that observed in primary colon tumour (P=0.32). In liver, DPD activity was significantly lower in primary liver tumour than in uninvolved liver specimens (P=0.001). In inflammatory liver tissue (hepatitis), DPD activity ranged between normal and tumour tissues, and did not differ significantly either from normal tissue or primary liver cancer. Conclusions: DPD activity was modified in colon and in liver during a pathological process and the dysregulation of DPD increased from a benign to a malignant tissue.

A Phase I Dose-Escalating and Pharmacokinetic Study of Docetaxel and Vinorelbine as First-Line Chemotherapy for Metastatic Breast Cancer

Docetaxel and vinorelbine are both active drugs as single agents in the treatment of metastatic breast cancer. We performed a phase I dose-escalating and pharmacokinetic study to assess the safety profile of a new combination regimen and the pharmacokinetic interaction of vinorelbine and docetaxel. Patients with metastatic breast cancer received first-line treatment with both drugs on days 1–5. Treatment was restarted on day 21 of each cycle. We had to stop the escalation at the first step of the study (vinorelbine 20 mg/m2 followed by docetaxel 30 mg/m2 on days 1 and 5) because of hematological toxicity. In 4 additional patients who received G-CSF supplementation, no major leukopenia occurred, suggesting that the toxicity profile of this combination is very homogenous and focused on neutrophils. We found no pharmacokinetic interaction between the two drugs. These results suggest that a pharmacodynamic interaction was the cause of the hematological toxicity and that sequential regimens should be preferably further explored.

Cytotoxic effect of interferon-alpha2a in combination with all-trans retinoic acid or cisplatin in human ovarian carcinoma cell lines.

Ovarian cancer has a poor prognosis due to the frequent appearance of a drug-resistant state. An alternative therapeutic approach may lie in combinations of conventional chemotherapeutic agents with new classes of drug, such as interferons (IFN) and differentiation-inducing agents. There is clinical evidence that both IFN-α2a–all-trans retinoic acid (ATRA) and IFN-α2a–cisplatin have significant activities on growth of malignant cells, cell differentiation or programmed cell death in solid tumors. In order to throw more light on the cellular basis of these findings and to optimize a schedule of such drug combinations, we examined the cytotoxic effects of various combinations on five human ovarian carcinoma cell lines. The experiments were based on a clonogenic assay on plastic. The different cell lines exhibited different sensitivities to the three drugs tested. Using the cell line most sensitive to these drugs, we then examined the effect of different sequences of two drug combinations. We observed a potentiation after pretreatment with ATRA followed by IFN-α2a and ATRA or after pretreatment with IFN-α2a followed by IFN-α2a and cisplatin. Using this schedule of administration, cytotoxic interactions between the two drugs were investigated by median effect analysis. Synergism or antagonism were observed depending on the intrinsic sensitivity of the cell line to the first drug and the concentrations used. The magnitude of these interactions was found to be influenced by the cellular sensitivity to the second drug. These results show that schedules of drug combinations are not easy to design and may help account for the various failures and the discrepant effects observed in clinical trials.

Unexpected High Levels of Vorinostat when Combined with Vinorelbine in Patients with Advanced Cancer

BACKGROUND This study was a multi-centre, dose-escalation trial in patients with advanced cancers. Primary objective was to determine maximum tolerated dose (MTD) of vorinostat, a competitive inhibitor of histone deacetylase (HDAC), in combination with vinorelbine. Secondary aims were to determine (1) corresponding pharmacokinetics, (2) safety of this regimen, and (3) impact of UGT1A1 and 2B17 polymorphisms on vorinostat pharmacokinetics. METHODS Starting dose of once daily oral vorinostat was 200 mg for 7 days every 21 days in combination with a 20-min intraveinous weekly infusion of vinorelbine 25 mg/m2, starting 4 hours after the first vorinostat dose. During cycle 1, blood samples were collected at day 1 for vorinostat and at days 1 and 8 for vinorelbine for pharmacokinetic evaluation. RESULTS Seven patients were included. Most of adverse events observed were mild (grades 0-2) and reversible after treatment discontinuation (hemotological toxicity, asthenia, diarrhea, dyspnea, fever, hyperglycemia and nausea). Two patients had a dose limiting toxicity at the first dose level that consisted of grade 3 hyperglycemia and vinorelbine administration was delayed. The first dose-level was considered as the MDT and therefore dose escalation was stopped. Mean vorinostat plasma AUC was higher than reported previously at a similar dose when used as single agent or in combination with other cytotoxics. There was no obvious vinorelbine-vorinostat interaction nor any correlation with UGT1A1 or 2B17 polymorphisms. CONCLUSION MDT of the combination was 200 mg oral vorinostat for 7 days in combination with 25 mg/m2 weekly vinorelbine. Severity of hyperglycemia was most likely related to unexpected high vorinostat exposures.