Pharmacokinetics and toxicity of two modalities of etoposide infusion in metastatic non-small-cell lung carcinoma

Population pharmacokinetics of the BEACOPP polychemotherapy regimen in Hodgkin's lymphoma and its effect on myelotoxicity

BACKGROUND AND OBJECTIVE

The BEACOPP (bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine and prednisone) chemotherapy regimen for the treatment of advanced Hodgkin's lymphoma has a superior outcome, but its toxicity (mainly haematotoxicity) is pronounced and highly variable. The present study was conducted to address the role of pharmacokinetics in individual toxicity.

STUDY DESIGN

Three plasma samples and a 24-hour urine collection for day 1 of the first three cycles of chemotherapy were analysed in 30 patients, and the pharmacokinetic parameters of the respective drugs were estimated by population pharmacokinetic methods (nonlinear mixed-effects model [NONMEM] software). Demographic data, doses and durations of infusion were also recorded. The effect of these parameters on platelet counts was estimated by analysis of covariance using a general linear model.

RESULTS

The pharmacokinetic parameters and respective covariates were similar to the published data. The body surface area, peak concentrations of etoposide, urinary recovery of dechloroethylcyclophosphamide (formed by cytochrome P450 [CYP] 3A4) relative to the cyclophosphamide dose and number of cycles had a significant effect on toxicity. These factors explained 37% of the interindividual variability in the change in platelet counts from day 1 to day 8 of each cycle.

CONCLUSION

The results show that the individual pharmacokinetics of BEACOPP drugs are an important link between dosage and toxicity. Accordingly, individualisation of treatment based on pharmacokinetics may result in more uniform toxicity. Individualisation may also allow escalation of the mean dose, which is probably related to better efficacy. As a consequence of the present study, infusion rates should be standardised, and the potential of a dose reduction in the first cycle and of CYP3A4 phenotyping should be addressed in clinical studies.

Pharmacokinetic Optimisation of Treatment with Oral Etoposide

Etoposide is a derivative of podophyllotoxin widely used in the treatment of several neoplasms, including small cell lung cancer, germ cell tumours and non-Hodgkin's lymphomas. Prolonged administration of etoposide aims for continuous inhibition of topoisomerase II, the intracellular target of etoposide, thus preventing tumour cells from repairing DNA breaks. However, the clinical advantages of extended schedules as compared with conventional short-term infusions remain unclear. Oral administration of etoposide represents the most feasible and economic strategy to maintain effective concentrations of drug for extended times. Nevertheless, the efficacy of oral etoposide therapy is contingent on circumventing pharmacokinetic limitations, mainly low and variable bioavailability. Inhibition of small bowel and hepatic metabolism of etoposide with specific cytochrome P450 inhibitors or inhibition of the intestinal P-glycoprotein efflux pump have been attempted to increase the bioavailability of oral etoposide, but the best results were obtained with daily oral administration of low etoposide doses (50-100 mg/day for 14-21 days). Saturable absorption of etoposide was reported for doses greater than 200 mg/day, whereas lower doses were associated with increased bioavailability, although they were characterised by high inter- and intrapatient variability. Pharmacokinetic parameters such as plasma trough concentration between two oral administrations (C(24,trough)), drug exposure time above a threshold value and area under the plasma concentration-time curve have been correlated with the pharmacodynamic effect of oral etoposide. Pharmacokinetic-pharmacodynamic relationships indicate that severe toxicity is avoided when peak plasma concentrations do not exceed 3-5 mg/L and C(24,trough) is under the threshold limit of 0.3 mg/L. To maintain effective etoposide plasma concentrations during prolonged oral administration, pharmacokinetic variability must be monitored in each patient, taking account of factors from many pharmacokinetic studies of etoposide, including absorption, distribution, protein binding, metabolism and elimination. Dosage reduction is generally useful to avoid haematological toxicity in patients with renal dysfunction (creatinine clearance <50 mL/min). The need for dosage adjustment based on liver function in patients with liver dysfunction is not completely defined, but generally is not indicated in patients with minor liver dysfunction. Adaptive dosage adjustment based on individual pharmacokinetic parameters, estimated using limited sampling strategies and population pharmacokinetic models, is more appropriate. This approach has been used with success in different clinical trials to increase the etoposide dosage, without significantly increasing toxicity. Various pharmacodynamic models have been proposed to guide etoposide oral dosage. However, they lack precision and accuracy and need to be refined by considering other predictor variables in order to extend their application in current clinical practice.

Etoposide for the treatment of paediatric tumours: what is the best way to give it?

Etoposide is one of the most important drugs available for the treatment of paediatric malignancies. Although there is evidence of schedule dependency for etoposide therapy in adults with small-cell lung cancer, the relevance of this observation to childhood cancers is uncertain. Prolonged parenteral or oral etoposide therapy has not yet shown a clear-cut advantage over intermittent treatment, and there are still no data to show that the administration of etoposide as a short intravenous (i.v.) daily infusion for 5 days does not represent acceptable therapy for primary disease. The pharmacokinetic variability seen with etoposide argues strongly for the use of pharmacologically guided dosing, and the introduction of etoposide phosphate will simplify both parenteral etoposide administration and the future evaluation of alternative etoposide schedules. Although the impact of molecular and cellular pharmacological investigations on the clinical use of etoposide has yet to be felt, the tools to perform these studies are now available and prospective trials can be designed. Such studies, performed in the setting of a pharmacologically guided trial to ensure control over pharmacokinetic variability, should identify the best way of treating children with etoposide.

Limited sampling models for reliable estimation of etoposide area under the curve

Limited sampling models are able to estimate the area under the concentration-time curve (AUC) from plasma concentrations measured at only a few time points. The purpose of this study was to establish a model estimating etoposide AUC independently of specific chemotherapy protocols, underlying malignancies, concomitant diseases and age. Pharmacokinetic parameters were measured in 30 patients treated with polychemotherapy including etoposide (80-150 mg/m2). Etoposide analysis was performed by thin layer chromatography and consecutive quantitative sample detection by 252Cf-plasma desorption mass spectrometry. Data from the first 15 patients formed the training set. Based on the training data, five different models were generated, with the multiple regression coefficient r ranging from 0.91 to 0.96. The following model was selected as "most accurate": AUC = 343 (min)C4h(micrograms/ml) + 650(min)C8h(micrograms/ml) + 1252 (min micrograms/mol), where C4h is the plasma concentration of etoposide at 4 h after the end of infusion and C8h at 8 h. This model was validated on the test set, comprising the data of the remaining 15 patients. The mean predictive error (MPE) was -0.2% and the root mean square predictive error (RMSE) was 4.7%. When used for a large number of patients, this practicable and simple model is an instrument for use in prospective studies, to measure a correlation between drug dosage and efficacy or toxicity of the drug.

Etoposide protein binding in cancer patients

The protein binding of etoposide was studied in vivo in 36 cancer patients receiving etoposide therapy. Free etoposide was separated from plasma using an ultrafiltration method and the etoposide concentrations (free and total) were measured by high-performance liquid chromatography (HPLC). Considerable interpatient variation in the protein binding of etoposide was observed. The protein binding of etoposide varied from 80% to 97% (mean, 93%). Univariate analysis showed a significant inverse correlation between the free fraction of etoposide and serum albumin (r = 0.74), daily dose (r = 0.37) and age (r = -0.34). Multivariate analysis demonstrated that serum albumin and age were independent predictors of the etoposide free fraction. Serum bilirubin showed no correlation with etoposide protein binding. There is wide variation in etoposide protein binding in cancer patients, which is mostly dependent on serum albumin concentration.

Inhibition of prostate cancer growth by estramustine and etoposide: evidence for interaction at the nuclear matrix

Metastatic prostate cancer which is refractory to hormone therapy remains an incurable disease for which there is no effective therapy. We have begun to investigate the nuclear matrix, the RNA-protein network of the nucleus that plays an important role in DNA replication and gene expression, as a target for cancer chemotherapy. It was postulated that estramustine phosphate (EMP), an estradiol-nitrogen mustard conjugate that binds to the nuclear matrix, might enhance the cytotoxicity of etoposide (VP-16), a topoisomerase II inhibitor that acts at the level of the nuclear matrix. In a nascent DNA synthesis assay, EMP and etoposide interact to selectively inhibit new DNA synthesis on the nuclear matrix. In vitro, EMP and etoposide appeared to act synergistically to inhibit the growth of the metastatic Dunning rat prostate adenocarcinoma cell line Mat-LyLu as well as the metastatic human prostate adenocarcinoma cell line PC-3. In vivo, EMP and etoposide inhibited prostate adenocarcinoma growth in the Dunning Copenhagen rat model. These data have formed the basis of a Phase I/II clinical trial to examine the effect of EMP and etoposide in patients with stage D hormone-refractory prostate cancer.

Phase II study of a 72-h concurrent continuous infusion of cisplatin and etoposide in advanced non-small-cell lung cancer

We conducted a phase II study to evaluate the antitumor activity and safety of concurrent continuous infusion of cisplatin and etoposide in advanced non-small-cell lung cancer (NSCLC). Cisplatin (30 mg/m2 daily) and etoposide (80 mg/m2 daily) were given as a 24-h continuous infusion for 72 h to 48 patients with previously untreated advanced NSCLC. Of the 46 evaluable patients, 9 achieved a partial response, for an overall response rate of 20% (95% confidence interval, 9.4%-33.9%). The median duration of response was 23 weeks. The median duration of survival for all patients was 34.4 weeks. The major toxicity was hematologic. Leukopenia (WHO grade > or = 3) was observed in 22 patients (48%) and thrombocytopenia (WHO grade > or = 3), in 13 patients (28%). In all, 20 patients (43%) experienced severe anemia (WHO grade > or = 3). Nonhematologic toxicity mainly consisted of moderate to severe alopecia in 33 patients (72%) and moderate to severe nausea and vomiting in 25 patients (54%). No significant nephrotoxicity was seen. We conclude that a 72-h concurrent continuous infusion of cisplatin and etoposide does not appear to be active against advanced NSCLC.