Population pharmacokinetics of cisplatin in adult cancer patients

Purpose To characterize the pharmacokinetics of the anticancer agent cisplatin, and explore the influence of patient covariates and interoccasion variability on drug disposition.Methods Data were obtained from 285 patients (519 complete curves; 3483 plasma samples) who received the drug as a 3-h intravenous infusion at a mean dose of 144 mg (range 75–210 mg). The population model was built with the use of NONMEM, performing generalized-additive modeling to identify candidate covariates including body-surface area (BSA), age, sex, height, weight, hematocrit, total protein, albumin, serum creatinine, and creatinine clearance, and using a backward deletion protocol to obtain the final models for clearance (CL) and volume of distribution (V).Results The final model was a one-compartment linear model with BSA (in meters squared) as the only significant covariate that impacted on both CL and V: TVCL (in liters per hour)=51.7+26.3×(BSA–1.855) and TVV (in liters)=41.1+24.6×(BSA–1.855), where TVCL and TVV are referred to as typical values that could be used a priori in dosage regimen design. The interindividual and interoccasion variability estimates for CL and V were 16.82 and 20.35%, and 13.93 and 22.91%, respectively.Conclusion A population pharmacokinetic model for cisplatin has been developed that incorporates measures of body size to predict clearance. In this patient population, cisplatin pharmacokinetics were not associated with age, sex, or measures of renal dysfunction.Presented previously in part at the 92nd Annual Meeting of the American Association for Cancer Research, 24–28 March 2001, in New Orleans, LA, USA.     

Population pharmacokinetics of pemetrexed disodium (ALIMTA) in patients with cancer

Purpose: To evaluate the population pharmacokinetics of pemetrexed disodium in cancer patients enrolled in four different open-label, multicenter, nonrandomized phase II studies. Methods: Pemetrexed disodium was administered as a 10-min intravenous infusion (600 mg/m²) every 21 days. A total of four blood samples were to be collected each cycle per patient (n=103 patients) during cycles 1 and 3. Plasma concentration-time data were analyzed by nonlinear mixed-effect modeling using NONMEM to estimate pemetrexed disodium pharmacokinetic parameters (mean, and between- and within-patient variability) as well as relationships between the pharmacokinetic parameters and various patient-specific factors (demographic and physiologic data). Results/Conclusions: The pharmacokinetics of pemetrexed disodium were best characterized by a two-compartment model with initial distribution and terminal elimination half-lives of 0.63 h and 2.73 h, respectively. The typical value of systemic clearance (CL) in liters per hour included a relationship to creatinine clearance (CrCL) with a slope of 0.0292. Typical values of central volume (V_c), distributional CL (Q), and peripheral volume (V_p) were 11.3 l, 3.21 l/h, and 5.20 l, respectively. Between-patient variability was 19.6%, 15.6%, and 21.7% for CL, V_c, and V_p, respectively. A combined additive/proportional error model was used to describe residual variability, with a coefficient of variation of 23.7% for the proportional component and a standard deviation of 0.0410 μg/ml for the additive component. Significant patient-specific factors on CL were calculated CrCL, body weight, and to a lesser extent alanine transaminase and folate deficiency. Gender and body weight were significant factors on V_c while both body surface area and albumin were significant factors on V_p. In conclusion, population pharmacokinetic modeling revealed relationships between pharmacokinetic parameters and various patient specific factors. Received: 18 November 1999 / Accepted: 28 March 2000     

Pharmacokinetics and toxicity of 120-hour continuous-infusion hydroxyurea in patients with advanced solid tumors

 A group of 18 patients with advanced cancer were entered on a phase I study of a 120-h continuous intravenous infusion of hydroxyurea. The dose of hydroxyurea was escalated in cohorts of patients from 1 to 2 to 3.2 g/m² per day. The primary dose-limiting toxicity was neutropenia, often accompanied by leukopenia, thrombocytopenia and generalized skin rash. Prophylactic treatment of patients with dexamethasone and diphenhydramine hydrochloride prevented the skin rash, but not the hematopoietic toxicities. The pharmacokinetics of hydroxyurea were studied in all patients. The steady-state concentrations of hydroxyurea were linearly correlated with the dose (R ² = 0.71, n = 18, P<0.0001). The mean±SE concentrations were 93±16, 230±6 and 302±27 μM at 1, 2 and 3.2 g/m² per day, respectively. The mean±SE renal and nonrenal clearances of hydroxyurea were 2.14±0.18 and 3.39±0.28 l/h per m² (n = 16), neither of which correlated with the dose. The concentration of hydroxyurea in plasma decayed monoexponentially with a mean±SE half-life of 3.25±0.18 h (n = 17). The steady-state concentration of hydroxyurea was >200 μM in all nine patients treated at 2 g/m² per day, a dose which was well tolerated for 5 days. We recommend this dose for phase II trials in combination with other antineoplastic agents. Received: 28 November 1995 / Accepted: 18 May 1996     

Population pharmacokinetics of docetaxel during phase I studies using nonlinear mixed-effect modeling and nonparametric maximum-likelihood estimation

Docetaxel, a novel anticancer agent, was given to 26 patients by short i.v. infusion (1–2 h) at various dose levels (70–115 mg/m², the maximum tolerated dose) during 2 phase I studies. Two population analyses, one using NONMEM (nonlinear mixed-effect modeling) and the other using NPML (nonparametric maximum-likelihood), were performed sequentially to determine the structural model; estimate the mean population parameters, including clearance (Cl) and interindividual variability; and find influences of demographic covariates on them. Nine covariates were included in the analyses: age, height, weight, body surface area, sex, performance status, presence of liver metastasis, dose level, and type of formulation. A three-compartment model gave the best fit to the data, and the final NONMEM regression model for Cl wasCl=BSA(1+2×AGE), expressing Cl (in liters per hour) directly as a function of body surface area. Only these two covariates were considered in the NPML analysis to confirm the results found by NONMEM. Using NONMEM [for a patient with mean AGE (52.3 years) and mean BSA (1.68 m²)] and NPML, docetaxel Cl was estimated to be 35.6 l/h (21.2 lh^–1 m^–2) and 37.2 l/h with interpatient coefficients of variation (CVs) of 17.4% and 24.8%, respectively. The intraindividual CV was estimated at 23.8% by NONMEM; the corresponding variability was fixed in NPML in an additive Gaussian variance error model with a 20% CV. Discrepancies were found in the mean volume at steady state (Vss; 83.2 l for NPML versus 124 l for NONMEM) and in terminal half-lives, notably the meant _1/2, which was shorter as determined by NPML (7.89 versus 12.2 h), although the interindividual CV was 89.1% and 62.7% for Vss andt _1/2, respectively. However, the NPML-estimated probability density function (pdf) oft _1/2, was bimodal (5 and 11.4 h), probably due to the imbalance of the data. Both analyses suggest a similar magnitude of mean Cl decrease with small BSA and advanced age.     

Population pharmacokinetics of trastuzumab in patients With HER2+ metastatic breast cancer

Purpose: To characterize the population pharmacokinetics of trastuzumab in patients with metastatic breast cancer. Methods: A nonlinear mixed effect model was based on pharmacokinetic data from phase I, II, and III studies of 476 patients. The phase I study enrolled patients with advanced solid tumors. The phase II and III studies enrolled patients with HER2-positive metastatic breast cancer. Patients in the pivotal phase II and III studies were treated with a 4 mg/kg loading dose of trastuzumab followed by 2 mg/kg weekly for up to 840 days. The model adequately predicted observed trastuzumab concentrations. Model stability and performance were verified using bootstrap simulations. Percentiles, mean, and standard deviation of observed levels were compared with their distributions from 100 replicates of datasets simulated under the model. Results: A two-compartment linear pharmacokinetic model best described the data and accounted for the long-term accumulation observed following weekly administration of trastuzumab. Population estimates from the base model for clearance (CL) and volume of distribution of the central compartment (V₁) of trastuzumab were 0.225 L/day, and 2.95 L, respectively. Estimated terminal halflife (t_1/2) based on the population estimate was 28.5 days. Interpatient variabilities in clearance and volume were 43 and 29%, respectively. The number of metastatic sites, plasma level of extracellular domain of the HER2 receptor, and patient weight were significant baseline covariates for clearance, volume, or both (P<0.005). However, these covariate effects on trastuzumab exposure were modest and not clinically important in comparison with the large inter-patient variability of CL. Concomitant chemotherapy (anthracycline plus cyclophosphamide, or paclitaxel) did not appear to influence clearance. Conclusion: This population pharmacokinetic model can predict trastuzumab exposure in the long-term treatment of patients with metastatic breast cancer and provide comparison of alternative dosage regimens via simulation.     

Population analysis of the pharmacokinetics and the haematological toxicity of the fluorouracil-epirubicin-cyclophosphamide regimen in breast cancer patients

Purpose: The aims of the study were (a) to characterise the pharmacokinetics (PK), including inter-individual variability (IIV) and inter-occasion variability (IOV) as well as covariate relationships and (b) to characterise the relationship between the PK and the haematological toxicity of the component drugs of the fluorouracil (5-FU)—epirubicin (EPI)—cyclophosphamide (CP) regimen in breast cancer patients. Patients and methods: Data from 140 breast cancer patients, either within one of different studies or in routine clinical management, were included in the analyses. The patients were all treated with the fluorouracil-epirubicin-cyclophosphamide (FEC) regimen every third week for 3–12 courses, either in standard doses, i.e. 600/60/600 mg/m² of 5-FU, EPI and CP, respectively, or according to a dose escalation/reduction protocol (tailored dosing). PK data were available from 84 of the patients, whereas time-courses of haematological toxicity were available from 87 patients. The data analysis was carried out using mixed effects models within the NONMEM program. Results: The PK of 5-FU, EPI and 4-hydroxy-cyclophosphamide (4-OHCP), the active metabolite of CP, were described with a one-compartment model with saturable elimination, a three-compartment linear model and a two-compartment linear model, respectively. No clinical significant correlation was found between PK across drugs. The unexplained variability in clearance was found to be less within patients, between courses (inter-occasion variability, IOV) than between patients (inter-individual variability, IIV) for EPI and 5-FU. For 4-OHCP, however, the IIV diminished by approximately 45% when significant covariates were included and the final population model predicts an IIV that is equal to IOV. Significant covariates for elimination capacity parameters were serum albumin (5-FU, EPI and 4-OHCP), creatinine clearance (5-FU), bilirubin (EPI) and body surface area (BSA) (4-OHCP). Elimination capacity of 5-FU and EPI was not related to BSA and for none of the studied drugs did body weight explain the PK variability. The time-course of haematological toxicity after treatment was well described by a semi-physiological model that assumes additive haematological toxicity between CP and EPI with negligible contribution from 5-FU. The influence of G-CSF could be incorporated into the model in a mechanistic manner as shortening the maturation time to 43% of the normal duration and increasing the mitotic activity to 269% of normal activity. Conclusions: The models presented describe the dose-concentration-toxicity relationships for the FEC therapy and may provide a basis for implementation and comparison of different individualisation strategies based on covariates, therapeutic drug monitoring and/or pharmacodynamic (PD) feedback. The PD model extends on previous semi-mechanistic models in that it also takes G-CSF administration into account.This work was presented previously in part at the 12th Annual Meeting of the Population Approach Group Meeting, 12–13 June 2003, in Verona, Italy     

Population pharmacokinetics of oral busulfan in children

Purpose To characterize the population pharmacokinetics of oral busulfan in 48 children including pooled data from three transplantation centres with the aim of estimating the variability in the kinetics of busulfan and to identify covariates that could be used for dose calculation.Methods A total of 508 plasma samples from 250 administrations (mean 9 samples per patient over 4 days of treatment) were collected from 48 children receiving busulfan orally every 6 h. The dosing varied between 13 and 20 mg/kg with seven patients receiving a dose of 600 mg/m². The busulfan formulations administered varied considerably. They included 2-mg tablets (Myleran), gelatine capsules, crushed tablets suspended in water and suspension for administration via nasogastric tube. Samples were analysed for busulfan either by HPLC using postcolumn photolysis or by LC-MS. Plasma concentration-time data were analysed by population pharmacokinetic modelling using NONMEM.Results Busulfan kinetics were best described by a one-compartment model (subroutine ADVAN 2 TRANS 2). Residual variability was modelled using a combined additive and proportional error model. The influence of different covariates on the pharmacokinetic parameters was tested. The best results were obtained by inclusion of body surface area (BSA) as a covariate for clearance (Cl/F) and volume of distribution (V/F). The final population estimates were: Cl/F 4.13 l/h per m² ±26%, V/F 21.3 l/m² ±31% and ka 1.31 h^–1 ±110% (population mean ± interindividual variability, IIV). Variability in one patient during the 4 days of treatment (interoccasion variability, IOV) for Cl/F (10%) and V/F (19%) were calculated to be less than interindividual variability, fulfilling the condition for individualization of busulfan dosage regimens.Conclusions In our paediatric population, BSA, not body weight, is the best predictor of Cl/F and V/F. Our final estimations reflect the wide interpatient variability after oral administration of busulfan with an IIV for ka of 110%.     

Effects of demographic variables on vorozole pharmacokinetics in healthy volunteers and in breast cancer patients

Purpose: Vorozole (VOR) is a selective nonsteroidal inhibitor of the cytochrome P450-dependent aromatase that catalyzes the conversion of androgens to estrogens. It is currently being developed as a therapeutic agent in the endocrine treatment of postmenopausal women with breast cancer. This work was aimed to explore the effects of demographic and other variables on VOR pharmacokinetics. Methods: VOR plasma concentration-time data were obtained in healthy volunteers and in breast cancer patients after the oral administration of 2.5 mg of VOR as a single dose or once daily. The data obtained in 6 formal pharmacokinetics (PK) studies with frequent plasma sampling were included in the data base (84 healthy male and female volunteers and 13 breast cancer patients). Also included were data from 2 clinical efficacy trials involving 286 breast cancer patients who were treated for several months (1 sample per visit, up to 14 samples/patient). The nonlinear mixed-effect modeling (NONMEM) approach was applied. The two-compartment linear PK model with first-order absorption parameterized in terms of apparent clearance (CL), apparent central and peripheral volumes of distribution (Vc and Vp, respectively), apparent distributional flow (Q), and absorption constant (k _a ) was used. A population model was developed using data from formal PK studies. The final estimates of fixed and random effect parameters were obtained using both formal study data and clinical-efficacy trial data. Results: The typical CL value obtained after a single dose was lower in patients (4.8 l/h) as compared with healthy volunteers (8.6 l/h) and did not depend on gender. The multiple- to single-dose ratio was 0.76. CL was constant over ages of up to 50 years and then decreased slightly (0.047 l/h per year). The typical CL value did not depend on any demographic variable related to body size (total body weight, WT; body surface area; lean body mass). Q and Vc were proportional to WT (0.17 l h⁻¹ kg⁻¹ and 0.43 l/kg, respectively). Vp was also proportional to WT and was higher in women as compared with men (0.64 and 0.40 l/kg, respectively). The same was true for the apparent steady-state volume of distribution. No effect of race or the duration of therapy (0.5–28 months) was seen. The unexplained variability in CL and the residual variability in VOR plasma concentrations were 39% and 28% (coefficient of variation), respectively. Conclusions: Healthy volunteer/patient, single/multiple dosing differences, and age were identified as the fixed effects influencing the CL of VOR. WT was the main determinant of distributional PK parameters. The peripheral and steady-state volumes of distribution were gender-dependent. In view of the relatively high degree of residual interpatient variability in CL, the slight effect of age on it is unlikely to be clinically significant. Received: 20 April 1997 / Accepted: 9 January 1998     

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

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. Received: 17 November 1997 / Accepted: 25 August 1998     

Myelosuppression in patients benefiting from imatinib with hydroxyurea for recurrent malignant gliomas

Reports suggest reasonable efficacy and minimal myelosuppression from combination imatinib and hydroxyurea for recurrent malignant glioma. We retrospectively reviewed 16 patients treated with this regimen who were evaluable for toxicity; 14 were also evaluable for response. The incidence of grade 3–4 hematologic toxicity was 25%. The best radiographic response, by Macdonald criteria, was partial response (PR) in three patients (21%), stable disease (SD) in four (29%), and progressive disease (PD) in seven (50%). One patient with a PR developed therapy-limiting hematologic toxicity on day 19 of treatment, progressing to grade 4 on day 64, and persisting until death on day 127 despite discontinuing both drugs. Another patient with PR and two of four patients with SD also developed grade 3 hematologic toxicity. All patients with grade 3–4 hematologic toxicity had disease control (PR or SD) as best radiographic response, whereas none with PD suffered grade 3–4 hematologic toxicity. Combining imatinib with hydroxyurea is effective in some patients with malignant glioma. However, myelosuppression can persist for months after discontinuing the regimen, precluding further chemotherapy. Disease control may also correlate with hematologic toxicity (p = 0.08), suggesting that glioma and marrow stem cells may share a common sensitivity to this chemotherapy regimen.     

Population pharmacokinetic model for daunorubicin and daunorubicinol coadministered with zosuquidar.3HCl (LY335979)

Purpose The impact of zosuquidar.3HCl, an inhibitor of P-glycoprotein, on the pharmacokinetics of daunorubicin and daunorubicinol was examined in a phase I trial using a population approach. Pharmacokinetic and pharmacodynamic properties of zosuquidar.3HCl were also determined.Methods The pharmacokinetics of daunorubicin and daunorubicinol were studied following daunorubicin administration on day 1 (50 mg/m² i.v. infusion over 10 min) alone and on day 3 concomitantly with zosuquidar.3HCl (i.v. 200 or 300 mg/m² over 6 h or 400 mg over 3 h). Of a total of 18 patients entered, 16 with acute leukemia completed the study.Results A three-compartment pharmacokinetic model adequately described daunorubicin concentration-time profiles. Five- and four-compartment models adequately described the daunorubicin-daunorubicinol pharmacokinetics in the absence and presence of zosuquidar.3HCl, respectively. The impact of zosuquidar.3HCl on coadministered daunorubicin was minimal, with a 10% reduction in daunorubicin clearance. The model predicted a 50% decrease in daunorubicinol apparent clearance in the presence of zosuquidar.3HCl. A direct concentration-effect relationship between zosuquidar.3HCl concentrations and inhibition of rhodamine 123 (Rh123) efflux in CD56 lymphocytes was defined by a sigmoid E_max model. The IC₅₀ was 31.7 g/l. The zosuquidar.3HCl dosing regimen led to concentrations in excess of the IC₉₀ (169.6 g/l) and provided maximal P-glycoprotein inhibition during the distribution phases of daunorubicin.Conclusions The decrease in daunorubicin and daunorubicinol clearance in the presence of zosuquidar.3HCl likely reflects inhibition of P-glycoprotein in the bile canaliculi impeding their biliary excretion. The results need to be interpreted carefully due to the sequential nature of daunorubicin administration and analysis.     

The influence of ageing on cisplatin pharmacokinetics in lung cancer patients with normal organ function

This study was performed to identify any relationship between age and cisplatin (CDDP) pharmacokinetics in lung cancer patients. CDDP was given at a dose of 80 mg/m² by 1-h intravenous infusion to 23 lung cancer patients. All patients had normal renal, hepatic, and bone marrow functions. We measured ultrafilterable platinum (U-Pt) and total plasma platinum (T-Pt) using atomic absorption spectrometry. There was significant correlation between the age of the patients and U-Pt pharmacokinetic parameters such as the area under the plasma concentration versus time curve (AUC), total clearance (Cl), and peak plasma concentration (Cmax) as well as the AUC of T-Pt (P<0.05). We performed univariate regression analysis to examine the influence of factors aside from age on the AUC of U-Pt and T-Pt. Creatinine and GPT levels were significantly related to the AUC of U-Pt, and creatinine clearance and creatinine concentrations were significantly related to the AUC of T-Pt. Therefore, stepwise multiple-regression models for the AUC of U-Pt and T-Pt were developed to assess an age effect. Age was consistently an independent and significant predictor of the AUC of U-Pt and T-Pt.     

Population pharmacokinetic analysis of ten phase II clinical trials of pemetrexed in cancer patients

Purpose: The objectives of these population pharmacokinetic analyses were to (1) assess the overall disposition of pemetrexed, (2) characterize between-patient and within-patient variability and identify influential covariates with respect to pemetrexed pharmacokinetics; and, (3) provide individual empirical Bayesian estimates of pharmacokinetic parameters for use in a subsequent pharmacokinetic/pharmacodynamic evaluation of neutropenia following pemetrexed administration. Patients and methods: Data from 287 patients who received 441 cycles without folic acid or vitamin B₁₂ supplementation during participation in one of ten phase II cancer trials were evaluated by population pharmacokinetic analysis using NONMEM. Starting doses were 500 or 600 mg pemetrexed per m² body surface area, administered as 10-min intravenous infusions every 21 days (1 cycle). The model was developed using data from eight of the ten studies. Predictive performance was evaluated using data from the other two studies. Results: The population pharmacokinetics of pemetrexed administered as a 10-min intravenous infusion are well characterized by a two-compartment model. Typical values of total systemic clearance, central volume of distribution, distributional clearance, and peripheral volume of distribution were 91.6 ml/min, 12.9 l, 14.4 ml/min, and 3.38 l, respectively. Based on these parameter estimates, the terminal elimination half-life of pemetrexed was approximately 3.5 h. Renal function was identified as a covariate with respect to total systemic clearance, and body surface area as a covariate with respect to the central volume of distribution. Conclusion: Total systemic exposure (AUC) for a given dose of pemetrexed increases as renal function decreases. Since pharmacodynamic analyses have shown that AUC and not C _max is the primary determinant of neutropenic response to pemetrexed, this suggests that dose adjustments based on renal function, rather than body surface area, might be considered for pemetrexed. Robert D Johnson was an employee of Eli Lilly and Company, Indianapolis, USA, at the time this work was completed     

Salivary and plasma pharmacokinetics of topotecan in patients with metastatic epithelial ovarian cancer

The comparative saliva/plasma pharmacokinetics of topotecan were investigated in 13 patients with metastatic epithelial ovarian cancer receiving topotecan (30-min intravenous (i.v.) infusion) on a five consecutive day schedule every 3 weeks. During the first and the second courses of treatment, each patient underwent pharmacokinetic evaluation. Quantitation of the total topotecan (lactone plus carboxylate form) was assessed by a highly specific high-performance liquid chromatographic (HPLC) method. Large patient-to-patient variations in the plasma and saliva concentrations were observed. Plasma and saliva pharmacokinetics could be described using a biexponential pattern. From the saliva data, the half-life of the terminal part of the curve was 2.64 h, it was of the same order of magnitude as the topotecan elimination half-life determined from the plasma data, 3.18 h. Topotecan concentrations were higher in the saliva than in the plasma, the saliva/plasma concentration ratio averaged 2.31 and the ratio area under the parotid saliva (AUC_s) over plasma (AUC_p) concentration–time curve (AUC_s/AUC_p) averaged 2.11. For each individual, a significant relationship was found between topotecan concentrations in the saliva and in the plasma, the coefficients of correlation ranged from 0.75 to 0.92 according to the patient. Myelosuppression, especially granulocytopenia was the most frequent toxicity encountered during the trial. The percent decrease in the leucocyte count, absolute neutrophil count and platelet count were related to the AUCp/day using sigmoidal E_max models. The high values of the Hill constant found reflect the very steep AUC-haematoxicity relationship observed. In most cases, abdominal pain occurred in patients presenting high saliva concentrations. One patient with high salivary concentrations (mean S/P RATIO=4.60) had grade 1 mucositis. In conclusion, the concentration of topotecan in saliva appeared to be useful as an indirect, non-invasive estimation of the levels of topotecan in the plasma; thus, saliva concentrations could be a good predictor of the behaviour of topotecan in the body.     

Protein binding of brequinar in the plasma of healthy donors and cancer patients and analysis of the relationship between protein binding and pharmacokinetics in cancer patients

The protein binding of weakly acidic and basic drugs has been shown to be altered in cancer patients. Brequinar is a weakly acidic, low-clearance, and highly protein-bound (>98% bound) antitumor agent. The pharmacokinetic parameters of brequinar are subject to large interpatient variability. This large interpatient variability may be related to brequinar's plasma protein-binding capacity (assuming no change in the intrinsic clearance of the unbound drug). The objectives of this study, therefore, were (a) to characterize brequinar's protein binding in the plasma of healthy donors and cancer patients and (b) to examine the relationships between brequinar's plasma protein binding and its pharmacokinetics in patients. Brequinar protein binding was determined in human serum albumin (HSA) solution, drug-free donor plasma, and brequinar-free, predose plasma samples obtained from a phase I cancer trial. Pharmacokinetic results from this study were used to examine relationships between plasma protein binding and drug disposition. In HSA solution and healthy donor plasma, brequinar's protein binding as determined using spiked samples was concentration-dependent. The unbound brequinar fraction increased by a factor of 3 (from 0.3% to 0.9% free) in 4% HSA solution and by a factor of 4 (from 0.4% to 1.6% free) in donor plasma as the brequinar concentrations increased from 0.1 to 2.3 mM in the HSA solution and from 0.076 to 1.5 mM in the donor plasma. Analysis of brequinar binding characteristics using the binding ratio and Rosenthal binding plots showed that albumin was the primary protein for brequinar binding in human plasma. The addition of various concentrations of ₁-acid glycoprotein to 4% HSA solution did not affect the protein binding of brequinar to HSA. The protein binding determined in the plasma of cancer patients was not quantitatively different, except for variability, from that observed in the plasma of healthy donors. Examination of relationships between the unbound brequinar fraction and pharmacokinetics suggested that plasma protein binding was not a major determinant of brequinar disposition in cancer patients.     

Investigation of bioavailability and pharmacokinetics of treosulfan capsules in patients with relapsed ovarian cancer

Purpose: Treosulfan (l-threitol-1,4-bis-methanesulfonate, Ovastat) is a prodrug of a bifunctional alkylating agent with activity in ovarian carcinoma and other solid tumors. In a pharmacologic study of the bioavailability of treosulfan in a capsule formulation, patients with relapsed ovarian carcinoma were treated with alternating doses of oral and intravenous (i.v.) treosulfan of 1.5 or 2.0 g daily for 5 to 8 days. Methods: A sensitive method for the determination of treosulfan in plasma and urine by reversed-phase high-performance liquid chromatography had previously been developed. Pharmacokinetic analyses of treosulfan were carried on plasma and urine samples from 20 i.v. courses and 20 courses of oral administration. Results: The bioavailability ratio (f) of oral to i.v. administration was calculated as 0.97 ± 0.18 (mean ± SD) using the values AUC_oral=82.1 ± 39.4 μg/ml h and AUC_i.v.=85.4 ± 30.3 μg/ml h. The peak plasma concentration c_max (29 ± 14 μg/ml vs 65 ± 23 μg/ml) was significantly (P < 0.01) higher after i.v. administration and the t_max after oral administration was 1.5 ± 0.34 h. The terminal half-life of treosulfan was about 1.8 h. The mean urinary excretion of the parent compound was about 15% of the administered total dose over 24 h (range 6–26%). Conclusions: The high and relatively constant bioavailability of treosulfan indicates that capsules provide a satisfactory noninvasive treatment alternative. A feasible and reliable oral treosulfan formulation could provide the basis for the development of long-term low-dose outpatient treatment of patients with malignant diseases. Received: 28 July 1999 / Accepted: 16 December 1999     

Lack of effect of aprepitant on the pharmacokinetics of docetaxel in cancer patients

Background Aprepitant is a selective neurokinin-1 receptor antagonist that is effective for the prevention of nausea and vomiting caused by highly emetogenic chemotherapy. In vitro, aprepitant is a moderate inhibitor of the CYP3A4 enzyme, which is involved in the clearance of several chemotherapeutic agents. In this study we examined the potential for aprepitant to affect the pharmacokinetics and toxicity of intravenously administered docetaxel, a chemotherapeutic agent that is primarily metabolized by CYP3A4.Methods A total of 11 cancer patients (4 male, 7 female, aged 50–68 years) were enrolled in this multicenter, randomized, open-label, two-period, crossover study. Patients received a single infusion of docetaxel monotherapy, 60–100 mg/m², on two occasions at least 3 weeks apart. During one of the cycles (treatment A), patients received docetaxel alone. During the alternate cycle (treatment B), they also received aprepitant 125 mg orally 1 h prior to docetaxel infusion (day 1), and a single oral dose of aprepitant 80 mg on days 2 and 3. The pharmacokinetic profile of docetaxel was assessed over 30 h following docetaxel infusion. Blood counts were monitored on days 1, 4, 7, and 14.Results Ten patients completed the study. Concomitant administration of aprepitant did not cause any statistically or clinically significant changes in docetaxel pharmacokinetics. Values for docetaxel alone (treatment A) versus docetaxel with aprepitant (treatment B) were as follows: geometric mean AUC_0–last was 3.26 vs 3.17 g h/ml (P>0.25; ratio B/A 0.97); geometric mean AUC_0– 3.51 vs 3.39 g h/ml (P>0.25; ratio B/A 0.96); geometric mean C_max was 3.53 vs 3.37 g/ml (P>0.25; ratio B/A 0.95); and geometric mean plasma clearance was 23.3 vs 24.2 l/h/m² (P>0.25; ratio B/A 1.04). The corresponding harmonic mean half-life values were 10.1 and 8.5 h. The two treatment regimens had similar tolerability profiles; the median absolute neutrophil count nadirs were 681/mm³ during treatment with docetaxel alone and 975/mm³ during aprepitant coadministration.Conclusions Aprepitant had no clinically significant effect on either the pharmacokinetics or toxicity of standard doses of docetaxel in cancer patients. Aprepitant at clinically recommended doses may have a low potential to affect the pharmacokinetics of intravenous chemotherapeutic agents metabolized by CYP3A4.     

Mechanistic population pharmacokinetics of total and unbound paclitaxel for a new nanodroplet formulation versus Taxol in cancer patients

Purpose

Our objectives were (1) to compare the disposition and in vivo release of paclitaxel between a tocopherol-based Cremophor-free formulation (Tocosol Paclitaxel^®) and Cremophor^® EL-formulated paclitaxel (Taxol^®) in human subjects, and (2) to develop a mechanistic model for unbound and total paclitaxel pharmacokinetics.

Methods

A total of 35 patients (average ± SD age: 59 ±13 years) with advanced non-hematological malignancies were studied in a randomized two-way crossover trial. Patients received 175 mg/m² paclitaxel as 15 min (Tocosol Paclitaxel) or 3 h (Taxol) intravenous infusion in each study period. Paclitaxel concentrations were determined by LC–MS/MS in plasma ultrafiltrate and whole blood. NONMEM VI was used for population pharmacokinetics.

Results

A linear disposition model with three compartments for unbound paclitaxel and a one-compartment model for Cremophor were applied. Total clearance of unbound paclitaxel was 845 L/h (variability: 25% CV). The prolonged release with Tocosol Paclitaxel was explained by the limited solubility of unbound paclitaxel of 405 ng/mL (estimated) in plasma. The 15 min Tocosol Paclitaxel infusion yielded a mean time to 90% cumulative input of 1.14 ± 0.16 h. Tocosol Paclitaxel was estimated to release 9.8% of the dose directly into the deep peripheral compartment. The model accounted for the presence of drug-containing nanodroplets in blood.

Conclusions

Population pharmacokinetic analysis indicated linear disposition and a potentially higher bioavailability of unbound paclitaxel following Tocosol Paclitaxel administration due to direct release at the target site. The prolonged release of Tocosol Paclitaxel supports 15 min paclitaxel infusions. This mechanistic model may be important for development of prolonged release formulations that distribute in and from the systemic circulation.