Estimation of Unbound Carboplatin Clearance From Total Plasma Concentrations as a Means of Facilitating Therapeutic Drug Monitoring.

BACKGROUND: Therapeutic drug monitoring of carboplatin is based on its unbound clearance (CLU) determined by Bayesian analysis on unbound (U) concentrations. However, the ultrafiltration of plasma samples presents technical and time constraints. Therefore, this study aims to estimate CLU using total plasma (P) concentrations. METHODS: U and P concentration data of 407 patients were obtained from 2 clinical studies in which actual CLU had been determined for each patient. The patients were then split into development (277 patients) and prospective data sets (130 patients). Two approaches were evaluated. PK-model-only approach: a 3-compartment pharmacokinetic (PK) model based on U and P concentrations and taking into account the protein binding process was developed. The model with patient covariates was also evaluated. Linear regression approach: an equation (CLU = aCLP + b) was obtained by linear regression analysis between actual CLU and CLP, which is the total plasma clearance obtained by analyzing P concentrations according to a 2-compartment PK model. Predictive performance was then assessed within the prospective data set by estimating CLU from P concentrations using each approach and computing the relative percentage error (PE) between estimated CLU and actual CLU. RESULTS: The linear regression equation was CLU (L/h) = 1.15 CLP (L/h) + 0.13. The mean PE (MPE) between CLU (estimated using the equation) and the actual CLU was +1.2% (ranging from -31% to +33%) and the mean absolute PE (MAPE) was 9.7%. With the 3-compartment PK model, the MPE was +2.3% (ranging from -41% to +31%) and the MAPE was 11.1%. Inclusion of covariates in the 3-compartment model did not improve the estimation of CLU [MPE = +6.3% (from -33% to +37%); MAPE = 11.4%]. CONCLUSIONS: The linear equation gives a relatively good estimation of CLU based on P concentrations, making PK-based carboplatin dose adaptation possible for centers without ultrafiltration facilities.

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). 0.847(sex), with Scr in micromol/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 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/m(2) followed by docetaxel 30 mg/m(2) 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.

Pharmacokinetics of platinum after oral or intravenous cisplatin: a phase 1 study in 32 adult patients.

AIMS: To develop a population pharmacokinetic model for simultaneous analysis of oral/intravenous cisplatin data in order to estimate the mean population pharmacokinetic parameters, mainly the bioavailability, of cisplatin and to evaluate the influence of covariates on the pharmacokinetic variability. METHODS: Pharmacokinetic and demographic data were collected from 32 adult patients (20 males/12 females, age range 47-76 years) receiving 30-min infusions or an oral formulation of cisplatin, 10-30 mg/m2, for various malignancies. Both total plasma and ultrafilterable or unbound platinum concentrations were determined. RESULTS: Unbound and total platinum concentrations were ascribed to a two-compartment model, with first-order absorption and elimination. The oral bioavailability (F) population estimates were, respectively, 0.39 and 0.30 with associated intersubject variabilities (ISV) of 24% and 26%. Peak concentrations following oral dosing occurred at 1.0 h and 1.6 h for unbound and total platinum, respectively. Clearance (CL) and central distribution volume (V1) of unbound platinum were significantly related to body surface area (BSA). The CL and V1 mean estimates were, respectively, 37 l/h and 23 l with an associated ISV of 15%. The final pharmacokinetic models were validated using 1000 bootstrap samples of the original datasets. CONCLUSIONS: Both unbound and total platinum data allowed a fair evaluation of oral cisplatin disposition, with close estimations for both absorption rates and oral bioavailability. These results also support the conventional dose adjustment of cisplatin based on BSA.

Population pharmacokinetics of peritoneal, plasma ultrafiltrated and protein-bound oxaliplatin concentrations in patients with disseminated peritoneal cancer after intraperitoneal hyperthermic chemoperfusion of oxaliplatin following cytoreductive surgery: correlation between oxaliplatin exposure and thrombocytopenia.

PURPOSE: First, to evaluate the peritoneal (IP), plasma ultrafiltrated (UF) and protein-bound (B) pharmacokinetics (PK) of oxaliplatin after intraperitoneal hyperthermic chemoperfusion (HIPEC) following cytoreductive surgery. Second, to evaluate the relationship between oxaliplatin exposure and observed toxicity. METHODS: IP, UF, and B concentrations from 75 patients treated by 30-min oxaliplatin-based HIPEC procedures were analysed according to a pharmacokinetic modelling approach using NONMEM. Oxaliplatin was administered in a 5 % dextrose solution (2 L/m(2)) at 360 (n = 58) or 460 mg/m(2) (n = 17). The most frequently observed toxicities were related to the peritoneal, systemic exposures and to the parameters corresponding to the oxaliplatin absorption from peritoneal cavity into plasma. RESULTS: IP (n = 536), UF (n = 669) and B (n = 661) concentrations were simultaneously described according to a five-compartment PK model with irreversible nonlinear binding from UF to B according to a Michaelis-Menten equation. The mean (±SD) maximum fraction of dose absorbed and elimination half-life from the peritoneum was 53.7 % (±8.5) and 0.49 h (±0.1), respectively. The mean (±SD) ratio AUC(IP)/AUC(UF) was 5.3 (±2) confirming the pharmacokinetic advantage of the procedure. Haemoperitoneum (22.7 %), neuropathy (18.7 %), grade 3/4 thrombocytopenia (13.3 %) were the most frequently reported toxicities. AUC(UF) accounts for approximately 12 % of the variation in the maximum percentage of platelet decrease (r = 0.35, p = 0.002). Thrombocytopenia was correlated with higher AUCUF, partly dependent on the extent and rate of oxaliplatin absorption. CONCLUSIONS: Despite a common dose administered, variability in peritoneal and systemic oxaliplatin exposures are observed, leading to differences in haematological toxicity between patients.

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.

Dexamethasone as a probe for vinorelbine clearance.

AIM: To assess the value of using dexamethasone as an in vivo probe for predicting vinorelbine clearance (CL). METHODS: A population approach (implemented with NONMEM) was used to analyse blood vinorelbine pharmacokinetic data from 20 patients who received a 20-min intravenous infusion of vinorelbine (from 20 to 30 mg m(-2)). Selected patient clinical data as well as known functional single CYP3A5 and ABCB1 genotype were also tested as covariates. RESULTS: The best covariate model (with +/- 95% confidence intervals) was based on dexamethasone plasma clearance (DPC) and alkaline phosphatase (ALP): vinorelbine blood CL (l h(-1)) = 39.8(+/- 4.0) x (DPC/13.2)(0.524(+/-0.322)) x (ALP/137)(-0.198(+/-0.158)). Interindividual variability in vinorelbine CL decreased from 29.7% (model without covariate) to 14.7% when including DPC and ALP. Vinorelbine CL was not correlated with body surface area (BSA) or associated with CYP3A5 and ABCB1 genotype. CONCLUSIONS: These results indicate that individualization of vinorelbine dose would be improved by using dexamethasone clearance rather than BSA. Dexamethasone merits further evaluation as a probe of CYP3A metabolism.