Saturable absorption of sorafenib in patients with solid tumors: a population model.

Sorafenib is an oral tyrosine kinase inhibitor approved for the treatment of advanced renal cell carcinoma and hepatocellular carcinoma. By using a population approach, this study aimed to characterise its pharmacokinetics. Plasma concentration-time data (n = 372) from 71 patients under sorafenib were analysed using nonlinear mixed-effect modelling to estimate population pharmacokinetic parameters, as well as relationships between these parameters and different covariates (demographic, biological). Simulations were done to compare different daily dosing regimens in a context of dose-escalation. A 1-compartment model with saturated absorption, first-order intestinal loss and elimination best described the pharmacokinetics of sorafenib. Absolute bioavailability significantly dropped with increasing daily doses of sorafenib. AUC increased less than proportionally with increasing doses [47.3 (41.3-63.3), 60.3 (56.3-64.4), 71.4 (51.3-99.1), 75.9 (45.5-100.9) mg/L.h for 400, 800, 1,200 and 1,600 mg/day, respectively]. According to the simulations, dividing the daily dose in three or four doses for daily dose >800 mg would significantly increase AUC compared with a twice daily dosing regimen (101.7 vs 81.6 mg/L.h for 400 mg q8h and 600 mg q12h respectively; 131.6 vs 91.5 mg/L.h for 400 mg q6h and 800 mg q12h, respectively). Thrice daily regimen may be most suitable in a context of dose-escalation (>800 mg/day) in non-responders to standard-dosing regimen.

Functional and clinical evidence of the influence of sorafenib binding to albumin on sorafenib disposition in adult cancer patients.

PURPOSE: Sorafenib, an oral multitargeted tyrosine kinase inhibitor, is highly bound to plasma proteins (>99.5%). Little is known about the influence of variations in sorafenib protein binding on its disposition. The aims of this study were to characterize in vitro sorafenib binding properties to albumin using the quenching fluorescence method and investigate the influence of albuminemia and bilirubinemia on sorafenib disposition in 54 adult cancer patients. RESULTS: In vitro estimate of sorafenib dissociation constant (Kd) for albumin was 0.22 µM [CI95 0.20-0.23]. In physiological conditions, sorafenib unbound fraction would increase 1.7-fold as albuminemia decreased from 45 g/L (680 µM) to 30 g/L (453 µM). In presence of bilirubin, apparent Kd of sorafenib was ~1.5-fold greater for bilirubin/albumin molar ratio of 1:4. In clinical settings, median sorafenib clearance (CL) was 1.42 L/h (0.75-2.13 L/h). In univariate analysis, sex, body mass index, and albuminemia were associated with CL (p = 0.04, 0.048, and 0.008, respectively). In multivariate analysis, albuminemia (p = 0.0036) was the single parameter independently associated with CL. CONCLUSION: These findings highlight the major influence of albuminemia on sorafenib clearance and its disposition in cancer patients.

Comparison of 3 estimation methods of mycophenolic acid AUC based on a limited sampling strategy in renal transplant patients.

A significant relationship between mycophenolic acid (MPA) area under the plasma concentration-time curve (AUC) and the risk for rejection has been reported. Based on 3 concentration measurements, 3 approaches have been proposed for the estimation of MPA AUC, involving either a multilinear regression approach model (MLRA) or a Bayesian estimation using either gamma absorption or zero-order absorption population models. The aim of the study was to compare the 3 approaches for the estimation of MPA AUC in 150 renal transplant patients treated with mycophenolate mofetil and tacrolimus. The population parameters were determined in 77 patients (learning study). The AUC estimation methods were compared in the learning population and in 73 patients from another center (validation study). In the latter study, the reference AUCs were estimated by the trapezoidal rule on 8 measurements. MPA concentrations were measured by liquid chromatography. The gamma absorption model gave the best fit. In the learning study, the AUCs estimated by both Bayesian methods were very similar, whereas the multilinear approach was highly correlated but yielded estimates about 20% lower than Bayesian methods. This resulted in dosing recommendations differing by 250 mg/12 h or more in 27% of cases. In the validation study, AUC estimates based on the Bayesian method with gamma absorption model and multilinear regression approach model were, respectively, 12% higher and 7% lower than the reference values. To conclude, the bicompartmental model with gamma absorption rate gave the best fit. The 3 AUC estimation methods are highly correlated but not concordant. For a given patient, the same estimation method should always be used.

Comparison of a new enzymatic assay with a high-performance liquid chromatography/ ultraviolet detection method for therapeutic drug monitoring of mycophenolic acid in adult liver transplant recipients.

Mycophenolic acid (MPA) is used to prevent graft rejection. The methods used for determining the plasma MPA concentration in liver transplant recipients are the enzyme-multiplied immunoassay technique (EMIT), high-performance liquid chromatography with ultraviolet detection (HPLC-UV), and most recently mass spectrometry. EMIT has been reported to overestimate the MPA concentration by 30% to 35% in comparison with HPLC-UV. Recently, a new automated enzymatic assay based on inosine monophosphate dehydrogenase inhibition has been designed. The aim of the present investigation was to compare this technique with validated HPLC-UV in adult liver transplant recipients treated with tacrolimus or cyclosporine. One hundred seventy-six samples from 50 adult liver transplant recipients were analyzed with both techniques. Patients received mycophenolate mofetil (2 or 3 times daily) coadministered with cyclosporine microemulsion (n = 18) or tacrolimus (n = 32). Samples were drawn over an interdose interval during the early or late posttransplantation period. The Passing-Bablok regression and Bland-Altman plot were used to compare the 2 techniques. The Passing-Bablock regression, calculated from 166 samples, showed very good agreement between the enzymatic assay and the HPLC-UV method: enzymatic assay = 1.0204 (95% confidence interval, 0.9942, 1.0478) x HPLC-UV + 0.0201 (-0.0442, 0.0882). No significant bias was found between the techniques (Bland-Altman plot), and the median relative difference was 2.7% (95% confidence interval, -0.4, 6.6). In conclusion, the enzymatic assay showed an excellent correlation with HPLC-UV. Therefore, this method was proved valid and reliable for the monitoring of the plasma MPA concentration in adult liver transplant recipients treated with cyclosporine microemulsion or tacrolimus.

Early sorafenib-induced toxicity is associated with drug exposure and UGTIA9 genetic polymorphism in patients with solid tumors: a preliminary study.

BACKGROUND: Identifying predictive biomarkers of drug response is of key importance to improve therapy management and drug selection in cancer therapy. To date, the influence of drug exposure and pharmacogenetic variants on sorafenib-induced toxicity remains poorly documented. The aim of this pharmacokinetic/pharmacodynamic (PK/PD) study was to investigate the relationship between early toxicity and drug exposure or pharmacogenetic variants in unselected adult outpatients treated with single-agent sorafenib for advanced solid tumors. METHODS: Toxicity was recorded in 54 patients on days 15 and 30 after treatment initiation and sorafenib exposure was assessed in 51 patients. The influence of polymorphisms in CYP3A5, UGT1A9, ABCB1 and ABCG2 was examined in relation to sorafenib exposure and toxicity. Clinical characteristics, drug exposure and pharmacogenetic variants were tested univariately for association with toxicities. Candidate variables with p<0.1 were analyzed in a multivariate analysis. RESULTS: Gender was the sole parameter independently associated with sorafenib exposure (p = 0.0008). Multivariate analysis showed that increased cumulated sorafenib (AUC(cum)) was independently associated with any grade ≥ 3 toxicity (p = 0.037); UGT1A9 polymorphism (rs17868320) with grade ≥ 2 diarrhea (p = 0.015) and female gender with grade ≥ 2 hand-foot skin reaction (p = 0.018). Using ROC curve, the threshold AUC(cum) value of 3,161 mg/L.h was associated with the highest risk to develop any grade ≥ 3 toxicity (p = 0.018). CONCLUSION: In this preliminary study, increased cumulated drug exposure and UGT1A9 polymorphism (rs17868320) identified patients at high risk for early sorafenib-induced severe toxicity. Further PK/PD studies on larger population are warranted to confirm these preliminary results.

A simple HPLC-UV method for the simultaneous quantification of gefitinib and erlotinib in human plasma.

Gefitinib and erlotinib are two oral tyrosine kinase inhibitors (TKI) approved for the treatment of advanced non-small cell lung cancer (NSCLC). Published methods for simultaneous analysis of erlotinib and gefitinib in plasma are exclusively based on mass spectrometry. The purpose of this study was to develop a simple and sensitive HPLC-UV method to simultaneously quantify these two TKI in plasma. Following liquid-liquid extraction, gefitinib, erlotinib and sorafenib (internal standard), were separated with gradient elution (on a C8+ Satisfaction(®) using a mobile phase of acetonitrile/20mM ammonium acetate pH 4.5). Samples were eluted at a flow rate of 0.4 ml/min throughout the 15-min run. Dual UV wavelength mode was used, with gefitinib and erlotinib monitored at 331 nm, and sorafenib at 249 nm. The calibration was linear in the range 20-1000 ng/ml and 80-4000 ng/ml for gefitinib and erlotinib, respectively. Inter- and intra-day imprecision were less than 7.2% and 7.6% for gefitinib and erlotinib, respectively. This analytical method was successfully applied to assess the steady state plasma exposure to these TKI in NSCLC patients. This simple, sensitive, accurate and cost-effective method can be used in routine clinical practice to monitor gefitinib or erlotinib concentrations in plasma from NSCLC patients.

Variability in free mycophenolic acid exposure in adult liver transplant recipients during the early posttransplantation period.

Mycophenolate mofetil (MMF) pharmacokinetics variability in liver transplant recipients during the early posttransplantation period may be related to changes in mycophenolic acid (MPA) protein binding. This study aimed at characterizing the variation of free MPA exposure with respect to time since transplantation. Three groups (A, B, C) were compared. The median posttransplantation time was 12 days (A, n = 26 pharmacokinetic sessions), 36 days (B, n = 25), and 867 days (C, n = 21). The median MPA AUC(0-12) in group A (26.8 mg x h/L) was significantly lower than in groups B (45.2 mg x h/L, P = .031) and C (43.5 mg x h/L, P = .004). Free MPA AUC(0-12) was comparable whatever the time (0.41, 0.34, and 0.33 mg x h/L, respectively). MPA apparent clearance (CL/F) was significantly correlated with MPA free fraction (r = 0.60, P < .0001) and approximately 1.7-fold higher in group A compared to groups B and C (P < .05). Enhanced CL/F in relation with an increase in MPA free fraction results in a low AUC of total MPA during the first postoperative month, but on average, at the population level, the exposure to free MPA is not altered, suggesting that total MPA AUC should not be used to adapt MMF dosing during this period.

Development and validation of an HPLC-UV-visible method for sunitinib quantification in human plasma.

BACKGROUND: Sunitinib malate is a novel oral multitargeted tyrosine kinase inhibitor with antitumor and antiangiogenic activities. Only mass spectrometry detection is currently available to determine sunitinib in human plasma. The purpose of this study was to develop a simple and sensitive high-performance liquid chromatographic method with UV-Visible detection for quantification of sunitinib concentrations in human plasma. METHODS: After a liquid-liquid extraction with ethyl acetate, sunitinib and ranitidine (internal standard) are separated on cyanopropyl column using a simple binary mobile phase of ammonium acetate buffer (20 mM; pH 6.8):acetonitrile (55:45,v/v). Samples were eluted isocratically at a flow rate of 1 mL/min throughout the 10 min run. Dual wavelength mode was used, with ranitidine monitored at 255 nm, and sunitinib at 431 nm. RESULTS: The calibration was linear in the range 20-200 ng/mL. Inter- and intra-day coefficients of variation were less than 7%. This method is sensitive, accurate and selective. It has been successfully implemented to monitor trough sunitinib concentrations in plasma samples (n = 39) from 14 unselected cancer patients treated with the recommended once daily dose of 50 mg or less. CONCLUSION: This method can be used in routine clinical practice to monitor plasma sunitinib concentrations in cancer patients treated with once daily administration.