Physiologically-Based Pharmacokinetic Models for Evaluating Membrane Transporter Mediated Drug-Drug Interactions: Current Capabilities, Case Studies, Future Opportunities, and Recommendations.

Physiologically-based pharmacokinetic (PBPK) modeling has been extensively used to quantitatively translate in vitro data and evaluate temporal effects from drug-drug interactions (DDIs), arising due to reversible enzyme and transporter inhibition, irreversible time-dependent inhibition, enzyme induction, and/or suppression. PBPK modeling has now gained reasonable acceptance with the regulatory authorities for the cytochrome-P450-mediated DDIs and is routinely used. However, the application of PBPK for transporter-mediated DDIs (tDDI) in drug development is relatively uncommon. Because the predictive performance of PBPK models for tDDI is not well established, here, we represent and discuss examples of PBPK analyses included in regulatory submission (the US Food and Drug Administration (FDA), the European Medicines Agency (EMA), and the Pharmaceuticals and Medical Devices Agency (PMDA)) across various tDDIs. The goal of this collaborative effort (involving scientists representing 17 pharmaceutical companies in the Consortium and from academia) is to reflect on the use of current databases and models to address tDDIs. This challenges the common perceptions on applications of PBPK for tDDIs and further delves into the requirements to improve such PBPK predictions. This review provides a reflection on the current trends in PBPK modeling for tDDIs and provides a framework to promote continuous use, verification, and improvement in industrialization of the transporter PBPK modeling.

Physiologically Based Pharmacokinetic Model Qualification and Reporting Procedures for Regulatory Submissions: A Consortium Perspective.

This work provides a perspective on the qualification and verification of physiologically based pharmacokinetic (PBPK) platforms/models intended for regulatory submission based on the collective experience of the Simcyp Consortium members. Examples of regulatory submission of PBPK analyses across various intended applications are presented and discussed. European Medicines Agency (EMA) and US Food and Drug Administration (FDA) recent draft guidelines regarding PBPK analyses and reporting are encouraging, and to advance the use and acceptability of PBPK analyses, more clarity and flexibility are warranted.

Interindividual variability in the concentration-effect relationship of antilymphocyte globulins - a possible influence of FcgammaRIIIa genetic polymorphism.

AIMS: Polyclonal antilymphocyte globulins (ALGs) are currently used in transplantation, but the sources of interindividual variability of their effect are poorly understood. No pharmacokinetic-pharmacodynamic (PK-PD) study of ALG is available. Moreover, the genetic polymorphism of FcgammaRIIIa, a receptor for the Fc portion of immunoglobulins involved in antibody-dependent cellular cytotoxicity (ADCC), may influence their concentration-effect relationship. METHODS: Fourteen kidney transplant patients treated by horse ALG were included in a prospective, noncomparative study. A population two-compartment PK model including a time dependence of the central volume of distribution was developed. Total lymphocyte count was used as biomarker of effect. Concentration-effect data were described using a physiological indirect response model, combining concentration-dependent and -independent inhibitions of lymphocyte input into the circulation. In addition, six kidney transplant patients in whom ALG concentrations were not available were included retrospectively. All patients were genotyped for FCGR3A. RESULTS: Both the PK and the PK-PD model described the data satisfactorily and showed high interindividual variability. Asymptotic T(1/2)-alpha and T(1/2)-beta-values were 1.3 and 25 days, respectively. The concentration of ALG leading to a 50% inhibition of lymphocyte input (IC(50)) was lower in FCGR3A-V carriers than in FCGR3A-F/F patients (383 +/- 199 vs. 593 +/- 209 mg l(-1), P = 0.008). CONCLUSIONS: This is the first description of the ALG effect on lymphocyte count using PK-PD modelling. Our results show that part of the variability in their concentration-effect relationship may be explained by FcgammaRIIIa genetic polymorphism and therefore that horse ALG may deplete lymphocytes by ADCC.

Relationship between 5-fluorouracil exposure and outcome in patients receiving continuous venous infusion with or without concomitant radiotherapy.

AIMS: Toxicity and response are correlated with plasma 5-fluorouracil (5-FU) concentration in patients treated with 5-FU at a dose of 1000 mg m(-2) day(-1). Head and neck cancer patients are treated with various therapeutic regimens, including chemotherapy with 5-FU at a dose of 600 mg m(-2) day(-1) with radiotherapy. We investigated the plasma concentration-effect relationship for this regimen, with the aim of developing recommendations for dose adjustment. METHODS: Patients received 5-FU at doses of 600 or 1000 mg m(-2) day(-1), as a continuous infusion over 4 or 5 days, with or without radiotherapy for the 600 mg m(-2) day(-1) regimen. The area under the curve (AUC) for 5-FU concentration was estimated, based on a single morning blood sample taken each day during treatment. AUC values were compared between patients with and without toxicity. This simplified method for AUC estimation was compared with the standard two-samples-per-day method in an independent group of 50 patients. RESULTS: Forty-six patients, corresponding to 115 courses, were included in this prospective study. Considerable interindividual variability in estimated AUC was observed for both doses. Grade 3-4 toxicity occurred in 10 and 21% of patients given doses of 600 and 1000 mg m(-2) day(-1), respectively. Ths study confirmed the relationship between plasma 5-FU concentration and toxicity previously reported for 1000 mg m(-2) day(-1), but found no such relationship for the 600 mg m(-2) day(-1) regimen with concomitant radiotherapy. CONCLUSIONS: Our results do not support the use of therapeutic drug monitoring to improve tolerance for the 600 mg m(-2) day(-1) regimen with concomitant radiotherapy. A simplified method is proposed for 5-FU monitoring for the 1000 mg m(-2) day(-1) regimen.

Higher exposure to mycophenolic acid with sirolimus than with cyclosporine cotreatment.

INTRODUCTION: Therapeutic drug monitoring of mycophenolate mofetil is recommended because of the interindividual variability in the exposition to its active moiety, mycophenolic acid. However, most of the pharmacokinetic studies involved patients cotreated with cyclosporine (INN, ciclosporin). METHODS: We analyzed the pharmacokinetics of mycophenolic acid in 13 renal graft recipients treated with sirolimus in an anticalcineurin-free regimen and compared it with that of 17 patients cotreated with cyclosporine. The area under the concentration versus time curve over a 12-hour period (AUC 0-12 ) of mycophenolic acid was estimated at 2 weeks, 1 month, 2 months, and 3 months after transplantation. RESULTS: At the first 3 time points, patients cotreated with sirolimus had significantly higher mycophenolic acid AUC 0-12 values compared with patients cotreated with cyclosporine, as follows: 81 mg . h/L (SD, 39 mg . h/L) versus 43 mg . h/L (SD, 11 mg . h/L) (P < .001), 72 mg . h/L (SD, 17 mg . h/L) versus 48 mg . h/L (SD, 13 mg . h/L) (P < .001), and 70 mg . h/L (SD, 25 mg . h/L) versus 47 mg . h/L (SD, 17 mg . h/L) (P < .01) at week 2, month 1, and month 2, respectively. At all time points, patients cotreated with sirolimus had significantly higher dose-normalized mycophenolic acid AUC 0-12 values. At months 1 and 2, white blood cell counts were lower in the sirolimus group than in the cyclosporine group, as follows: 4.8 x 10(3)/mL (SD, 1.1 x 10(3)/mL) versus 6.5 x 10(3)/mL (SD, 2.2 x 10(3)/mL) (P < .01) at month 1 and 4.6 x 10(3)/mL (SD, 1.1 x 10(3)/mL) versus 5.9 x 10(3)/mL (SD, 2.0 x 10(3)/mL) (P < .05) at month 2. CONCLUSION: These data show that exposure to mycophenolic acid is higher in patients cotreated with sirolimus than in those cotreated with cyclosporine.

[Biomarkers and pharmacokinetic-pharmacodynamic studies of immunosuppressive agents]. / Biomarqueurs et étude pharmacocinétique-pharmacodynamique des immunosuppresseurs.

Biomarkers are characteristics that are objectively measured and evaluated as indicators of normal biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention. Biomarkers of pharmacological responses allow pharmacokinetic-pharmacodynamic modelling based on what is known of the mechanism of action of the drug. Characteristics predictive of the pharmacological response, such as a genotype, constitute a specific category of biomarkers and can be used as covariates in the model. In the case of "classical" immunosuppressive agents, the biomarkers of response most studied are lymphocyte calcineurin activity for ciclosporin and tacrolimus, and inosine monophosphate dehydrogenase activity for mycophenolate. Pharmacokinetic-pharmacodynamic analysis of monoclonal antibodies with immunosuppressive properties requires complex models and immunological biomarkers such as, for example, the number of circulating lymphocytes with a given surface antigen. Pharmacodynamic indirect response models are particularly relevant in this instance.