药物转运体和代谢酶在抗生素药动学中的作用

近年来,对体内药物转运体的研究取得了重大进展,越来越多的转运体被发现及研究,其对药物的跨膜转运,具有重要的意义。各种转运体包括摄取转运体和外排转运体对药物的体内过程以及药物相互作用均有着重要影响。研究表明大多数抗生素的体内过程都与转运体和代谢酶有关,因此,归纳总结了转运体和代谢酶在抗生素的药动学和药物相互作用中的最新研究进展,为临床合理用药提供参考。     

药物体内过程的立体选择性

立体选择性问题对药物代谢围化的冲击越来越大、药物的吸收、分布、转化和排泄都存在立体选择性。本文旨在对药物体内过程听立体选择性、首过效应中的立体选择性、对映体之间的相互作用和对映体之间的药代学差别阐述，以更深刻了解药物体内过程的规律。     

手性药物代谢的研究进展

在临床上使用的药物中，约有50％的药物为手性药物（chiral drugs）的外消旋体，而在生物体内，生物大分子均处于高度复杂的手性环境中。药物的作用过程大多涉及与这些大分子的相互作用，药物进入体内后，其药物作用是通过与体内的某些靶分子之间的严格手性匹配和分子识别，并且以不同途径被吸收、活化或降解，导致对映体药物在体内的药理活性、代谢过程存在显著的差异，     

转运体介导的食物-药物相互作用

食物与药物之间的相互作用普遍存在,且作用机制也多种多样。目前,研究较多的是单个食物或食物中的某些营养成分通过调节药物转运体或代谢酶的功能从而影响药物的体内过程。食物对药物体内过程的影响包括吸收、分布、代谢、排泄四个方面,并且主要是调节其中参与的药物转运体和代谢酶的功能。转运体介导的食物对药物体内吸收的影响主要是通过调节肠上皮摄取型和外排型的转运体,从而影响药物的吸收;对分布的影响主要是通过调节体内一些屏障中的转运体;对代谢的影响主要是同时调节药物代谢酶和转运体;对排泄的影响是通过调节肾脏和肝脏胆汁排泄的药物转运体,从而影响药物的清除率。因此,转运体介导的食物与药物相互作用直接影响药物治疗的效果。     

药物转运体与药物体内过程

关于药物在机体内的跨膜转运机制,以往的研究多侧重于药物理化性质.近年,发现体内存在多种转运蛋白(转运体)系统,对药物体内跨膜转运,有重要意义,有时甚至起决定性作用,因此,药物转运体对药物的体内过程,即药物的吸收、分布、代谢和排泄及药物之间的相互作用有重要影响,并可影响或决定药物的动力学过程.     

临床药理学讲座（2）掌握药物相互作用的机理实行合理的联合用药（续一）

2.3 药代动力学方面的相互作用 机体对药物的处理是药物与机体相互作用的一个重要组成部分。这一药代动力学过程包括药物的吸收、分布、代谢和排泄四个环节。在这四个环节上均有可能发生药物相互作用,即一种药物使另一种药物的体内过程发生变化,从而影响另一种药物的血浆浓度,进而改变其作用强度。     

基于细胞色素P450酶的药物相互作用机制探讨

细胞色素P450酶是药物体内代谢的关键酶,药物合用时可能因与同一种代谢酶的相互作用,导致药物在体内的处置过程发生改变.本文旨在探讨常见的细胞色素P450酶相关药物相互作用类型和其机制,为临床联合用药的合理、安全、有效提供依据.     

抗感染药物的相互作用及处置

在抗感染药物治疗中，为达到增强药物疗效并减少其不良反应、防止病原菌产生耐药性等目的，常采用联合用药。当两种或两种以上药物联合使用时，不可避免地会出现药物间的相互作用（drug interaction）。广义地讲，药物相互作用是指两种或两种以上药物在体外所产生的物理化学变化（配伍禁忌），以及在体内由变化造成的药理作用与效应的改变。近年来对于药物与食物、烟、酒和饮料、临床检验试剂以及与中草药中的植物药成分等之间的相互作用也列入了药物相互作用讨论的范畴。专业地讲，药物相互作用是指在体内药物间所产生的药物动力学（简称药动学，[第一段]     

肠道药物转运体对药物吸收的研究进展

药物与体内各种转运体的相互作用是药物体内药动学性质的决定性因素之一。本文从肠道转运体出发,介绍了它们在药物吸收过程中的作用,旨在利用肠道转运体的作用增加药物向组织器官的靶向分布;利用转运体的作用改变药物的消除途径,从而减轻其毒副作用;利用转运体的作用进行新药设计从而避免药物间有害相互作用的产生;最后通过构建转运体的高通量筛选系统模型,进行新化合物筛选和候选药物的药动学机制研究,为新药的开发和临床合理化给药提供新的策略和思路。     

抗肿瘤药物伊马替尼酶代谢相关的研究进展

伊马替尼是治疗慢性粒细胞白血病的一线药物,它在体内经多种CYP450酶广泛代谢,由此导致的显著个体差异以及药物相互作用,对临床治疗带来影响。从伊马替尼的代谢途径、主要代谢酶、基因多态性和药物相互作用影响进行综述,为进一步了解体内处置过程以及临床用药提供了理论依据,促进伊马替尼的临床安全、有效用药。     

Mechanism-based inactivation of human cytochrome P450 enzymes: strategies for diagnosis and drug–drug interaction risk assessment

Among drugs that cause pharmacokinetic drug–drug interactions, mechanism-based inactivators of cytochrome P450 represent several of those agents that cause interactions of the greatest magnitude. In vitro inactivation kinetic data can be used to predict the potential for new drugs to cause drug interactions in the clinic. However, several factors exist, each with its own uncertainty, that must be taken into account in order to predict the magnitude of interactions reliably. These include aspects of in vitro experimental design, an understanding of relevant in vivo concentrations of the inactivator, and the extent to which the inactivated enzyme is involved in the clearance of the affected drug. Additionally, the rate of enzyme degradation in vivo is also an important factor that needs to be considered in the prediction of the drug interaction magnitudes. To address mechanism-based inactivation for new drugs, various in vitro experimental approaches have been employed. The selection of approaches for in vitro kinetic characterization of inactivation as well as in vitro–in vivo extrapolation should be guided by the purpose of the exercise and the stage of drug discovery and development, with an increase in the level of sophistication throughout the research and development process.     

A regulatory viewpoint on transporter-based drug interactions

1.?Pharmacokinetic drug interactions can lead to serious adverse events and the evaluation of a new molecular entity's (NME) drug–drug interaction potential is an integral part of drug development and regulatory review before its market approval. Clinically relevant interactions mediated by transporters are of increasing interest in clinical development and research in this emerging area and it has been revealed that drug transporters can play an important role in modulating drug absorption, distribution, metabolism and elimination.

2.?Acting alone or in concert with drug-metabolizing enzymes transporters can affect the pharmacokinetics and/or pharmacodynamics of a drug. The newly released drug interaction guidance by the US Food and Drug Administration (USFDA) includes new information addressing drug transporter interactions with a primary focus on P-glycoprotein (P-gp, ABCB1).

3.?This paper provides a regulatory viewpoint on transporters and their potential role in drug–drug interactions. It first outlines information that might be needed during drug development and ultimately included in new drug application (NDA) submissions to address potential transporter-mediated drug interactions. Next, it explains criteria that may warrant conduct of in vivo P-gp-mediated drug interaction studies based on in vitro assessment. In addition, it includes a review case that describes the evaluation of data suggesting a P-gp-based induction interaction.     

Assessment of drug-drug interactions: concepts and approaches

1. A priori knowledge of the enzyme inhibitory potential of new drug entities and the drug-metabolizing enzymes involved can be used in support of important decisions on the future progress of a drug in clinical development. 2. Important advances in the knowledge of human drug-metabolizing enzymes have largely fuelled the integration of in vitro drug metabolism and clinical drug interaction studies for use in drug development programmes. 3. The likelihood of correctly predicting in vivo drug-drug interactions appears highly dependent on selecting the correct enzyme inhibition model for use in deriving the inhibitor constant (K_i) and correctly determining the available concentration of inhibitor at the active site of the enzyme(s) of interest. 4. The uncertainty and inaccuracy of predicting the extent and duration of in vivo drug interactions currently stems from a lack of definitive models by which to assess likely substrate and inhibitor concentrations at the active site of metabolism. Additional issues contributing to the uncertainty of predicting drug interactions include assumptions of the contribution of presystemic drug extraction and the effect of inhibitors on the processes involved. 5. This review considers the practical aspects of in vitro enzyme inhibition studies and the use of in vitro-in vivo correlation approaches described in the literature to predict in vivo drug-drug interactions.     

Predicting Drug–Drug Interactions: An FDA Perspective

Pharmacokinetic drug interactions can lead to serious adverse events, and the evaluation of a new molecular entity’s drug–drug interaction potential is an integral part of drug development and regulatory review prior to its market approval. Alteration of enzyme and/or transporter activities involved in the absorption, distribution, metabolism, or excretion of a new molecular entity by other concomitant drugs may lead to a change in exposure leading to altered response (safety or efficacy). Over the years, various in vitro methodologies have been developed to predict drug interaction potential in vivo. In vitro study has become a critical first step in the assessment of drug interactions. Well-executed in vitro studies can be used as a screening tool for the need for further in vivo assessment and can provide the basis for the design of subsequent in vivo drug interaction studies. Besides in vitro experiments, in silico modeling and simulation may also assist in the prediction of drug interactions. The recent FDA draft drug interaction guidance highlighted the in vitro models and criteria that may be used to guide further in vivo drug interaction studies and to construct informative labeling. This report summarizes critical elements in the in vitro evaluation of drug interaction potential during drug development and uses a case study to highlight the impact of in vitro information on drug labeling.     

Advances in predicting CYP-mediated drug interactions in the drug discovery setting

Advances in high-throughput screening methodologies, biological reagents and in silico techniques relating to cytochrome p450 (CYP)-mediated drug–drug interactions have led to reduced clinical attrition rates and to the development of safer therapeutics. Greater understanding of the impact of genetic variability and CYP induction on drug interactions, particularly for low therapeutic index drugs, has facilitated improved clinical study design. This review outlines recent developments using in vitro and in silico technologies to study CYP-mediated drug interactions and describes how those tools have been combined to drive improved candidate selection and in vivo predictions early in the drug discovery process.     

纳米药物制剂体内分析方法及药动学研究进展和问题策略分析

近年来随着纳米技术的不断发展,纳米药物制剂在改善药物递送、提高生物利用度方面显示出独特优势,已成为临床新药开发研究的热点,为诸多疾病尤其是恶性肿瘤的治疗提供了新思路。然而,由于对纳米药物制剂的体内过程了解不够全面,导致纳米药物制剂的临床转化率极低,严重制约了纳米药物制剂的发展。基于纳米药物制剂良好的应用前景及目前药动学研究中存在的关键问题,调研了国内外的相关文献,首先介绍了常见的具有不同纳米载体类型的纳米药物制剂的种类,对纳米药物制剂体内药物浓度分析测定的方法进行归纳总结,最后分析纳米载体的理化性质对纳米药物制剂体内药动学行为的影响,旨在为纳米药物制剂的体内过程研究提供参考,以获取更为全面的体内药动学数据,提高药物的临床转化率。同时针对目前纳米药物制剂的载体研究、体内浓度定量分析方法以及药动学研究中存在的问题进行讨论,以期为纳米药物制剂的研究与开发利用提供方向。     

CYP Induction-Mediated Drug Interactions: in Vitro Assessment and Clinical Implications

Cytochrome P450 (CYP) induction-mediated interaction is one of the major concerns in clinical practice and for the pharmaceutical industry. There are two major issues associated with CYP induction: a reduction in therapeutic efficacy of comedications and an induction in reactive metabolite-induced toxicity. Because CYP induction is a metabolic liability in drug therapy, it is highly desirable to develop new drug candidates that are not potent CYP inducer to avoid the potential of CYP induction-mediated drug interactions. For this reason, today, many drug companies routinely include the assessment of CYP induction at the stage of drug discovery as part of the selection processes of new drug candidates for further clinical development. The purpose of this article is to review the molecular mechanisms of CYP induction and the clinical implications, including pharmacokinetic and pharmacodynamic consequences. In addition, factors that affect the degree of CYP induction and extrapolation of in vitro CYP induction data to in vivo situations will also be discussed. Finally, assessment of the potential of CYP induction at the drug discovery and development stage will be discussed.     

Thermodynamic studies for drug design and screening

Introduction: A key part of drug design and development is the optimization of molecular interactions between an engineered drug candidate and its binding target. Thermodynamic characterization provides information about the balance of energetic forces driving binding interactions and is essential for understanding and optimizing molecular interactions.

Areas covered: This review discusses the information that can be obtained from thermodynamic measurements and how this can be applied to the drug development process. Current approaches for the measurement and optimization of thermodynamic parameters are presented, specifically higher throughput and calorimetric methods. Relevant literature for this review was identified in part by bibliographic searches for the period 2004 – 2011 using the Science Citation Index and PUBMED and the keywords listed below.

Expert opinion: The most effective drug design and development platform comes from an integrated process utilizing all available information from structural, thermodynamic and biological studies. Continuing evolution in our understanding of the energetic basis of molecular interactions and advances in thermodynamic methods for widespread application are essential to realize the goal of thermodynamically driven drug design. Comprehensive thermodynamic evaluation is vital early in the drug development process to speed drug development toward an optimal energetic interaction profile while retaining good pharmacological properties. Practical thermodynamic approaches, such as enthalpic optimization, thermodynamic optimization plots and the enthalpic efficiency index, have now matured to provide proven utility in the design process. Improved throughput in calorimetric methods remains essential for even greater integration of thermodynamics into drug design.     

Inhibition of In Vitro Metabolism of Simvastatin by Itraconazole in Humans and Prediction of In Vivo Drug-Drug Interactions

Purpose. To evaluate an interaction between simvastatin and itraconazole in in vitro studies and to attempt a quantitative prediction of in vivo interaction in humans. Methods. The inhibitory effect of itraconazole on simvastatin metabolism was evaluated using human liver microsomes and the K_i values were calculated for the unbound drug in the reaction mixture. A physiologically-based pharmacokinetic model was used to predict the maximum in vivo drug-drug interaction. Results. Itraconazole competitively inhibited the metabolism of simvastatin to M-1 and M-2 with K_i values in the nM range. The area under the curve (AUC) of simvastatin after concomitant dosing with itraconazole was predicted to increase ca. 84-101-fold compared with that without administration of itraconazole. Taking into consideration the fact that this method predicts the maximum interaction, this agrees well with the clinical observation of a 19-fold increase. A similar prediction, based on the K_i value without taking into account the drug adsorption to microsomes, led to an underevaluation of the interaction. Conclusions. It was demonstrated that the competitive inhibition of CYP3A4-mediated simvastatin metabolism by itraconazole is the main cause of the drug interaction and that a K_i value corrected for drug adsorption to microsomes is the key factor in quantitatively predicting the maximum in vivo drug interactions.     

Use of the hollow fiber assay for the evaluation of DNA damaging agents

Introduction

The preclinical development and clinical progression of potential anticancer agents are highly time and resource-intensive. Traditionally, promising compounds in vitro undergo further screening in xenograft models, a long process that uses large numbers of animals. In order to hasten compound progression, the hollow fiber assay (HFA) was developed by the US National Cancer Institute as an additional filtering step in drug development, bridging the gap between in vitro and xenograft compound screening. The HFA demonstrates a good correlation in terms of clinical predictivity, and has significant reduction and refinement benefits for animal usage. In addition, the assay enables the study of basic pharmacological properties of compounds under investigation. The HFA has been mainly used as a rapid in vivo cytotoxicity screen, but has also been shown to be amenable to study drug/target interactions in vivo. One of the challenges of the HFA is the small sample sizes obtained, which can limit sensitivity.

Methods

Here we specifically focus on the detection of DNA double-strand breaks, monitoring the effects of standard and novel anti-cancer agents on human lung, colon and breast cancer cell lines using immunoblotting and flow cytometry techniques for γ-H2A.X. This presented a further challenge due to the low abundance of the target event.

Results

We found a good correlation between techniques in terms of rate of detection and sensitivity confirming the ability to use the HFA for detection of these specific drug–target interactions.

Discussion

The results demonstrate good sensitivity and predictability for drug behavior in an assay where cell number is limited. In contrast to conventional xenograft studies, this short-term assay also enables analysis of pharmacodynamic endpoints in tumor cells in vivo. Importantly, there is a significant impact on reduction and refinement of the use of animals in incorporating this assay into the drug development process.