Microdialysis in drug discovery

Microdialysis has been developed during the last 25 years by several authors primarily to study brain function and changes in levels of endogenous compounds such as neurotransmitters or metabolites. The development of microdialysis for the purpose of measuring drugs was initiated during the late eighties. This technique provides a means of continuous plasma sampling without repeated blood sampling and the applicability to the study of drug metabolism and pharmacokinetics in experimental animals and human. Also, the microdialysis technique allows the study of plasma protein binding and the saturation of protein binding. The implantation of the microdialysis probe in other tissues and organs, like central nervous system, adipose tissue and heart, allows the study of drug distribution. On the other hand, the measurement of endogenous substances using the microdialysis technique permits the study of the effect of drugs on neurotransmission and metabolism. Moreover, as this technique allows the simultaneous determination of different physiological parameters such as blood pressure, locomotor and convulsive activity, it is a suitable tool for pharmacokinetic-pharmacodynamic studies of drugs and pharmacokinetic-pharmacodynamic (PK-PD) modeling. Lastly, the reverse microdialysis is a powerful technique for the study of local actions of drugs in different tissues such as specific brain nuclei, myocardium, liver or skeletal muscle. So, this article reviewed the vast applications of the microdialysis technique for the study of pharmacokinetic and pharmacodynamic properties of drugs.     

微透析技术在肿瘤药物研究中的应用进展

微透析技术具有连续动态微创取样优势,能实时在线研究正常生理和肿瘤病理情况下肿瘤药物在体内,尤其是肿瘤组织局部的分布、代谢和消除,利用PK/PD参数模型设计个体化给药方案,预防和减少肿瘤药物的毒性反应。同时,微透析技术还可以应用于肿瘤细胞外间质微环境中生化物质的监测以及肿瘤药物局部给药治疗,是肿瘤药物研究的重要技术手段。本文对近年来微透析在肿瘤药物研究中的应用进展进行检索和归纳,为微透析技术在取样、监测以及治疗领域的进一步研究应用提供参考。     

Applicability of reverse microdialysis in pharmacological and toxicological studies

A recent application of microdialysis is the introduction of a substance into the extracellular space via the microdialysis probe. The inclusion of a higher amount of a drug in the perfusate allows the drug to diffuse through the microdialysis membrane to the tissue. This technique, actually called as reverse microdialysis, not only allows the local administration of a substance but also permits the simultaneous sampling of the extracellular levels of endogenous compounds. Local effects of exogenous compounds have been studied in the central nervous system, hepatic tissue, dermis, heart and corpora luteae of experimental animals by means of reverse microdialysis. In central nervous studies, reverse microdialysis has been extensively used for the study of the effects on neurotransmission at different central nuclei of diverse pharmacological and toxicological agents, such as antidepressants, antipsychotics, antiparkinsonians, hallucinogens, drugs of abuse and experimental drugs. In the clinical setting, reverse microdialysis has been used for the study of local effects of drugs in the adipose tissue, skeletal muscle and dermis. The aim of this review is to describe the principles of the reverse microdialysis, to compare the technique with other available methods and finally to describe the applicability of reverse microdialysis in the study of drugs properties both in basic and clinical research.     

Methodological issues in microdialysis sampling for pharmacokinetic studies

Microdialysis is an in vivo technique that permits monitoring of local concentrations of drugs and metabolites at specific sites in the body. Microdialysis has several characteristics, which makes it an attractive tool for pharmacokinetic research. About a decade ago the microdialysis technique entered the field of pharmacokinetic research, in the brain, and later also in peripheral tissues and blood. Within this period much has been learned on the proper use of this technique. Today, it has outgrown its child diseases and its potentials and limitations have become more or less well defined. As microdialysis is a delicate technique for which experimental factors appear to be critical with respect to the validity of the experimental outcomes, several factors should be considered. These include the probe; the perfusion solution; post-surgery interval in relation to surgical trauma, tissue integrity and repeated experiments; the analysis of microdialysate samples; and the quantification of microdialysate data. Provided that experimental conditions are optimized to give valid and quantitative results, microdialysis can provide numerous data points from a relatively small number of individual animals to determine detailed pharmacokinetic information. An example of one of the added values of this technique compared with other in vivo pharmacokinetic techniques, is that microdialysis reflects free concentrations in tissues and plasma. This gives the opportunity to assess information on drug transport equilibration across membranes such as the blood-brain barrier, which already has provided new insights. With the progress of analytical methodology, especially with respect to low volume/low concentration measurements and simultaneous measurement of multiple compounds, the applications and importance of the microdialysis technique in pharmacokinetic research will continue to increase.     

微透析技术在抗菌药物药动学和药效学中的应用

微透析技术是一项新兴的体内药物分析技术。通过微透析技术与药动学和药效学模型结合,实现对组织或细胞外游离态药物浓度及其相应药理效应的同时研究,不仅有利于进一步明确药物的剂量-效应关系,制定临床最佳给药方案,而且也为个体化给药提供了科学依据。本文综合近年文献,对微透析技术的基本原理以及在抗菌药物药动学和药效学研究中的应用作一综述。     

Microdialysis in peripheral tissues

The objective of this review is to survey the recent literature regarding the applications of microdialysis in pharmacokinetic studies and facilitating many other studies in peripheral tissues such as muscle, subcutaneous adipose tissue, heart, lung, etc. It has been reported extensively that microdialysis is a useful technique for monitoring free concentrations of compounds in extracellular fluid (ECF), and it is gaining popularity in pharmacokinetic and pharmacodynamic studies, both in experimental animals and humans. The first part of this review discusses the use of microdialysis technique for ECF sampling in peripheral tissues in animal studies. The second part of the review describes the use of microdialysis for ECF sampling in peripheral tissues in human studies. Microdialysis has been applied extensively to measure both endogenous and exogenous compounds in ECF. Of particular benefit is the fact that microdialysis measures the unbound concentrations in the peripheral tissue fluid which have been shown to be responsible for the pharmacological effects. With the increasing number of applications of microdialysis, it is obvious that this method will have an important place in studying drug pharmacokinetics and pharmacodynamics.     

Application of microdialysis in clinical pharmacology

Microdialysis has been developed during the last 25 years by several authors primarily to study brain function and changes in levels of endogenous compounds such as neurotransmitters or metabolites in different laboratory animals. However, in the last ten years microdialysis sampling has been introduced as a versatile technique in the clinical setting. Although, microdialysis sampling has been extensively used for metabolic monitoring in patients, it was also employed for the study of distribution of different therapeutic agents especially anti-infective and antineoplasic drugs. In addition, clinical effect of drugs in patients could be also determined by means of microdialysis. So, this article reviewed the vast applications of the microdialysis technique for the study of pharmacokinetic and pharmacodynamic properties of drugs in the clinical setting.     

Application of microdialysis to characterize drug disposition in tumors

Microdialysis is an in vivo sampling technique that was initially developed to measure endogenous substances in the field of neurotransmitter research. In the past decade, microdialysis has been increasingly applied to study the pharmacokinetics and drug metabolism in the blood and various tissues of both animals and humans. This paper describes the general aspects of this in vivo sampling technique followed by the survey of the recent papers regarding the application of microdialysis to characterize anticancer drug disposition in solid tumors. It can be concluded that microdialysis is a very suitable method to obtain drug concentration-time profiles in the interstitial fluid of solid tumors as well as of other variety of tissues.     

Intracerebral microdialysis: 30 years as a tool for the neuroscientist

1. Microdialysis is an established technique for studying physiological, pharmacological and pathological changes of a wide range of low molecular weight substances in the brain extracellular fluid. Many studies have proven its sensitivity in sampling the extracellular space in discrete brain locations, such as the striatum, and monitoring the action of exogenous substances. 2. The two main areas of application of microdialysis are the recovery of endogenous substances, primarily the neurotransmitters, and the infusion of drugs through the microdialysis cannula (retrodialysis). 3. Microdialysis in awake animals is the tool of choice for studying the relationship between changes in behaviour and neurotransmitters in certain brain areas. In addition, the concomitant recording of the electroencephalogram at the site of microdialysis has been shown to be extremely useful in determining the role of certain neurotransmitters in paroxysmal activity. 4. Clinical applications of microdialysis have included monitoring of ischaemic injury, subarachnoid haemorrhage, trauma and epilepsy. With the recent availability of standardized equipment, the use of microdialysis in the neurological clinic is likely to become more common.     

Microdialysis as an Important Technique in Systems Pharmacology—a Historical and Methodological Review

Microdialysis has contributed with very important knowledge to the understanding of target-specific concentrations and their relationship to pharmacodynamic effects from a systems pharmacology perspective, aiding in the global understanding of drug effects. This review focuses on the historical development of microdialysis as a method to quantify the pharmacologically very important unbound tissue concentrations and of recent findings relating to modeling microdialysis data to extrapolate from rodents to humans, understanding distribution of drugs in different tissues and disease conditions. Quantitative microdialysis developed very rapidly during the early 1990s. Method development was in focus in the early years including development of quantitative microdialysis, to be able to estimate true extracellular concentrations. Microdialysis has significantly contributed to the understanding of active transport at the blood-brain barrier and in other organs. Examples are presented where microdialysis together with modeling has increased the knowledge on tissue distribution between species, in overweight patients and in tumors, and in metabolite contribution to drug effects. More integrated metabolomic studies are still sparse within the microdialysis field, although a great potential for tissue and disease-specific measurements is evident.     

Human microdialysis

Microdialysis has been used extensively in animal studies for decades and in human pharmacokinetic studies for about 10 years. Microdialysis is based on the passive diffusion of a compound along its concentration gradient from the tissue through the membrane into the dialysate. Microdialysis samples from the interstitial space which is a defined, anatomical compartment; there is no net loss of body fluid; the sample is "purified" and no enzymatic degradation takes place because proteins do not pass through the probe membrane into the dialysate; microdialysis data relate to the intact molecule; time resolution is high compared to biopsy and skin blister techniques; radioabelling or induction of a magnetic response is not needed; microdialysis is also an alternative method to determine protein binding of a compound in vivo; microdialysis can readily be set up in clinical research units without expensive infrastructure. Microdialysis has been used to measure tissue concentrations of endogenous compounds and to investigate the tissue penetration of drugs in a variety of tissues in humans in vivo in both healthy volunteers and patients. Microdialysis data have also been used in PK-PD modelling and to obtain concentration-response relationships locally in tissues in vivo. There are also studies combining microdialysis with imaging techniques, e.g. PET. Microdialysis data may be used in early studies to select the appropriate compound, to optimise dosing regimens and to investigate the kinetic and dynamic consequences in the tissues of drug-drug and drug-disease interactions. Microdialysis can also be used in late phase studies to provide tissue concentration data in support of therapeutic efficacy trials or to create a niche for an already marketed drug. FDA and CPMP documents emphasise the value and importance of human tissue drug concentration data and support the use of microdialysis in humans to obtain such information. Microdialysis can satisfy regulatory requirements by providing data on drug concentrations in a well-defined anatomical tissue compartment at or close to the effect target site. Microdialysis is a versatile technique because of its multifaceted utility, low cost, ease of use, adaptability to different types of compounds and its feasibility for a number of organs and tissues. Equipment and probes for use in various organs have been commercially available for years.     

Blood microdialysis in pharmacokinetic and drug metabolism studies

Microdialysis is a sampling technique allowing measurement of endogenous and exogenous substances in the extracellular fluid surrounding the probe. In vivo microdialysis sampling offers several advantages over conventional methods of studying the pharmacokinetics and metabolism of xenobiotics, both in experimental animals and humans. In the first part of this review article various practical aspects related to blood microdialysis will be discussed, such as: probe design, surgical implantation techniques, methods to determine the in vivo relative recovery of the analyte of interest by the probe, special analytical considerations related to small volume microdialysate samples, and pharmacokinetic calculations based on microdialysis data. In the second part of this review a few selected applications of in vivo microdialysis sampling to investigate pharmacokinetic processes are briefly discussed: determination of in vivo plasma protein binding in small laboratory animals, distribution of drugs across the blood-brain barrier, the use of microdialysis sampling to study biliary excretion and enterohepatic cycling, blood microdialysis sampling in man and in the mouse, and in vivo drug metabolism studies.     

Microdialysis: current applications in clinical pharmacokinetic studies and its potential role in the future

Microdialysis is a probe-based sampling method, which, if linked to analytical devices, allows for the measurement of drug concentration profiles in selected tissues. During the last two decades, microdialysis has become increasingly popular for preclinical and clinical pharmacokinetic studies. The advantage of in vivo microdialysis over traditional methods relates to its ability to continuously sample the unbound drug fraction in the interstitial space fluid (ISF). This is of particular importance because the ISF may be regarded as the actual target compartment for many drugs, e.g. antimicrobial agents or other drugs mediating their action through surface receptors. In contrast, plasma concentrations are increasingly recognised as inadequately predicting tissue drug concentrations and therapeutic success in many patient populations. Thus, the minimally invasive microdialysis technique has evolved into an important tool for the direct assessment of drug concentrations at the site of drug delivery in virtually all tissues. In particular, concentrations of transdermally applied drugs, neurotransmitters, antibacterials, cytotoxic agents, hormones, large molecules such as cytokines and proteins, and many other compounds were described by means of microdialysis. The combined use of microdialysis with non-invasive imaging methods such as positron emission tomography and single photon emission tomography opened the window to exactly explore and describe the fate and pharmacokinetics of a drug in the body. Linking pharmacokinetic data from the ISF to pharmacodynamic information appears to be a straightforward approach to predicting drug action and therapeutic success, and may be used for decision making for adequate drug administration and dosing regimens. Hence, microdialysis is nowadays used in clinical studies to test new drug candidates that are in the pharmaceutical industry drug development pipeline.     

Microdialysis for the evaluation of penetration through the human skin barrier — a promising tool for future research?

The direct measurement of local drug concentration levels at discreet skin locations with minor trauma has recently become possible with the introduction of cutaneous microdialysis. Cutaneous microdialysis is an in vivo sampling technique for measuring solutes in the extracellular fluid of the dermis. When used in combination with other experimental approaches, for example with a variety of non-invasive techniques to describe the functional status of the skin (bioengineering methods), it may help investigators to gain new insights into the fields of skin diseases, metabolism and drug absorption/penetration. An important parameter to describe the efficacy of microdialysis is the relative recovery. This is the ratio between the concentration of a substance in the dialysate and the true extracellular concentration. Several methods are in common use to describe the relative recovery (no-net-flux method or retrodialysis). Parameters such as probe design, depth of the probe in the dermis, physico-chemical properties of the compound of interest, and analytical aspects are important factors influencing microdialysis. Microdialysis has been used to investigate the influence of penetration enhancers, vehicles or iontophoresis on percutaneous absorption, performed by in vivo studies in rats. In human volunteers, most of the experiments have been performed to study the kinetics of fast penetrating substances, e.g. nicotine, non-steroidal antiinflammatory drugs, local anaesthetics, or solvents. Problems have been encountered in the detection of lipophilic and highly protein-bound substances. Further, dermal metabolism and the influence of barrier perturbation on percutaneous absorption have been analyzed. Investigations suggest that microdialysis, in combination with traditional techniques, might give valuable information regarding the assessment of the penetration of drugs and other exogenous agents through the skin. In spite of the clearly defined and accepted advantages of microdialysis technology for studies of transdermal drug delivery, to date no standardized test procedure exists nor has the reproducibility of the results been evaluated. In the future, these problems have to be solved to enable this method to find its place in standard research.     

In vivo brain microdialysis: advances in neuropsychopharmacology and drug discovery

INTRODUCTION: Microdialysis is an important in vivo sampling technique, useful in the assay of extracellular tissue fluid. The technique has both pre-clinical and clinical applications but is most widely used in neuroscience. The in vivo microdialysis technique allows measurement of neurotransmitters such as acetycholine (ACh), the biogenic amines including dopamine (DA), norepinephrine (NE) and serotonin (5-HT), amino acids such as glutamate (Glu) and gamma aminobutyric acid (GABA), as well as the metabolites of the aforementioned neurotransmitters, and neuropeptides in neuronal extracellular fluid in discrete brain regions of laboratory animals such as rodents and non-human primates. AREAS COVERED: In this review we present a brief overview of the principles and procedures related to in vivo microdialysis and detail the use of this technique in the pre-clinical measurement of drugs designed to be used in the treatment of chemical addiction, neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD) and as well as psychiatric disorders such as attention-deficit/hyperactivity disorder (ADHD) and schizophrenia. This review offers insight into the tremendous utility and versatility of this technique in pursuing neuropharmacological investigations as well its significant potential in rational drug discovery. EXPERT OPINION: In vivo microdialysis is an extremely versatile technique, routinely used in the neuropharmacological investigation of drugs used for the treatment of neurological disorders. This technique has been a boon in the elucidation of the neurochemical profile and mechanism of action of several classes of drugs especially their effects on neurotransmitter systems. The exploitation and development of this technique for drug discovery in the near future will enable investigational new drug candidates to be rapidly moved into the clinical trial stages and to market thus providing new successful therapies for neurological diseases that are currently in demand.     

Application of Microdialysis in Pharmacokinetic Studies

The objective of this review is to survey the recent literature regarding the various applications of microdialysis in pharmacokinetics. Microdialysis is a relatively new technique for sampling tissue extracellular fluid that is gaining popularity in pharmacokinetic and pharmacodynamic studies, both in experimental animals and humans. The first part of this review discusses various aspects of the technique with regard to its use in pharmacokinetic studies, such as: quantitation of the microdialysis probe relative recovery, interfacing the sampling technique with analytical instrumentation, and consideration of repeated procedures using the microdialysis probe. The remainder of the review is devoted to a survey of the recent literature concerning pharmacokinetic studies that apply the microdialysis sampling technique. While the majority of the pharmacokinetic studies that have utilized microdialysis have been done in the central nervous system, a growing number of applications are being found in a variety of peripheral tissue types, e.g. skin, muscle, adipose, eye, lung, liver, and blood, and these are considered as well. Given the rising interest in this technique, and the ongoing attempts to adapt it to pharmacokinetic studies, it is clear that microdialysis sampling will have an important place in studying drug disposition and metabolism.     

微透析技术在靶组织局部药物浓度检测中的应用

微透析技术是一项越来越被广泛使用的在体研究技术,其遵循透析原理,以探针为基础取样,可连续检测局部组织细胞外液的药物浓度,能满足常规的药代动力学/药效学(PK-PD)研究。本文就其在靶组织局部药物浓度检测中的应用作一简要介绍。     

Microdialysis as a tool to determine free kidney levels of voriconazole in rodents: a model to study the technique feasibility for a moderately lipophilic drug

Microdialysis has been employed for the in vivo measurement of endogenous compounds and a variety of drugs in different tissues. The applicability of this technique can be limited by drug lipophilicity which can impair the diffusion through dialysis membrane. The objective of this study was to evaluate the feasibility of using microdialysis to study kidney penetration of voriconazole, a moderately lipophilic antifungal triazolic agent (LogD7.4=1.8). Microdialysis probe recoveries were investigated in vitro by dialysis and retrodialysis using four different drug concentrations (0.1-2 microg/mL) at five flow rates (1-5 microL/min). Recoveries were dependent on the method used for the determination as well as on the flow rate, but independent of drug concentration. The average apparent recoveries determined by dialysis and retrodialysis, at flow rate of 2 microL/min, were 21.1+/-1.5% and 28.7+/-2.0%, respectively. Recovery by retrodialysis was bigger than the recovery by dialysis. The average apparent dialysis/retrodialysis recovery ratio in vitro was 0.73 for all concentrations investigated. The differences between retrodialysis and dialysis recoveries were attributed to the drug's binding to the plastic tubing before and after the dialysis membrane which was experimentally evaluated and mathematically modeled. The in vivo apparent recovery determined by retrodialysis in healthy Wistar rats' kidney was 38.5+/-3.5%, similar to that observed in vitro using the same method (28.7+/-2.0%). The in vivo apparent recovery after correcting for plastic tubing binding (25.1+/-2.8%) was successfully used for determining free kidney levels of voriconazole in rats following 40 and 60mg/kg oral dosing. The results confirmed that microdialysis can be used as sampling technique to determine free tissue levels of moderately lipophilic drugs once the contribution of tubing binding and membrane diffusion on the apparent recovery are disentangled.     

Microdialysis--theoretical background and recent implementation in applied life-sciences.

In the past decade microdialysis has become a method of choice in the study of unbound tissue concentrations of both endogenous and exogenous substances. Microdialysis has been shown to offer information about substances directly at the site of action while being well tolerable and safe. The large variety of its field of application has been demonstrated. However, a few challenges have to be met to make this method generally applicable in routine applications. This review will provide an overview over theoretical aspects that have to be considered during the implementation of microdialysis. Moreover, a comparison between microdialysis and other tissue sampling techniques will demonstrate advantages and limitations of the methods mentioned. Subsequently, it will present a critical synopsis of a variety of scientific/biomedical applications of this method with emphasis on the most recent literature, focussing on target tissues while giving examples of substances examined. It is concluded that microdialysis will be of great value in future investigations of pharmacokinetics, pharmacodynamics and in monitoring of disease status and progression.