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1.  Pharmacogenomic Responses of Rat Liver to Methylprednisolone: An Approach to Mining a Rich Microarray Time Series 
The AAPS journal  2005;7(1):E156-E194.
A data set was generated to examine global changes in gene expression in rat liver over time in response to a single bolus dose of methylprednisolone. Four control animals and 43 drug-treated animals were humanely killed at 16 different time points following drug administration. Total RNA preparations from the livers of these animals were hybridized to 47 individual Affymetrix RU34A gene chips, generating data for 8799 different probe sets for each chip. Data mining techniques that are applicable to gene array time series data sets in order to identify drug-regulated changes in gene expression were applied to this data set. A series of 4 sequentially applied filters were developed that were designed to eliminate probe sets that were not expressed in the tissue, were not regulated by the drug treatment, or did not meet defined quality control standards. These filters eliminated 7287 probe sets of the 8799 total (82%) from further consideration. Application of judiciously chosen filters is an effective tool for data mining of time series data sets. The remaining data can then be further analyzed by clustering and mathematical modeling techniques.
PMCID: PMC2607485  PMID: 16146338
Data mining; gene arrays; glucocorticoids; mathematical modeling; pharmacogenomics
3.  Pharmacogenomic responses of rat liver to methylprednisolone: An approach to mining a rich microarray time series 
The AAPS Journal  2005;7(1):E156-E194.
A data set was generated to examine global changes in gene expression in rat liver over time in response to a single bolus dose of methylprednisolone. Four control animals and 43 drug-treated animals were humanely killed at 16 different time points following drug administration. Total RNA preparation from the livers of these animals were hybridized to 47 individual Affymetrix RU34A gene chips, generating data for 8799 different probe sets for each chip. Data mining techniques that are applicable to gene array time series data sets in order to identify drug-regulated changes in gene expression were applied to this data set. A series of 4 sequentially applied filters were developed that were designed to eliminate probe sets that were not expressed in the tissue, were not regulated by the drug treatment, or did not meet defined quality control standards. These filters eliminated 7287 probe sets of the 8799 total (82%) from further consideration. Application of judiciously chosen filters is an effective tool for data mining of time series data sets. The remaining data can then be further analyzed by clustering and mathematical modeling techniques.
PMCID: PMC2607485  PMID: 16146338
Data mining; gene arrays; glucocorticoids; mathematical modeling; pharmacogenomics
5.  Transport systems for opioid peptides in mammalian tissues 
The AAPS Journal  2005;7(4):E852-E856.
Transmembrane transport of endogenous as well as synthetic opioid peptides is a critical determinant of pharmacokinetics and biologic efficacy of these peptides. This transport process influences the distribution of opioid peptides across the blood-brain barrier and their elimination from the body. A multitude of transport systems that recognize opioid peptides as substrates have been characterized at the functional level, and these transport systems are expressed differentially at different sites in the body. Many of these transport systems have been identified at the molecular level. These include the H+-coupled peptide transporters PEPT1 and PEPT2, the adenosine triphosphate-dependent efflux transporters P-glycoprotein and multidrug resistance-related protein 2, and several members of the organic anion-transporting polypeptide gene family. There are however many additional transport systems that are known to transport opioid peptides but their molecular identities still remain unknown.
PMCID: PMC2750954  PMID: 16594637
opioid peptides; transmembrane transport; peptide transporters; P-glycoprotein; multidrug resistance-related protein 2; organic anion-transporting polypeptides; sodium-coupled transporters
6.  Role of monoamine transporters in mediating psychostimulant effects 
The AAPS Journal  2005;7(4):E847-E851.
Monoamine transporters such as the dopamine (DA) transporter (DAT) and the vesicular monoamine transporter-2 (VMAT-2) are critical regulators of DA disposition within the brain. Alterations in DA disposition can lead to conditions such as drug addiction, Parkinson’s disease, and schizophrenia, a fact that underscores the importance of understanding DAergic signaling. Psychostimulants alter DAergic signaling by influencing both DAT and VMAT-2, and although the effects of these drugs result in increased levels of synaptic DA, the mechanisms by which this occurs and the effects that these drugs exert on DAT and VMAT-2 vary. Many psychostimulants can be classified as releasers (ie, amphetamine analogs) or uptake blockers (ie, cocaine-like drugs) based on the mechanism of their acute effects on neurotransmitter flux through the DAT. Releasers and uptake blockers differentially modulate the activity and subcellular distribution of monoamine transporters, a phenomenon likely related to the neurotoxics potential of these drugs to DAergic neurons. This article will review some of the recent findings whereby releasers and uptake blockers alter DAT and VMAT-2 activity and how these alterations may be involved in neurotoxicity, thus providing insight on the neuro-degeneration observed in Parkinson’s disease.
PMCID: PMC2750953  PMID: 16594636
dopamine transporter; vesicular monoamine transporter-2; amphetamine; cocaine; methylphenidate; Parkinson’s disease
7.  Mechanisms of drug-induced delayed-type hypersensitivity reactions in the skin 
The AAPS Journal  2005;7(4):E834-E846.
Cutaneous drug reactions (CDRs) are the most commonly reported adverse drug reactions. These reactions can range from mildly discomforting to life threatening. CDRs can arise either from immunological or nonimmunological mechanisms, though the preponderance of evidence suggests an important role for immunological responses. Some cutaneous eruptions appear shortly after drug intake, while others are not manifested until 7 to 10 days after initiation of therapy and are consistent with delayed-type hypersensitivity. This review discusses critical steps in the initiation of delayed-type hypersensitivity reactions in the skin, which include protein haptenation, dendritic cell activation/migration and T-cell propagation. Recently, an alternative mechanism of drug presentation has been postulated that does not require bioactivation of the parent drug or antigen processing to elicit a drug-specific T-cell response. This review also discusses the role of various immune-mediators, such as cytokines, nitric oxide, and reactive oxygen species, in the development of delayed-type drug hypersensitivity reactions in skin. As keratinocytes have been shown to play a crucial role in the initiation and propagation of cutaneous immune responses, we also discuss the means by which these cells may initiate or modulate CDRs.
PMCID: PMC2750952  PMID: 16594635
cutaneous drug reactions; delayed-type hypersensitivity; dendritic cells; keratinocytes; T-cells; cytokines
8.  Ophthalmic drug design based on the metabolic activity of the eye: Soft drugs and chemical delivery systems 
The AAPS Journal  2005;7(4):E820-E833.
Despite its apparent easy accessibility, the eye is, in fact, well protected against the absorption of foreign materials, including therapeutic agents, by the eyelids, by the tearflow, and by the permeability barriers imposed by the cornea on one side and the blood-retinal barrier on the other. Most existing ophthalmic drugs were adapted from other therapeutic applications and were not specifically developed for the treatment of eye diseases; hence, they are not well suited to provide eye-specific effects without causing systemic side effects. A real breakthrough in the area of ophthalmic therapeutics can be achieved only by specifically designing new drugs for ophthalmic applications to incorporate the possibility of eye targeting into their chemical structure. Possibilities provided along these lines by designing chemical delivery systems (CDSs) and soft drugs within the framework of retrometabolic drug design are reviewed here. Both are general concept applicable in almost any therapeutic area. This review will concentrate on \-adrenergic agonists and anti-inflammatory corticosteroids, where clinical results obtained with new chemical entities, such as betaxoxime, adaprolol, loteprednol etabonate, and etiprednol dicloacetate, exist to support the advantages of such metabolism-focused, ophthalmic-specific drug design approaches.
PMCID: PMC2750951  PMID: 16594634
beta-blockers; corticosteroids; eye-targeted delivery; glaucoma; intraocular pressure; oxime
9.  The role of crystallography in drug design 
The AAPS Journal  2005;7(4):E813-E819.
Structure and function are intimately related. Nowhere is this more important than the area of bioactive molecules. It has been shown that the enantioselectivity of an enzyme is directly related to its chirality. X-ray crystallography is the only method for determining the “absolute” configuration of a molecule and is the most comprehensive technique available to determine the structure of any molecule at atomic resolution. Results from crystallographic studies provide unambiguous, accurate, and reliable 3-dimensional structural parameters, which are prerequisites for rational drug design and structure-based functional studies.
PMCID: PMC2750950  PMID: 16594633
structure; absolute configuration; opioid; pharmacophore; X-ray diffraction
10.  Equivalence studies for complex active ingredients and dosage forms 
The AAPS Journal  2005;7(4):E786-E812.
This article examines the United States Pharmacopeia (USP) and its role in assessing the equivalence and inequivalence of biological and biotechnological drug substances and products—a role USP has played since its founding in 1820. A public monograph in theUnited States Pharmacopeia-National Formulary helps practitioners and other interested parties understand how an article’s strenght, quality, and purity should be controlled. Such a monograph is a standard to which all manufactured ingredients and products should conform, and it is a starting point for subsequent-entry manufactures, recognizing that substantial additional one-time characterization studies may be needed to document equivalence. Review of these studies is the province of the regulatory agency, but compendial tests can provide clarity and guidance in the process.
PMCID: PMC2750949  PMID: 16594632
US Pharmacopeia; biological or biotechnological drug; equivalence; generic biologics; complex active ingredient
11.  Simultaneous population optimal design for pharmacokinetic-pharmacodynamic experiments 
The AAPS Journal  2005;7(4):E759-E785.
Multiple outputs or measurement types are commonly gathered in biological experiments. Often, these experiments are expensive (such as clinical drug trials) or require careful design to achieve the desired information content. Optimal experimental design protocols could help alleviate the cost and increase the accuracy of these experiments. In general, optimal design techniques ignore between-individual variability, but even work that incorporates it (population optimal design) has treated simultaneous multiple output experiments separately by computing the optimal design sequentially, first finding the optimal design for one output (eg, a pharmacokinetic [PK] measurement) and then determining the design for the second output (eg, a pharmacodynamic [PD] measurement). Theoretically, this procedure can lead to biased and imprecise results when the second model parameters are also included in the first model (as in PK-PD models). We present methods and tools for simultaneous population D-optimal experimental designs, which simultaneously compute the design of multiple output experiments, allowing for correlation between model parameters. We then apply these methods to simulated PK-PD experiments. We compare the new simultaneous designs to sequential designs that first compute the PK design, fix the PK parameters, and then compute the PD design in an experiment. We find that both population designs yield similar results in designs for low sample number experiments, with simultaneous designs being possibly superior in situations in which the number of samples is unevenly distributed between outputs. Simultaneous population D-optimality is a potentially useful tool in the emerging field of experimental design.
PMCID: PMC2750948  PMID: 16594631
pharmacokinetics; pharmacodynamics; D-optimality; estimator; bias; precision; experiment design
12.  A general procedure for the enantioselective synthesis of the minor tobacco alkaloids nornicotine, anabasine, and anatabine 
The AAPS Journal  2005;7(3):E752-E758.
The minor tobacco alkaloids nornicotine, anabasine, and anatabine fromNicotiana tobacum are known to possess nicotinic receptor agonist activity, although they are relatively less potent than S-(−)-nicotine, the principal tobacco alkaloid. Previous pharmacological investigations and structure-activity studies have been limited owing to the lack of availability of the optically pure forms of these minor alkaloids. We now report a 2-step synthetic procedure for the enantioselective synthesis of the optical isomers of nornicotine and anabasine, and a modified procedure for the synthesis of anatabine enantiomers. These procedures involve initial formation of the chiral ketimine resulting from the condensation of either 1R, 2R, 5R-(+)- or 1S, 2S, 5S-(−)-2-hydroxy-3-pinanonewith3-(aminomethyl)pyridine followed by enantioselective C-alkylation with an appropriate halogenoalkane or halogenoalkene species, N-deprotection, and base-catalyzed intramolecular ring closure, to form the appropriate, chirally pure minor tobacco alkaloid. Using this approach, theR-(+)-andS-(−)-enantiomers of the above minor tobacco alkaloids were obtained in good overall chemical yield and excellent enantomeric excess.
PMCID: PMC2751277  PMID: 16353951
Nicotiana alkaloids; tobacco; stereoselective synthesis
13.  Recognition of psychostimulants, antidepressants, and other inhibitors of synaptic neurotransmitter uptake by the plasma membrane monoamine transporters 
The AAPS Journal  2005;7(3):E739-E751.
The plasma membrane monoamine transporters terminate neurotransmission by removing dopamine, norepinephrine, or serotonin from the synaptic cleft between neurons. Specific inhibitors for these transporters, including the abused psychostimulants cocaine and amphetamine and the tricyclic and SSRI classes of antidepressants, exert their physiological effects by interfering with synaptic uptake and thus prolonging the actions of the monoamine. Pharmacological, biochemical, and immunological characterization of the many site-directed, chimeric, and deletion mutants generated for the plasma membrane monoamine transporters have revealed much about the commonalities and dissimilarities between transporter substrate, ion, and inhibitor binding sites. Mutations that alter the binding affinity or substrate uptake inhibition potency of inhibitors by at least 3-fold are the focus of this review. These findings are clarifying the picture regarding substrate uptake inhibitor/transporter protein interactions at the level of the drug pharmacophore and the amino acid residue, information necessary for rational design of novel medications for substance abuse and a variety of psychiatric disorders.
PMCID: PMC2751276  PMID: 16353950
transporter; neurotransmitter; antidepressant; addiction; cocaine
14.  Regulation of monoamine transporters: Influence of psychostimulants and therapeutic antidepressants 
The AAPS Journal  2005;7(3):E728-E738.
Synaptic neurotransmission in the central nervous system (CNS) requires the precise control of the duration and the magnitude of neurotransmitter action at specific molecular targets. At the molecular level, neurotransmitter signaling is dynamically regulated by a diverse set of macromolecules including biosynthetic enzymes, secretory proteins, ion channels, pre- and postsynaptic receptors and transporters. Monoamines, 5-hydroxytryptamine or serotonin (5-HT), norepinephrine (NE), and dopamine (DA) play an important modulatory role in the CNS and are involved in numerous physiological functions and pathological conditions. Presynaptic plasma membrane transporters for 5-HT (SERT), NE (NET), and DA (DAT), respectively, control synaptic actions of these monoamines by rapidly clearing the released amine. Monoamine transporters are the sites of action for widely used antidepressants and are high affinity molecular targets for drugs of abuse including cocaine, amphetamine, and 3,4-methylenedioxymetamphetamine (MDMA) “Ecstasy”. Monoamine transporters also serve as molecular gateways for neurotoxins. Emerging evidence indicates that regulation of transporter function and surface expression can be rapidly modulated by “intrinsic” transporter activity itself, and antidepressant and psychostimulant drugs that block monoamine transport have a profound effect on transporter regulation. Therefore, disregulations in the functioning of monoamine transporters may underlie many disorders of transmitter imbalance such as depression, attention deficit hyperactivity disorder, and schizophrenia. This review integrates recent progress in understanding the molecular mechanisms of monoamine transporter regulation, in particular, posttranscriptional regulation by phosphorylation and trafficking linked to cellular protein kinases, protein phosphatases, and transporter interacting proteins. The review also discusses the possible role of psychostimulants and antidepressants in influencing monoamine transport regulation.
PMCID: PMC2751275  PMID: 16353949
phosphorylation; trafficking; interacting proteins; substrates; and ligands
15.  Patent issues in drug development: Perspectives of a pharmaceutical scientist-attorney 
The AAPS Journal  2005;7(3):E723-E727.
The major purpose of this article is to emphasize the need for pharmaceutical scientists to have a better understanding of patent fundamentals. This need is illustrated by analyses of key scientific and legal issues that arose during recent patent infringement cases involving Prozac, Prilosec, and Buspar. Economic incentives for drug discovery and development clash with societal needs for low-cost pharmaceuticals in the United States and all over the world. The Hatch-Waxman Act of 1984 was enacted to promote public health by balancing the interests of brand name and generic companies. Patent protection, which provides a monopoly for a limited time, is aimed to provide such incentives. Creation of patents requires the interaction between scientists and lawyers, an endeavor made difficult by the differing intellectual spheres of their respective disciplines. Therefore, in the first place, a thorough understanding of patent fundamentals among pharmaceutical scientists will help them work more efficiently with patent attorneys. Second, it will enable them to appreciate the strengths and weaknesses of individual patents, which is critical in developing strategies amidst the ongoing patent tug-of-war between brandname and generic companies.
PMCID: PMC2751274  PMID: 16353948
Hatch-Waxman Act; Brand Drugs; Generic Drugs; Patent Strategies; Paragraph IV certification; ANDA; Prozac; Buspar; Prilosec
16.  Kappa opioid antagonists: Past successes and future prospects 
The AAPS Journal  2005;7(3):E704-E722.
Antagonists of the kappa opioid receptor were initially investigated as pharmacological tools that would reverse the effects of kappa opioid receptor agonists. In the years following the discovery of the first selective kappa opioid antagonists, much information about their chemistry and pharmacology has been elicited and their potential therapeutic uses have been investigated. The review presents the current chemistry, ligand-based structure activity relationships, and pharmacology of the known nonpeptidic selective kappa opioid receptor antagonists. This manuscript endeavors to provide the reader with a useful reference of the investigations made to define the structure-activity relationships and pharmacology of selective kappa opioid receptor antagonists and their potential uses as pharmacological tools and as therapeutic agents in the treatment of disease states.
PMCID: PMC2751273  PMID: 16353947
Opioid; Opiate; Receptor; Kappa; Antagonist
17.  Population pharmacokinetics of recombinant factor XIII in cynomolgus monkeys 
The AAPS Journal  2005;7(3):E693-E703.
Hemostasis in humans and other animals is a complex process that controls blood loss after a vascular injury. Factor XIII (FXIII) stabilizes clots primarily by cross-linking fibrin, thus protecting a newly formed clot from fibrinolysis by plasmin. Congenital deficiencies in humans involving FXIII are associated with delayed bleeding and wound healing and severe spontaneous hemorrhaging. These symptoms can be alleviated by intravenous administration of enriched FXIII plasma fractions. Circulating plasma FXIII is found as a heterotetramer that dissociates in the presence of calcium and thrombin into an active dimer and 2 inactive monomers. The recombinant FXIII under investigation is the active dimer alone. A 3-compartment, nonlinear population pharmacokinetic model was implemented in NON-MEM V and then used to analyze data from preclinical studies in cynomolgus monkeys. The model simultaneously describes endogenous production of dimer (0.622 μg kg−1 hr−1) and monomer (12.1 μg kg−1 hr−1), and the administration of recombinant dimer. The model incorporates the rate and extent of complexation of recombinant dimer with available endogenous monomer (6.59 mg−1 kg hr−1) to form the heterotetramer. Half-lives for dimer, heterotetramer, and monomer (3.33 hours, 2.83 days, and 3.94 hours for A2, A2B2, and B, respectively) were estimated, along with their variability in the population studied.
PMCID: PMC2751272  PMID: 16353946
pharmacokinetics; modeling; FXIII; population kinetics
18.  Microdialysis of large molecules 
The AAPS Journal  2005;7(3):E686-E692.
Microdialysis has been used in many tissues, including skin, brain, adipose tissue, muscle, kidney, and gastrointestinal tract, to recover low-molecular mass endogenous mediators, metabolites, and xenobiotics from the interstitial space. Recently, molecules of larger molecular mass, such as plasma proteins, cytokines, growth factors, and neuropeptides, have also been recovered successfully using largerpore membranes. Microdialysis recovery of large molecules offers the opportunity to identify patterns of protein expression in a variety of tissue spaces and to evaluate clinically useful biomarkers of disease. From this may develop a better understanding of the disease process and its diagnosis and more targeted approaches to therapy.
PMCID: PMC2751271  PMID: 16353945
microdialysis; proteins; cytokines
19.  Molecular modeling of mono- and bis-quaternary ammonium salts as ligands at the α4β2 nicotinic acetylcholine receptor subtype using nonlinear techniques 
The AAPS Journal  2005;7(3):E678-E685.
The neuronal nicotinic acetylcholine receptor (nAChR) has been a target for drug development studies for over a decade. A series ofmono- andbis-quaternary ammonium salts, known to be antagonists at nAChRs, were separated into 3 structural classes and evaluated using both self-organizing map (SOM) and genetic functional approximation (GFA) algorithm models. Descriptors from these compounds were used to create several nonlinear quantitative structure-activity relationships (QSARs). The SOM methodology was effective in appropriately grouping these compounds with diverse structures and activities. The GFA models were also able to predict the activities of these molecules. Charge distribution and the hydrophobic free energies were found to be important indicators of bioactivity for this particular class of molecules. These QSAR approaches may be a useful to screen and selectin silico new drug candidates from larger compound libraries to be further evaluated in in vitro biological assays.
PMCID: PMC2751270  PMID: 16353944
self-organizing map; genetic functional approximation; neuronal nicotinic acetylcholine receptor
20.  Anion-induced water flux as drug release mechanism through cationic Eudragit RS 30D film coatings 
The AAPS Journal  2005;7(3):E668-E677.
The objective of this study was to investigate the anion-controlled drug release mechanism through the cationic coating polymer Eudragit RS 30 D as a function of the anion attraction toward the polymer’s quarternary ammonium group (QAG), anion valence, and film composition. The mechanism was investigated by dissolution testing, determination of chloride ion exchange using ion chromatography, plasticizer leaching by means of differential scanning calorimetry, and water uptake by Karl Fischer titration. All experiments were performed on coated theophylline micro tablets or isolated films of various compositions using 0.01 M sodium nitrate, sodium sulfate, disodium succinate, sodium acetate, and succinic acid as dissolution media. The mechanism of drug release involved an immediate penetration of dissolution medium into the polymer followed by an instant exchange of chloride against the medium’s anion species at completely different rates compared with the drug release. Dependent on the attraction of the anion toward the QAGs, a water flux was induced by back and forth exchanging anions. Strong attraction (nitrate, sulfate) resulted in a low water flux while weak attraction resulted in a high flux (acetate, succinic acid). The water flux increased at increasing number of QAGs. Plasticizer acted as a diluent in respect of the number of QAGs, thus higher plasticizer concentrations led to lower drug release.
PMCID: PMC2751269  PMID: 16353943
Eudragit; ion exchange; water uptake; plasticizer leaching
21.  In vivo microdialysis for PK and PD studies of anticancer drugs 
The AAPS Journal  2005;7(3):E659-E667.
In vivo microdialysis technique has become one of the major tools to sample endogenous and exogenous substances in extracellular spaces. As a well-validated sampling technique, microdialysis has been frequently employed for quantifying drug disposition at the desired target in both preclinical and clinical settings. This review addresses general methodological considerations critical to performing microdialysis in tumors, highlights selected preclinical and clinical studies that characterized drug disposition in tumors by the use of microdialysis, and illustrates the potential application of microdialysis in the assessment of tumor response to cancer treatment.
PMCID: PMC2751268  PMID: 16353942
microdialysis; in vivo sampling; tumors; drug distribution; pharmacokinetics
22.  It’s time 
The AAPS Journal  2005;7(3):E655-E658.
Statistical inference involves taking the results of models and knowledge about probability to make decisions about the relationship in question. This commentary explains the usefulness of statistical inference to the drug development process, as well as some common pitfalls. It also examines reasons why statistical inference does not seem to be fully integrated into pharmacometric modeling. An example is shown that demonstrates the inferential advantages of mechanistic models. Both statisticians and pharmacometricians ought to take note of these advantages and integrate their efforts in order to maximize the decision-making potential of clinical research.
PMCID: PMC2751267  PMID: 16370065
mechanistic models; statistical inference
23.  The therapeutic potential of drugs that target cannabinoid receptors or modulate the tissue levels or actions of endocannabinoids 
The AAPS Journal  2005;7(3):E625-E654.
There are at least 2 types of cannabinoid receptor, CB1 and CB2, both G protein coupled. CB1 receptors are expressed predominantly at nerve terminals and mediate inhibition of transmitter release, whereas CB2 receptors are found mainly on immune cells, their roles including the modulation of cytokine release and of immune cell migration. Endogenous agonists for cannabinoid receptors also exist. These “endocannabinoids” are synthesized on demand and removed from their sites of action by cellular uptake and intracellular enzymic hydrolysis. Endocannabinoids and their receptors together constitute the endocannabinoid system. This review summarizes evidence that there are certain central and peripheral disorders in which increases take place in the release of endocannabinoids onto their receptors and/or in the density or coupling efficiency of these receptors and that this upregulation is protective in some disorders but can have undesirable consequences in others. It also considers therapeutic strategies by which this upregulation might be modulated to clinical advantage. These strategies include the administration of (1) a CB1 and/or CB2 receptor agonist or antagonist that does or does not readily cross the blood brain barrier; (2) a CB1 and/or CB2 receptor agonist intrathecally or directly to some other site outside the brain; (3) a partial CB1 and/or CB2 receptor agonist rather than a full agonist; (4) a CB1 and/or CB2 receptor agonist together with a noncannabinoid, for example, morphine or codeine; (5) an inhibitor or activator of endocannabinoid biosynthesis, cellular uptake, or metabolism; (6) an allosteric modulator of the CB1 receptor; and (7) a CB2 receptor inverse agonist.
PMCID: PMC2751266  PMID: 16353941
cannabinoid receptors; endocannabinoids; fatty acid amide hydrolase inhibitors; autoprotection; therapeutic strategies
24.  Pharmacokinetic-pharmacodynamic modeling in the data analysis and interpretation of drug-induced QT/QTc prolongation 
The AAPS Journal  2005;7(3):E609-E624.
In this review, factors affecting the QT interval and the methods that are currently in use in the analysis of drug effects on the QT interval duration are overviewed with the emphasis on (population) pharmacokinetic-pharmacodynamic (PK-PD) modeling. Among which the heart rate (HR) and the circadian rhythm are most important since they may interfere with the drug effect and need to be taken into account in the data analysis. The HR effect or the RR interval (the distance between 2 consecutive R peaks) effect is commonly eliminated before any further analysis, and many formulae have been suggested to correct QT intervals for changes in RR intervals. The most often used are Bazett and Fridericia formulae introduced in 1920. They are both based on the power function and differ in the exponent parameter. However, both assume the same exponent for different individuals. More recent findings do not confirm this assumption, and individualized correction is necessary to avoid under- or overcorrection that may lead to artificial observations of drug-induced QT interval prolongation. Despite the fact that circadian rhythm in QT and QTc intervals is a well-documented phenomenon, it is usually overlooked when drug effects are evaluated. This may result in a false-positive outcome of the analysis as the QTc peak due to the circadian rhythm may coincide with the peak of the drug plasma concentration. In view of these effects interfering with a potential drug effect on the QTc interval and having in mind low precision of QT interval measurements, a preferable way to evaluate the drug effect is to apply a population PK-PD modeling. In the literature, however, there are only a few publications in which population PK-PD modeling is applied to QT interval prolongation data, and they all refer to antiarrhythmic agents. In this review, after the most important sources of variability are outlined, a comprehensive population PK-PD model is presented that incorporates an individualized QT interval correction, a circadian rhythm in the individually corrected QT intervals, and a drug effect. The model application is illustrated using real data obtained with 2 compounds differing in their QT interval prolongation potential. The usefulness of combining data of several studies is stressed. Finally, the standard approach based on the raw observations and formal statistics, as described in the Preliminary Concept paper of the International Conference on Harmonization, is briefly compared with the method based on population PK-PD modeling, and the advantages of the latter are outlined.
PMCID: PMC2751265  PMID: 16353940
cardiovascular safety of drugs; QT/QTc prolongation caused by drugs; concentration-response relationship; pharmacokinetic-pharmacodynamic modeling
25.  Lung microdialysis—A powerful tool for the determination of exogenous and endogenous compounds in the lower respiratory tract (mini-review) 
The AAPS Journal  2005;7(3):E600-E608.
In vivo measurement of concentrations of drugs and endogenous substances at the site of action has become a primary focus of research. In this context the minimal invasive microdialysis (MD) technique has been increasingly employed for the determination of pharmacokinetics in lung. Although lung MD is frequently employed to investigate various drugs and endogenous substances, the majority of lung MD studies were performed to determine the pharmacokinetic profile of antimicrobials that can be related to the importance of respiratory tract infections. For the lower respiratory tract various methods, such as surgical collection of whole lung tissue and bonchoalveolar lavage (BAL), are currently available for the determination of pharmacokinetics of antimicrobials. Head-to-head comparison of pharmacokinetics of antibiotics in lung revealed high differences between MD and conventional methods. MD might be regarded as a more advantageous approach because of its higher anatomical resolution and the ability to obtain dynamic time-vs-concentration profiles within one subject. However, due to ethical objections lung MD is limited to animals or patients undergoing elective thoracic surgery. From these studies it was speculated that the concentrations in healthy lung tissue may be predicted reasonably by the measurement of concentrations in skeletal muscle tissue. However, until now this was only demonstrated for β-lactam antibiotics and needs to be confirmed for other classes of antimicrobials. In conclusion, the present review shows that MD is a promising method for the determination of antimicrobials in the lung, but might also be applicable for measuring a wide range of other drugs and for the investigation of metabolism in the lower respiratory tract.
PMCID: PMC2751264  PMID: 16353939
lung; microdialysis; pharmacokinetic; antibiotic

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