Identification of Human Cytochrome P450 Isozymes Involved in Diphenhydramine N-Demethylation

Effects of diphenhydramine exposure on reproduction of mature Japanese medaka (Oryzias latipes)

Diphenhydramine (DPH) is an antihistamine drug. It has been frequently detected in the environment, because it is not completely degraded in wastewater treatment plants. Recent studies have shown the adverse effects of DPH exposure to various aquatic organisms; however, its chronic effects on fish have been poorly elucidated. In this study, several pairs of mature Japanese medaka (Oryzias latipes) were exposed to DPH for a long period to determine the effects of DPH exposure on the subsequent generations, number of spawned and fertilized eggs, expression of sex-related genes, feeding behavior, embryo development, hatching rate, malformations among the hatched larvae, and mortality rate. The number of spawned eggs significantly decreased, when the parent fish were continuously exposed to 31.6 μg/L DPH for over 46 days. DPH exposure also altered the feeding behavior of medaka individuals, and increased the larval mortality rate. The effects of DPH exposure to fish may occur to some extent in the actual aquatic environment, although the risk evaluations in the field are limited.

CYP2D6 inhibition by diphenhydramine leading to fatal hydrocodone overdose

OBJECTIVES

Fatal drug overdoses often involve multiple co-intoxicants, including opioids. Hydrocodone, the most prescribed opioid for pain management, is metabolized to the active metabolite hydromorphone by hepatic CYP2D6. Inhibition of CYP2D6 by other compounds can disrupt the analgesic properties of hydrocodone and extend its half-life. Diphenhydramine is an over-the-counter cold medication and is known to inhibit CYP2D6 activity.

CASE PRESENTATION

A woman in her late 50s was prescribed hydrocodone/acetaminophen (Norco® 10/325). Days before her death, she began taking diphenhydramine for cold symptoms. A post-mortem toxicology report detected the following compounds by High Performance Liquid Chromatography/Time of Flight-Mass Spectrometry (LC/TOF-MS) analysis: acetaminophen (14 μg/mL), hydrocodone (410 ng/mL), dihydrocodeine (24 ng/mL), and diphenhydramine (150 ng/mL). Hydromorphone was not detected (<2 ng/mL). All compounds were detected in therapeutic concentrations, except for hydrocodone, which was present at lethal concentrations.

CONCLUSIONS

This case highlights a fatal drug-drug interaction between hydrocodone and diphenhydramine. The estimated total body burden of hydrocodone was 6- to 12-fold higher than acetaminophen, which is unexpected, as these two drugs were administered as a single formulation and have similar half-lives. Furthermore, hydromorphone was undetectable. Taken together, these findings are highly suggestive of a fatal opioid overdose precipitated by diphenhydramine.

Identification and quantification of diphenhydramine, haloperidol, and its metabolite, reduced haloperidol in a saponified brain specimen that was immersed in the sea water for more than 10 years

In forensic toxicology, blood and urine specimens are commonly used for detecting and quantifying drugs and their metabolites. When the cadaver is so damaged or decomposed such that the specimens mentioned above cannot be collected, it is necessary to perform drug analysis using alternative specimens such as hair, nails, oral fluids and meconium. Adipocere is resistant to further degradation; it is thus possible to be used as an alternative specimen to analyze drugs and their metabolites. Some researchers indeed have reported drug concentrations in saponified samples that were collected years after decedents' deaths. In this study, we subjected saponified brain, which remained under sea for over 10 years after death, to forensic toxicological analysis using liquid chromatography/tandem mass spectrometry (LC/MS/MS). Using product ion scan analysis, we confirmed the presence of diphenhydramine, haloperidol, and reduced haloperidol, a metabolite of haloperidol. In addition, drugs and metabolite quantification were performed using the standard addition method. Correlation coefficients of the calibration curves were over 0.98. Analyte concentrations in the saponified brain were as follows: diphenhydramine was 1.84 ng/g, haloperidol was 1.30 ng/g, and reduced haloperidol was 3.02 ng/g. Our results suggest that it can be possible to quantify not only parent drugs but also their metabolites in saponified brain. These findings indicate that saponified tissues could be applied as alternative specimens for forensic toxicology, and could be useful as supporting information for victim identification.

Construction of a fused grid-based CYP2C19-Template system and the application

A ligand-accessible space in the CYP2C19 active site was reconstituted as a fused grid-based Template with the use of structural data of the ligands. An evaluation system of CYP2C19-mediated metabolism has been developed on Template with the introduction of the idea of Trigger-residue initiated ligand-movement and fastening. Reciprocal comparison of the data of simulation on Template with experimental results suggested a unified way of the interaction of CYP2C19 and its ligands through the simultaneous plural-contact with Rear-wall of Template. CYP2C19 was expected to have a room for ligands between vertically standing parallel walls termed Facial-wall and Rear-wall, which were separated by a distance corresponding to 1.5-Ring (grid) diameter size. The ligand sittings were stabilized through contacts with Facial-wall and the left-side borders of Template including specific Position 29 or Left-end after Trigger-residue initiated ligand-movement. Trigger-residue movement is suggested to force ligands to stay firmly in the active site and then to initiate CYP2C19 reactions. Simulation experiments for over 450 reactions of CYP2C19 ligands supported the system established.

Integrated biomarker response in signal crayfish Pacifastacus leniusculus exposed to diphenhydramine

Diphenhydramine (DPH) is a pharmaceutical with multiple modes of action, primarily designed as an antihistamine therapeutic drug. Among antihistamines, DPH is a significant contaminant in the environment, frequently detected in surface waters, sediments, and tissues of aquatic biota. In the present study, signal crayfish Pacifastacus leniusculus was used as a model organism because of their prominent ecological roles in freshwater ecosystems. The biochemical effects were investigated in crayfish exposed to the environmental (low: 2 μg L^-1), ten times elevated (medium: 20 μg L^-1), and the sublethal (high: 200 μg L^-1) nominal concentrations of DPH in water for 96 h. Lipid peroxidation, antioxidant enzyme activities, and acetylcholinesterase activity were assessed as toxicological biomarkers in crayfish hepatopancreas, gills, and muscles. Low and medium DPH exposure caused imbalances only in glutathione-like enzyme activities. Integrated biomarker response showed the absolute DPH toxicity effects on all tested tissues under high exposure. This study identified that high, short-term DPH exposure induced oxidative stress in crayfish on multiple tissue levels, with the most considerable extent in muscles.

The pharmacological treatment of acute vestibular syndrome

Acute vestibular syndrome (AVS) represents a clinical picture that involves urgent management due to the important procession of symptoms accompanying the event, which can be positively or negatively influenced by therapeutic choices and intervention timing. This forces a differential diagnosis and therapeutic choices to be made in conditions that are not always favorable and often not in the specialist field. In this work, we will examine in detail the pharmacological therapeutic possibilities, correlating them to the differential and, as far as possible, to the etiological diagnosis. In particular, the pharmacological possibilities for the two main conditions we can face will be investigated, namely, vestibular neuritis and posterior circulation stroke.

Non-invasive skin sampling detects systemically administered drugs in humans

Clinical testing typically relies on invasive blood draws and biopsies. Alternative methods of sample collection are continually being developed to improve patient experience; swabbing the skin is one of the least invasive sampling methods possible. To show that skin swabs in combination with untargeted mass spectrometry (metabolomics) can be used for non-invasive monitoring of an oral drug, we report the kinetics and metabolism of diphenhydramine in healthy volunteers (n = 10) over the course of 24 hours in blood and three regions of the skin. Diphenhydramine and its metabolites were observed on the skin after peak plasma levels, varying by compound and skin location, and is an illustrative example of how systemically administered molecules can be detected on the skin surface. The observation of diphenhydramine directly from the skin supports the hypothesis that both parent drug and metabolites can be qualitatively measured from a simple non-invasive swab of the skin surface. The mechanism of the drug and metabolites pathway to the skin’s surface remains unknown.

N-Dealkylation of Amines

N-dealkylation, the removal of an N-alkyl group from an amine, is an important chemical transformation which provides routes for the synthesis of a wide range of pharmaceuticals, agrochemicals, bulk and fine chemicals. N-dealkylation of amines is also an important in vivo metabolic pathway in the metabolism of xenobiotics. Identification and synthesis of drug metabolites such as N-dealkylated metabolites are necessary throughout all phases of drug development studies. In this review, different approaches for the N-dealkylation of amines including chemical, catalytic, electrochemical, photochemical and enzymatic methods will be discussed.

Towards understanding microbial degradation of chloroquine in large saltwater systems

Circulating saltwater aquariums hosting marine animals contain a wide range of microorganisms, which have strong implications on promoting animal health. In this study, we investigated the degradation of chloroquine phosphate, an anti-parasitic bath pharmaceutical used in saltwater quarantine and exhibition systems, and attributed the reduction in drug concentration to microbial degradation of chloroquine associated with pipeline microbial communities. To advance our knowledge on chloroquine degradation in aquatic systems, we conducted microbial and chemical analyses on three tropical saltwater systems. Our findings show that aquarium microbiome composition is shaped by sampling location (i.e., tank water and pipeline; PERMANOVA R² = 0.09992, p = 0.0134), chloroquine dosing (PERMANOVA R² = 0.05700, p = 0.0030), and whether the aquarium is occupied by marine animals (PERMANOVA R² = 0.07019, p = 0.0009). Several microbial taxa belonging to the phyla Actinobacteria, Bacteroidetes, Chloroflexi, and Proteobacteria, along with functional genes related to pathways such as phenylethylamine degradation and denitrification, appeared to have differential (relative) abundance between samples where chloroquine degradation was observed and those without degradation (Benjamini-Hochberg adjusted p-value <0.05). Together, these results provide practical mitigation options to prevent or delay the development of chloroquine-degrading microbial communities in saltwater aquariums. Our results further demonstrate the need to improve our understanding of the interactions between nitrogen availability and microbial activity in saltwater systems.

Drug-Drug Interactions in Vestibular Diseases, Clinical Problems, and Medico-Legal Implications

Peripheral vestibular disease can be treated with several approaches (e.g., maneuvers, surgery, or medical approach). Comorbidity is common in elderly patients, so polytherapy is used, but it can generate the development of drug-drug interactions (DDIs) that play a role in both adverse drug reactions and reduced adherence. For this reason, they need a complex kind of approach, considering all their individual characteristics. Physicians must be able to prescribe and deprescribe drugs based on a solid knowledge of pharmacokinetics, pharmacodynamics, and clinical indications. Moreover, full information is required to reach a real therapeutic alliance, to improve the safety of care and reduce possible malpractice claims related to drug-drug interactions. In this review, using PubMed, Embase, and Cochrane library, we searched articles published until 30 August 2021, and described both pharmacokinetic and pharmacodynamic DDIs in patients with vestibular disorders, focusing the interest on their clinical implications and on risk management strategies.

Bacterial Biosynthetic P450 Enzyme PikCD50N: A Potential Biocatalyst for the Preparation of Human Drug Metabolites

Human drug metabolites (HDMs) are important chemicals widely used in drug-related studies. However, acquiring these enzyme-derived and regio-/stereo-selectively modified compounds through chemical approaches is complicated. PikC is a biosynthetic P450 enzyme involved in pikromycin biosynthesis from the bacterium Streptomyces venezuelae. Here, we identify the mutant PikC_D50N as a potential biocatalyst, with a broad substrate scope, diversified product profile, and high catalytic efficiency, for preparation of HDMs. Remarkably, PikC_D50N can mediate the drug-metabolizing reactions using the low-cost H₂O₂ as a direct electron and oxygen donor.

Predictive Value of Microdose Pharmacokinetics

Phase 0 microdose trials are exploratory studies to early assess human pharmacokinetics of new chemical entities, while limiting drug exposure and risks for participants. The microdose concept is based on the assumption that microdose pharmacokinetics can be extrapolated to pharmacokinetics of a therapeutic dose. However, it is unknown whether microdose pharmacokinetics are actually indicative of the pharmacokinetics at therapeutic dose. The aim of this review is to investigate the predictive value of microdose pharmacokinetics and to identify drug characteristics that may influence the scalability of these parameters. The predictive value of microdose pharmacokinetics was determined for 46 compounds and showed adequate predictability for 28 of 41 orally administered drugs (68%) and 15 of 16 intravenously administered drugs (94%). Microdose pharmacokinetics were considered predictive if the mean observed values of the microdose and the therapeutic dose were within twofold. Nonlinearity may be caused by saturation of enzyme and transporter systems, such as intestinal and hepatic efflux and uptake transporters. The high degree of success regarding linear pharmacokinetics shows that phase 0 microdose trials can be used as an early human model for determination of drug pharmacokinetics.

Metabolomic Investigations of the Temporal Effects of Exposure to Pharmaceuticals and Personal Care Products and Their Mixture in the Eastern Oyster (Crassostrea virginica)

The eastern oyster (Crassostrea virginica) supports a large aquaculture industry and is a keystone species along the Atlantic seaboard. Native oysters are routinely exposed to a complex mixture of contaminants that increasingly includes pharmaceuticals and personal care products (PPCPs). Unfortunately, the biological effects of chemical mixtures on oysters are poorly understood. Untargeted gas chromatography-mass spectrometry metabolomics was utilized to quantify the response of oysters exposed to fluoxetine, N,N-diethyl-meta-toluamide, 17α-ethynylestradiol, diphenhydramine, and their mixture. Oysters were exposed to 1 µg/L of each chemical or mixture for 10 d, followed by an 8-d depuration period. Adductor muscle (n = 14/treatment) was sampled at days 0, 1, 5, 10, and 18. Trajectory analysis illustrated that metabolic effects and class separation of the treatments varied at each time point and that, overall, the oysters were only able to partially recover from these exposures post-depuration. Altered metabolites were associated with cellular energetics (i.e., Krebs cycle intermediates), as well as amino acid metabolism and fatty acids. Exposure to these PPCPs also affected metabolic pathways associated with anaerobic metabolism, osmotic stress, and oxidative stress, in addition to the physiological effects of each chemical's postulated mechanism of action. Following depuration, fewer metabolites were altered, but none of the treatments returned them to their initial control values, indicating that metabolic disruptions were long-lasting. Interestingly, the mixture did not directly cluster with individual treatments in the scores plot from partial least squares discriminant analysis, and many of its affected metabolic pathways were not well predicted from the individual treatments. The present study highlights the utility of untargeted metabolomics in developing exposure biomarkers for compounds with different modes of action in bivalves. Environ Toxicol Chem 2020;39:419-436. © 2019 SETAC.

Sleep Pharmacogenetics: The Promise of Precision Medicine

Pharmacogenetics is the branch of personalized medicine concerned with the variability in drug response occurring because of heredity. Advances in genetics research, and decreasing costs of gene sequencing, are promoting tremendous growth in pharmacogenetics in all areas of medicine, including sleep medicine. This article reviews the body of research indicating that there are genetic variations that affect the therapeutic actions and adverse effects of agents used for the treatment of sleep disorders to show the potential of pharmacogenetics to improve the clinical practice of sleep medicine.

Clinical and Experimental Human Sleep-Wake Pharmacogenetics

Sleep and wakefulness are highly complex processes that are elegantly orchestrated by fine-tuned neurochemical changes among neuronal and non-neuronal ensembles, nuclei, and networks of the brain. Important neurotransmitters and neuromodulators regulating the circadian and homeostatic facets of sleep-wake physiology include melatonin, γ-aminobutyric acid, hypocretin, histamine, norepinephrine, serotonin, dopamine, and adenosine. Dysregulation of these neurochemical systems may cause sleep-wake disorders, which are commonly classified into insomnia disorder, parasomnias, circadian rhythm sleep-wake disorders, central disorders of hypersomnolence, sleep-related movement disorders, and sleep-related breathing disorders. Sleep-wake disorders can have far-reaching consequences on physical, mental, and social well-being and health and, thus, need be treated with effective and rational therapies. Apart from behavioral (e.g., cognitive behavioral therapy for insomnia), physiological (e.g., chronotherapy with bright light), and mechanical (e.g., continuous positive airway pressure treatment of obstructive sleep apnea) interventions, pharmacological treatments often are the first-line clinical option to improve disturbed sleep and wake states. Nevertheless, not all patients respond to pharmacotherapy in uniform and beneficial fashion, partly due to genetic differences. The improved understanding of the neurochemical mechanisms regulating sleep and wakefulness and the mode of action of sleep-wake therapeutics has provided a conceptual framework, to search for functional genetic variants modifying individual drug response phenotypes. This article will summarize the currently known genetic polymorphisms that modulate drug sensitivity and exposure, to partly determine individual responses to sleep-wake pharmacotherapy. In addition, a pharmacogenetic strategy will be outlined how based upon classical and opto-/chemogenetic strategies in animals, as well as human genetic associations, circuit mechanisms regulating sleep-wake functions in humans can be identified. As such, experimental human sleep-wake pharmacogenetics forms a bridge spanning basic research and clinical medicine and constitutes an essential step for the search and development of novel sleep-wake targets and therapeutics.

The prognostic value of CYP2C subfamily genes in hepatocellular carcinoma

Cytochrome P2C (CYP2C) subfamily members (CYP2C8, CYP2C9, CYP2C18, and CYP2C19) are known to participate in clinical drug metabolism. However, the association between CYP2C subfamily members and hepatocellular carcinoma (HCC) remains unclear. This study investigated the prognostic value of CYP2C subfamily gene expression levels with HCC prognosis. Data of 360 HCC patients in The Cancer Genome Atlas database and 231 in the Gene Expression Omnibus database were analyzed. Kaplan-Meier analysis and a Cox regression model were used to ascertain overall survival and recurrence-free survival, and to calculate median survival time using hazard ratios (HR) and 95% confidence intervals (CI). In TCGA database, low expression of CYP2C8, CYP2C9, and CYP2C19 in tumor tissue was associated with a short median survival time (all crude P = 0.001, adjusted P = 0.004, P = 0.047, and P = 0.020, respectively). In TCGA database, joint effects analysis of the combinations of CYP2C8 and CYP2C9, CYP2C8 and CYP2C19, and CYP2C9 and CYP2C19 revealed that high expression of two genes (group 4; group IV, group d) was associated with a reduced risk of death as compared to low expression (group 1, group I, and group a) (adjusted P = 0.005, P = 0.013, and P = 0.016, respectively). In TCGA database, joint effects analysis of CYP2C8, CYP2C9, and CYP2C19 showed that the risk of death from HCC was lower for groups C and D than for group A (adjusted P = 0.012 and P = 0.008, respectively). CYP2C8, CYP2C9, and CYP2C19 gene expression levels are potential prognostic markers of HCC following hepatectomy.

Effects of multiwalled carbon nanotubes on the bioavailability and toxicity of diphenhydramine to Pimephales promelas in sediment exposures

Multiwalled carbon nanotubes (MWCNTs) and pharmaceutical compounds are classified by the US Environmental Protection Agency as contaminants of emerging concern, with significant research devoted to determining their potential environmental and toxicological effects. Multiwalled carbon nanotubes are known to have a high adsorptive capacity for organic contaminants, leading to potential uses in water remediation; however, there is concern that co-exposure with MWCNTs may alter the bioavailability of organic compounds. Existing studies investigating MWCNT/organic contaminant co-exposures have shown conflicting results, and no study to date has examined the combined effects of MWCNTs and a common pharmaceutical. In the present study, juvenile fathead minnows (Pimephales promelas) were exposed to sublethal concentrations of the over-the-counter antihistamine diphenhydramine (DPH) in the presence of natural sediment for 10 d, with some treatment groups receiving MWCNTs. Addition of MWCNTs did not have a protective effect on DPH-related growth inhibition, and did not reduce the whole-body burden of DPH in exposed fish. Mass-balance calculations indicated that significant amounts of DPH were adsorbed to MWCNTs, and DPH concentrations in water and sediment were commensurately reduced. Bioconcentration factor and biota-sediment accumulation factor increased in the presence of MWCNTs, indicating that P. promelas accumulates DPH adsorbed to MWCNTs in sediment, likely by co-ingestion of MWCNTs during feeding from the sediment surface. Environ Toxicol Chem 2017;36:320-328. © 2016 SETAC.

Pharmaceutical Metabolism in Fish: Using a 3-D Hepatic In Vitro Model to Assess Clearance

At high internal doses, pharmaceuticals have the potential for inducing biological/pharmacological effects in fish. One particular concern for the environment is their potential to bioaccumulate and reach pharmacological levels; the study of these implications for environmental risk assessment has therefore gained increasing attention. To avoid unnecessary testing on animals, in vitro methods for assessment of xenobiotic metabolism could aid in the ecotoxicological evaluation. Here we report the use of a 3-D in vitro liver organoid culture system (spheroids) derived from rainbow trout to measure the metabolism of seven pharmaceuticals using a substrate depletion assay. Of the pharmaceuticals tested, propranolol, diclofenac and phenylbutazone were metabolised by trout liver spheroids; atenolol, metoprolol, diazepam and carbamazepine were not. Substrate depletion kinetics data was used to estimate intrinsic hepatic clearance by this spheroid model, which was similar for diclofenac and approximately 5 fold higher for propranolol when compared to trout liver microsomal fraction (S9) data. These results suggest that liver spheroids could be used as a relevant and metabolically competent in vitro model with which to measure the biotransformation of pharmaceuticals in fish; and propranolol acts as a reproducible positive control.

Drug interactions in HIV treatment: complementary & alternative medicines and over-the-counter products

INTRODUCTION

Use of complementary and alternative medicines (CAMs) and over-the-counter (OTC) medications are very common among HIV-infected patients. These products can cause clinically significant drug-drug interactions (DDIs) with antiretroviral (ARV) medications, thereby increasing risk for negative outcomes such as toxicity or loss of virologic control. Areas covered: This article provides an updated review of the different mechanisms by which CAM and OTC products are implicated in DDIs with ARV medications. Expert commentary: Much of the literature published to date involves studies of CAMs interacting with older ARV agents via the cytochrome P450 (CYP450) system. However, the HIV treatment and prevention arsenal is continually evolving. Furthermore, our elucidation of the role of non-CYP450 mediated DDIs with ARV medications is greatly increasing. Therefore, clinicians are well served to understand the various mechanisms and extent by which new ARV therapies may be involved in drug interactions with CAMs and OTC medications.

Bioconcentration, metabolism and effects of diphenhydramine on behavioral and biochemical markers in crucian carp (Carassius auratus)

Diphenhydramine (DPH), an antihistamine used to alleviate human allergies, is widespread in aquatic environments. However, little is known about the biochemical and behavioral effects of DPH on non-target aquatic animals. In the present study, the tissue distribution, bioconcentration, metabolism, biochemical and behavioral effects were investigated in crucian carp (Carassius auratus) exposed to various concentrations of DPH (0.84, 4.23, 21.7 and 112 μg L(-1)) for 7d. DPH can accumulate in crucian carp, and high concentrations have been observed in the liver and brain with maximum bioconcentration factors of 148 and 81.6, respectively. A portion of the absorbed DPH was metabolized by the crucian carp to N-demethyl DPH and N,N-didemethyl DPH via N-demethylation. Direct fluorimetric assay was employed to assess metabolic activity, while oxidative stress and neurotransmission biomarkers were determined by Diagnostic Reagent Kits. DPH was found to increase hepatic 7-ethoxyresorufin O-deethylase activity in crucian carp with maximal induction of 119%. Concerning the oxidative stress status, DPH significantly inhibited superoxide dismutase (SOD, 37-58%) and glutathione S-transferase (GST, 43-65%) activities and led to a significant increase in malondialdehyde (MDA, 67-140%) levels and catalase (CAT, 38-143%) and glutathione peroxidase (GPx, 39-189%) activities in fish liver. Brain acetylcholinesterase activity was also induced in DPH-exposed crucian carp with maximal induction of 174%. In addition, shoaling was significantly enhanced, while swimming activity and feeding rates were markedly suppressed at DPH concentrations equal to or higher than 21.7 μg L(-1). Furthermore, significant correlations were found between oxidative stress biomarkers (SOD, CAT, GPx, GST and MDA) and behavioral parameters. Collectively, our results confirmed that DPH can accumulate and be metabolized in fish and exert a negative effect at different levels of biological organization.

Over-the-Counter Agents for the Treatment of Occasional Disturbed Sleep or Transient Insomnia: A Systematic Review of Efficacy and Safety

OBJECTIVE

To investigate the level of evidence supporting the use of common over-the-counter (OTC) agents (diphenhydramine, doxylamine, melatonin, and valerian) for occasional disturbed sleep or insomnia.

DATA SOURCES

A systematic review of the literature was conducted on July 31, 2014, using MEDLINE (PubMed) and the search terms (insomnia OR sleep) AND (over*the*counter OR OTC OR non*prescription OR antihistamine OR doxylamine OR diphenhydramine OR melatonin OR valerian) with the filters English, human, and clinical trials.

STUDY SELECTION

Identified publications (from 2003 to July 31, 2014, following previous published literature reviews) that met the inclusion criteria were selected. The criteria included randomized placebo-controlled clinical studies that utilized overnight objective (polysomnography) or next-day participant-reported sleep-related endpoints and that were conducted in healthy participants with or without occasional disturbed sleep or diagnosed insomnia.

RESULTS

Measures of efficacy and tolerability were summarized for each study individually and grouped according to OTC agent: H1 antagonists or antihistamines (3 studies, diphenhydramine), melatonin (8), and valerian or valerian/hops (7). Of the 3 sleep agents, studies conducted with melatonin, especially prolonged-release formulations in older individuals with diagnosed insomnia, demonstrated the most consistent beneficial effects (vs placebo) on sleep measures, specifically sleep onset and sleep quality, with favorable tolerability. In contrast, the clinical trial data for diphenhydramine, immediate-release melatonin, and valerian suggested limited beneficial effects.

CONCLUSIONS

A review of randomized controlled studies over the past 12 years suggests commonly used OTC sleep-aid agents, especially diphenhydamine and valerian, lack robust clinical evidence supporting efficacy and safety.

Prolonged neuropsychiatric effects following management of chloroquine intoxication with psychotropic polypharmacy

Susceptibility to quinoline antimalarial intoxication may reflect individual genetic and drug-induced variation in neuropharmacokinetics. In this report, we describe a case of chloroquine intoxication that appeared to be prolonged by subsequent use of multiple psychotropic medications. This case highlights important new considerations for the management of quinoline antimalarial intoxication.

Flavin monooxygenase metabolism: why medicinal chemists should matter

FMO enzymes (FMOs) play a key role in the processes of detoxification and/or bioactivation of specific pharmaceuticals and xenobiotics bearing nucleophilic centers. The N-oxide and S-oxide metabolites produced by FMOs are often active metabolites. The FMOs are more active than cytochromes in the brain and work in tandem with CYP3A4 in the liver. FMOs might reduce the risk of phospholipidosis of CAD-like drugs, although some FMOs metabolites seem to be neurotoxic and hepatotoxic. However, in silico methods for FMO metabolism prediction are not yet available. This paper reports, for the first time, a substrate-specificity and catalytic-activity model for FMO3, the most relevant isoform of the FMOs in humans. The application of this model to a series of compounds with unknown FMO metabolism is also reported. The model has also been very useful to design compounds with optimal clearance and in finding erroneous literature data, particularly cases in which substances have been reported to be FMO3 substrates when, in reality, the experimentally validated in silico model correctly predicts that they are not.

Comparative pharmaceutical metabolism by rainbow trout (Oncorhynchus mykiss) liver S9 fractions

The occurrence of pharmaceuticals in the environment presents a challenge of growing concern. In contrast to many industrial compounds, pharmaceuticals undergo extensive testing prior to their introduction to the environment. In principle, therefore, it may be possible to employ existing pharmacological safety data using biological "read-across" methods to support screening-level bioaccumulation environmental risk assessment. However, few approaches and robust empirical data sets exist, particularly for comparative pharmacokinetic applications. For many pharmaceuticals, the primary cytochrome P450 (CYP) enzymes responsible for their metabolism have been identified in humans. The purpose of the present study was to employ a comparative approach to determine whether rainbow trout biotransform pharmaceuticals known to be substrates for specific human CYPs. Seven compounds were selected based on their primary metabolism in humans by CYP3A4, CYP2D6, or CYP2C9. Five additional test compounds are known to be substrates for multiple CYPs. Metabolism by rainbow trout liver S9 fractions was evaluated using a substrate-depletion approach, which provided an estimate of intrinsic hepatic clearance (CLIN VITRO,INT ). An isotope dilution liquid chromatography-tandem mass spectrometry method was employed for quantitation of parent chemical concentrations. Only 2 general CYP substrates demonstrated measurable levels of substrate depletion. No significant biotransformation was observed for known substrates of human CYP2D6, CYP2C9, or CYP3A4. The results of this study provide novel information for therapeutics that fish models are likely to metabolize based on existing mammalian data. Further, these results suggest that pharmaceuticals may possess a greater tendency to bioaccumulate in fish than previously anticipated.

From known knowns to known unknowns: predicting in vivo drug metabolites

'It is better to be useful than perfect'. This review attempts to critically cover and assess the currently available approaches and tools to answer the crucial question: Is it possible (and if it is, to what extent is it possible) to predict in vivo metabolites and their abundances on the basis of in vitro and preclinical animal studies? In preclinical drug development, it is possible to produce metabolite patterns from a candidate drug by virtual means (i.e., in silico models), but these are not yet validated. However, they may be useful to cover the potential range of metabolites. In vitro metabolite patterns and apparent relative abundances are produced by various in vitro systems employing tissue preparations (mainly liver) and in most cases using liquid chromatography-mass spectrometry analytical techniques for tentative identification. The pattern of the metabolites produced depends on the enzyme source; the most comprehensive source of drug-metabolizing enzymes is cultured human hepatocytes, followed by liver homogenate fortified with appropriate cofactors. For specific purposes, such as the identification of metabolizing enzyme(s), recombinant enzymes can be used. Metabolite data from animal in vitro and in vivo experiments, despite known species differences, may help pinpoint metabolites that are not apparently produced in in vitro human systems, or suggest alternative experimental approaches. The range of metabolites detected provides clues regarding the enzymes attacking the molecule under study. We also discuss established approaches to identify the major enzymes. The last question, regarding reliability and robustness of metabolite extrapolations from in vitro to in vivo, both qualitatively and quantitatively, cannot be easily answered. There are a number of examples in the literature suggesting that extrapolations are generally useful, but there are only a few systematic and comprehensive studies to validate in vitro-in vivo extrapolations. In conclusion, extrapolation from preclinical metabolite data to the in vivo situation is certainly useful, but it is not known to what extent.

Profound changes in drug metabolism enzymes and possible effects on drug therapy in neonates and children

INTRODUCTION

There are profound changes that take place in drug metabolism enzymes during fetal and postnatal development. These changes may significantly impact drug therapy in children.

AREAS COVERED

A combination of focused and comprehensive literature searches using PubMed and reference lists (from inception to 7 November 2009) is undertaken to identify reports on in vitro and in vivo development of drug metabolism enzymes as well disposition of selected drugs and their effect in children. The article provides an update on development of drug metabolism enzymes and their impact on drug substrate disposition and disease, which may aid to improve clinical practice and optimally design clinical trials in children.

EXPERT OPINION

Drug metabolism enzyme activity changes profoundly throughout the continuum of postnatal development and often results in different disposition pathways than in adults. Genetics and co-morbidity interact significantly with these developmental changes. Translation of existing knowledge into age-adjusted dosing guidelines and clinical trial design is highly needed for there to be an improvement in drug therapy in children.

Next-day residual sedative effect after nighttime administration of an over-the-counter antihistamine sleep aid, diphenhydramine, measured by positron emission tomography

Antihistamines often are self-administered at night as over-the-counter (OTC) sleep aids, but their next-day residual sedative effect has never been evaluated using a reliable quantitative method such as positron emission tomography (PET). We performed a double-blind, placebo-controlled, crossover study in which we evaluated the residual effect the next day after nighttime administration of diphenhydramine, a commonly used OTC sleep aid, in terms of brain H₁ receptor occupancy (H₁RO) measured using ¹¹C-doxepin-PET. We also compared the results of diphenhydramine with those of bepotastine, a second-generation antihistamine. Eight healthy adult male subjects underwent PET measurement the morning (11:00) after random oral administration of diphenhydramine (50 mg), bepotastine (10 mg), or placebo the night before (23:00). Binding potential ratios and H₁ROs were calculated in different brain regions of interest such as the cingulate gyrus, frontotemporal cortex, and cerebellum. Subjective sleepiness and plasma drug concentration also were measured. Calculation of binding potential ratios revealed significantly lower values for diphenhydramine than for bepotastine or placebo in all regions of interest (P < 0.01). Cortical mean H₁RO after diphenhydramine treatment was 44.7% compared with 16.6% for bepotastine treatment (P < 0.01). Subjective sleepiness was not significantly different among the subjects treated with each test drug or the placebo. In conclusion, the next-day residual sedative effect after nighttime administration of the OTC sleep aid diphenhydramine was verified for the first time by direct PET measurement of H₁RO. Taking into account the possible hangover effect of OTC antihistamine sleep aids, care needs to be taken during their administration.

Structure, function, regulation and polymorphism and the clinical significance of human cytochrome P450 1A2

Human CYP1A2 is one of the major CYPs in human liver and metabolizes a number of clinical drugs (e.g., clozapine, tacrine, tizanidine, and theophylline; n > 110), a number of procarcinogens (e.g., benzo[a]pyrene and aromatic amines), and several important endogenous compounds (e.g., steroids). CYP1A2 is subject to reversible and/or irreversible inhibition by a number of drugs, natural substances, and other compounds. The CYP1A gene cluster has been mapped on to chromosome 15q24.1, with close link between CYP1A1 and 1A2 sharing a common 5'-flanking region. The human CYP1A2 gene spans almost 7.8 kb comprising seven exons and six introns and codes a 515-residue protein with a molecular mass of 58,294 Da. The recently resolved CYP1A2 structure has a relatively compact, planar active site cavity that is highly adapted for the size and shape of its substrates. The architecture of the active site of 1A2 is characterized by multiple residues on helices F and I that constitutes two parallel substrate binding platforms on either side of the cavity. A large interindividual variability in the expression and activity of CYP1A2 has been observed, which is largely caused by genetic, epigenetic and environmental factors (e.g., smoking). CYP1A2 is primarily regulated by the aromatic hydrocarbon receptor (AhR) and CYP1A2 is induced through AhR-mediated transactivation following ligand binding and nuclear translocation. Induction or inhibition of CYP1A2 may provide partial explanation for some clinical drug interactions. To date, more than 15 variant alleles and a series of subvariants of the CYP1A2 gene have been identified and some of them have been associated with altered drug clearance and response and disease susceptibility. Further studies are warranted to explore the clinical and toxicological significance of altered CYP1A2 expression and activity caused by genetic, epigenetic, and environmental factors.

Understanding the relative roles of pharmacogenetics and ontogeny in pediatric drug development and regulatory science

Understanding the dose-exposure-response relationship across the pediatric age spectrum from preterm and term newborns to infants, children, adolescents, and adults is a major challenge for clinicians, pharmaceutical companies, and regulatory agencies. Over the past 3 decades, clinical investigations of many drugs commonly used in pediatric therapeutics have provided valuable insights into age-associated differences in drug disposition and action. However, our understanding of the contribution of genetic variation to variability in drug disposition and response in children generally has lagged behind that of adults. This article proposes a systematic approach that can be used to assess the relative contributions of ontogeny and genetic variation for a given compound. Application of the strategy is illustrated using the current regulatory dilemma posed by the safety and effectiveness of over-the-counter cough and cold remedies as an example. The results of the analysis can be used to aid in the design of studies to yield maximally informative data in pediatric populations of different ages and developmental stages and thereby improve the efficiency of study design.

New insights into the structural characteristics and functional relevance of the human cytochrome P450 2D6 enzyme

To date, the crystal structures of at least 12 human CYPs (1A2, 2A6, 2A13, 2C8, 2C9, 2D6, 2E1, 2R1, 3A4, 7A1, 8A1, and 46A1) have been determined. CYP2D6 accounts for only a small percentage of all hepatic CYPs (< 2%), but it metabolizes approximately 25% of clinically used drugs with significant polymorphisms. CYP2D6 also metabolizes procarcinogens and neurotoxins, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1,2,3,4-tetrahydroquinoline, and indolealkylamines. Moreover, the enzyme utilizes hydroxytryptamines and neurosteroids as endogenous substrates. Typical CYP2D6 substrates are usually lipophilic bases with an aromatic ring and a nitrogen atom, which can be protonated at physiological pH. Substrate binding is generally followed by oxidation (5-7 A) from the proposed nitrogen-Asp301 interaction. A number of homology models have been constructed to explore the structural features of CYP2D6, while antibody studies also provide useful structural information. Site-directed mutagenesis studies have demonstrated that Glu216, Asp301, Phe120, Phe481, and Phe483 play important roles in determining the binding of ligands to CYP2D6. The structure of human CYP2D6 has been recently determined and shows the characteristic CYP fold observed for other members of the CYP superfamily. The lengths and orientations of the individual secondary structural elements in the CYP2D6 structure are similar to those seen in other human CYP2 members, such as CYP2C9 and 2C8. The 2D6 structure has a well-defined active-site cavity located above the heme group with a volume of approximately 540 A(3), which is larger than equivalent cavities in CYP2A6 (260 A(3)), 1A2 (375 A(3)), and 2E1 (190 A(3)), but smaller than those in CYP3A4 (1385 A(3)) and 2C8 (1438 A(3)). Further studies are required to delineate the molecular mechanisms involved in CYP2D6 ligand interactions and their implications for drug development and clinical practice.

Pharmacokinetics in special populations

Pharmacokinetics are typically dependent on a variety of physiological variables (e.g., age, ethnicity, or pregnancy) or pathological conditions (e.g., renal and hepatic insufficiency, cardiac dysfunction, obesity, etc.). The influence of some of these conditions has not always been thoroughly assessed in the clinical studies of antiallergic drugs. However, the knowledge of the physiological grounds of the pharmacokinetics can provide some insight for predicting the potential alterations and guiding the initial prescription strategies. It is important to recognize that both pharmacokinetic and pharmacodynamic differences between populations should be considered. The available information on drugs used for the therapy of allergic diseases is reviewed in this chapter.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Polymorphisms of human cytochrome P450 2C9 and the functional relevance

Human cytochrome P450 2C9 (CYP2C9) accounts for ∼20% of hepatic total CYP content and metabolizes ~15% clinical drugs such as phenytoin, S-warfarin, tolbutamide, losartan, and many nonsteroidal anti-inflammatory agents (NSAIDs). CYP2C9 is highly polymorphic, with at least 33 variants of CYP2C9 (*1B through *34) being identified so far. CYP2C9*2 is frequent among Caucasians with ~1% of the population being homozygous carriers and 22% are heterozygous. The corresponding figures for the CYP2C9*3 allele are 0.4% and 15%, respectively. There are a number of clinical studies addressing the impact of CYP2C9 polymorphisms on the clearance and/or therapeutic response of therapeutic drugs. These studies have highlighted the importance of the CYP2C9*2 and *3 alleles as a determining factor for drug clearance and drug response. The CYP2C9 polymorphisms are relevant for the efficacy and adverse effects of numerous NSAIDs, sulfonylurea antidiabetic drugs and, most critically, oral anticoagulants belonging to the class of vitamin K epoxide reductase inhibitors. Warfarin has served as a practical example of how pharmacogenetics can be utilized to achieve maximum efficacy and minimum toxicity. For many of these drugs, a clear gene-dose and gene-effect relationship has been observed in patients. In this regard, CYP2C9 alleles can be considered as a useful biomarker in monitoring drug response and adverse effects. Genetic testing of CYP2C9 is expected to play a role in predicting drug clearance and conducting individualized pharmacotherapy. However, prospective clinical studies with large samples are warranted to establish gene-dose and gene-effect relationships for CYP2C9 and its substrate drugs.

CYP2D6 genotyping for psychiatric patients treated with risperidone: considerations for cost–effectiveness studies

In order to ascertain data availability and feasibility for conducting cost–effectiveness studies in pharmacogenetics, and as part of a European Commission Joint Research Center, Institute for Prospective Technological Studies (JRC-IPTS) study, data concerning risperidone use and cytochrome P450 (CYP2D6) genotyping in medical care was collected in Germany, Spain and the USA, and are summarized in this perspective. The gene coding for CYP2D6 is highly polymorphic, resulting in a significant part of the population being poor metabolizers and ultrarapid metabolizers. Individuals who are CYP2D6 poor metabolizers, have an increased risk of adverse drug reactions (ADRs) when treated with CYP2D6-metabolized drugs, suggesting that CYP2D6 genotyping might be beneficial for patient care. This might be especially important in psychiatry, where approximately 50% of the patients use at least one drug primarily metabolized by CYP2D6. In particular, ADRs and poor response to treatment are major problems for some antipsychotics, including risperidone. However, there are no published cost–effectiveness studies on CYP2D6 genotyping, and the benefit that pharmacogenetic testing might represent by identifying problematic patients is still unclear. The present European Commission study found that current clinical and economical data concerning the frequency and direct healthcare costs of risperidone-related ADRs, the relation of such ADRs with the patients CYP2D6 genotypes, and costs for CYP2D6 genotyping, are not sufficient for determining if routine CYP2D6 genotyping might be cost beneficial for patients treated with risperidone. Therefore, efforts should be put on performing prospective cost–benefit studies with randomized treatment according to the CYP2D6 genotype to establish the utility of CYP2D6 genotyping for personalizing antipsychotic treatment.

A compendium of placebo-controlled trials of the risks/benefits of pharmacological treatments for insomnia: the empirical basis for U.S. clinical practice

For many years practitioners have had limited data from double-blind, placebo-controlled studies to guide the types of decision-making needed to optimally manage patients with insomnia in clinical practice. However, in recent years there has been a great increase in insomnia research studies that address issues of clinical importance. This body of work represents an increasingly useful empirical basis for making clinical practice decisions. The purpose of this article is to compile the body of work on the pharmacological management of insomnia to make it available in as accessible form as possible for optimal application in clinical practice with the hopes that doing so will decrease the gap separating the available research and the clinical management of insomnia and, thereby, improve the care of the many individuals who suffer from this condition. The review of studies consists of the following sections: 1) basic pharmacology; 2) double-blind, placebo-controlled trials in adults with primary insomnia; 3) double-blind, placebo-controlled trials in elderly patients with primary insomnia; 4) adverse effects reported in placebo-controlled trials in elderly primary insomnia patients; 5) double-blind, placebo-controlled trials in adults and the elderly as a function of treatment duration; 6) double-blind, placebo-controlled trials of the treatment of comorbid insomnia. Issues related to the application of these data to clinical practice are discussed in the text.

Comparison of metabolite profiles generated in Aroclor-induced rat liver and human liver subcellular fractions: considerations for in vitro genotoxicity hazard assessment

Because it is well known that metabolites of chemicals and drugs are frequently the ultimate species responsible for genotoxicity and carcinogenicity, in vitro testing to identify the human genotoxicity hazard potential of new chemicals and drugs routinely utilizes liver S-9 fraction from rats treated with Aroclor 1254 as a system that can generate metabolites. However, it is frequently questioned as to whether such an in vitro metabolite generation system is the most relevant for human risk, or whether the assay would be better served by using a human-derived in vitro system. To address this, 16 common drugs have been examined for profiles of metabolites in Aroclor-induced rat liver S-9 and pooled human liver S-9. Metabolite profiles were compared using high pressure liquid chromatography coupled with ion trap mass spectrometry, in line with ultraviolet or radiometric detection to help make semiquantitative comparisons. Results showed that, with few exceptions, metabolites generated in the human system were also generated in the rat system. Also, in several cases the rat system generated considerably more metabolites, suggesting that there is a potential that positive genotoxicity findings could be caused by metabolites that have no relevance to humans. These findings suggest that when conducting in vitro genotoxicity testing using the Aroclor-induced rat liver S-9 system, knowledge of the metabolite profile in the system is important, and a comparison to the profile generated in human liver S-9 could be of value when interpreting the genotoxicity results.

Functional pharmacogenetics/genomics of human cytochromes P450 involved in drug biotransformation

We investigated the elimination routes for the 200 drugs that are sold most often by prescription count in the United States. The majority (78%) of the hepatically cleared drugs were found to be subject to oxidative metabolism via cytochromes P450 of the families 1, 2 and 3, with major contributions from CYP3A4/5 (37% of drugs) followed by CYP2C9 (17%), CYP2D6 (15%), CYP2C19 (10%), CYP1A2 (9%), CYP2C8 (6%), and CYP2B6 (4%). Clinically well-established polymorphic CYPs (i.e., CYP2C9, CYP2C19, and CYP2D6) were involved in the metabolism of approximately half of those drugs, including (in particular) NSAIDs metabolized mainly by CYP2C9, proton-pump inhibitors metabolized by CYP2C19, and beta blockers and several antipsychotics and antidepressants metabolized by CYP2D6. In this review, we provide an up-to-date summary of the functional polymorphisms and aspects of the functional genomics of the major human drug-metabolizing cytochrome P450s, as well as their clinical significance.