CYP2C19 genotype affects diazepam pharmacokinetics and emergence from general anesthesia

Application of Advanced Technologies-Nanotechnology, Genomics Technology, and 3D Printing Technology-In Precision Anesthesia: A Comprehensive Narrative Review

There has been increasing interest and rapid developments in precision medicine, which is a new medical concept and model based on individualized medicine with the joint application of genomics, bioinformatics engineering, and big data science. By applying numerous emerging medical frontier technologies, precision medicine could allow individualized and precise treatment for specific diseases and patients. This article reviews the application and progress of advanced technologies in the anesthesiology field, in which nanotechnology and genomics can provide more personalized anesthesia protocols, while 3D printing can yield more patient-friendly anesthesia supplies and technical training materials to improve the accuracy and efficiency of decision-making in anesthesiology. The objective of this manuscript is to analyze the recent scientific evidence on the application of nanotechnology in anesthesiology. It specifically focuses on nanomedicine, precision medicine, and clinical anesthesia. In addition, it also includes genomics and 3D printing. By studying the current research and advancements in these advanced technologies, this review aims to provide a deeper understanding of the potential impact of these advanced technologies on improving anesthesia techniques, personalized pain management, and advancing precision medicine in the field of anesthesia.

Clinical Impact of the CYP2C19 Gene on Diazepam for the Management of Alcohol Withdrawal Syndrome

Diazepam is a benzodiazepine widely prescribed for the management of patients with severe alcohol withdrawal syndrome to prevent agitation, withdrawal seizures, and delirium tremens. Despite standard dosing of diazepam, a subset of patients experience refractory withdrawal syndromes or adverse drug reactions, such as impaired motor coordination, dizziness, and slurred speech. The CYP2C19 and CYP3A4 enzymes play a key role in the biotransformation of diazepam. Given the highly polymorphic nature of the CYP2C19 gene, we reviewed the clinical impact of variants in the CYP2C19 gene on both the pharmacokinetics of diazepam and treatment outcomes related to the management of alcohol withdrawal syndrome.

Association between CYP2C19 and CYP2B6 phenotypes and the pharmacokinetics and safety of diazepam

Diazepam is a benzodiazepine (BZD) used worldwide for a variety of conditions. Long-term use of diazepam increases the risk for developing tolerance and dependence and for the occurrence of adverse drug reactions (ADRs). CYP3A4 and CYP2C19 mainly metabolize diazepam and are therefore the primary pharmacogenetic candidate biomarkers. In this work, we aimed to explore the impact of CYP3A4 and CYP2C19 phenotypes and of 99 additional variants in other 31 pharmacogenes (including other CYP, UGT, NAT2 and CES enzymes, ABC and SLC transporters) on diazepam pharmacokinetic variability and safety. 30 healthy volunteers that had participated in a single-dose bioequivalence clinical trial of two diazepam formulations were enrolled in the present candidate gene pharmacogenetic study. CYP2C19 poor metabolizers (PMs) showed an almost 2-fold increase in AUC_0-∞/DW compared to rapid (RMs) or normal (NM) metabolizers, and a 1.46-fold increase compared to intermediate metabolizers (IMs). CYP2B6 PMs showed a 2,74-fold higher AUC_0-∞/DW compared to RMs, and 2.10-fold compared to NMs (p < 0.007). A dose reduction of 25-50 % may be appropriate for CYP2C19 or CYP2B6 PMs to avoid ADRs, dependence and tolerance. Combined CYP2C19 +CYP2B6 PMs may not use diazepam or sharper dose adjustments (e.g., a dose reduction of 50-70 %) may be advisable. To our knowledge, this is the first work to report a strong relationship between CYP2B6 phenotype and diazepam pharmacokinetics. Additional nominal associations (i.e., 0.007 <p < 0.05) between ABCG2, ABCB1, NAT2 and UGT1A4 polymorphisms and pharmacokinetic variability were observed; further research should elaborate on the clinical relevance of the described associations.

Pharmacokinetics of Diazepam and Its Metabolites in Urine of Chinese Participants

BACKGROUND

Urine is conventionally used as a specimen to document diazepam-related crimes; however, few reports have described the pharmacokinetics of diazepam and its metabolites in urine.

OBJECTIVE

This study aimed to investigate the pharmacokinetics of diazepam and its metabolites, including glucuronide compounds, in the urine of Chinese participants.

METHODS

A total of 28 volunteers were recruited and each participant ingested 5 mg of diazepam orally. Ten milliliters of urine were collected from each participant at post-consumption timepoints of prior (zero), 1, 2, 4, 8, 12, and 24 h and 2, 3, 6, 12, and 15 days. All samples were extracted by solid-phase extraction and analyzed using high-performance liquid chromatography-tandem mass spectrometry. Diazepam and its main metabolites, except for temazepam, were detected in the urine of volunteers. Pharmacokinetic parameters were analyzed using the pharmacokinetic software DAS according to the non-compartment model.

RESULTS

Urinary diazepam peaked at 2.38 ng/mL (C_max) and 1.93 h (T_max). The urinary metabolite nordiazepam peaked at 1.17 ng/mL and 100.21 h; temazepam glucuronide (TG) peaked at 145.61 ng/mL and 41.14 h; and oxazepam glucuronide (OG) peaked at 101.57 ng/mL and 165.86 h. The elimination half-life (t_½z) and clearance (CLz/F) for diazepam were 119.58 h and 65.77 L/h, respectively. The t_½z of the metabolites nordiazepam, TG, and OG was 310.58 h, 200.17 h, and 536.44 h, respectively. Finally, this study found that both diazepam and its main metabolites in urine were detectable for at least 15 days, although there were individual differences.

CONCLUSION

The results regarding diazepam pharmacokinetics in urine would be of great help in forensic science and drug screening.

Group-based pharmacogenetic prediction: is it feasible and do current NHS England ethnic classifications provide appropriate data?

Inter-individual variation of drug metabolising enzymes (DMEs) leads to variable efficacy of many drugs and even adverse drug responses. Consequently, it would be desirable to test variants of many DMEs before drug treatment. Inter-ethnic differences in frequency mean that the choice of SNPs to test may vary across population groups. Here we examine the utility of testing representative groups as a way of assessing what variants might be tested. We show that publicly available population information is potentially useful for determining loci for pre-treatment genetic testing, and for determining the most prevalent risk haplotypes in defined groups. However, we also show that the NHS England classifications have limitations for grouping for these purposes, in particular for people of African descent. We conclude: (1) genotyping of hospital patients and people from the hospital catchment area confers no advantage over using samples from appropriate existing ethnic group collections or publicly available data, (2) given the current NHS England Black African grouping, a decision as to whether to test, would have to apply to all patients of recent Black African ancestry to cover reported risk alleles and (3) the current scarcity of available genome and drug effect data from Africans is a problem for both testing and treatment decisions.

An Experimental Pharmacokinetics Study of Diazepam and Its Metabolites in Oral Fluid of Chinese Population

Diazepam abuse is widespread all over the word, leading to an increasing number of forensic cases such as suicide, drug-driving and robbery, but relevant studies are limited regarding the extraction of diazepam and its metabolites in oral fluid. This study aimed to investigate the pharmacokinetics of diazepam and its metabolites in oral fluid after a single oral dose in healthy volunteers. There was a total of 28 volunteers, and each ingested 5 mg diazepam orally, then ~2 mL oral fluid were collected from each participant at post-consumption time-points of prior (zero), 1, 2, 4, 8, 12, 24 h and 2, 3, 6, 12 and 15 days, respectively. All samples were extracted with solid-phase extraction and analyzed with high-performance liquid chromatography-tandem mass spectrometry method, and diazepam and nordazepam were detected in the oral fluid of volunteers. Pharmacokinetics of diazepam in oral fluid conformed to a two-compartment model, and k01_HL, k12_HL, k10_HL were 0.7 ± 1.1, 31.4 ± 68.5, 12.1 ± 11.6 h, respectively, nordazepam conformed to an one-compartment model, and k01_HL, k10_HL were 41.5 ± 44.8, 282.3 ± 365.5 h, respectively. Both diazepam and nordazepam could be detected continuously for 15 days, although there were individual differences, and the results regarding diazepam detecting in oral fluid will be of much help in forensic science and drug screening filed.

Challenges in anesthesia personalization: resolving the pharmacogenomic puzzle

Clinicians are witnessing differences in the doses required for induction and maintenance of anesthesia, as well as prolonged recovery in some patients. Predictable factors like patient characteristics, factors related to the procedure, pharmacological characteristics of anesthetics and adjunctive drugs, might explain some of the observed differences. However, the role of various polymorphisms of genes encoding for drugs’ molecular targets, transporters and metabolic enzymes can have a significant impact on anesthesia outcome, too. In the present paper, we critically discuss pharmacological characteristics of the most common drugs used in anesthesia, with a focus on the possible genetic background of unpredictable diversities in anesthesia outcomes.

Pharmacogenetics of alcohol addiction: current perspectives

Genetics of alcohol addiction is currently a contradictive and complex field, where data in the most studies reflect methods’ limitations rather than meaningful and complementary results. In our review, we focus on the genetics of alcohol addiction, leaving genetics of acute alcohol intoxication out of the scope. A review of the literature on pharmacogenetic biomarkers development for the pharmacotherapy personalization reveals that today the evidence base concerning these biomarkers is still insufficient. In particular, now the researches with the design of randomized controlled trials and meta-analysis investigating the effect of the SNPs as biomarkers on the therapy efficacy are available for naltrexone only. For other medications, there are only a few studies in small samples. It decreases the possibilities to implement the pharmacogenetic algorithms for the pharmacotherapy personalization in patients with alcohol use disorders (AUD). In view of the importance of the precision approaches development not in addiction medicine only, but in other fields of medicine also to increase the efficacy and safety of the therapy, studies on pharmacogenetic biomarkers development for the medications used in patients with AUD (eg, naltrexone, disulfiram, nalmefene, acamprosate, etc.) remain relevant to this day.

Using a personalized clinical decision support system for bromdihydrochlorphenylbenzodiazepine dosing in patients with anxiety disorders based on the pharmacogenomic markers

INTRODUCTION

Although pharmacogenetic tests provide the information on a genotype and the predicted phenotype, these tests themselves do not provide the interpretation of data for a physician. There are currently approximately two dozen pharmacogenomic clinical decision support systems used in psychiatry. Implementation of clinical decision support systems capable of forming recommendations on drug and dose selection according to the results of pharmacogenetic testing is an urgent task. Fulfillment of this task may allow increasing the efficacy of therapy and decreasing the risk of undesirable side effects.

MATERIALS AND METHODS

The study included 51 male patients (21 in the main group and 30 in the control group) with alcohol withdrawal syndrome. To evaluate the efficacy and safety of therapy, several international psychometric scales and rating scales to measure side effects were used. Genotyping was performed using real-time polymerase chain reaction with allele-specific hybridization. Pharmacogenetic test results were interpreted using free software PGX2 (www.pgx2.com).

RESULTS

Statistically significant differences between the scores derived from all psychometric scales were revealed. For instance, the total score on CIWA-Ar scale by day 3 was 13.5 [11.2; 16.0] for the main group and 18.0 [17.0; 22.0] (p < 0.001) for the control group; by day 5, it was 6.5 [4.2; 8.0] for the main group and 15.0 [14.0; 16.0] (p < 0.001) for the control group. The UKU side effect rating scale (UKU) also revealed a statistically significant difference. The total score on UKU scale by day 3 was 6.0 [5.0; 7.0] for the main group and 7.0 [6.0; 8.0] (p < 0.001) for the control group; by day 5, this difference grew significantly: 5.5 [3.0; 9.0] for the main group and 14.0 [12.0; 19.0] (p < 0.001) for the control group. The groups were representative (there was no difference between the scores at the inclusion of patients).

CONCLUSION

Pharmacogenetic-guided personalization of drug dose in patients with alcohol withdrawal syndrome can reduce the risk of undesirable side effects and pharmacoresistance. It allows recommending the use of pharmacogenomic clinical decision support systems for optimizing drug dosage.

A review of the pharmacology and clinical efficacy of brivaracetam

Brivaracetam (BRV; Briviact) is a new antiepileptic drug (AED) approved for adjunctive treatment of focal (partial-onset) seizures in adults. BRV is a selective, high-affinity ligand for synaptic vesicle 2A (SV2A) with 15- to 30-fold higher affinity than levetiracetam, the first AED acting on SV2A. It has high lipid solubility and rapid brain penetration, with engagement of the target molecule, SV2A, within minutes of administration. BRV has potent broad-spectrum antiepileptic activity in animal models. Phase I studies indicated BRV was well tolerated and showed a favorable pharmacokinetic profile over a wide dose range following single (10–1,000 mg) and multiple (200–800 mg/day) oral dosing. Three pivotal Phase III studies have demonstrated promising efficacy and a good safety and tolerability profile across doses of 50–200 mg/day in the adjunctive treatment of refractory focal seizures. Long-term data indicate that the response to BRV is sustained, with good tolerability and retention rate. BRV is highly effective in patients experiencing secondarily generalized tonic–clonic seizures. Safety data to date suggest a favorable psychiatric adverse effect profile in controlled studies, although limited postmarketing data are available. BRV is easy to use, with no titration and little drug–drug interaction. It can be initiated at target dose with no titration. Efficacy is seen on day 1 of oral use in a significant percentage of patients. Intravenous administration in a 2-minute bolus and 15-minute infusion is well tolerated. Here, we review the pharmacology, pharmacokinetics, and clinical data of BRV.

Metabolic profile of oxazepam and related benzodiazepines: clinical and forensic aspects

Anxiolytic drugs, namely benzodiazepines, are the most commonly used psychoactive substances since anxiety disorders are prevalent mental disorders particularly in the Western world. Oxazepam is a short-acting benzodiazepine and one of the most frequently prescribed anxiolytic drugs. It is also the active metabolite of a wide range of other benzodiazepines, such as diazepam, ketazolam, temazepam, chlordiazepoxide, demoxazepam, halazepam, medazepam, prazepam, pinazepam, and chlorazepate. Therefore, relevant clinical and forensic outocomes may arise, namely those related to interference in driving performance. It is clinically available as a racemic formulation, with S-enantiomer being more active than R-enantiomer. In humans, it is mainly polimorphically metabolized by glucuronide conjugation at the 3-carbon hydroxyl group, yielding stable diastereomeric glucuronides (R- and S-oxazepam glucuronide). Relevant metabolic and stereoselective interspecies differences have been reported. In this work, the pharmacokinetics of oxazepam with particular focus on metabolic pathways is fully reviewed. Moreover, the metabolic profile of other prescribed benzodiazepines that produce oxazepam as a metabolite is also discussed. It is aimed that knowing the metabolism of oxazepam and related benzodiazepines may lead to the development of new analytical strategies for its early detection and help in further toxicological and clinical interpretations.

Falls: the adverse drug reaction of the elderly and the impact of pharmacogenetics

Falls is a frequent type of adverse drug reactions causing significant morbidity and mortality in the elderly. We reviewed, with which drugs the risk of falls is relevant and might depend on genomic variation. Pharmacogenetic variability may contribute to drug-induced falls for instance mediated by impaired drug elimination due to inherited deficiency in enzymes like CYP2C9, CYP2C19 and CYP2D6. The relative role of specific genes and polymorphisms in old age may differ from younger people. Biomarkers for frailty, but also genomic biomarkers might help identifying patients at high risk for drug-induced falls. Many other factors including disease and drug-drug interactions also contribute to risk of falls. Further studies analyzing the impact of genomic variation on the medication-related fall risk in the older adult are urgently needed.

Notable Drug-Drug Interaction Between Etizolam and Itraconazole in Poor Metabolizers of Cytochrome P450 2C19

In this study, impact of a polymorphism of CYP2C19 on drug-drug interaction (DDI) was examined for etizolam. The effect of itraconazole (a strong CYP3A inhibitor) on the pharmacokinetics of etizolam (a substrate of CYP2C19 and CYP3A) was assessed in both extensive metabolizers (EMs) and poor metabolizers (PMs) of CYP2C19. Sixteen participants (8 EMs and 8 PMs) received a single oral dose of etizolam (0.25 mg) on day 1. The participants ingested itraconazole (200 mg twice a day) on days 2-5. On day 5, participants received an oral dose of etizolam (0.25 mg) again. Before coadministration of itraconazole (day 1), the area under the time-plasma concentration curve from time zero to infinity (AUC_∞ ) of etizolam was higher in PMs than in EMs (2.65-fold, P < .01). Coadministration of itraconazole increased the AUC_∞ of etizolam 1.66-fold and 2.34-fold in EMs and PMs, respectively (day 5). Consequently, AUC_∞ was 6.18-fold higher in PMs with itraconazole than that in EMs without itraconazole. The increase by itraconazole was larger in PMs (P < .01). In heterozygous EMs (hEMs), AUC_∞ was simulated to be 2.56-fold higher with itraconazole than that in EMs without itraconazole. We found that in vitro measurements of fraction metabolized (f_m ) using the liver microsome prepared from PM donors would be helpful to predict polymorphism-dependent DDIs. These results suggest that the PMs and hEMs of a polymorphic CYP would be at higher risk of DDIs relative to EMs for drugs metabolized by both polymorphic and nonpolymorphic CYPs such as etizolam.

Role of CYP2C19 gene polymorphism in acute alcohol withdrawal treatment with loading dose of diazepam in a South Indian population

PURPOSE

Alcohol dependence is a public health problem worldwide, commonly associated with withdrawal symptoms for which diazepam is a frequently used drug. We studied the effect of CYP2C19 gene polymorphisms on diazepam loading dose requirement and time to reversal of acute alcohol withdrawal symptoms. We also studied the influence of the polymorphism in this gene on the persistent symptoms after loading dose of diazepam.

METHODS

Sixty-nine patients who reported to the psychiatry department with symptoms of alcohol withdrawal diagnosed by DSM-IV criteria were included for the study. A 10-mg loading dose of diazepam was administered iv after baseline assessment of withdrawal severity using CIWA-Ar scoring. The patients were assessed for improvement of the symptoms every two hourly and 20 mg oral diazepam was given based on improvement of symptoms. Genotyping for CYP2C19*2, CYP2C19*3 and CYP2C19*17 was done by PCR-RFLP and RT-PCR methods.

RESULTS

The diazepam dose requirement as well as the time required for reversal of acute symptoms was not statistically different among the different genotype groups. Similarly, the frequency of patients with persistent symptoms after successful treatment of the acute episode was not different among the groups. However, the total diazepam dose requirement was influenced by baseline CIWA-Ar scores (adjusted OR 0.21, p = 0.026). In addition, the odds of treatment with a lower dose (10 mg) of diazepam were higher in smokers (adjusted OR 5.22, p = 0.025) and patients with other addiction (adjusted OR 9.26, p = 0.026).

CONCLUSION

We found that CYP2C19 polymorphism did not have any significant effect on the diazepam dose requirement, time duration needed for successful treatment or on the persistent symptoms after loading dose of diazepam in South Indian population. However, diazepam dose requirement was influenced by baseline CIWA-Ar score, smoking status and other comorbid addictions.

Where Failure Is Not an Option -Personalized Medicine in Astronauts

Drug safety and efficacy are highly variable among patients. Most patients will experience the desired drug effect, but some may suffer from adverse drug reactions or gain no benefit. Pharmacogenetic testing serves as a pre-treatment diagnostic option in situations where failure or adverse events should be avoided at all costs. One such situation is human space flight. On the international space station (ISS), a list of drugs is available to cover typical emergency settings, as well as the long-term treatment of common conditions for the use in self-medicating common ailments developing over a definite period. Here, we scrutinized the list of the 78 drugs permanently available at the ISS (year 2014) to determine the extent to which their metabolism may be affected by genetic polymorphisms, potentially requiring genotype-specific dosing or choice of an alternative drug. The purpose of this analysis was to estimate the potential benefit of pharmacogenetic diagnostics in astronauts to prevent therapy failure or side effects.

Effect of variations in treatment regimen and liver cirrhosis on exposure to benzodiazepines during treatment of alcohol withdrawal syndrome

Purpose:

Benzodiazepines (BDZs) are the drugs of choice to prevent the symptoms of alcohol withdrawal syndrome (AWS). Various treatment protocols are published and have been shown to be effective in both office-managed and facility-managed treatment of AWS. The aim of this scientific commentary is to demonstrate the differences in the expected exposure to BDZs during AWS treatment using different treatment regimens available in the literature, in patients with or without alcoholic liver cirrhosis.

Methods:

Diazepam and lorazepam AWS protocols were examined and reviewed in the literature, and blood plasma levels were examined and compared, respectively.

Results:

Considerable variation in the blood levels with the different dosing schedules was found. Because the drugs are metabolized differently, we have also shown that liver disease affects the blood levels of diazepam, but not of lorazepam.

Conclusions:

Differences in treatment regimens, the choice of BDZ, as well as the presence of liver cirrhosis can substantially alter the exposure of patients to drugs used for AWS treatment. Outpatient treatment of AWS has been shown to be relatively safe and effective for the treatment of AWS but patients should be carefully monitored.

Pharmacogenetics in Jewish populations

Spanning over 2000 years, the Jewish population has a long history of migration, population bottlenecks, expansions, and geographical isolation, which has resulted in a unique genetic architecture among the Jewish people. As such, many Mendelian disease genes and founder mutations for autosomal recessive diseases have been discovered in several Jewish groups, which have prompted recent genomic studies in the Jewish population on common disease susceptibility and other complex traits. Although few studies on the genetic determinants of drug response variability have been reported in the Jewish population, a number of unique pharmacogenetic variants have been discovered that are more common in Jewish populations than in other major racial groups. Notable examples identified in the Ashkenazi Jewish (AJ) population include the vitamin K epoxide reductase complex subunit 1 (VKORC1) c.106G>T (p.D36Y) variant associated with high warfarin dosing requirements and the recently reported cytochrome P450 2C19 (CYP2C19) allele, CYP2C19*4B, that harbors both loss-of-function [*4 (c.1A>G)] and increased-function [*17 (c.-806C>T)] variants on the same haplotype. These data are encouraging in that like other ethnicities and subpopulations, the Jewish population likely harbors numerous pharmacogenetic variants that are uncommon or absent in other larger racial groups and ethnicities. In addition to unique variants, common multi-ethnic variants in key drug metabolism genes (e.g., ABCB1, CYP2C8, CYP2C9, CYP2C19, CYP2D6, NAT2) have also been detected in the AJ and other Jewish groups. This review aims to summarize the currently available pharmacogenetics literature and discuss future directions for related research with this unique population.

Brivaracetam single and multiple rising oral dose study in healthy Japanese participants: influence of CYP2C19 genotype

Brivaracetam is a high-affinity synaptic vesicle protein 2A ligand, in phase 3 clinical development for epilepsy. A phase 1, single-center, randomized, double-blind, placebo-controlled, single (2.5-100 mg) and multiple (2.5-50 mg twice daily) rising oral dose study (N01209) was conducted to assess the adverse event profile and pharmacokinetics of brivaracetam in healthy Japanese men, and the influence of the cytochrome P450 (CYP) 2C19 genotype. Plasma and urine were collected serially for analysis of brivaracetam and its three main metabolites: acid, hydroxy and hydroxy acid. Overall, 79/80 randomized participants completed the study. Brivaracetam was generally well tolerated. After single- and multiple-dose administration, brivaracetam was rapidly absorbed, with dose-proportional pharmacokinetics over the dose ranges tested. Steady state was reached after 2 days of repeated dosing. Brivaracetam clearance (averaged across the five single dose levels) was reduced from 0.99 mL/min/kg in homozygous extensive metabolizers (EM; n = 10) to 0.81 mL/min/kg (-18%) in heterozygous EM (n = 17) and 0.70 mL/min/kg (-29%) in poor metabolizers (PM; n = 9). Exposure and urinary excretion of hydroxy metabolite were reduced 10-fold in PM participants, compared with EM participants. Results suggest that brivaracetam is hydroxylated by CYP2C19, but this pathway is minor compared with hydrolysis to the acid metabolite.

Urinary diazepam metabolite distribution in a chronic pain population

Diazepam is often used as an adjuvant to pain therapy. Cytochrome P450 (CYP) 3A4 and 2C19 metabolize diazepam into the active metabolites: nordiazepam, temazepam and oxazepam. Owing to diazepam's side-effect profile, mortality risk and potential for drug-drug interactions with CYP 3A4 and/or CYP 2C19 inhibitors, urine drug testing (UDT) could be a helpful monitoring tool. This was a retrospective data analysis that evaluated urine specimens from pain management practices for the distribution of diazepam metabolites with and without CYP 3A4 and 2C19 inhibitors. Intersubject nordiazepam, temazepam and oxazepam geometric mean fractions were 0.16, 0.34 and 0.47, respectively. Intrasubject geometric mean fractions were 0.157, 0.311 and 0.494, respectively. Sex, but not age or urinary pH, had an effect on metabolite fractions. Methadone significantly increased temazepam and oxazepam urinary fractions via CYP3A4 inhibition, whereas fluoxetine and esomeprazole increased nordiazepam fractions via CYP2C19 inhibition. Although more studies are needed, these results suggest the viability of UDT for increased monitoring for therapy and possible drug-drug interactions.

Pharmacokinetic drug interactions between drugs of abuse and antiretroviral medications: implications and management for clinical practice

Substance abuse and HIV/AIDS are two of the most serious, yet treatable diseases worldwide. Global access to HIV treatment continues to expand. In settings where both active illicit drug use and HIV treatment are concurrent, potentional problematic pharmacokinetic drug interactions may arise and complicate therapy. Clinical case series and carefully controlled pharmacokinetic interaction studies have been conducted between only a few drugs of abuse and approved antiretroviral therapies. Important pharmacokinetic drug interactions have been described for benzodiazepines, 3,4-methylenedioxymethamphetamine, methadone and buprenorphine; however, most have not been studied and few well-controlled studies have been conducted to adequately address the clinical implications of these interactions. The metabolism of drugs of abuse, description of the known interactions, and clinical implications and management of these interactions are reviewed. Certain interactions between drugs of abuse and antiretroviral therapies are known and others are likely based upon shared metabolic pathways. These may result in important clinical consequences. To optimize care, clinicians must be alert, knowledgeable about known and possible interactions and equipped to clinically manage the medical consequences. Moreover, there is considerable need for carefully controlled studies in this important and emerging area.

Sedation for critically ill or injured adults in the intensive care unit: a shifting paradigm

As most critically ill or injured patients will require some degree of sedation, the goal of this paper was to comprehensively review the literature associated with use of sedative agents in the intensive care unit (ICU). The first and selected latter portions of this article present a narrative overview of the shifting paradigm in ICU sedation practices, indications for uninterrupted or prolonged ICU sedation, and the pharmacology of sedative agents. In the second portion, we conducted a structured, although not entirely systematic, review of the available evidence associated with use of alternative sedative agents in critically ill or injured adults. Data sources for this review were derived by searching OVID MEDLINE and PubMed from their first available date until May 2012 for relevant randomized controlled trials (RCTs), systematic reviews and/or meta-analyses and economic evaluations. Advances in the technology of mechanical ventilation have permitted clinicians to limit the use of sedation among the critically ill through daily sedative interruptions or other means. These practices have been reported to result in improved mortality, a decreased length of ICU and hospital stay and a lower risk of drug-associated delirium. However, in some cases, prolonged or uninterrupted sedation may still be indicated, such as when patients develop intracranial hypertension following traumatic brain injury. The pharmacokinetics of sedative agents have clinical importance and may be altered by critical illness or injury, co-morbid conditions and/or drug-drug interactions. Although use of validated sedation scales to monitor depth of sedation is likely to reduce adverse events, they have no utility for patients receiving neuromuscular receptor blocking agents. Depth of sedation monitoring devices such as the Bispectral Index (BIS©) also have limitations. Among existing RCTs, no sedative agent has been reported to improve the risk of mortality among the critically ill or injured. Moreover, although propofol may be associated with a shorter time to tracheal extubation and recovery from sedation than midazolam, the risk of hypertriglyceridaemia and hypotension is higher with propofol. Despite dexmedetomidine being linked with a lower risk of drug-associated delirium than alternative sedative agents, this drug increases risk of bradycardia and hypotension. Among adults with severe traumatic brain injury, there are insufficient data to suggest that any single sedative agent decreases the risk of subsequent poor neurological outcomes or mortality. The lack of examination of confounders, including the type of healthcare system in which the investigation was conducted, is a major limitation of existing pharmacoeconomic analyses, which likely limits generalizability of their results.

Individualized therapy for gastroesophageal reflux disease: potential impact of pharmacogenetic testing based on CYP2C19

The main therapeutic agent for gastroesophageal reflux disease (GERD) is a proton pump inhibitor (PPI). Plasma levels and the acid inhibitory effect of PPIs depend on the activity of cytochrome P450 (CYP) 2C19, which is polymorphic. Genotypes of CYP2C19 are classified into three groups: rapid metabolizers (RMs: *1/*1), intermediate metabolizers (IMs: *1/*X), and poor metabolizers (PMs: *X/*X), where *1 and X represent the wild type and the mutant allele, respectively. RMs include ultra-rapid metabolizers, who possess the CYP2C19*17 allele. The pharmacokinetics and pharmacodynamics of PPIs differ among different CYP2C19 genotype groups. Plasma PPI levels and intragastric pH values during PPI treatment are lowest in the RM group, intermediate in the IM group, and highest in the PM group. These CYP2C19-genotype-dependent differences in the pharmacokinetics and pharmacodynamics of PPIs influence the healing and recurrence of GERD during PPI treatment, suggesting the need for CYP2C19 genotype-based tailored therapy for GERD. CYP2C19 pharmacogenetics should be taken into consideration for the personalization of PPI-based therapy. However, the clinical usefulness of CYP2C19 genotype testing in GERD therapy should be verified in clinical studies.

Individualized therapy for gastroesophageal reflux disease: potential impact of pharmacogenetic testing based on CYP2C19

The main therapeutic agent for gastroesophageal reflux disease (GERD) is a proton pump inhibitor (PPI). Plasma levels and the acid inhibitory effect of PPIs depend on the activity of cytochrome P450 (CYP) 2C19, which is polymorphic. Genotypes of CYP2C19 are classified into three groups: rapid metabolizers (RMs: *1/*1), intermediate metabolizers (IMs: *1/*X), and poor metabolizers (PMs: *X/*X), where *1 and X represent the wild type and the mutant allele, respectively. RMs include ultra-rapid metabolizers, who possess the CYP2C19*17 allele. The pharmacokinetics and pharmacodynamics of PPIs differ among different CYP2C19 genotype groups. Plasma PPI levels and intragastric pH values during PPI treatment are lowest in the RM group, intermediate in the IM group, and highest in the PM group. These CYP2C19-genotype-dependent differences in the pharmacokinetics and pharmacodynamics of PPIs influence the healing and recurrence of GERD during PPI treatment, suggesting the need for CYP2C19 genotype-based tailored therapy for GERD. CYP2C19 pharmacogenetics should be taken into consideration for the personalization of PPI-based therapy. However, the clinical usefulness of CYP2C19 genotype testing in GERD therapy should be verified in clinical studies.

Drug delivery system for poorly water-soluble compounds using lipocalin-type prostaglandin D synthase

Lipocalin-type prostaglandin D synthase (L-PGDS) is a member of the lipocalin superfamily and a secretory lipid-transporter protein, which binds a wide variety of hydrophobic small molecules. Here we show the feasibility of a novel drug delivery system (DDS), utilizing L-PGDS, for poorly water-soluble compounds such as diazepam (DZP), a major benzodiazepine anxiolytic drug, and 6-nitro-7-sulfamoylbenzo[f]quinoxaline-2,3-dione (NBQX), an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist and anticonvulsant. Calorimetric experiments revealed for both compounds that each L-PGDS held three molecules with high binding affinities. By mass spectrometry, the 1:3 complex of L-PGDS and NBQX was observed. L-PGDS of 500μM increased the solubility of DZP and NBQX 7- and 2-fold, respectively, compared to PBS alone. To validate the potential of L-PGDS as a drug delivery vehicle in vivo, we have proved the prospective effects of these compounds via two separate delivery strategies. First, the oral administration of a DZP/L-PGDS complex in mice revealed an increased duration of pentobarbital-induced loss of righting reflex. Second, the intravenous treatment of ischemic gerbils with NBQX/L-PGDS complex showed a protective effect on delayed neuronal cell death at the hippocampal CA1 region. We propose that our novel DDS could facilitate pharmaceutical development and clinical usage of various water-insoluble compounds.

Identification of CYP2C19*4B: pharmacogenetic implications for drug metabolism including clopidogrel responsiveness

CYP2C19 is a principal enzyme involved in the bioactivation of the antiplatelet prodrug clopidogrel and common CYP2C19 loss-of-function alleles are associated with adverse cardiovascular events. To assess the impact of the CYP2C19*17 increased activity allele in the Ashkenazi Jewish (AJ) and Sephardi Jewish (SJ) populations and to determine the frequencies of additional variant alleles, 250 AJ and 135 SJ individuals were genotyped for CYP2C19*2-*10, *12-*17, *22 and P-glycoprotein (ABCB1) c.3435C>T. Importantly, CYP2C19*4, a loss-of-function allele, was identified in linkage disequilibrium with *17. This novel haplotype, designated CYP2C19*4B, significantly alters the interpretation of CYP2C19 genotyping when testing *17. Moreover, genotyping CYP2C19*17 changed the frequency of extensive metabolizers from ∼70 to ∼40%, reclassifying ∼30% as ultrarapid metabolizers. Combining CYP2C19 and ABCB1 identified ∼1 in 3 AJ and ∼1 in 2 SJ individuals at increased risk for adverse responses to clopidogrel. These data underscore the importance of including *4B and *17 when clinically genotyping CYP2C19.

Enhancement of GABAergic activity: neuropharmacological effects of benzodiazepines and therapeutic use in anesthesiology

GABA is the major inhibitory neurotransmitter in the central nervous system (CNS). The type A GABA receptor (GABA(A)R) system is the primary pharmacological target for many drugs used in clinical anesthesia. The α1, β2, and γ2 subunit-containing GABA(A)Rs located in the various parts of CNS are thought to be involved in versatile effects caused by inhaled anesthetics and classic benzodiazepines (BZD), both of which are widely used in clinical anesthesiology. During the past decade, the emergence of tonic inhibitory conductance in extrasynaptic GABA(A)Rs has coincided with evidence showing that these receptors are highly sensitive to the sedatives and hypnotics used in anesthesia. Anesthetic enhancement of tonic GABAergic inhibition seems to be preferentially increased in regions shown to be important in controlling memory, awareness, and sleep. This review focuses on the physiology of the GABA(A)Rs and the pharmacological properties of clinically used BZDs. Although classic BZDs are widely used in anesthesiological practice, there is a constant need for new drugs with more favorable pharmacokinetic and pharmacodynamic effects and fewer side effects. New hypnotics are currently developed, and promising results for one of these, the GABA(A)R agonist remimazolam, have recently been published.

[Human toxicokinetic of hexobarbital after acute multi-drug intoxication]

A 33-year-old man was hospitalized unconscious on suspicion of acute diazepam and hexobarbital intoxication, a barbiturate not marketed in France. Its quantification was developed by gas chromatography coupled with mass spectrometry detection and validated on one-hundred microL of plasma extracted by a liquid/liquid method. Hexobarbital and diazepam concentrations in initial plasma samples were at toxic levels, respectively 15 900 ng/mL and 13 800 ng/mL. Hexobarbital toxicokinetic was studied during 175 h and analysed with a non-compartmental model. Half-life value of 61,8 h was found, being much longer than already published hexobarbital half-lives (between 3.2 h and 6.9 h). The reasons of this long half-life were discussed according to metabolism and pharmacogenetic.

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.

Perioperative genomic profiles using structure-specific oligonucleotide probes

OBJECTIVES

Many complications in the perioperative interval are associated with genetic susceptibilities that may be unknown in advance of surgery and anesthesia, including drug toxicity and inefficacy, thrombosis, prolonged neuromuscular blockade, organ failure and sepsis. The aims of this study were to design and validate the first genetic testing platform and panel designed for use in perioperative care, to establish allele frequencies in a target population, and to determine the number of mutant alleles per patient undergoing surgery. DESIGN/SETTING/PARTICIPANTS AND METHODS: One hundred fifty patients at Marshfield Clinic, Marshfield, Wisconsin, 100 patients at the Medical College of Wisconsin Zablocki Veteran's Administration Medical Center, Milwaukee, Wisconsin, and 200 patients at the University of Wisconsin Hospitals and Clinics, Madison, Wisconsin undergoing surgery and anesthesia were tested for 48 polymorphisms in 22 genes including ABC, BChE, ACE, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5, beta2AR, TPMT, F2, F5, F7, MTHFR, TNFalpha, TNFbeta, CCR5, ApoE, HBB, MYH7, ABO and Gender (PRKY, PFKFB1). Using structure-specific cleavage of oligonucleotide probes (Invader, Third Wave Technologies, Inc., Madison, WI), 96-well plates were configured so that each well contained reagents for detection of both the wild type and mutant alleles at each locus.

RESULTS

There were 21,600 genotypes confirmed in duplicate. After withdrawal of polymorphisms in non-pathogenic genes (i.e., the ABO blood group and gender-specific alleles), 376 of 450 patients were found to be homozygous for mutant alleles at one or more loci. Modes of two mutant homozygous loci and 10 mutant alleles in aggregate (i.e., the sum of homozygous and heterozygous mutant polymorphisms) were observed per patient.

CONCLUSIONS

Significant genetic heterogeneity that may not be accounted for by taking a family medical history, or by obtaining routine laboratory test results, is present in most patients presenting for surgery and may be detected using a newly developed genotyping platform.

Drug interaction studies with dexlansoprazole modified release (TAK-390MR), a proton pump inhibitor with a dual delayed-release formulation: results of four randomized, double-blind, crossover, placebo-controlled, single-centre studies

BACKGROUND AND OBJECTIVE

Most proton pump inhibitors are extensively metabolized by cytochrome P450 (CYP) isoenzymes, as are many other drugs, giving rise to potential drug-drug interactions. Dexlansoprazole modified release (MR) [TAK-390MR] is a modified-release formulation of dexlansoprazole (TAK-390), an enantiomer of lansoprazole, which employs an innovative Dual Delayed Release technology designed to prolong the plasma dexlansoprazole concentration-time profile following once-daily oral administration. As with lansoprazole, dexlansoprazole is metabolized mainly by CYP3A and CYP2C19. Based on in vitro studies, dexlansoprazole has the potential to inhibit activity of these isoenzymes and also may induce human hepatic CYP1A and CYP2C9 activity. To determine whether dexlansoprazole has an effect on these isoenzymes in vivo, drug interaction studies with dexlansoprazole MR were conducted.

METHODS

Four separate randomized, double-blind, two-way crossover, placebo-controlled, single-centre studies were conducted in healthy volunteers to evaluate the effect of dexlansoprazole on the pharmacokinetics of four test substrates (diazepam, phenytoin, theophylline [administered as intravenous aminophylline] and warfarin), which were selected based on in vitro and/or in vivo data that suggest a potential drug interaction with CYP isoenzymes or potentially coadministered narrow therapeutic index drugs. In each study, dexlansoprazole MR 90 mg or placebo was administered once daily for 9 or 11 days in each period. Subjects received a single dose of test substrate in each study period. Pharmacokinetic parameters of the test substrates were estimated using noncompartmental methods. A conclusion of no effect of dexlansoprazole MR on the test substrate was made if the 90% confidence intervals (CIs) for the ratios of the central values for the observed maximum plasma drug concentration (C(max)) and the area under the plasma concentration-time curve (AUC) of test substrate administered with dexlansoprazole MR versus placebo were within 0.80-1.25 based on an analysis of variance model. The potential for a pharmacodynamic interaction was also assessed for warfarin using prothrombin time, measured as the international normalized ratio. Routine safety assessments were conducted in these studies.

RESULTS

Mean C(max) and AUC values were generally similar for each test substrate when administered with multiple once-daily doses of dexlansoprazole MR or placebo. The 90% CIs for the bioavailability of these test substrates administered with dexlansoprazole MR relative to that obtained when the substrates were administered with placebo were within the bioequivalency range of 0.80-1.25, indicating that multiple doses of dexlansoprazole MR had no effect on the pharmacokinetics of these drugs. Additionally, dexlansoprazole MR had no effect on the pharmacodynamics of warfarin. Administration of these drugs with dexlansoprazole MR 90 mg or placebo was well tolerated; the only serious adverse event, which led to a subject's discontinuation from the study, was considered unrelated to study drugs.

CONCLUSIONS

Coadministration of dexlansoprazole MR with diazepam, phenytoin or theophylline did not affect the pharmacokinetics of these drugs, and therefore is unlikely to alter the pharmacokinetic profile of other drugs metabolized by CYP2C19, CYP2C9, CYP1A2 and perhaps CYP3A. Additionally, dexlansoprazole MR coadministered with warfarin did not affect the pharmacokinetics of the warfarin enantiomers and had no effect on the anticoagulant activity of warfarin. Dexlansoprazole MR was well tolerated in these trials of healthy subjects.

Pharmacogenetic testing in psychiatry: a review of features and clinical realities

This article focuses on the first generation of pharmacogenetic tests that are potentially useful in psychiatry. All pharmacogenetic tests currently on the market, or soon to be marketed in psychiatry, for which some information has been published in peer-reviewed journal articles (or abstracts), were selected. Five pharmacogenetic tests are reviewed in detail: the Roche AmpliChip CYP450 Test, the Luminex Tag-It Mutation Detection Kit, the LGC clozapine response test, the PGxPredict: Clozapine test, and the Genomas PhyzioType system. After reviewing these tests, three practical aspects of implementing pharmacogenetic testing in psychiatric clinical practice are briefly reviewed: (1) the evaluation of these tests in clinical practice, (2) cost-effectiveness, and (3) regulatory oversight. Finally, the future of these and other pharmacogenetic tests in psychiatry is discussed.

Comparison of model-based tests and selection strategies to detect genetic polymorphisms influencing pharmacokinetic parameters

We evaluate by simulation three model-based methods to test the influence of a single nucleotide polymorphism on a pharmacokinetic parameter of a drug: analysis of variance (ANOVA) on the empirical Bayes estimates of the individual parameters, likelihood ratio test between models with and without genetic covariate, and Wald tests on the parameters of the model with covariate. Analyses are performed using the FO and FOCE method implemented in the NONMEM software. We compare several approaches for model selection based on tests and global criteria. We illustrate the results with pharmacokinetic data on indinavir from HIV-positive patients included in COPHAR 2-ANRS 111 to study the gene effect prospectively. Only the tests based on the EBE obtain an empirical type I error close to the expected 5%. The approximation made with the FO algorithm results in a significant inflation of the type I error of the LRT and Wald tests.

DNA microarray technology in the clinical environment: the AmpliChip CYP450 test for CYP2D6 and CYP2C19 genotyping

INTRODUCTION

An important technological advance in genetic testing is the DNA microarray, which allows for the simultaneous testing of thousands of DNA sequences. The AmpliChip CYP450 Test employs this microarray technology for cytochrome P450 (CYP) 2D6 and CYP2C19 genotyping. Isoenzymes encoded by these genes are responsible for the metabolism of many widely prescribed drugs. The objectives of this study were to identify CYP2D6 and CYP2C19 alleles and phenotypes in a psychiatric patient population in Kentucky, and to describe practical issues associated with DNA microarray technology.

METHODS

A total of 4,532 psychiatric patients were recruited from three state hospitals in Kentucky. Whole blood, buccal swabs, or saliva samples were genotyped with the AmpliChip CYP450 Test to derive a predicted phenotype.

RESULTS

In this cohort, the overall prevalence of CYP2D6 poor metabolizers was 7.6% (95% CI 7%, 8.3%), 8.2% in the Caucasians (95% CI 7.4%, 9.%) and 1.8% in the African Americans (95% CI 0.9%, 3.5%). The overall prevalence of CYP2D6 ultrarapid metabolizers was 1.5% (95% CI 1.2%, 1.9%), 1.5% in the Caucasians (95% CI 1.1%, 1.9%) and 2.0% in the African Americans (95% CI 1.1%, 3.7%). The overall prevalence of CYP2C19 poor metabolizers was 2.0% (95% CI 1.8%, 2.7%), 2.2% in Caucasians (95% CI 1.6%, 2.5%) and 4.0% in African Americans (95% CI 2.6%, 6.1%).

CONCLUSION

We also propose a numeric system for expression of CYP2D6 and CYP2C19 enzyme activity to aid clinicians in determining treatment strategy for patients receiving therapeutics that are metabolized by the CYP2D6 or CYP2C19 gene products.

CYP2C9, CYP2C19 and CYP2D6 allele frequencies in the Ashkenazi Jewish population

OBJECTIVE

To determine and compare the cytochrome P450 (CYP)2C9, CYP2C19 and CYP2D6 allele and genotype frequencies in the Ashkenazi Jewish (AJ) population with other populations.

METHODS

CYP2C9, CYP2C19 and CYP2D6 genotypes were determined in 250 anonymous, unrelated, healthy AJ individuals from the greater New York (USA) metropolitan area. Genotyping was performed using the Tag-Ittrade mark Mutation Detection system and the recently redefined CYP2D6*41A allele was identified by a restriction fragment length polymorphism assay.

RESULTS

Among the 250 AJ individuals, the CYP2C9*1, *2, *3 and *5 allele frequencies were 0.772, 0.140, 0.086 and 0.002, respectively, and the genotypes were distributed into extensive- (60.8%), intermediate- (32.8%) and poor- (6.4%) metabolizer phenotypes. The CYP2C19*1, *2 and *4 allele frequencies were 0.830, 0.152 and 0.018, respectively, and the genotypes were distributed into extensive (69.2%), intermediate (27.6%) and poor (3.2%) metabolizers. The most common CYP2D6 alleles identified were *1, *2A, *4 and *41A, and their frequencies were 0.286 0.152 0.226 and 0.140, respectively. The CYP2D6 genotypes were distributed into ultrarapid- (8.8%), extensive- (70.0%), intermediate- (16.0%) and poor- (5.2%) metabolizer phenotypes.

CONCLUSION

Although the CYP2C9 allele and genotype frequencies in the AJ subjects were similar to those in other North American Caucasian populations, genotyping the CYP2C19*4 and CYP2D6*41A alleles in the AJ population resulted in the clinically relevant reclassification of the predicted metabolizer phenotypes. Inclusion of CYP2C19*4 reclassified individuals from either extensive- or intermediate- to the intermediate- or poor-metabolizer phenotypes, respectively. Inclusion of the redefined CYP2D6*41A allele increased the ultrarapid-, intermediate- and poor-metabolizer phenotype combined frequencies to 30%, indicating that approximately one in three AJ individuals may benefit from genotype-based drug selection and dosage. In addition, the ultrarapid CYP2D6 genotype frequency in the AJ population (8.8%) was approximately twofold higher than that in other North American Caucasians.

Influence of cytochrome P450 polymorphisms on drug therapies: pharmacogenetic, pharmacoepigenetic and clinical aspects

The polymorphic nature of the cytochrome P450 (CYP) genes affects individual drug response and adverse reactions to a great extent. This variation includes copy number variants (CNV), missense mutations, insertions and deletions, and mutations affecting gene expression and activity of mainly CYP2A6, CYP2B6, CYP2C9, CYP2C19 and CYP2D6, which have been extensively studied and well characterized. CYP1A2 and CYP3A4 expression varies significantly, and the cause has been suggested to be mainly of genetic origin but the exact molecular basis remains unknown. We present a review of the major polymorphic CYP alleles and conclude that this variability is of greatest importance for treatment with several antidepressants, antipsychotics, antiulcer drugs, anti-HIV drugs, anticoagulants, antidiabetics and the anticancer drug tamoxifen. We also present tables illustrating the relative importance of specific common CYP alleles for the extent of enzyme functionality. The field of pharmacoepigenetics has just opened, and we present recent examples wherein gene methylation influences the expression of CYP. In addition microRNA (miRNA) regulation of P450 has been described. Furthermore, this review updates the field with respect to regulatory initiatives and experience of predictive pharmacogenetic investigations in the clinics. It is concluded that the pharmacogenetic knowledge regarding CYP polymorphism now developed to a stage where it can be implemented in drug development and in clinical routine for specific drug treatments, thereby improving the drug response and reducing costs for drug treatment.

Voriconazole and fluconazole increase the exposure to oral diazepam

OBJECTIVE

We assessed the effect of voriconazole and fluconazole on the pharmacokinetics and pharmacodynamics of diazepam.

METHODS

Twelve healthy volunteers took 5 mg of oral diazepam in a randomised order on three study sessions: without pretreatment, after oral voriconazole 400 mg twice daily on the first day and 200 mg twice daily on the second day, or after oral fluconazole 400 mg on the first day and 200 mg on the second day. Plasma concentrations of diazepam and N-desmethyldiazepam were determined for up to 48 h. Pharmacodynamic variables were measured for 12 h.

RESULTS

In the voriconazole phase, the area under the plasma concentration time curve (AUC 0-infinity) of diazepam was increased (geometric mean ratio) 2.2-fold (p < 0.05; 90% confidence interval [CI] 1.56 to 2.82). This was associated with the prolongation of the mean elimination half-life (t(1/2)) from 31 h to 61 h (p < 0.01) after voriconazole. In the fluconazole phase, the AUC 0-infinity of diazepam was increased 2.5-fold (p < 0.01; 90% CI 1.94 to 3.40), and the t(1/2) was prolonged from 31 h to 73 h (p < 0.001). The peak plasma concentration of diazepam was practically unchanged by voriconazole and fluconazole. The pharmacodynamics of diazepam were changed only modestly.

CONCLUSION

Both voriconazole and fluconazole considerably increase the exposure to diazepam. Recurrent administration of diazepam increases the risk of clinically significant interactions during voriconazole or fluconazole treatment, because the elimination of diazepam is impaired significantly.

CYP2C19 polymorphism in Korean patients on warfarin therapy

This study was designed to assess the effect of CYP2C19 polymorphism on warfarin dosage requirements and bleeding complications in the Korean population. Patients were placed into one of four groups according to the dose of warfarin they received and the presence of bleeding complications: regular dose control, regular dose bleeding, low dose control, and low dose bleeding. Genotyping for CYP2C19*2 and CYP2C19*3 was performed by the restriction fragment length polymorphism method for each patient and each study group. The measured internal normalized ratio (INR) in each dose group was similar even though the administered dosage was significantly different. A total of 66 patients were evaluated for CYP2C19 polymorphism. Among them 25 patients (37.9%) were homozygous wild type. Four patients (6.1%) had heterozygous mutations at both loci. Others had mutations on either the CYP2C19*2 or *3 locus. Higher genetic variation was observed in CYP2C19*2 than in CYP2C19*3 among Korean patients on warfarin therapy. Our data suggested that there is a higher incidence of bleeding complications in patients who have a higher allele frequency of CYP2C19. It was also revealed that the distribution of CYP2C19 polymorphism among Asian populations is more similar than of the distribution among Caucasian populations.

The role of pharmacogenetics in the metabolism of antiepileptic drugs: pharmacokinetic and therapeutic implications

Several different factors, including pharmacogenetics, contribute to interindividual variability in drug response. Like most other agents, many antiepileptic drugs (AEDs) are metabolised by a variety of enzymatic reactions, and the cytochrome P450 (CYP) superfamily has attracted considerable attention. Some of those CYPs exist in the form of genetic (allelic) variants, which may also affect the plasma concentrations or drug exposure (area under the plasma concentration-time curve [AUC]) of AEDs. With regard to the metabolism of AEDs, the polymorphic CYP2C9 and CYP2C19 are of interest. This review summarises the evidence as to whether such polymorphisms affect the clinical action of AEDs. In the case of mephenytoin, defects in its metabolism may be attributable to >10 mutated alleles (designated as *2, *3 and others) of the gene expressing CYP2C19. Consequently, poor metabolisers (PMs) and extensive metabolisers (EMs) could be differentiated, whose frequencies vary among ethnic populations. CYP2C19 contributes to the metabolism of diazepam and phenytoin, the latter drug also representing a substrate of CYP2C9, with its predominant variants being defined as *2 and *3. For both AEDs, there is maximally a 2-fold difference in the hepatic elimination rate (e.g. clearance) or the AUC between the extremes of EMs and PMs which, in the case of phenytoin (an AED with a narrow 'therapeutic window'), would suggest a dosage reduction only for patients who are carriers of mutated alleles of both CYP2C19 and CYP2C9, a subgroup that is very rare among Caucasians (about 1% of the population) but more frequent in Asians (about 10%). The minor contribution of CYP2C19 to the metabolism of phenobarbital (phenobarbitone) can be overlooked. In rare cases, valproic acid can be metabolised to the reactive (hepatotoxic) metabolite, 4-ene-valproic acid. It is not yet clear whether genetic variants of the involved enzyme (CYP2C9) are responsible for this problem. Likewise, the active metabolite of carbamazepine, carbamazepine-10,11-epoxide, is transformed by the microsomal epoxide hydrolase, an enzyme that is also highly polymorphic, but the pharmacokinetic and clinical consequences still need to be evaluated. Pharmacogenetic investigations have increased our general knowledge of drug disposition and action. As for old and especially new AEDs the pharmacogenetic influence on their metabolism is not very striking, it is not surprising that there are no treatment guidelines taking pharmacogenetic data into account. Therefore, the traditional and validated therapeutic drug monitoring approach, representing a direct 'phenotype' assessment, still remains the method of choice when an individualised dosing regimen is anticipated. Nevertheless, pharmacogenetics and pharmacogenomics can offer some novel contributions when attempts are made to maximise drug efficacy and enhance drug safety.