Influence of CYP2C9 and CYP2C19 genetic polymorphisms on pharmacokinetics of gliclazide MR in Chinese subjects

A web-based scoping review assessing the influence of smoking and smoking cessation on antidiabetic drug meabolism: implications for medication efficacy

Currently 1.3 billion individuals globally engage in smoking, leading to significant morbidity and mortality, particularly among diabetic patients. There is urgent need for a better understanding of how smoking influences antidiabetic treatment efficacy. The review underscores the role of cigarette smoke, particularly polycyclic aromatic hydrocarbons (PAHs), in modulating the metabolic pathways of antidiabetic drugs, primarily through the induction of cytochrome P450 (CYP450) enzymes and uridine diphosphate (UDP)-glucuronosyltransferases (UGTs), thus impacting drug pharmacokinetics and therapeutic outcomes. Furthermore, the review addresses the relatively uncharted territory of how smoking cessation influences diabetes treatment, noting that cessation can lead to significant changes in drug metabolism, necessitating dosage adjustments. Special attention is given to the interaction between smoking cessation aids and antidiabetic medications, a critical area for patient safety and effective diabetes management. This scoping review aims to provide healthcare professionals with the knowledge to better support diabetic patients who smoke or are attempting to quit, ensuring tailored and effective treatment strategies. It also identifies gaps in current research, advocating for more studies to fill these voids, thereby enhancing patient care and treatment outcomes for this at-risk population.

The impact of gene polymorphism and hepatic insufficiency on voriconazole dose adjustment in invasive fungal infection individuals

Voriconazole (VRZ) is a broad-spectrum antifungal medication widely used to treat invasive fungal infections (IFI). The administration dosage and blood concentration of VRZ are influenced by various factors, posing challenges for standardization and individualization of dose adjustments. On the one hand, VRZ is primarily metabolized by the liver, predominantly mediated by the cytochrome P450 (CYP) 2C19 enzyme. The genetic polymorphism of CYP2C19 significantly impacts the blood concentration of VRZ, particularly the trough concentration (Ctrough), thereby influencing the drug's efficacy and potentially causing adverse drug reactions (ADRs). Recent research has demonstrated that pharmacogenomics-based VRZ dose adjustments offer more accurate and individualized treatment strategies for individuals with hepatic insufficiency, with the possibility to enhance therapeutic outcomes and reduce ADRs. On the other hand, the security, pharmacokinetics, and dosing of VRZ in individuals with hepatic insufficiency remain unclear, making it challenging to attain optimal Ctrough in individuals with both hepatic insufficiency and IFI, resulting in suboptimal drug efficacy and severe ADRs. Therefore, when using VRZ to treat IFI, drug dosage adjustment based on individuals' genotypes and hepatic function is necessary. This review summarizes the research progress on the impact of genetic polymorphisms and hepatic insufficiency on VRZ dosage in IFI individuals, compares current international guidelines, elucidates the current application status of VRZ in individuals with hepatic insufficiency, and discusses the influence of CYP2C19, CYP3A4, CYP2C9, and ABCB1 genetic polymorphisms on VRZ dose adjustments and Ctrough at the pharmacogenomic level. Additionally, a comprehensive summary and analysis of existing studies' recommendations on VRZ dose adjustments based on CYP2C19 genetic polymorphisms and hepatic insufficiency are provided, offering a more comprehensive reference for dose selection and adjustments of VRZ in this patient population.

Effects of CYP2C9 and CYP2C19 genetic polymorphisms on the pharmacokinetics and pharmacodynamics of gliclazide in healthy subjects

Gliclazide metabolism is mediated by genetically polymorphic CYP2C9 and CYP2C19 enzymes. We investigated the effects of CYP2C9 and CYP2C19 genetic polymorphisms on the pharmacokinetics and pharmacodynamics of gliclazide. Twenty-seven Korean healthy volunteers were administered a single oral dose of gliclazide 80 mg. The plasma concentration of gliclazide was quantified for the pharmacokinetic analysis and plasma concentrations of glucose and insulin were measured as pharmacodynamic parameters. The pharmacokinetics of gliclazide showed a significant difference according to the number of defective alleles of combined CYP2C9 and CYP2C19. The two defective alleles group (group 3) and one defective allele group (group 2) showed 2.34- and 1.46-fold higher AUC_0-∞ (P < 0.001), and 57.1 and 32.3% lower CL/F (P < 0.001), compared to those of the no defective allele group (group 1), respectively. The CYP2C9IM-CYP2C19IM group had AUC_0-∞ increase of 1.49-fold (P < 0.05) and CL/F decrease by 29.9% (P < 0.01), compared with the CYP2C9 Normal Metabolizer (CYP2C9NM)-CYP2C19IM group. The CYP2C9NM-CYP2C19PM group and CYP2C9NM-CYP2C19IM group showed 2.41- and 1.51-fold higher AUC_0-∞ (P < 0.001), and 59.6 and 35.4% lower CL/F (P < 0.001), compared to those of the CYP2C9NM-CYP2C19NM group, respectively. The results represented that CYP2C9 and CYP2C19 genetic polymorphisms significantly affected the pharmacokinetics of gliclazide. Although the genetic polymorphism of CYP2C19 had a greater effect on the pharmacokinetics of gliclazide, the genetic polymorphism of CYP2C9 also had a significant effect. On the other hand, plasma glucose and insulin responses to gliclazide were not significantly affected by the CYP2C9-CYP2C19 genotypes, requiring further well-controlled studies with long-term dosing of gliclazide in diabetic patients.

Machine-learning models utilizing CYP3A4*1G show improved prediction of hypoglycemic medication in Type 2 diabetes

The effectiveness and side effects of Type 2 diabetes (T2D) medication are related to individual genetic background. SNPs CYP3A4 and CYP2C19 were introduced to machine-learning models to improve the performance of T2D medication prediction. Two multilabel classification models, ML-KNN and WRank-SVM, trained with clinical data and CYP3A4/ CYP2C19 SNPs were evaluated. Prediction performance was evaluated with Hamming loss, one-error, coverage, ranking loss and average precision. The average precision of ML-KNN and WRank-SVM using clinical data was 92.74% and 92.9%, respectively. Combined with CYP2C19*2*3, the average precision dropped to 88.84% and 89.93%, respectively. While combined with CYP3A4*1G, the average precision was enhanced to 97.96% and 97.82%, respectively. Results suggest that CYP3A4*1G can improve the performance of ML-KNN and WRank-SVM models in predicting T2D medication performance.

Effects of CYP2C19, CYP2C9 and CYP3A4 gene polymorphisms on plasma voriconazole levels in Chinese pediatric patients

OBJECTIVES

Voriconazole is the most commonly used antifungal agent in clinical application. Previous studies suggested that voriconazole was extensively metabolized by CYP450 enzyme system, including CYP2C19, CYP2C9 and CYP3A4, which contributed to the individual variability of the pharmacokinetic process of voriconazole. This study aimed to investigate the effects of CYP2C19, CYP2C9 and CYP3A4 gene polymorphisms on plasma voriconazole concentrations in Chinese pediatric patients.

METHODS

This study prospectively evaluated pediatric patients administrating voriconazole for the treatment or prophylaxis of invasive fungal infections from October 2018 to July 2020. Seven single-nucleotide polymorphisms in CYP2C19 (CYP2C19*2, CYP2C19*3, and CYP2C19*17), CYP2C9 (CYP2C9*3, CYP2C9*13) and CYP3A4 (CYP3A4*22, rs4646437) were detected by real-time fluorescent PCR with TaqMan probes. The voriconazole trough plasma concentration was determined by UPLC-MS/MS.

RESULTS

A total of 68 pediatric patients were enrolled in this study. Our results showed that voriconazole plasma concentrations of patients with CYP2C19*2 or CYP2C19*3 allele were significantly higher than that with wild-type carriers (P < 0.0001, P = 0.004, respectively). However, CYP2C9*3 and CYP3A4 rs4646437 were not significantly associated with voriconazole plasma levels. The CYP2C19*17, CYP2C9*13 and CYP3A4*22 alleles were not observed in our study. Additionally, multiple linear regression analysis indicated that CYP2C19*2 and CYP2C19*3 alleles remained predictors of voriconazole plasma concentration (r2 = 0.428; P < 0.0001). For CYP2C19 metabolizer phenotype, trough concentration of voriconazole was significantly lower in NM group compared with IM (P < 0.0001) and PM (P = 0.004) groups.

CONCLUSION

Voriconazole plasma levels in pediatric patients are mainly affected by CYP2C19 gene polymorphisms.

The role of sulfonylureas in the treatment of type 2 diabetes

INTRODUCTION

Type 2 diabetes (T2D) is increasingly prevalent and associated with increased risk for cardiovascular and renal disease. After lifestyle modification, metformin is usually the first-line pharmacotherapy and sulfonylureas are traditionally added after metformin failure. However, with newer glucose lowering drugs that may have less risk of hypoglycemia or that may reduce cardiovascular and renal events, the position of sulfonylureas is being reevaluated.

AREAS COVERED

In this article, the authors review relevant publications related to the use of sulfonylureas.

EXPERT OPINION

Sulfonylureas are potent glucose lowering drugs. The risk of hypoglycemia varies with different drugs within the class and can be minimized by using the safer drugs, possibly in lower doses. Cardiovascular events do not appear to be increased with some of the newer generation drugs. The durability of glycemic control also appears comparable to other newer agents. Sulfonylureas are the preferred treatment for some types of monogenic diabetes and selection of T2D patients who may have greater benefit from sulfonylureas based on certain phenotypes and genotypes is likely to be refined further by precision medicine. Sulfonylureas are inexpensive and readily available everywhere and they are still the most frequently used second-line treatment for T2D in many parts of the world.

CYP2C19 Loss-of-function Polymorphisms are Associated with Reduced Risk of Sulfonylurea Treatment Failure in Chinese Patients with Type 2 Diabetes

Sulfonylureas (SUs) are predominantly metabolized by cytochrome p450 2C9 (CYP2C9) and cytochrome p450 2C19 (CYP2C19) enzymes. CYP2C9 polymorphisms are associated with greater treatment response and hypoglycemic risk in SU users. However, there are no large scale pharmacogenetic studies investigating the effect of loss‐of‐function alleles CYP2C19*2 and CYP2C19*3, which occur frequently in East Asians. Retrospective pharmacogenetic analysis was performed in 11,495 genotyped patients who were enrolled in the Hong Kong Diabetes Register between 1995 and 2017, with follow‐up to December 31, 2019. The associations of CYP2C19 polymorphisms with SU treatment failure, early HbA1c response, and severe hypoglycemia were analyzed by Cox regression or logistic regression assuming an additive genetic model. There were 2341 incident SU users that were identified (mean age 59 years, median diabetes duration 9 years), of which 324 were CYP2C19 poor metabolizers (CYP2C19 *2/*2 or *2/*3 or *3/*3). CYP2C19 poor metabolizers had lower risk of SU treatment failure (hazard ratio 0.83, 95% confidence interval (CI) 0.72–0.97, P = 0.018) and were more likely to reach the HbA1c treatment target < 7% (odds ratio 1.52, 95% CI 1.02–2.27, P = 0.039) than wild‐type carriers (CYP2C19 *1/*1) following adjustment for multiple covariates. There were no significant differences in severe hypoglycemia rates among different CYP2C19 genotype groups. CYP2C19 polymorphisms should be considered during personalization of SU therapy.

Interaction between Omeprazole and Gliclazide in Relation to CYP2C19 Phenotype

The antidiabetic drug gliclazide is partly metabolized by CYP2C19, the main enzyme involved in omeprazole metabolism. The aim of the study was to explore the interaction between omeprazole and gliclazide in relation to CYP2C19 phenotype using physiologically based pharmacokinetic (PBPK) modeling approach. Developed PBPK models were verified using in vivo pharmacokinetic profiles obtained from a clinical trial on omeprazole-gliclazide interaction in healthy volunteers, CYP2C19 normal/rapid/ultrarapid metabolizers (NM/RM/UM). In addition, the association of omeprazole cotreatment with gliclazide-induced hypoglycemia was explored in 267 patients with type 2 diabetes (T2D) from the GoDARTS cohort, Scotland. The PBPK simulations predicted 1.4–1.6-fold higher gliclazide area under the curve (AUC) after 5-day treatment with 20 mg omeprazole in all CYP2C19 phenotype groups except in poor metabolizers. The predicted gliclazide AUC increased 2.1 and 2.5-fold in intermediate metabolizers, and 2.6- and 3.8-fold in NM/RM/UM group, after simulated 20-day dosing with 40 mg omeprazole once and twice daily, respectively. The predicted results were corroborated by findings in patients with T2D which demonstrated 3.3-fold higher odds of severe gliclazide-induced hypoglycemia in NM/RM/UM patients concomitantly treated with omeprazole. Our results indicate that omeprazole may increase exposure to gliclazide and thus increase the risk of gliclazide-associated hypoglycemia in the majority of patients.

The Comparison of Plasma and Cerebrospinal Fluid R(-)- and S(+)-Flurbiprofen Concentration After Intravenous Injection of Flurbiprofen Axetil in Human Subjects

Background: Flurbiprofen axetil is a prodrug that releases the active substance through enzymatic removal of the ester moiety. It is formulated through encapsulation in a lipid microsphere carrier, and widely used to treat perioperative pain. Here, we studied the distribution of R (-)- and S (+)-flurbiprofen in human plasma and cerebrospinal fluid (CSF) after intravenous injection of flurbiprofen axetil. Methods: A total of 70 adult patients undergoing elective lower limb surgery under spinal anesthesia were given a single intravenous injection of 100-mg flurbiprofen axetil. The patients were randomly assigned to 10 groups for plasma and CSF sampling at 10 time points (5-50 min) after subarachnoid puncture and before actual spinal anesthesia. R (-)- and S (+)-flurbiprofen and CSF/plasma ratio were determined by liquid chromatography-tandem mass spectrometry. Results: R (-)-flurbiprofen concentration ranged from 2.01 to 10.9 μg/mL in plasma and 1.46-34.4 ng/mL in CSF. S (+)-flurbiprofen concentration ranged from 1.18 to 10.8 μg/mL in plasma and from 2.53 to 47 ng/mL in CSF. In comparison to S (+)-flurbiprofen, R (-)-flurbiprofen concentration was significantly higher in plasma at all time points (p < 0.05) except at 30 or 40 min, and lower in CSF at all time points (p < 0.05) except at 10, 15 and 40 min. Analysis after correcting drug concentration for body mass index also revealed higher plasma and lower CSF R (-)-flurbiprofen concentration. In comparison to S (+)-flurbiprofen, AUC_0-50 for R (-)-flurbiprofen was larger in plasma and smaller in CSF (p < 0.05 for both), and accordingly smaller CSF/plasma AUC_0-50 ratio (p < 0.05). There was a positive correlation between R (-)-flurbiprofen concentration and S (+)-flurbiprofen concentration in plasma (r = 0.725, p < 0.001) as well as in CSF (r = 0.718, p < 0.001), and a negative correlation between plasma and CSF concentration of S (+)-flurbiprofen (r = -0.250, p = 0.037), but not R (-)-flurbiprofen. Conclusion: Distribution of R (-)- and S (+)-flurbiprofen in plasma and CSF differed significantly. Penetration of R (-)-flurbiprofen into the CNS was lower than S (+)-flurbiprofen.

PAMPA model of gliclazide permeability: The impact of probiotic bacteria and bile acids

Gut microbiota and bile acids possess the ability to modify absorption and pharmacokinetic profile of numerous drugs. Since the variability of gliclazide response in patients cannot be explained only by genetic factors, the influence of gut microbiota and bile acids should be considered. The aim of this study was to determine the effects of probiotic bacteria and bile acids on the gliclazide permeability. The permeability of gliclazide with and without probiotic bacteria and bile acids (cholic acid, CA and deoxycholic acid, DCA) was tested using in vitro PAMPA model, at three different pH values (5.8, 6.5 and 7.4). Concentrations of gliclazide were determined by HPLC analysis. The interactions of gliclazide and bile acids were also investigated by molecular mechanics calculations (MM2). Probiotic bacteria significantly increased the permeability of gliclazide across the PAMPA membrane at all observed pH values while the total amount of gliclazide during incubation with bacteria was significantly reduced at pH 7.4, which could be a consequence of partial metabolism of the drug by enzymes of probiotic bacteria. Bile acids decreased the permeability of gliclazide through PAMPA membrane, with more pronounced effects of DCA, by forming more stable complexes with gliclazide. Given that probiotic bacteria and bile acids are naturally present in the gut and that each individual has a specific bacterial fingerprint, future research should extend the explanation of their effect on the gliclazide bioavailability and therapy individualization in in vivo conditions.

Diabetes: Is There a Future for Pharmacogenomics Guided Treatment?

Diabetes is a disease defined on the basis of hyperglycemia. There are monogenic forms of diabetes where defining the genetic cause has a dramatic impact on treatment—with patients being able to transition from insulin to sulfonylureas. However, the majority of diabetes is type 2 diabetes. This review outlines the robust evidence accrued to date for pharmacogenetics of metformin, sulfonylureas, thiazolidinediones, and dipeptidyl peptidase‐4 inhibitors but highlights that these variants will only be of clinical utility when the genotype is already known at the point of prescribing. The future of pharmacogenetics in diabetes and other common complex disease relies on a paradigm shift—that of preemptive panel genotyping and use of clinical decision support tools to assimilate this genetic information with other clinical phenotypic data and to present this information simply to the prescriber. Given the recent dramatic fall in genotyping costs, this future is not far off.

CYP2C19*2 Polymorphism Is Associated with Impaired Oral Clearance of Gliclazide in Healthy Chinese

Background

Previous studies suggest gliclazide is metabolised primarily by CYP2C19 rather than CYP2C9, unlike other sulphonylureas. CYP2C19 *2 and *3 polymorphisms are more common in Asians.

Methods

We investigated the effect of CYP2C19 polymorphisms on gliclazide pharmacokinetics in 15 healthy male Chinese subjects after a single 80mg oral dose.

Results

In CYP2C19 poor metabolisers (*2/*2, n=4), plasma area-under-the-curve was higher by nearly two-fold compared with intermediate metabolisers (*2 and *3 heterozygotes, n=7) and extensive metabolisers (*1/*1, n=4) (p<0.001). Apparent oral clearance was mean (SD) 0.70 (0.12), 1.22 (0.22) and 1.52 (0.47) mL/min/kg in poor, intermediate and extensive metabolisers, respectively (p = 0.005).

Conclusion

CYP2C19*2 polymorphism is associated with increased total gliclazide concentration and reduced oral clearance. Pharmacogenetic studies are warranted on the impact of CYP2C19 polymorphisms on treatment response and hypoglycaemia.

Population pharmacokinetic modeling of flurbiprofen, the active metabolite of flurbiprofen axetil, in Chinese patients with postoperative pain

Background

Flurbiprofen axetil, a lipid-microsphere-carrier targeting preparation, is a non-steroidal anti-inflammatory drug indicated for the treatment of postoperative pain.

Aim

The aim of the study was to develop a population pharmacokinetic (PPK) model of flurbiprofen, the active metabolite of flurbiprofen axetil, and optimize the treatment of flurbiprofen axetil in Chinese patients.

Methods

A total of 144 therapeutic drug-monitoring samples of flurbiprofen axetil from 72 patients were included in this study. The pharmacologically active metabolite flurbiprofen was used as the analytical target and determined 5–45 minutes after intravenous administration. The PPK model for flurbiprofen was developed using Phoenix NLME 1.3 with a nonlinear mixed-effect model. Bootstrap and visual predictive checks were used simultaneously to validate the final PPK model. Potential covariates of age, sex, body weight, height, and body-mass index were tested for PK parameters.

Results

The PPK model of flurbiprofen was explained by a one-compartment model with first-order elimination, in which a hypothetical-effect compartment was linked to a PK compartment. Population mean values of PK parameters estimated in the final model were θ_Ke=0.0015/h, θ_Vd=7.91 L, and θ_CL=1.55 L/h. Analysis of covariates showed that height and weight influenced the K_e of flurbiprofen. The final model was proved to be robust.

Conclusion

The final PPK model was demonstrated to be appropriate and effective, and can be used to assess the PK parameters of flurbiprofen in Chinese patients with postoperative pain.

Population pharmacokinetics of gliclazide in normal and diabetic rabbits

Gliclazide is a second-generation sulphonylurea drug widely used in the treatment of type 2 diabetes. However, there is no single report to describe the population pharmacokinetics of gliclazide in animal models. This study was aimed to evaluate the population pharmacokinetics (PK) of gliclazide in normal and alloxan-induced diabetic rabbits using nonlinear mixed effects modeling. A total of 90 New Zealand white rabbits were administered with three doses (4.13, 8.27 and 16.53 mg/kg b.wt) of gliclazide by an oral route. Blood samples were collected up to 24 hr and the gliclazide concentrations in rabbit were determined using the HPLC method. The non-compartmental and classical compartmental PK analyses were performed using Phoenix WinNonlin. Population PK analysis of gliclazide was performed using nonlinear mixed-effects model software NONMEM and Phoenix NLME considering the weight, age, sex, health and dose as covariates. The final population values for clearance (CL), volume of distribution (V) and the absorption rate constant (k_a ) were 5270 ml/hr, 55700 ml and 0.708 hr^-1 , respectively. The inter-individual variability in gliclazide CL, V and k_a was 16.3%, 14.9% and 26.5%, respectively. There was no significant difference between NONMEM and Phoenix NLME pharmacokinetic results. The visual predictive check and bootstrap analysis confirmed the predictive ability, model stability and precision of the parameter estimates from this model. This population PK model demonstrated that gliclazide pharmacokinetics is best described by one-compartment model with first-order absorption in rabbits. Body weight is a covariate that significantly influences gliclazide kinetic disposition in rabbits.

Pharmacogenetics of Antidiabetic Drugs

Pharmacogenetic studies of antidiabetic drugs have so far focused largely on response to metformin, which is the first-line therapy for treatment of type 2 diabetes (T2D). The first studies of metformin pharmacogenetics were focused on candidate genes that were implicated in metformin pharmacokinetics and transport. Since 2011, genome-wide association studies have been conducted in large cohorts of individuals with T2D identifying genes that are associated with glycemic response to metformin. There have been fewer pharmacogenetic studies of other antidiabetic drugs, and those have been largely limited to candidate gene studies with small sample sizes. Understanding the pharmacogenetics of antidiabetes medications is important for the integration of genetic screening into therapeutic decision making, and to achieve the goal of "precision medicine" for patients with T2D. In this chapter, we provide a review of the pharmacogenetics investigations of metformin and other antidiabetes medications. In addition, we highlight the importance of collaborative efforts with large sample size and representation from multiple ethnic groups in pharmacogenetics studies.

Pharmacokinetics of CYP2C9, CYP2C19, and CYP2D6 substrates in healthy Chinese and European subjects

PURPOSE

The aim of this analysis is to compare the pharmacokinetics of drug substrates in healthy Chinese and European subjects of aligned CYP2C9, CYP2C19, or CYP2D6 enzyme activity, providing further insight into drivers of interethnic differences in pharmacokinetics.

METHODS

Following identification of appropriate drug substrates, a comprehensive and structured literature search was conducted to identify single-dose pharmacokinetic data in healthy Chinese or European subjects with reported CYP2C9, CYP2C19, or CYP2D6 activity (genotype or phenotype). The ratio of drug AUC in the Chinese and European subjects classified with aligned enzyme activity was calculated (ethnicity ratio (ER)).

RESULTS

For 22/25 drugs identified, the ERs calculated indicated no or only limited interethnic differences in exposure (<twofold) in Chinese and European subjects with aligned polymorphic enzyme activity. The interethnic differences observed can reflect differences across populations in additional determinants of pharmacokinetics, although the notable between study variation and change over time in methods used to assign enzyme activity may also be contributing factors. There was no association between drug substrate fraction metabolized (fm) for CYP2C9, CYP2C19, or CYP2D6 and the ERs calculated.

CONCLUSION

The spectrum of pharmacokinetic determinants for each drug substrate and their differences across ethnic groups must be considered on a case-by-case basis in addition to metabolism by CYP2C9, CYP2C19, or CYP2D6. This analysis has also highlighted the challenges which arise when comparing published datasets if consistent methods to assign polymorphic enzyme activity have not been used.

Pooled bioequivalence study database from Turkey: characterization of adverse events and determination of split points based on Gini Index as a promising method

Background

Manufacturing of and medication with generic drugs is increasing around the world. Bioequivalence (BE) studies are being performed routinely by Contract Research Organisations (CROs) in Turkey. However, an overall evaluation for the attended volunteers, examined Active Pharmaceutical Ingredients (APIs) and the observed adverse events have not been studied in the field.

Objective

Our aim was to revisit and compile the BE studies carried out between the years 2000–2013 of a CRO (N-CRO) in Turkey.

Methods

A dataset of 261 BE studies has been created for the observed adverse events with regards to the frequency, type, and drug subgroups. As an advanced evaluation, the Gini Index method has been used in the 63 available BE studies to obtain split points for two pharmacokinetic parameters, area under the plasma/serum concentration (AUC) and maximum plasma/serum concentration (Cmax), in order to investigate their likely effect on the adverse events.

Results

Thousand six hundred and forty two adverse events were found in the 261 BE studies involving 7828 volunteers with the frequency of 6.29 per study and 0.21 per volunteer. The most frequently observed adverse events were; headache, somnolence, nausea, dizziness and vomiting, respectively. Hundred and nine different APIs were observed. ‘Genitourinary system and sex hormones’ subgroup drugs had the highest frequency of the adverse events. Adverse event frequencies above the identified split points for Cmax and AUC values were higher than the frequencies below them.

Conclusion

The review of 13 years period of BE studies revealed that the demographic properties of the volunteers and the study designs were in compliance with national and international guidelines. The promising outcome could be showing the increase of the adverse event frequencies above the obtained split points as the reflection of the likely individual pharmacokinetic differences in the adverse event occurence.

Electronic supplementary material

The online version of this article (doi:10.1186/s40064-016-2527-4) contains supplementary material, which is available to authorized users.

Pharmacogenomics in diabetes mellitus: insights into drug action and drug discovery

Genomic studies have greatly advanced our understanding of the multifactorial aetiology of type 2 diabetes mellitus (T2DM) as well as the multiple subtypes of monogenic diabetes mellitus. In this Review, we discuss the existing pharmacogenetic evidence in both monogenic diabetes mellitus and T2DM. We highlight mechanistic insights from the study of adverse effects and the efficacy of antidiabetic drugs. The identification of extreme sulfonylurea sensitivity in patients with diabetes mellitus owing to heterozygous mutations in HNF1A represents a clear example of how pharmacogenetics can direct patient care. However, pharmacogenomic studies of response to antidiabetic drugs in T2DM has yet to be translated into clinical practice, although some moderate genetic effects have now been described that merit follow-up in trials in which patients are selected according to genotype. We also discuss how future pharmacogenomic findings could provide insights into treatment response in diabetes mellitus that, in addition to other areas of human genetics, facilitates drug discovery and drug development for T2DM.

Pharmacogenetics in type 2 diabetes: influence on response to oral hypoglycemic agents

Type 2 diabetes is one of the leading causes of morbidity and mortality, consuming a significant proportion of public health spending. Oral hypoglycemic agents (OHAs) are the frontline treatment approaches after lifestyle changes. However, huge interindividual variation in response to OHAs results in unnecessary treatment failure. In addition to nongenetic factors, genetic factors are thought to contribute to much of such variability, highlighting the importance of the potential of pharmacogenetics to improve therapeutic outcome. Despite the presence of conflicting results, significant progress has been made in an effort to identify the genetic markers associated with pharmacokinetics, pharmacodynamics, and ultimately therapeutic response and/or adverse outcomes to OHAs. As such, this article presents a comprehensive review of current knowledge on pharmacogenetics of OHAs and provides insights into knowledge gaps and future directions.

Inhibition of P-glycoprotein expression and function by anti-diabetic drugs gliclazide, metformin, and pioglitazone in vitro and in situ

P-glycoprotein (P-gp) is a trans-membrane drug efflux pump. Several drugs are P-gp substrates. Some drugs may affect the activity of P-gp by inhibiting its function, resulting in significant drug-drug interactions (DDIs). It is critical to understand which drugs are inhibitors of P-gp so that adverse DDIs can be minimized or avoided. This study investigated the effects of gliclazide, metformin, and pioglitazone on the function and expression of P-gp. Rhodamine 123 (Rh 123) efflux assays in Caco-2 cells and western blot testing were used to study in vitro the effect of the drugs on P-gp function and expression. The in situ rat single-pass intestinal permeability model was developed to study the effect of the drugs on P-gp function. Digoxin and verapamil were used as a known substrate and inhibitor of P-gp, respectively. Digoxin levels in intestinal perfusion samples were analyzed by high-performance liquid chromatography. Intestinal effective permeability (Peff) of digoxin in the presence of 0.1, 10, and 500 μM gliclazide, 100 and 7000 μM metformin, and 50 and 300 μM pioglitazone was significantly increased relative to the digoxin treated cells (P < 0.01). P-gp expression was decreased by gliclazide, metformin and pioglitazone. Intracellular accumulation of Rh 123 by the drugs increased, but the differences were not significant relative to the control cells (P > 0.05). It was found that gliclazide, metformin, and pioglitazone inhibited P-gp efflux activity in situ and down-regulated P-gp expression in vitro. Further investigations are necessary to confirm the obtained results and to define the mechanism underlying P-gp inhibition by the drugs.

Genomic-based tools for the risk assessment, management, and prevention of type 2 diabetes

Type 2 diabetes (T2D) is a common and serious disorder and is a significant risk factor for the development of cardiovascular disease, neuropathy, nephropathy, retinopathy, periodontal disease, and foot ulcers and amputations. The burden of disease associated with T2D has led to an emphasis on early identification of the millions of individuals at high risk so that management and intervention strategies can be effectively implemented before disease progression begins. With increasing knowledge about the genetic basis of T2D, several genomic-based strategies have been tested for their ability to improve risk assessment, management and prevention. Genetic risk scores have been developed with the intent to more accurately identify those at risk for T2D and to potentially improve motivation and adherence to lifestyle modification programs. In addition, evidence is building that oral antihyperglycemic medications are subject to pharmacogenomic variation in a substantial number of patients, suggesting genomics may soon play a role in determining the most effective therapies. T2D is a complex disease that affects individuals differently, and risk prediction and treatment may be challenging for health care providers. Genomic approaches hold promise for their potential to improve risk prediction and tailor management for individual patients and to contribute to better health outcomes for those with T2D.

[The use of gliclazide in individualized sulfonylurea therapy]

In addition to the common blood glucose lowering effect, sulfonylurea compounds are different in many aspects from each other. Based on earlier findings the second generation gliclazide has special advantages within this group. Although the number of experimental and clinical observations on gliclazide is continuously increasing, these novel findings are not in the focus anymore due to the appearance of new antidiabetics. This article reviews recent experimental (effect on receptors, the absence of Epac2 activation, antioxidant properties, possible incentive of factors participating in beta-cell differentiation) and pharmacogenomic data, and compares them with clinical observations obtained from gliclazide treatment (hypoglycemias, parameters of cardiovascular outcome). The data underline the advantages of gliclazide, the highly pancreas-selective nature, preservation of the ischemic precondition, favourable hemodynamic properties and potential reduction of the beta-cell loss as compared to other compounds of the group. However, gliclazide is not free from disadvantages characteristic to sulfonylureas in general (blood glucose independent insulin stimulation, beta-cell depletion). Comparing gliclazide with other derivatives of the group, the above data indicate individual benefits for the application when sulfonylurea compound is the drug of choice.

CYP2C9, KCNJ11 and ABCC8 polymorphisms and the response to sulphonylurea treatment in type 2 diabetes patients

PURPOSE

Sulphonylureas (SU) are widely used in the management of type 2 diabetes. We investigated the influence of CYP2C9, KCNJ11 and ABCC8 polymorphisms on the response to SU currently used in everyday clinical practice.

METHODS

Patients treated for type 2 diabetes with sulphonylurea in monotherapy (n = 21) or in combination with metformin (n = 135) were provided with glucose-monitoring devices and instructed to measure fasting blood glucose levels once per week and additionally at any signs and symptoms suggesting low blood glucose for a period of three months. All patients were genotyped for CYP2C9 rs1799853 and rs1057910 (*2 and *3 allele, respectively), KCNJ11 rs5219 and rs5215, and ABCC8 rs757110.

RESULTS

The average duration of diabetes in the study group was 10.6 ± 7.1 years. Most of the patients achieved relatively good blood glucose control (HbA1c 7.0 ± 0.9). In total, 76 hypoglycemia events were observed (mean 0.48 ± 1.3). No severe hypoglycemia was reported; the lowest blood glucose was 2.1 mmol/l. Although 124 (79.5 %) patients never experienced hypoglycemia, 32 (20.5 %) patients experienced from one to eight events. None of the investigated polymorphisms influenced HbA1c levels or risk for hypoglycemia episodes in the whole group of patients. CYP2C9 genotype significantly influenced the occurrence of hypoglycemia events among the elderly patients (aged 60 years and over; n = 103). Among them, carriers of two wild-type alleles suffered 0.36 ± 0.98 events, while patients with one or two polymorphic alleles had 0.79 ± 1.7 or 2.67 ± 4.6 events, respectively (p = 0.014).

CONCLUSIONS

Our results indicate that the CYP2C9 genotype may influence the risk for hypoglycemia events in elderly patients, but not in the overall population of type 2 diabetes patients.

CYP2C metabolism of oral antidiabetic drugs--impact on pharmacokinetics, drug interactions and pharmacogenetic aspects

INTRODUCTION

The cytochrome P4502C enzymes account for the metabolism of approximately 20% of therapeutic drugs including certain oral antidiabetic drugs (OADs).

AREAS COVERED

This review focuses on the effect of CYP2C enzymes on metabolism of sulphonylureas (SUs), meglitinides, and thiazolidinediones (TZDs) discussing their impact on pharmacokinetics, drug interactions and toxicological profiles. Pharmacogenetic aspects reflecting individual gene variants and variable drug effects are also considered.

EXPERT OPINION

Genetic polymorphisms of CYP2C9 enzymes (*2/*2, *2/*3, *3/*3) influence the glycaemic response to SUs and impair their substrate metabolism. Restricted data from small-sized studies with heterogenous definitions of hypoglycaemia revealed no clear association between CYP2C9 genotypes and the risk of hypoglycaemia. Functional polymorphisms of CYP2C8- and CYP2C9 drug metabolizing genes affect markedly pharmacokinetics of meglitinides. Compared to wild-type carriers, patients treated with TZDs and carrying the common CYP2C8*3 and *4 variants showed a reduced glycaemic control. The strong CYP2C8 and OATP1B1 inhibitor gemfibrozil increases substantially the plasma concentrations of repaglinide and TZDs. Numerous metabolic drug interactions exist between SUs and commonly prescribed drugs, especially anti-infectives. The complex pharmacokinetic and pharmacogenetic properties and the unfavourable short and long term risk profile of glibenclamide and glimepiride raise the question whether their use can be justified any longer.

Distribution of CYP2C9*13 allele in the Chinese Han and the long-range haplotype containing CYP2C9*13 and CYP2C19*2

Cytochrome P450 2C9 (CYP2C9) and CYP2C19, located in tandem on chromosome 10q23-24, are known as genetically polymorphic. CYP2C9*13 is an important CYP2C9 variant in Asian populations, and is correlated with the reduced plasma clearance of some clinically important drugs. In this research, the allele frequency of CYP2C9*13 was determined to be 0.42% (95% CI of 0.17% to 0.86%) in 839 Chinese Han, male subjects. All detected subjects with CYP2C9*13 carry the CYP2C19*2 allele, too. Sequencing results infer the CYP2C9*13 haplotype, which contains eight linked SNPs, originates from the CYP2C9*1B haplotype group. CYP2C9*1B has been reported to be linked with CYP2C19*2. These indicate a long-range haplotype containing the CYP2C9*13 and CYP2C19*2 mutation, which means most CYP2C9*13 carriers will carry the CYP2C19*2 allele and the six SNPs of the CYP2C9*1B haplotype group, and may have more reduced intrinsic clearance of drugs such as phenytoin, tolbutamide and chlorpropamide that are metabolized by both CYP2C9 and CYP2C19.

In vivo quantitative prediction of the effect of gene polymorphisms and drug interactions on drug exposure for CYP2C19 substrates

We present a unified quantitative approach to predict the in vivo alteration in drug exposure caused by either cytochrome P450 (CYP) gene polymorphisms or CYP-mediated drug-drug interactions (DDI). An application to drugs metabolized by CYP2C19 is presented. The metrics used is the ratio of altered drug area under the curve (AUC) to the AUC in extensive metabolizers with no mutation or no interaction. Data from 42 pharmacokinetic studies performed in CYP2C19 genetic subgroups and 18 DDI studies were used to estimate model parameters and predicted AUC ratios by using Bayesian approach. Pharmacogenetic information was used to estimate a parameter of the model which was then used to predict DDI. The method adequately predicted the AUC ratios published in the literature, with mean errors of -0.15 and -0.62 and mean absolute errors of 0.62 and 1.05 for genotype and DDI data, respectively. The approach provides quantitative prediction of the effect of five genotype variants and 10 inhibitors on the exposure to 25 CYP2C19 substrates, including a number of unobserved cases. A quantitative approach for predicting the effect of gene polymorphisms and drug interactions on drug exposure has been successfully applied for CYP2C19 substrates. This study shows that pharmacogenetic information can be used to predict DDI. This may have important implications for the development of personalized medicine and drug development.

Mild hypoglycaemic attacks induced by sulphonylureas related to CYP2C9, CYP2C19 and CYP2C8 polymorphisms in routine clinical setting

AIM

To evaluate the impact of polymorphisms in the cytochrome P450 (CYP) 2C9, 2C19 and 2C8 genes on the risk of mild hypoglycaemic attacks in patients treated with sulphonylureas.

METHODS

One hundred and eight type 2 diabetic patients (50 men, 58 women), treated with oral antidiabetics, including at least one from the sulphonylurea group (glimepiride n = 50, gliclazide n = 46, or glipizide n = 12) for 3 months or longer, were included in the study. Symptoms of hypoglycaemia (sweating, tremor, anxiety and palpitations) during a 3 month period were recorded and confirmed by home glucose measurements. Gender, age, body mass index, creatinine clearance, HbA1c, oral antidiabetic dose and concomitant medication were assessed together with functional CYP2C9, CYP2C19 and CYP2C8 polymorphisms, analysed by real-time PCR methods.

RESULTS

Fifteen patients (eight men, seven women) reported hypoglycaemia symptoms which were validated by their home glucose measurements (< 70 mg/dl). Heterozygosity and homozygosity for CYP2C9 variant alleles (*2 or *3) tended to be more frequent among patients who reported hypoglycaemic attacks (60 and 7%) than those who did not (39 and 3%). Similarly, the CYP2C8*1/*3 genotype tended to be more frequent in patients with (47%) than without (27%) hypoglycaemia, while no such trend was observed for CYP2C19 variants. However, only in the gliclazide group a significant association between CYP2C9 genotype and hypoglycaemic attacks was observed (P = 0.035). None of the other covariates showed any significant association with the risk of hypoglycaemic attacks.

CONCLUSIONS

CYP2C9 polymorphisms leading to decreased enzyme activity show a modest impact on the risk of mild hypoglycaemia attacks during oral antidiabetic treatment, with a significant association in patients treated with gliclazide.

Effect of CYP2C9 polymorphisms on prescribed dose and time-to-stable dose of sulfonylureas in primary care patients with Type 2 diabetes mellitus

AIMS

Sulfonylureas are mainly metabolized by the enzyme CYP2C9. Two allelic variants, CYP2C9*2 and CYP2C9*3, result in decreased metabolic capacity and have been associated with elevated sulfonylurea serum levels. However, most of the available data originates from pharmacokinetic analyses performed in healthy individuals. In this study, the effect of CYP2C9*2 and CYP2C9*3 alleles on prescribed dose and time-to-stable dose of sulfonylureas was investigated.

MATERIALS & METHODS

A group of 207 incident sulfonylurea users treated in four university affiliated primary care centers were identified. The effect of the CYP2C9*2 and CYP2C9*3 alleles on prescribed dose and time-to-stable dose was then assessed.

RESULTS

No significant effects of the CYP2C9*2 and CYP2C9*3 alleles were found. However, a trend towards a lower stable glimepiride dose for carriers of the CYP2C9*3 allele was observed.

CONCLUSION

Genotyping for the CYP2C9*2 and CYP2C9*3 alleles currently appears to have no clinical implications for dosing of sulfonylureas in primary care patients with Type 2 diabetes mellitus.

Influence of CYP2C9 and CYP2C19 genetic polymorphisms on pharmacokinetics and pharmacodynamics of gliclazide in healthy Chinese Han volunteers

BACKGROUND AND OBJECTIVE

CYP2C9 is the major contributor to gliclazide metabolic clearance in vitro, while the pharmacokinetics of gliclazide modified release are affected mainly by CYP2C19 genetic polymorphisms in vivo. This study aims to investigate the influence of CYP2C9 and CYP2C19 genetic polymorphisms on the pharmacokinetics and pharmacodynamics of gliclazide in healthy Chinese Han volunteers.

METHODS

Eighteen healthy Han subjects with various combinations of CYP2C9 and CYP2C19 genotypes received 80 mg gliclazide. Plasma gliclazide concentrations were measured by a liquid chromatography-tandem mass spectrometry method for 84 h and plasma glucose and insulin levels were measured up to 15 h post-dose.

RESULTS AND DISCUSSION

There was no difference in either pharmacokinetic and or pharmacodynamic parameters of gliclazide when group A (CYP2C9*1/*1, CYP2C19 extensive metabolizers) was compared with group B (CYP2C9*1/*3, CYP2C19 *1/*1). When group C (CYP2C9*1/*1 and CYP2C19 poor metabolizers) was compared with group A, the AUC(0-∞) and C(max) in group C were significantly higher [83.94 ± 40.41 vs. 16.39 ± 5.10 μg·h/mL (P = 0.000) and 1.50 ± 0.85 vs. 0.45 ± 0.18 μg/mL (P = 0.000)], and the oral clearance was significantly lower [1.17 ± 0.63 vs. 5.38 ± 1.86 L/h (P = 0.000)]. The half-life of gliclazide was also significantly prolonged in group C subjects when compared with that of group A (33.47 ± 12.39 vs. 19.34 ± 10.45 h), but the difference was not significant (P = 0.052). The increase in serum glucose level at 11 h after dosing (ΔC(glu11)) in group C was significantly higher than that of group A (-1.08 ± 0.42 vs. 0.22 ± 1.01 mmol/L, P = 0.022). The corresponding insulin levels showed no difference between the two groups.

CONCLUSION

CYP2C9*3 was not associated with any change in the disposition of gliclazide. CYP2C19 polymorphisms appear to exert the dominant influence on the pharmacokinetics of gliclazide in healthy Chinese Han subjects, and may also affect the observed pharmacodynamics of the drug as a result.

Cytochrome P450-dependent toxicity of dapsone in human erythrocytes

The most prominent adverse effects seen during treatment with dapsone, an antibacterial and antiprotozoal agent, are hemolysis and methemoglobinemia. An in vitro microsomal/cytochrome P(450) (CYP)-linked assay, which allows reactive metabolites generated in situ to react with the co-incubated human erythrocytes, was employed to profile CYP isoforms responsible for hemotoxicity of dapsone. Dapsone caused a robust generation of methemoglobin in human erythrocytes in the presence of human/mouse liver microsomes, which indicates contribution of CYP-mediated metabolism for hemotoxicity. The highest methemoglobin formation with dapsone was observed with CYP2C19, with minor contributions from CYP2B6, CYP2D6 and CYP3A4. Cimetidine and chloramphenicol completely abrogated methemoglobin generation by dapsone, thus confirming a predominant contribution of CYP2C19. The results provide useful insights into CYP-dependent hemotoxicity of dapsone in human erythrocytes.

Pharmacogenetics of Anti-Diabetes Drugs

A variety of treatment modalities exist for individuals with type 2 diabetes mellitus (T2D). In addition to dietary and physical activity interventions, T2D is also treated pharmacologically with nine major classes of approved drugs. These medications include insulin and its analogues, sulfonylureas, biguanides, thiazolidinediones (TZDs), meglitinides, α-glucosidase inhibitors, amylin analogues, incretin hormone mimetics, and dipeptidyl peptidase 4 (DPP4) inhibitors. Pharmacological treatment strategies for T2D are typically based on efficacy, yet favorable responses to such therapeutics are oftentimes variable and difficult to predict. Characterization of drug response is expected to substantially enhance our ability to provide patients with the most effective treatment strategy given their individual backgrounds, yet pharmacogenetic study of diabetes medications is still in its infancy. To date, major pharmacogenetic studies have focused on response to sulfonylureas, biguanides, and TZDs. Here, we provide a comprehensive review of pharmacogenetics investigations of these specific anti-diabetes medications. We focus not only on the results of these studies, but also on how experimental design, study sample issues, and definition of 'response' can significantly impact our interpretation of findings. Understanding the pharmacogenetics of anti-diabetes medications will provide critical baseline information for the development and implementation of genetic screening into therapeutic decision making, and lay the foundation for "individualized medicine" for patients with T2D.

Oral antidiabetic drug metabolism: pharmacogenomics and drug interactions

BACKGROUND

Type 2 diabetes is progressive in nature and so to control cardiovascular risk, most patients need combinations of oral antidiabetic drugs (OADs) plus or minus insulin. Thus, drug-drug interactions may substantially contribute to harmful effects of intensive glucose lowering therapy.

METHODS

A PubMed literature search was performed to select the most recent and relevant publications examining OAD metabolism and the effects of concomitant use of OADs.

RESULTS/CONCLUSION

Considering the individual sensitivity to OADs, pharmacogenetic factors could be of critical importance. The therapeutic range and efficacy as well as adverse effects of OADs may be significantly affected by genetic polymorphisms of cytochrome P450 drug metabolising enzymes, organic cation transporters or organic anion transporting polypeptides. Although current data suggest that modest pharmacokinetics interferences among some OAD combinations exist, they do not seem to have substantial clinical consequences. As long-term adherence to multi-drug treatment is poor in diabetic patients, the future will show a strong move towards earlier treatment with combination therapies. As metformin is cardiovascular protective and is not metabolised through the hepatic cytochrome P450 system, it is a key compound for any OAD combination. There is an overwhelming amount of small-sized in vitro studies and investigations mostly including healthy volunteers dealing with short-term effects and surrogate parameters of concomitant OAD use. Further evidence from large-scale studies including typical subjects with type 2 diabetes, in particular multimorbid and geriatric patients with polypharmacy, is needed. Postmarketing surveillance using large patients' registries could be helpful to improve the early detection of clinically relevant drug-drug interactions.

Relative impact of genotype and enzyme induction on the metabolic capacity of CYP2C9 in healthy volunteers

Pharmacokinetics in individual subjects is determined by genes and environment. The relative contributions of enzyme induction and inherited genomic variation to cytochrome P450 enzyme 2C9 (CYP2C9) activity are unknown. In 130 volunteers, CYP2C9 activity was measured in vivo using tolbutamide as a probe drug. Tolbutamide was administered orally, and the pharmacokinetics of the drug was analyzed twice--before and after four doses of 450 mg rifampin. Mean total apparent clearances (Cl/F) in the genotype groups CYP2C9*1/*1, *1/*2, *1/*3, *2/*3, and *3/*3 before rifampin were 0.78, 0.74, 0.52, 0.40, and 0.13 l/h, respectively. After rifampin administration, these clearances increased in all genotype groups by a median factor of 1.9 (range 1.1-4.8). The combined effects of genes and environment could be predicted by a simple additive model. Thus, enzyme induction resulted in an approximately twofold difference in CYP2C9 activity, irrespective of the CYP2C9 genotypes. But the difference in activity levels between the CYP2C9*1/*1 and *3/*3 genotypes before the administration of rifampin was sixfold.

Pharmacogenetics in diabetes

Genetic variation can impact on efficacy and risk of adverse events to commonly used oral agents in -diabetes. Metformin is not metabolized and its mechanism of action remains debated; however, several cation transporters have been identified. Variation in these pharmacokinetic genes might influence metformin response. Conversely, although the cytochrome P450 system has been implicated in sulfonylurea response in some small studies, to date variants affecting pharmacodynamics, including those in ABCC8 (SUR1) and TCF7L2, are the most promising. For thiazolidinedione response, variants in PPARG or ADIPOQ (adiponectin) have been variably associated with response. With increasing well-phenotyped cohorts and new methods, including genome-wide association studies, the next few years offer great hope to use pharmacogenetics to unravel drug and disease mechanisms, as well as the possibility to individualize therapy by genotype.

Effects of St John's wort and CYP2C9 genotype on the pharmacokinetics and pharmacodynamics of gliclazide

BACKGROUND AND PURPOSE

Patients commonly take complementary medicines in conjunction with conventional drugs without clear evidence of safety or the risk of herb-drug interactions. The aim of this study was to assess potential pharmacokinetic (PK) and pharmacodynamic (PD) interactions between St John's wort and gliclazide in healthy subjects with different cytochrome P450 2C9 (CYP2C9) genotypes.

EXPERIMENTAL APPROACH

A crossover controlled study was conducted in 21 healthy subjects. Each received gliclazide (80 mg) either alone or during 15 days treatment with St John's wort. The area under the plasma concentration-time curve (AUC(0-infinity)), apparent clearance (CL/F) and elimination half-life (t 1/2) of gliclazide and incremental changes in glucose and insulin AUC(0-4) were compared. CYP2C9*2 and CYP2C9*3 alleles were identified using PCR followed by restriction enzyme digestion analysis.

KEY RESULTS

St John's wort significantly altered gliclazide pharmacokinetics in all except for four healthy subjects. The mean ratio and 90% confidence interval (CI) of gliclazide AUC(0-infinity) and CL/F were 0.67 (0.55-0.81) and 1.50 (1.24-1.81), respectively, after St John's wort treatment. St John's wort decreased gliclazide t (1/2), with mean ratio and 90% CI of 0.85 (0.74-0.93). There were no significant changes in glucose or insulin AUC(0-4) after St John's wort treatment and no significant differences according to CYP2C9 genotype.

CONCLUSIONS AND IMPLICATIONS

Treatment with St John's wort significantly increases the apparent clearance of gliclazide which is independent of CYP2C9 genotype. People with diabetes receiving this combination should be closely monitored to evaluate possible signs of reduced efficacy.