Impact of CYP2C19 phenotypes on escitalopram metabolism and an evaluation of pupillometry as a serotonergic biomarker

Assessment of Pharmacokinetic Effects of Herbal Medicines on Escitalopram

Purpose

Herbal medicines are occasionally used in combination with conventional antidepressants to mitigate various depression-associated symptoms. However, there is limited information on herb-antidepressant interactions. In this study, we investigated the pharmacokinetic (PK) effects of four herbal medicines (Gami-soyosan, Banhasasim-tang, Ojeok-san, and Bojungikgi-tang) on escitalopram, a commonly used antidepressant.

Patients and Methods

In this open-label, fixed-sequence, three-period, crossover study, 18 participants were enrolled and divided into two groups. Each group received a 10 mg oral dose of escitalopram in period 1. Participants took escitalopram once daily and their assigned herbal medicines thrice a day for 7 d in periods 2 (group 1: Gami-soyosan, group 2: Ojeok-san) and 3 (group 1: Banhasasim-tang; group 2: Bojungikgi-tang). The primary endpoints were Cmax,ss and AUCtau,ss of escitalopram. Cmax,ss and AUCtau,ss in period 1 were obtained using nonparametric superposition from single-dose data. The PK endpoints were classified according to the CYP2C19 phenotype.

Results

Of 18 participants, 16 completed the study. Systemic exposure to escitalopram resulted in a minor increase in the presence of each herbal medicine. The geometric mean ratios (GMRs, combination with herbal medicines/escitalopram monotherapy) and their 90% confidence intervals (CIs) for Cmax,ss and AUCtau,ss were as follows: Gamisoyosan- 1.1454 (0.9201, 1.4258) and 1.0749 (0.8084, 1.4291), Banhasasim-tang-1.0470 (0.7779, 1.4092) and 1.0465 (0.7035, 1.5568), Ojeok-san-1.1204 (0.8744, 1.4357) and 1.1267 (0.8466, 1.4996), and Bojungikgi-tang-1.1264 (0.8594, 1.4762) and 1.1400 (0.8515, 1.5261), respectively. Furthermore, no significant differences in the GMRs of Cmax,ss and AUCtau,ss were observed across different CYP2C19 phenotypes in any of the groups.

Conclusion

The co-administration of escitalopram with Gami-soyosan, Banhasasim-tang, Ojeok-san, or Bojungikgi-tang did not exert significant PK effects on escitalopram. These findings provide valuable insights into the safe use of herbal medicines along with escitalopram.

Pharmacogenetic Dose Modeling Based on CYP2C19 Allelic Phenotypes

Pharmacogenetic variability in drug metabolism leads to patient vulnerability to side effects and to therapeutic failure. Our purpose was to introduce a systematic statistical methodology to estimate quantitative dose adjustments based on pharmacokinetic differences in pharmacogenetic subgroups, addressing the concerns of sparse data, incomplete information on phenotypic groups, and heterogeneity of study design. Data on psychotropic drugs metabolized by the cytochrome P450 enzyme CYP2C19 were used as a case study. CYP2C19 activity scores were estimated, while statistically assessing the influence of methodological differences between studies, and used to estimate dose adjustments in genotypic groups. Modeling effects of activity scores in each substance as a population led to prudential predictions of adjustments when few data were available ('shrinkage'). The best results were obtained with the regularized horseshoe, an innovative Bayesian approach to estimate coefficients viewed as a sample from two populations. This approach was compared to modeling the population of substance as normally distributed, to a more traditional "fixed effects" approach, and to dose adjustments based on weighted means, as in current practice. Modeling strategies were able to assess the influence of study parameters and deliver adjustment levels when necessary, extrapolated to all phenotype groups, as well as their level of uncertainty. In addition, the horseshoe reacted sensitively to small study sizes, and provided conservative estimates of required adjustments.

Effects of Cytochrome P450 (CYP) 2C19 Genotypes on Steady-State Plasma Concentrations of Escitalopram and its Desmethyl Metabolite in Japanese Patients With Depression

Background:

Plasma concentrations of the S-enantiomer of citalopram were different between extensive and poor CYP2C19 metabolizers in healthy subjects and depressed patients. However, most studies applied dose-corrected concentrations. Thus, we studied the effects of polymorphisms of the CYP2C19 gene on raw plasma drug concentrations in Japanese patients with depression.

Methods:

Subjects in this study consisted of 412 depressed patients receiving 5, 10, 15, or 20 mg of escitalopram once a day. Plasma concentrations of escitalopram and desmethylescitalopram were quantified using HPLC. CYP2C19 genotypes were identified using polymerase chain reaction methods.

Results:

There were no differences in the steady-state plasma concentrations of escitalopram or desmethylescitalopram in each dose group (5, 10, 15, or 20 mg of escitalopram) among CYP2C19 genotype groups. However, 1-way analysis of variance showed significant effects of CYP2C19 genotypes on the dose-adjusted plasma concentration of escitalopram but not in the dose-adjusted plasma concentration of desmethylescitalopram. Analysis of covariance including age, sex, and body weight showed significant effects of CYP2C19 genotypes on the dose-adjusted plasma concentration of escitalopram and the ratio of desmethylescitalopram to escitalopram.

Conclusions:

These findings suggest that the CYP2C19 variants are associated with steady-state plasma concentrations of escitalopram to some extent but are not associated with desmethylescitalopram.

The SSRI citalopram increases the sensitivity of the human circadian system to light in an acute dose

RATIONALE

Disturbances of the circadian system are common in depression. Though they typically subside when depression is treated with antidepressants, the mechanism by which this occurs is unknown. Despite being the most commonly prescribed class of antidepressants, the effect of selective serotonin reuptake inhibitors (SSRIs) on the human circadian clock is not well understood.

OBJECTIVE

To examine the effect of the SSRI citalopram (30 mg) on the sensitivity of the human circadian system to light.

METHODS

This study used a double-blind, placebo-controlled, within-subjects, crossover design. Participants completed two melatonin suppression assessments in room level light (~ 100 lx), taking either a single dose of citalopram 30 mg or a placebo at the beginning of each light exposure. Melatonin suppression was calculated by comparing placebo and citalopram light exposure conditions to a dim light baseline.

RESULTS

A 47% increase in melatonin suppression was observed after administration of an acute dose of citalopram, with all participants showing more suppression after citalopram administration (large effect, d = 1.54). Further, melatonin onset occurred later under normal room light with citalopram compared to placebo.

CONCLUSIONS

Increased sensitivity of the circadian system to light could assist in explaining some of the inter-individual variability in antidepressant treatment responses, as it is likely to assist in recovery in some patients, while causing further disruption for others.

Quantitation of escitalopram and its metabolites by liquid chromatography-tandem mass spectrometry in psychiatric patients: New metabolic ratio establishment

Therapeutic drug monitoring (TDM) is used to determine the concentration of drug in plasma/serum to adjust the dose of the therapeutic drug. Selective and sensitive analytical methods are used to determine drug and metabolite levels for the successful application of TDM. The aim of the study was to develop and validate using LC-MS/MS to analyse quantitative assay of escitalopram (S-CT) and metabolites in human plasma samples. In order to provide a convenient and safe treatment dose, it was aimed to determine the levels of S-CT and its metabolites in the patients' plasma. A new method with short sample preparation and analysis time was developed and validated using LC-MS/MS to analyse quantitative assay of S-CT and its metabolites in plasma. Also, plasma samples of 30 patients using 20 mg S-CT between the ages of 18 and 65 years were analysed by the validated method. The mean values of S-CT, demethyl escitalopram and didemethyl escitalopram in plasma of patients were 27.59, 85.52 and 44.30 ng/mL, respectively. At the end of the analysis, the metabolic ratio of S-CT and metabolites was calculated. It is considered that the method for the quantitative analysis of S-CT and its metabolites in human plasma samples may contribute to the literature on account of its sensitive and easy application. Additionally, the use of our data by physicians will contribute to the effective drug treatment for their patients who take S-CT.

Cancer Drug Delivery

Advancements in cancer drug delivery have led to the development of personalized oncology care through molecularly-driven targeted therapies. Understanding molecular and cellular mechanisms which drive tumor progression and resistance is critical in managing new treatment strategies which have shifted from empiric to biomarker-directed therapy selection. Biomarker-directed therapies have improved clinical outcomes in multiple malignancies as monotherapy and in combination with other treatment modalities, however the changing scope of treatment options presents new opportunities and challenges for research. Furthermore, pharmacogenetics may provide a rationale method of personalizing anticancer drug dosing and supportive care management for oncology patients. This chapter reviews biomarker classifications and pharmacogenetics in anticancer therapy and supportive care. Examples of biomarker-directed therapies and clinical assays, in addition to future directions of molecular profiling in oncology therapy management are discussed.

The impact of CYP2C19 polymorphisms on citalopram metabolism in patients with major depressive disorder

WHAT IS KNOWN AND OBJECTIVE

Genetic variations in drug-metabolizing enzyme genes change drug pharmacokinetics and response. CYP2C19 is a clinically important enzyme that metabolizes citalopram (CIT). The objective of this study was to determine CYP2C19 genetic polymorphisms and to evaluate the impact of these polymorphisms on the metabolism of citalopram in a sample of the Turkish population. We also assessed *17 polymorphism in healthy subjects in this population.

METHODS

The CYP2C19 genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism method (209 healthy individuals and 50 patients for CIT metabolism), and the plasma concentrations of CIT and demethylcitalopram (DCIT) were quantified by high-performance liquid chromatography.

RESULTS AND DISCUSSION

The CYP2C19*1 and *17 allele frequencies for the patient group and the healthy group were 71·0%, 18·0% and 81·1%, 18·9%, respectively. There was no significant difference between the two groups (P > 0·05). The mean plasma concentrations and the mean dose-corrected (C/D) plasma levels of DCIT were significantly higher in patients with the CYP2C19*1/*1 genotype compared to patients with CYP2C19*1/*2 and CYP2C19*2/*2 genotypes (P < 0·05). Furthermore, the mean metabolic ratio (MR, CIT/DCIT) was also significantly higher in the CYP2C19*1/*2 + CYP2C19*2/*2 genotypes (P < 0·05). On the other hand, plasma CIT, DCIT concentrations and M/R value in the CYP2C19*1/*1 genotypes were no different to those of the CYP2C19*1/*17 genotypes (P > 0·05).

WHAT IS NEW AND CONCLUSION

Our data suggest that CYP2C19*17 polymorphism does not have a significant effect on CIT metabolism. In contrast CYP2C19*2 polymorphism has a prominent role and is likely to contribute to interindividual variability in CIT metabolism in vivo at therapeutic doses.

Pharmacogenetics of drug oxidation via cytochrome P450 (CYP) in the populations of Denmark, Faroe Islands and Greenland

Denmark, the Faroe Islands and Greenland are three population-wise small countries on the northern part of the Northern Hemisphere, and studies carried out here on the genetic control over drug metabolism via cytochrome P450 have led to several important discoveries. Thus, CYP2D6 catalyzes the 2-hydroxylation, and CYP2C19 in part catalyzes the N-demethylation of imipramine. The phenomenon of phenocopy with regard to CYP2D6 was first described when Danish patients changed phenotype from extensive to poor metabolizers during treatment with quinidine. It was a Danish extensive metabolizer patient that became a poor metabolizer during paroxetine treatment, and this was due to the potent inhibition of CYP2D6 by paroxetine, which is also is metabolized by this enzyme. Fluoxetine and norfluoxetine are also potent inhibitors of CYP2D6, and fluvoxamine is a potent inhibitor of both CYP1A2 and CYP2C19. The bioactivation of proguanil to cycloguanil is impaired in CYP2C19 poor metabolizers. The O-demethylation of codeine and tramadol to their respective my-opioid active metabolites, morphine and (+)-O-desmethyltramadol was markedly impaired in CYP2D6 poor metabolizers compared to extensive metabolizers, and this impairs the hypoalgesic effect of the two drugs in the poor metabolizers. The frequency of CYP2D6 poor metabolizers is 2%-3% in Greenlanders and nearly 15% in the Faroese population. The frequency of CYP2C19 poor metabolizers in East Greenlanders is approximately 10%. A study in Danish mono and dizygotic twins showed that the non-polymorphic 3-N-demethylation of caffeine catalyzed by CYP1A2 is subject to approximately 70% genetic control.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6 and CYP2C19 Genotypes and Dosing of Selective Serotonin Reuptake Inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are primary treatment options for major depressive and anxiety disorders. CYP2D6 and CYP2C19 polymorphisms can influence the metabolism of SSRIs, thereby affecting drug efficacy and safety. We summarize evidence from the published literature supporting these associations and provide dosing recommendations for fluvoxamine, paroxetine, citalopram, escitalopram, and sertraline based on CYP2D6 and/or CYP2C19 genotype (updates at www.pharmgkb.org).

Effect of Cytochrome P450 polymorphism on the action and metabolism of selective serotonin reuptake inhibitors

INTRODUCTION

The aim of this article is to review the field of clinically relevant pharmacogenetic effects of cytochrome P450 polymorphisms on metabolism, kinetics, and action of selective serotonin reuptake inhibitors (SSRIs).

AREAS COVERED

The relevant literature in humans on the implications of genetic variation on SSRI drug exposure, drug safety, and efficacy was systematically evaluated. There is a large amount of evidence on the influences of CYP polymorphisms on the pharmacokinetics of SSRIs. Regulatory agencies have issued warnings or advice considering dose adjustments in the presence of affected metabolic phenotypes for several SSRIs. Evidence-based dose adjustments for drugs dependent on CYP genotype are available to clinicians. However, few data on the relationship between genetically determined elevated plasma concentrations of SSRIs and specific side effects or therapeutic failure are currently available.

EXPERT OPINION

Genetic polymorphisms in CYP2D6 and CYP2C19 exert large influences on the individual exposure to SSRIs, leading to the aim to achieve similar concentration time courses in different metabolizer phenotypes. The implementation of a stratified approach to medication with SSRIs in different metabolic phenotypes on a rational basis will require new studies assessing the association between clinical outcomes (such as adverse reactions) and genetically determined elevated plasma concentrations.

CYP2C19 variation, not citalopram dose nor serum level, is associated with QTc prolongation

Recently, a FDA Safety Communication warned of a dose-dependent risk for QTc prolongation with citalopram, which is metabolized by CYP2C19 of the cytochrome P450 system. We investigate associations between citalopram and escitalopram dose, serum concentration, CYP2C19 phenotype, and QTc. We undertook a retrospective chart review of citalopram or escitalopram patients with the inclusion criteria of consistent medication dose, CYP2C19 phenotype (extensive metabolizers [EM], intermediate metabolizers [IM], poor metabolizers [PM]), and QTc interval on ECG. We further identified 42 citalopram users with citalopram serum concentration measurements and ECG. Regression and one-way ANOVA were used to examine the relationship between citalopram dose, citalopram serum concentration, CYP2C19 phenotype, and QTc interval. Of 75 citalopram patients, the EM group had significantly shorter QTc intervals than a combined IM+PM group (427.1±23.6 ms vs. 440.1±26.6 ms, one-tailed t-test, p=0.029). In the 80 escitalopram cohort, there was no significant difference in QTc between phenotype groups. There was no statistical correlation between citalopram (p=0.62) or escitalopram (p=0.30) dose and QTc. QTc was not associated with citalopram serum level (p=0.45). In contrast to the FDA warning, this study found no association between citalopram/escitalopram dose and QTc. However, PM of the drug tended to have longer QTc intervals. Our findings suggest cytochrome P450 genotyping in select patients may be helpful to guide medication optimization while limiting harmful effects.

A cytochrome P450 phenotyping cocktail causing unexpected adverse reactions in female volunteers

BACKGROUND

A four-drug cytochrome P450 (CYP) phenotyping cocktail was developed to rapidly and safely determine CYP2D6, CYP2C19, CYP2C9 and CYP1A2 enzyme activity and phenotype.

METHODS

The cocktail consisted of the single CYP phenotyping probes of 50 mg tramadol (CYP2D6), 20 mg omeprazole (CYP2C19), 25 mg losartan (CYP2C9) and 200 mg caffeine (CYP1A2) and was administered as a single oral dose. For enzyme activity measurements, urine was collected as 8 h post-administration and blood was sampled at 4 h. The enzyme activity was determined by metabolic ratios of molar concentrations of the drugs and their enzyme catalyzed metabolites and was correlated to the relevant genotypes.

RESULTS

In a pilot study in 12 healthy male volunteers the CYP genotype-phenotype correlation and robustness of the cocktail was successfully determined without detection of any adverse drug reactions. In the subsequent population study, four female volunteers experienced unexpected and unacceptable moderate and severe adverse reactions (ARs) of headache, dizziness, nausea, vomiting, blue fingers, nails and lips and difficulties in urinating, which led to the study being prematurely terminated after inclusion of only 22 subjects (15 males, 7 females) [corrected].

CONCLUSION

Attention must be paid to adverse reactions when designing new combinations of phenotype cocktails regardless of the doses and drugs involved. We specifically warn against the combination of tramadol, omeprazole, losartan and caffeine.

Genetic variability of drug-metabolizing enzymes: the dual impact on psychiatric therapy and regulation of brain function

Polymorphic drug-metabolizing enzymes (DMEs) are responsible for the metabolism of the majority of psychotropic drugs. By explaining a large portion of variability in individual drug metabolism, pharmacogenetics offers a diagnostic tool in the burgeoning era of personalized medicine. This review updates existing evidence on the influence of pharmacogenetic variants on drug exposure and discusses the rationale for genetic testing in the clinical context. Dose adjustments based on pharmacogenetic knowledge are the first step to translate pharmacogenetics into clinical practice. However, also clinical factors, such as the consequences on toxicity and therapeutic failure, must be considered to provide clinical recommendations and assess the cost-effectiveness of pharmacogenetic treatment strategies. DME polymorphisms are relevant not only for clinical pharmacology and practice but also for research in psychiatry and neuroscience. Several DMEs, above all the cytochrome P (CYP) enzymes, are expressed in the brain, where they may contribute to the local biochemical homeostasis. Of particular interest is the possibility of DMEs playing a physiological role through their action on endogenous substrates, which may underlie the reported associations between genetic polymorphisms and cognitive function, personality and vulnerability to mental disorders. Neuroimaging studies have recently presented evidence of an effect of the CYP2D6 polymorphism on basic brain function. This review summarizes evidence on the effect of DME polymorphisms on brain function that adds to the well-known effects of DME polymorphisms on pharmacokinetics in explaining the range of phenotypes that are relevant to psychiatric practice.

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.

Effects of MDMA alone and after pretreatment with reboxetine, duloxetine, clonidine, carvedilol, and doxazosin on pupillary light reflex

RATIONALE

Pupillometry can be used to characterize autonomic drug effects.

OBJECTIVE

This study was conducted to determine the autonomic effects of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy), administered alone and after pretreatment with reboxetine, duloxetine, clonidine, carvedilol, and doxazosin, on pupillary function.

METHODS

Infrared pupillometry was performed in five placebo-controlled randomized studies. Each study included 16 healthy subjects (eight men, eight women) who received placebo-MDMA (125 mg), placebo-placebo, pretreatment-placebo, or pretreatment-MDMA using a crossover design.

RESULTS

MDMA produced mydriasis, prolonged the latency, reduced the response to light, and shortened the recovery time. The impaired reflex response was associated with subjective, cardiostimulant, and hyperthermic drug effects and returned to normal within 6 h after MDMA administration when plasma MDMA levels were still high. Mydriasis was associated with changes in plasma MDMA concentration over time and longer-lasting. Both reboxetine and duloxetine interacted with the effects of MDMA on pupillary function. Clonidine did not significantly reduce the mydriatic effects of MDMA, although it produced miosis when administered alone. Carvedilol and doxazosin did not alter the effects of MDMA on pupillary function.

CONCLUSIONS

The MDMA-induced prolongation of the latency to and reduction of light-induced miosis indicate indirect central parasympathetic inhibition, and the faster recovery time reflects an increased sympathomimetic action. Both norepinephrine and serotonin mediate the effects of MDMA on pupillary function. Although mydriasis is lasting and mirrors the plasma concentration-time curve of MDMA, the impairment in the reaction to light is associated with the subjective and other autonomic effects of MDMA and exhibits acute tolerance.

Translational evaluation of JNJ-18038683, a 5-hydroxytryptamine type 7 receptor antagonist, on rapid eye movement sleep and in major depressive disorder

In rodents 5-hydroxytryptamine type 7 (5-HT(7)) receptor blockade has been shown to be effective in models of depression and to increase the latency to rapid eye movement (REM) sleep and decrease REM duration. In the clinic, the REM sleep reduction observed with many antidepressants may serve as a biomarker. We report here the preclinical and clinical evaluation of a 5-HT(7) receptor antagonist, (3-(4-chlorophenyl)-1,4,5,6,7,8-hexahydro-1-(phenylmethyl)pyrazolo[3,4-d]azepine 2-hydroxy-1,2,3-propanetricarboxylate) (JNJ-18038683). In rodents, JNJ-18038683 increased the latency to REM sleep and decreased REM duration, and this effect was maintained after repeated administration for 7 days. The compound was effective in the mouse tail suspension test. JNJ-18038683 enhanced serotonin transmission, antidepressant-like behavior, and REM sleep suppression induced by citalopram in rodents. In healthy human volunteers JNJ-18038683 prolonged REM latency and reduced REM sleep duration, demonstrating that the effect of 5-HT(7) blockade on REM sleep translated from rodents to humans. Like in rats, JNJ-18038683 enhanced REM sleep suppression induced by citalopram in humans, although a drug-drug interaction could not be ruled out. In a double-blind, active, and placebo-controlled clinical trial in 225 patients suffering from major depressive disorder, neither treatment with pharmacologically active doses of JNJ-18038683 or escitalopram separated from placebo, indicating a failed study lacking assay sensitivity. Post hoc analyses using an enrichment window strategy, where all the efficacy data from sites with an implausible high placebo response [placebo group Montgomery-Åsberg Depression Rating Scale (MADRS) < = 12] and from sites with no placebo response (MADRS > = 28) are removed, there was a clinically meaningful difference between JNJ-18038683 and placebo. Further clinical studies are required to characterize the potential antidepressant efficacy of JNJ-18038683.

Pharmacogenetics of antidepressant drugs: current clinical practice and future directions

While antidepressants are widely used to treat mood and anxiety disorders, only half of the patients will respond to antidepressant treatment and only one-third of patients experience a full remission of symptoms. The identification of genetic biomarkers that predict antidepressant-treatment response can improve current clinical practice. This is an emerging field known as pharmacogenetics, which comprises of genetic studies on both the pharmacokinetics and pharmacodynamics of treatment response. Recent studies on antidepressant-treatment response have focused on both aspects of pharmacogenetics research, identifying new candidate genes that may predict better treatment response for patients. This paper reviews recent findings on the pharmacogenetics of antidepressant drugs and future clinical applications. Ultimately, these studies should lead to the use of genetic testing to guide the use of antidepressants in clinical practice.

Genetic polymorphisms of cytochrome P450 enzymes and antidepressant metabolism

INTRODUCTION

The cytochrome P450 (CYP) enzymes are the major enzymes responsible for Phase I reactions in the metabolism of several substances, including antidepressant medications. Thus, it has been hypothesized that variants in the CYP network may influence antidepressant efficacy and safety. Nonetheless, data on this field are still contradictory. The authors aim to give an overview of the published studies analyzing the influence of CYP highly polymorphic loci on antidepressant treatment in order to translate the acquired knowledge to a clinical level.

AREAS COVERED

The authors collected and compared experimental works and reviews published from the 1980s to the present and included in the Medline database. The included studies pertain to the effects of CYP gene polymorphisms on antidepressant pharmacokinetic parameters and clinical outcomes (response and drug-related adverse effects), with a focus on applications in clinical practice. The authors focused mainly on in vivo studies in humans (patients or healthy volunteers).

EXPERT OPINION

Great variability in antidepressant metabolism among individuals has been demonstrated. Thus, with the current interest in individualized medicine, several genetic tests to detect CYP variants have been produced. They provide a potentially useful way to anticipate some clinical outcomes of antidepressant treatment, although they will only be extensively used in clinical practice if precise and specific treatment options and guidelines based on genetic tests can be provided.

A candidate gene study of serotonergic pathway genes and pain relief during treatment with escitalopram in patients with neuropathic pain shows significant association to serotonin receptor2C (HTR2C)

PURPOSE

Previous studies have shown that a small fraction of patients with peripheral neuropathic pain experiences >50% pain relief during treatment with selective serotonin reuptake inhibitors (SSRIs), whereas most patients have no or only slight relief. The aim of this study was to investigate the association between polymorphisms in genes involved in the serotonergic pathway and the effect of escitalopram on peripheral neuropathic pain.

METHODS

We genotyped 34 participants from a placebo-controlled trial of escitalopram in peripheral neuropathic pain for polymorphisms in five genes: the serotonin receptor 2A (HTR2A) gene, the serotonin receptor 2C (HTR2C) gene, the ABCB1 gene encoding for the P-glycoprotein, the CYP2C19 gene, and the serotonin transporter gene (SLC6A4).

RESULTS

The SNP rs6318 (Cys23Ser) in the HTR2C gene showed significant association with treatment response in men (p = 0.047), with 75% carrying the C allele being responders. The same tendency was seen in women. Similarly, carriership of the C allele at rs6318 was associated with better pain relief during treatment with escitalopram [odds ratio (OR) 15.5, p = 0.014)] Furthermore, there was a tendency of better relief with increasing number of short alleles for the 5-HTTLPR polymorphism of the serotonin transporter (OR 5.7, p = 0.057). None of the other polymorphisms showed a significant association with treatment response to escitalopram.

CONCLUSION

This study indicates that variation in the HTR2C gene is associated to the pain-relieving effect of escitalopram in patients with painful polyneuropathy.

Genetic polymorphisms and drug interactions modulating CYP2D6 and CYP3A activities have a major effect on oxycodone analgesic efficacy and safety

BACKGROUND AND PURPOSE

The major drug-metabolizing enzymes for the oxidation of oxycodone are CYP2D6 and CYP3A. A high interindividual variability in the activity of these enzymes because of genetic polymorphisms and/or drug-drug interactions is well established. The possible role of an active metabolite in the pharmacodynamics of oxycodone has been questioned and the importance of CYP3A-mediated effects on the pharmacokinetics and pharmacodynamics of oxycodone has been poorly explored.

EXPERIMENTAL APPROACH

We conducted a randomized crossover (five arms) double-blind placebo-controlled study in 10 healthy volunteers genotyped for CYP2D6. Oral oxycodone (0.2 mg x kg(-1)) was given alone or after inhibition of CYP2D6 (with quinidine) and/or of CYP3A (with ketoconazole). Experimental pain (cold pressor test, electrical stimulation, thermode), pupil size, psychomotor effects and toxicity were assessed.

KEY RESULTS

CYP2D6 activity was correlated with oxycodone experimental pain assessment. CYP2D6 ultra-rapid metabolizers experienced increased pharmacodynamic effects, whereas cold pressor test and pupil size were unchanged in CYP2D6 poor metabolizers, relative to extensive metabolizers. CYP2D6 blockade reduced subjective pain threshold (SPT) for oxycodone by 30% and the response was similar to placebo. CYP3A4 blockade had a major effect on all pharmacodynamic assessments and SPT increased by 15%. Oxymorphone C(max) was correlated with SPT assessment (rho(S)= 0.7) and the only independent positive predictor of SPT. Side-effects were observed after CYP3A4 blockade and/or in CYP2D6 ultra-rapid metabolizers.

CONCLUSIONS AND IMPLICATIONS

The modulation of CYP2D6 and CYP3A activities had clear effects on oxycodone pharmacodynamics and these effects were dependent on CYP2D6 genetic polymorphism.

Pharmacogenetic testing and therapeutic drug monitoring are complementary tools for optimal individualization of drug therapy

Genetic factors contribute to the phenotype of drug response, but the translation of pharmacogenetic outcomes into drug discovery, drug development or clinical practice has proved to be surprisingly disappointing. Despite significant progress in pharmacogenetic research, only a few drugs, such as cetuximab, dasatinib, maraviroc and trastuzumab, require a pharmacogenetic test before being prescribed. There are several gaps that limit the application of pharmacogenetics based upon the complex nature of the drug response itself. First, pharmacogenetic tests could be more clinically applicable if they included a comprehensive survey of variation in the human genome and took into account the multigenic nature of many phenotypes of drug disposition and response. Unfortunately, much of the existing research in this area has been hampered by limitations in study designs and the nonoptimal selection of gene variants. Secondly, although responses to drugs can be influenced by the environment, only fragmentary information is currently available on how the interplay between genetics and environment affects drug response. Third, the use of a pharmacogenetic test as a standard of care for drug therapy has to overcome significant scientific, economic, commercial, political and educational barriers, among others, in order for clinically useful information to be effectively communicated to practitioners and patients. Meanwhile, the lack of efficacy is in this process is quite as costly as drug toxicity, especially for very expensive drugs, and there is a widespread need for clinically and commercially robust pharmacogenetic testing to be applied. In this complex scenario, therapeutic drug monitoring of parent drugs and/or metabolites, alone or combined with available pharmacogenetic tests, may be an alternative or complementary approach when attempts are made to individualize dosing regimen, maximize drug efficacy and enhance drug safety with certain drugs and populations (e.g. antidepressants in older people).