Will a new genotyping test help the clinician predict response to antidepressant drugs?

The increasing challenge of the possible impact of ethnicity on psychopharmacology

Ethnic differences may significantly influence the outcome of psychopharmacological treatment, in terms of prescription, adherence, clinical response, emergence of side effects, as well as pharmacokinetics and pharmacodynamics. The purpose of this review was to explore the available literature in order to provide general suggestions to help clinicians in choosing the best therapeutic option for patients, taking into account ethnicity. Although findings are sometimes controversial, the overall published studies suggest that ethnicities other than Caucasians tend to show a lower response to antidepressants and a reduced compliance. Africans tend to be more prescribed with antipsychotics, probably due to cultural stereotypes, except with clozapine, probably for their chronic benign neutropenia. Asians usually require less antipsychotic dosages than Caucasians. The differential response and side effect profile of antidepressants and antipsychotics have been related to individual intrinsic factors, to genetic make-up, but also to cultural and contextual variables. Interestingly, albeit limited data suggest ethnic-related genetic heterogeneity at the level of the serotonin transporters, the cytochromes and some neuroreceptors. Taken together, no conclusive findings are available about the role and impact of ethnicity in psychopharmacology. One of the main problems is that the majority of the studies in psychopharmacology have been conducted on Caucasians, so that there is an urgent need to have data in other populations. Furthermore, in the era of precision medicine, the role of ethnicity may be also supported by genetic analysis.

Pharmacokinetics of serotonergic drugs: focus on OCD

INTRODUCTION

Although the treatment of obsessive-compulsive disorder (OCD), a common, chronic, and disabling psychiatric condition, has significantly improved in the last decades, with the demonstration of the specific effectiveness of serotonin reuptake inhibitors (SRIs), a large proportion of patients still show high relapse rates. In addition, pharmacological treatments should be maintained for years, so that the clinicians should take into account the pharmacokinetic changes in the long-term, which may be responsible for dangerous side effects or interactions. Areas covered: The aim of this paper was to review the literature on the pharmacokinetics of SSRIs and clomipramine, and on their pharmacokinetic parameters in OCD patients. Expert opinion: Although the literature on the pharmacokinetics of both clomipramine and SSRIs is consistent, data on pharmacokinetic parameters in OCD patients are very few. Given the impact of OCD, its chronicity requiring long-term treatments, together with the need to increase the clinical response rate, more studies in this field are urgently required.

Pharmacogenetics and Imaging-Pharmacogenetics of Antidepressant Response: Towards Translational Strategies

Genetic variation underlies both the response to antidepressant treatment and the occurrence of side effects. Over the past two decades, a number of pharmacogenetic variants, among these the SCL6A4, BDNF, FKBP5, GNB3, GRIK4, and ABCB1 genes, have come to the forefront in this regard. However, small effects sizes, mixed results in independent samples, and conflicting meta-analyses results led to inherent difficulties in the field of pharmacogenetics translating these findings into clinical practice. Nearly all antidepressant pharmacogenetic variants have potentially pleiotropic effects in which they are associated with major depressive disorder, intermediate phenotypes involved in emotional processes, and brain areas affected by antidepressant treatment. The purpose of this article is to provide a comprehensive review of the advances made in the field of pharmacogenetics of antidepressant efficacy and side effects, imaging findings of antidepressant response, and the latest results in the expanding field of imaging-pharmacogenetics studies. We suggest there is mounting evidence that genetic factors exert their impact on treatment response by influencing brain structural and functional changes during antidepressant treatment, and combining neuroimaging and genetic methods may be a more powerful way to detect biological mechanisms of response than either method alone. The most promising imaging-pharmacogenetics findings exist for the SCL6A4 gene, with converging associations with antidepressant response, frontolimbic predictors of affective symptoms, and normalization of frontolimbic activity following antidepressant treatment. More research is required before imaging-pharmacogenetics informed personalized medicine can be applied to antidepressant treatment; nevertheless, inroads have been made towards assessing genetic and neuroanatomical liability and potential clinical application.

Clinical validity of cytochrome P450 metabolism and serotonin gene variants in psychiatric pharmacotherapy

Adverse events, response failures and medication non-compliance are common in patients receiving medications for the treatment of mental illnesses. A systematic literature review assessed whether pharmacokinetic (PK) or pharmacodynamic (PD) responses to 26 commonly prescribed antipsychotic and antidepressant medications, including efficacy or side effects, are associated with nucleotide polymorphisms in eight commonly studied genes in psychiatric pharmacotherapy: CYP2D6, CYP2C19, CYP2C9, CYP1A2, CYP3A4, HTR2C, HTR2A, and SLC6A4. Of the 294 publications included in this review, 168 (57%) showed significant associations between gene variants and PK or PD outcomes. Other studies that showed no association often had insufficient control for confounding variables, such as co-medication use, or analysis of medications not substrates of the target gene. The strongest gene-outcome associations were for the PK profiles of CYP2C19 and CYP2D6 (93% and 90%, respectively), for the PD associations between HTR2C and weight gain (57%), and for SLC6A4 and clinical response (54%), with stronger SLC6A4 response associations for specific drug classes (60-83%). The preponderance of evidence supports the validity of analyzing nucleotide polymorphisms in CYP and pharmacodynamic genes to predict the metabolism, safety, or therapeutic efficacy of psychotropic medications commonly used for the treatment of depression, schizophrenia, and bipolar illness.

Towards the implementation of CYP2D6 and CYP2C19 genotypes in clinical practice: update and report from a pharmacogenetic service clinic

Genetic testing may help to improve treatment outcomes in order to avoid non-response or severe side effects to psychotropic medication. Most robust data have been obtained for gene variants in CYP2D6 and CYP2C19 enzymes for antipsychotics and antidepressant treatment. We reviewed original articles indexed in PubMed from 2008-2013 on CYP2D6 and CYP2C19 gene variants and treatment outcome to antidepressant or antipsychotic medication. We have started providing CYP2D6 and CYP2C19 genotype information to physicians and conducted a survey where preliminary results are reported. Studies provided mixed results regarding the impact of CYP2D6 and CYP2C19 gene variation on treatment response. Plasma levels were mostly found associated with CYP metabolizer status. Higher occurrence/severity of side effects were reported in non-extensive CYP2D6 or CYP2C19 metabolizers. Results showed that providing genotypic information is feasible and generally well accepted by both patients and physicians. Although currently available studies are limited by small sample sizes and infrequent plasma drug level assessment, research to date indicates that CYP2D6 and CYP2C19 testing may be beneficial particularly for non-extensive metabolizing patients. In summary, clinical assessment of CYP2D6 and CYP2C19 metabolizer status is feasible, well accepted and optimizes drug treatment in psychiatry.

Influence of CYP2D6 and CYP2C19 gene variants on antidepressant response in obsessive-compulsive disorder

Numerous studies have reported on pharmacogenetics of antidepressant response in depression. In contrast, little is known of response predictors in obsessive-compulsive disorder (OCD), a disorder with among the lowest proportion of responders to medication (40-60%). Our study is the largest investigation to date (N=184) of treatment response and side effects to antidepressants in OCD based on metabolizer status for CYP2D6 and CYP2C19. We observed significantly more failed medication trials in CYP2D6 non-extensive compared with extensive metabolizers (P=0.007). CYP2D6 metabolizer status was associated with side effects to venlafaxine (P=0.022). There were nonsignificant trends for association of CYP2D6 metabolizer status with response to fluoxetine (P=0.056) and of CYP2C19 metabolizer status with response to sertraline (P=0.064). Our study is the first to indicate that CYP genes may have a role in antidepressant response in OCD. More research is required for a future clinical application of genetic testing, which could lead to improved treatment outcomes.

Fluoxetine pharmacogenetics in child and adult populations

Although fluoxetine is useful in the treatment of major depression, 30-40 % of the patients do not respond to therapy. The response seems to be influenced by certain genes which are involved in the drug's pharmacodynamics and pharmacokinetics. The present study reviews the literature on genetic contributions to fluoxetine response in children and adults, and concludes that the different polymorphisms of CYP2D6 and CYP2C9 may influence the blood concentrations of fluoxetine. If the childhood dose is adjusted for weight, differences between children and adults are unlikely. As regards the genes that influence the drug's pharmacodynamics, polymorphisms of SLC6A4, HTR1A and MAO-A seem to be involved in the response to fluoxetine, while the genes COMT, CRHR1, PDEA1, PDEA11 GSK3B and serpin-1 also seem to play a role. Comparison of different studies reveals that the results are not always consistent, probably due to methodological differences. Other factors such as gender or ethnicity may also influence treatment response.