Relationship between CYP 2D6 metabolic status and sexual dysfunction in paroxetine treatment

A Comprehensive Review of the Main Lignan Components of Schisandra chinensis (North Wu Wei Zi) and Schisandra sphenanthera (South Wu Wei Zi) and the Lignan-Induced Drug-Drug Interactions Based on the Inhibition of Cytochrome P450 and P-Glycoprotein Activities

Wu Wei Zi is the dried fruit of Schisandra chinensis (Turcz.) Baill. or Schisandra sphenanthera Rehd. et Wils. (family Magnoliaceae). As a homology of medicine and food, it has been widely used in China for thousands of years, to tonify the kidney, and ameliorate neurological, cardiovascular, liver, and gastrointestinal disorders. As its increasing health benefits and pharmacological value, many literatures have reported that the combination of Wu Wei Zi in patients has led to fluctuations in the blood level of the combined drug. Therefore, it is extremely important to evaluate its safety concern such as drug-drug interactions (DDIs) when patients are under the poly-therapeutic conditions. This review summarized the effects of Wu Wei Zi extract and its major lignan components on cytochrome P450 and P-glycoprotein activities, the change of which could induce metabolic DDIs. Our review also elaborated on the differences of the major lignan components of the two Schisandra species, as well as the absorption, distribution, metabolism, and elimination of the major lignans. In conclusion, these results would enhance our understanding of the DDI mechanisms involving Wu Wei Zi, and may potentially untangle some differing and conflicting results in the future.

Delayed Ejaculation: Pathophysiology, Diagnosis, and Treatment

Delayed ejaculation (DE) is a poorly defined and uncommon form of male sexual dysfunction, characterized by a marked delay in ejaculation or an inability to achieve ejaculation. It is often quite concerning to patients and their partners, and sometimes frustrates couples' attempts to conceive. This article aims to review the pathophysiology of DE and anejaculation (AE), to explore our current understanding of the diagnosis, and to present the treatment options for this condition. Electronic databases were searched from 1966 to October 2017, including PubMed (MEDLINE) and Embase. We combined “delayed ejaculation,” “retarded ejaculation,” “inhibited ejaculation,” or “anejaculation” as Medical Subject Headings (MeSH) terms or keywords with “epidemiology,” “etiology,” “pathophysiology,” “clinical assessment,” “diagnosis,” or “treatment.” Relevant sexual medicine textbooks were searched as well. The literature suggests that the pathophysiology of DE/AE is multifactorial, including both organic and psychosocial factors. Despite the many publications on this condition, the exact pathogenesis is not yet known. There is currently no single gold standard for diagnosing DE/AE, as operationalized criteria do not exist. The history is the key to the diagnosis. Treatment should be cause-specific. There are many approaches to treatment planning, including various psychological interventions, pharmacotherapy, and specific treatments for infertile men. An approved form of drug therapy does not exist. A number of approaches can be employed for infertile men, including the collection of nocturnal emissions, prostatic massage, prostatic urethra catheterization, penile vibratory stimulation, probe electroejaculation, sperm retrieval by aspiration from either the vas deferens or the epididymis, and testicular sperm extraction.

Sexual Dysfunction Due to Psychotropic Medications

Sexual functioning is important to assess in patients with psychiatric illness as both the condition and associated treatment may contribute to sexual dysfunction (SD). Antidepressant medications, mood stabilizers, antipsychotics, and antianxiety agents may be associated with SD related to drug mechanism of action. Sexual adverse effects may be related to genetic risk factors, impact on neurotransmitters and hormones, and psychological elements. Effective strategies to manage medication-induced sexual dysfunction are initial choice of a drug unlikely to cause SD, switching to a different medication, and adding an antidote to reverse SD. Appropriate interventions should be determined on a clinical case-by-case basis.

Genetic determinants of selective serotonin reuptake inhibitor related sexual dysfunction

Sexual dysfunction is a troubling obstacle for individuals being treated for depression and can be caused by both depressive symptoms as well as antidepressant drugs. Selective serotonin reuptake inhibitors (SSRIs) represent a class of antidepressants commonly associated with sexual dysfunction, even after symptomatic improvement. Candidate gene studies have identified associations between sexual dysfunction and altered SSRI pharmacokinetics or to the neurotransmitter systems affected by depression and SSRI treatment. The multifactorial nature of this phenotype and study heterogeneity are currently limitations to the translation of these findings to clinical use. Larger, prospective studies of genetic-guided antidepressant selection may help to clarify the clinical utility of pharmacogenetics in minimizing sexual side effects.

Antidepressant-induced sexual dysfunction in men

Most of the available antidepressant medications, including tricyclic antidepressants, monoamine oxidase inhibitors, selective serotonin reuptake inhibitors, and dual noradrenergic/serotonergic reuptake inhibitors have been reported to be associated with sexual dysfunction in both sexes. This manuscript reviews evidence concerning the relative incidence of treatment emergent sexual dysfunction in men being treated with antidepressant drugs. Both double-blind controlled trials and large clinical series report a high incidence of sexual dysfunction, especially ejaculatory delay, with serotonergic drugs. The incidence of sexual dysfunction in men appears to be much lower with drugs whose primary mechanism of action involves adrenergic or dopaminergic systems.

Sprague-Dawley and Fischer female rats differ in acute effects of fluoxetine on sexual behavior

INTRODUCTION

The selective serotonin reuptake inhibitor (SSRI), fluoxetine, leads to sexual dysfunction in a substantial proportion of women. In studies with the Fischer inbred rat, the 5-HT(1A) receptor has been implicated in this sexual dysfunction. Whether this association with 5-HT(1A) receptors holds for other rat strains is not known.

AIM

The effects of acute fluoxetine on sexual behavior in two strains of rats that differ in their response to a 5-HT(1A) receptor agonist were examined. Whether the strain difference is comparable in naturally cycling and hormonally primed, ovariectomized rats was determined.

METHODS

Proestrous rats and ovariectomized rats, hormonally primed with estradiol benzoate and progesterone, were treated with varying doses of fluoxetine. Sexual behavior was examined before and after treatment with the SSRI.

MAIN OUTCOME MEASURES

Lordosis to mount ratios, lordosis quality, and proceptive behaviors were quantified. Sprague-Dawley and Fischer females were compared on each of these measures. The IC(50) for inhibition of lordosis behavior was determined.

RESULTS

In both the intact and the hormonally primed, ovariectomized model, Sprague-Dawley females were less sensitive to the effects of fluoxetine on sexual behavior. In both groups, fluoxetine showed dose dependency in behavioral inhibition, but a higher dose was required for Sprague-Dawley than for Fischer females. Naturally cycling, proestrous rats required a higher dose of fluoxetine than hormonally primed ovariectomized rats to produce significant inhibition of sexual behavior. Thus, the strain difference in the response to fluoxetine does not parallel strain differences in the response to a 5-HT(1A) receptor agonist.

CONCLUSIONS

Acute treatment with fluoxetine inhibits lordosis behavior in both Fischer and Sprague-Dawley females and the strain difference cannot be explained by reported strain differences in the response to a 5-HT(1A) receptor agonist. Fluoxetine's inhibition of female rat sexual behavior may involve effects of the SSRI in addition to activation of the 5-HT(1A) receptor.

Antidepressant treatment and altered CYP2D6 activity: are pharmacokinetic variations clinically relevant?

BACKGROUND

Many currently used antidepressants are substrates of the cytochrome P450 (CYP) 2D6 enzyme. In patients who experience variations in the activity of this enzyme (e.g., CYP2D6 poor and ultrarapid metabolizers [PMs and UMs]), whether caused by genetic polymorphisms or concomitant administration of a CYP2D6 inhibitor (i.e., phenoconversion), the pharmacokinetics, and hence the effects, of CYP2D6 substrate antidepressants can be altered.

METHODS

This literature review describes the clinical and empirical evidence indicating that alterations in CYP2D6 activity can negatively affect treatment outcomes in patients receiving antidepressant pharmacotherapies that are CYP2D6 substrates.

RESULTS

Based on results from a small, prospective trial, a population analysis, and a pooled analysis, CYP2D6 PMs treated with agents dependent on CYP2D6 metabolism to form an active metabolite can experience a decline in antidepressant effect. Based on a population analysis and two case studies, CYP2D6 UMs treated with antidepressants that are CYP2D6 substrates and administered in a pharmacologically active form do not experience an antidepressant effect due to the agent being too rapidly eliminated from the body. Conversely, based on prospective trials, population analyses, and case studies, phenotypic and phenoconverted CYP2D6 PMs can experience an increase in concentration-dependent adverse events due to the agent being eliminated too slowly from the body.

CONCLUSIONS

Despite these examples, few large-scale, prospective trials exploring the effect of altered CYP2D6 metabolism on antidepressant outcomes have been conducted. Future clinical trials of CYP2D6-dependent antidepressants should be designed to allow for stratification of treatment outcomes by CYP2D6 metabolizer status.

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.

Pharmacogenetics of SSRIs and Sexual Dysfunction

Sexual dysfunction (SD) is a common and disconcerting side effect of selective serotonin reuptake inhibitors (SSRIs) that often influences a patient’s desire to continue long-term antidepressant treatment. Studies specifically assessing changes in sexual well-being over time illustrate that the incidence of sexual side effects from SSRIs ranges from 20% to 70%, depending on the characteristics of the study sample assessed. Developing strategies to predict who may be at the highest risk for adverse changes in their sexual well-being is an important step in improving the quality of life and treatment of patients who require antidepressant therapy. Pharmacogenetic studies of SSRI-associated SD have identified associations between serotonin and glutamate system genes with aspects of SD. The results of studies investigating genetic variations in drug metabolism enzymes and their relationships to antidepressant-associated adverse effects have been mixed. Continued efforts to characterize the relationships between genetic markers and antidepressant outcomes, and to translate this knowledge to patient care, have the potential to significantly improve the empiric selection of antidepressant agents and to minimize the risk for intolerable side effects.

Pharmacogenetics and pharmacogenomics of sexual dysfunction: current status, gaps and potential applications

Although treatment of different types of sexual dysfunction has improved in the past decade with the introduction of phosphodiesterase type 5 inhibitors and selective serotonin reuptake inhibitors, response rates to these targeted therapies are variable. There are a number of studies in the published literature that provide proof-of-concept that genetic variation contributes to the variable response. Pharmacogenomics will most likely be one part of our therapeutic armamentarium in the future and will provide a stronger scientific basis for optimizing drug therapy on the basis of each patient’s genetic constitution. This article will review English language medical literature on the state-of-the-art genetic polymorphisms of drug targets, transporters and signaling molecules as well as pharmacogenetic studies of sexual dysfunction and suggested possible applications. Collectively, the data demonstrate that pharmacogenomics in the field of sexual medicine is still in its infancy. More research will provide further intriguing new discoveries in years to come.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

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

Treatment-emergent sexual dysfunction related to antidepressants: a meta-analysis

BACKGROUND

Sexual dysfunction (SD) is an important underestimated adverse effect of antidepressant drugs. Patients, in fact, if not directly questioned, tend to scarcely report them. The aim of the present meta-analysis was to quantify SD caused by antidepressants on the basis of studies where sexual functioning was purposely investigated through direct inquiry and specific questionnaires.

METHODS

A literature search was conducted using MEDLINE, ISI Web of Knowledge, and references of selected articles. Selected studies performed on patients without previous SD were entered in the Cochrane Collaboration Review Manager (RevMan version 4.2). Our primary outcome measure was the rate of total treatment-emergent SD. Our secondary outcome measures were the rates of treatment-emergent desire, arousal, and orgasm dysfunction.

RESULTS

Our analyses indicated a significantly higher rate of total and specific treatment-emergent SD and specific phases of dysfunction compared with placebo for the following drugs in decreasing order of impact: sertraline, venlafaxine, citalopram, paroxetine, fluoxetine, imipramine, phenelzine, duloxetine, escitalopram, and fluvoxamine, with SD ranging from 25.8% to 80.3% of patients. No significant difference with placebo was found for the following antidepressants: agomelatine, amineptine, bupropion, moclobemide, mirtazapine, and nefazodone.

DISCUSSION

Treatment-emergent SD caused by antidepressants is a considerable issue with a large variation across compounds. Some assumptions, such as the inclusion of open-label studies or differences in scales used to assess SD, could reduce the significance of our findings. However, treatment-emergent SD is a frequent adverse effect that should be considered in clinical activity for the choice of the prescribed drug.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

ORIGINAL RESEARCH—PATHOPHYSIOLOGY: Clinical Biologic Pathophysiologies of Women's Sexual Dysfunction

INTRODUCTION

Data concerning the biologic pathophysiology of desire, arousal, and orgasm in women are limited.

AIM

To gain knowledge of biologic pathophysiology of female sexual function. METHODS. To provide state-of-the-art knowledge concerning female sexual dysfunction, representing the opinions of seven experts from five countries developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURE

An International Consultation in alliance with key urological and sexual medicine societies convened over 200 multidisciplinary specialists from 60 countries into 17 consultation committees. The aims, goals and intentions of each committee were defined. Expert opinion was based on grading of evidence-based medical literature, extensive internal committee dialogue, open presentation, and debate.

RESULTS

Three critical physiologic requirements, including intact sex steroids, autonomic/somatic nerves, and arterial inflow/perfusion pressure to women's genital organs play fundamental roles in maintaining women's sexual function. Despite this, there are nominal data supporting a direct pathophysiologic involvement of abnormal sex steroid values, and/or damage/injury to neurologic and/or blood flow integrity in women with problems in sexual desire, arousal, and/or orgasm. This summary details the available literature concerning hormonal, neurologic, and vascular organic pathophysiologies of women's sexual dysfunctions.

CONCLUSIONS

Additional research on clinical pathophysiologies in women's sexual dysfunction is needed. This chapter encompasses data presented at the 2nd International Consultation on Sexual Medicine in Paris, France, June 28-July 1, 2003.

Neuropsychiatric pharmacogenetics: moving toward a comprehensive understanding of predicting risks and response

Pharmacogenetic research in the area of neuropsychiatric illnesses is rapidly evolving. Due to the complexity of the human brain, it is not surprising that our knowledge about the interaction between genetics and the treatment of these illnesses is very small. The Human Genome Project (HGP) has identified > 30,000 genes; several thousand of which have been found to occur in the brain or serve a role that enhances the brain’s function. Much of the research in the post-HGP era is being driven by a desire to use genetics to predict which patients deviate from the norm in terms of drug response or side effects. By identifying these people, we will be able to direct clinical practice such that therapies for these disorders can be individualized. With this in mind, the following review is intended to cover a broad understanding of CNS pharmacogenetics with the goal of summarizing available literature on promising candidate gene targets, which may eventually help us predict clinical outcomes in patients taking medications commonly used to treat neuropsychiatric disorders.