Differential outcomes from metabolic ratios in the identification of CYP2D6 phenotypes–focus on venlafaxine and O-desmethylvenlafaxine

A fatal case of desvenlafaxine and paroxetine poisoning

Desvenlafaxine (O-desmethylvenlafaxine) and paroxetine are antidepressants that inhibit serotonin reuptake. Despite their relatively safe profiles, several serious side effects, including serotonin syndrome, bleeding, mania, and high blood pressure, are observed. We report the confirmation of the death of a 41-year-old female, with an overdose of desvenlafaxine and paroxetine suspected as the main cause of death. To quantify the level of desvenlafaxine and paroxetine in whole blood and urine, solid phase extraction combined with liquid chromatography-tandem mass spectrometry was developed and validated. Calibration curves were linear with coefficients of determination (r2) >0.999 for desvenlafaxine and paroxetine. The limits of detection and the limits of quantification for both desvenlafaxine and paroxetine were 0.001 µg/mL and 0.02 µg/mL, respectively. Desvenlafaxine and paroxetine were detected in the postmortem samples, along with various psychiatric drugs, and the blood alcohol content level was below 0.010%. The concentrations of desvenlafaxine and paroxetine in the heart blood were 11.0 µg/mL and 2.1 µg/mL, respectively, indicating lethal concentrations. In the urine, the concentrations of desvenlafaxine and paroxetine were 87.7 µg/mL and 3.5 µg/mL, respectively. This is the first report to determine the blood concentration of desvenlafaxine in a fatal intoxication caused by an overdose of desvenlafaxine single formulation.

Impact of COVID- 19 pandemic on antidepressants consumptions by wastewater analysis in Turkey

The COVID-19 pandemic has been a major challenge worldwide, forcing countries to take restrictive measures beyond conventional methods in their fight against the spread of the disease. Followingly, many studies have been conducted on the effects of these measures on mental health. Wastewater-based epidemiology (WBE) was used in this study to monitor and estimate changes in antidepressant use under normal conditions (2019) and COVID-19 pandemic conditions (2020). Likewise, this study utilized wastewater-based epidemiology (WBE) to monitor and assess changing trends from the pre-pandemic period (2019) to COVID-19 pandemic conditions in antidepressant use (2020). Wastewater samples were collected from 11 cities in Turkey throughout six sampling periods covering the pre-pandemic and during-pandemic periods (June 2019-December 2020). Then, samples were analyzed via LC-MS/MS method. As a result, we observed that venlafaxine was the drug with the highest concentration (mean ± SD: 103.6 ± 112.1 mg/1000p/day). Moreover, city number 6 presented the highest venlafaxine use and the most dramatic increase during the pandemic period. Finally, this study revealed the potential of WBE to estimate the changing trends in mental health during the ongoing pandemic.

Pharmacogenomics in Pain Management: A Review of Relevant Gene-Drug Associations and Clinical Considerations

OBJECTIVE

To provide an overview of clinical recommendations regarding genomic medicine relating to pain management and opioid use disorder.

DATA SOURCES

A literature review was conducted using the search terms pain management, pharmacogenomics, pharmacogenetics, pharmacokinetics, pharmacodynamics, and opioids on PubMed (inception to February 1, 2021), CINAHL (2016 through February 1, 2021), and EMBASE (inception through February 1, 2021).

STUDY SELECTION AND DATA EXTRACTION

All relevant clinical trials, review articles, package inserts, and guidelines evaluating applicable pharmacogenotypes were considered for inclusion.

DATA SYNTHESIS

More than 300 Food and Drug Administration-approved medications contain pharmacogenomic information in their labeling. Genetic variability may alter the therapeutic effects of commonly prescribed pain medications. Pharmacogenomic-guided therapy continues to gain traction in clinical practice, but a multitude of barriers to widespread pharmacogenomic implementation exist.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Pain is notoriously difficult to treat given the need to balance safety and efficacy when selecting pharmacotherapy. Pharmacogenomic data can help optimize outcomes for patients with pain. With improved technological advances, more affordable testing, and a better understanding of genomic variants resulting in treatment disparities, pharmacogenomics continues to gain popularity. Unfortunately, despite these and other advancements, pharmacogenomic testing and implementation remain underutilized and misunderstood in clinical care, in part because of a lack of health care professionals trained in assessing and implementing test results.

CONCLUSIONS

A one-size-fits-all approach to pain management is inadequate and outdated. With increasing genomic data and pharmacogenomic understanding, patient-specific genomic testing offers a comprehensive and personalized treatment alternative worthy of additional research and consideration.

Nifedipine Does Not Alter the Pharmacokinetics of Venlafaxine Enantiomers in Healthy Subjects Phenotyped for CYP2D6, CYP2C19, and CYP3A

Venlafaxine (VEN) is a P-glycoprotein (P-gp) substrate, and nifedipine has been described by in vitro and experimental studies as a P-gp inhibitor. The present study aimed to investigate whether nifedipine alters the kinetic disposition of VEN enantiomers and their metabolites in healthy subjects. A crossover study was conducted in 10 healthy subjects phenotyped as extensive metabolizers for cytochrome P450 (CYP) 2D6, CYP2C19, and CYP3A. In phase 1, the subjects received a single oral dose of 150 mg racemic VEN, and in phase 2, a single oral dose of 40 mg nifedipine was administered with the VEN treatment. Plasma concentrations of VEN enantiomers and their metabolites O-desmethylvenlafaxine and N, O- didesmethylvenlafaxine (ODV and DDV, respectively) were evaluated by liquid chromatography with tandem mass spectrometry up to 72 hours after drug administration. Phase 2 was compared with phase 1 using the 90% confidence interval (CI) of the ratio of geometric means for C_max and area under the curve (AUC). AUC enantiomeric ratios S-(+)/R-(-) were evaluated within each and between phases using the Wilcoxon test (P ≤ .05). The kinetic disposition of VEN was enantioselective (phase 1) with VEN S-(+)/R-(-) AUC ratio median of 2.83 (AUC_0-∞ , 526 vs 195 ng·h/mL). However, AUC median did not differ between enantiomers for the metabolites ODV (1971 vs 2226 ng·h/mL) and DDV (199 vs 151 ng·h/mL). The 90%CI of the ratio of geometric means showed that the phases are bioequivalent. A single oral dose of 40 mg nifedipine did not alter VEN enantiomer pharmacokinetics in healthy subjects.

Study of mental health outcomes associated with different brands of venlafaxine at the Kumeu medical centre from January 2017 to October 2018

BACKGROUND

The antidepressant venlafaxine has been available in New Zealand for two decades and is funded by the New Zealand Drug Purchasing Agency PHARMAC. This audit aimed to determine whether change to a different funded generic formulation of venlafaxine affected patient responses to venlafaxine.

METHODS

A retrospective review of patient records for all patients at Kumeu Medical Centre, Auckland, New Zealand who received a prescription for venlafaxine since January 2017 was performed. Outcomes for patients who had experienced a stable positive clinical response to either of the two previously funded venlafaxine formulations and who were switched to the newly funded formulation were summarised.

RESULTS

Of 49 patients who had been prescribed venlafaxine, 34 patients were excluded; 15 patients had experienced a stable positive clinical response to either of the two previously funded venlafaxine formulations and switched to the newly funded formulation. Of these, 12 (80%) had poor outcomes following the change in venlafaxine formulation. Nine patients switched back to the original brand venlafaxine and showed improvement in clinical symptoms.

CONCLUSION

These cases, reported from a single general practice, should be sufficient to call attention to the possibility of loss of effectiveness for patients treated with a funded generic brand of venlafaxine, and the need for further research.

CYP2D1 Gene Knockout Reduces the Metabolism and Efficacy of Venlafaxine in Rats

Rat CYP2D1 has been considered as an ortholog of human CYP2D6 To assess the role of CYP2D1 in physiologic processes and drug metabolism, a CYP2D1-null rat model was generated with a CRISPR/Cas9 method. Seven base pairs were deleted from exon 4 of CYP2D1 of Sprague-Dawley wild-type (WT) rats. The CYP2D1-null rats were viable and showed no abnormalities in general appearance and behavior. The metabolism of venlafaxine (VLF) was further studied in CYP2D1-null rats. The V _max and intrinsic clearance of the liver microsomes in vitro from CYP2D1-null rats were decreased (by ∼46% and ∼57% in males and ∼47% and ∼58% in females, respectively), while the Michaelis constant was increased (by ∼24% in males and ∼25% in females) compared with WT rats. In the pharmacokinetic studies, compared with WT rats, VLF in CYP2D1-null rats had significantly lower apparent total clearance and apparent volume of distribution (decreased by ∼36% and ∼48% in males and ∼23% and ∼25% in females, respectively), significantly increased area under the curve (AUC) from the time of administration to the last time point, AUC from the start of administration to the theoretical extrapolation, and C _max (increased by ∼64%, ∼59%, and ∼26% in males and ∼43%, ∼35%, and ∼15% in females, respectively). In addition, O-desmethyl venlafaxine formation was reduced as well in CYP2D1-null rats compared with that in WT rats. Rat depression models were developed with CYP2D1-null and WT rats by feeding them separately and exposing them to chronic mild stimulation. VLF showed better efficacy in the WT depression rats compared with that in the CYP2D1-null rats. In conclusion, a CYP2D1-null rat model was successfully generated, and CYP2D1 was found to play a certain role in the metabolism and efficacy of venlafaxine. SIGNIFICANCE STATEMENT: A novel CYP2D1-null rat model was generated using CRISPR/Cas9 technology, and it was found to be a valuable tool in the study of the in vivo function of human CYP2D6. Moreover, our data suggest that the reduced O-desmethyl venlafaxine formation was associated with a lower VLF efficacy in rats.

A Prospective Study to Evaluate the Effect of CYP2D6 Polymorphism on Plasma level of Risperidone and its Metabolite in North Indian Patients with Schizophrenia

BACKGROUND

Risperidone is one of commonly utilized antipsychotic in clinical practice. Various metabolizing enzymes effect the plasma levels of risperidone and its active metabolite and thus its clinical efficacy. So, we attempted to evaluate the relationship between CYP2D6*10 (rs1065852) and CYP2D6*4 (rs3892097) gene polymorphism and the plasma concentration of risperidone and its metabolite in patients with schizophrenia.

METHODOLOGY

It was a 12-week prospective study carried out in patients diagnosed with schizophrenia. The dose of risperidone was increased weekly by 1 mg and rating of psychopathology was done using Positive and Negative Syndrome Scale (PANSS). Quantification of plasma level of risperidone and 9-hydroxyrisperidone was carried out at week 6 and 12 of treatment. The *4 and *10 alleles of CYP2D6 were genotyped and their effect on metabolism of risperidone was assessed.

RESULTS

The number of CYP2D6*4 alleles affected the plasma levels of risperidone, 9-hydroxyrisperidone at 6 weeks of treatment but not at 12 weeks. On the other hand, the number of mutated alleles for CYP2D6*10 influenced the dose corrected plasma concentration of risperidone and active moiety at 12 weeks of treatment. The ratio of plasma concentration of risperidone and 9-hydroxyrisperidone was more than one in all study participants, thus, suggesting that they were poor metabolizers of risperidone.

CONCLUSION

The polymorphism of CYP2D6*10 affects the steady state plasma concentration of risperidone in Indian patients with schizophrenia.

Venlafaxine pharmacokinetics focused on drug metabolism and potential biomarkers

Venlafaxine (VEN) is one of the safest and most effective drugs used in the treatment of selective serotonin reuptake inhibitors-resistant depression, and thereby it is nowadays one of the most commonly prescribed antidepressants. Nevertheless, patients treated with antidepressant drugs including VEN have exhibited large inter-individual variability in drug outcomes, possibly due to the influence of genetic and nongenetic factors on the drug pharmacokinetics and/or pharmacodynamics. Among them, an increased interest has emerged over the last few years on the genetic and/or phenotypic profile for drug-metabolizing cytochrome P450 isoenzymes and drug transporters such as potential predictive pharmacokinetic-based biomarkers of the variability found in drug biodisposition and antidepressant response. The integration of some of these key therapeutic biomarkers with classic therapeutic drug monitoring constitutes a promising way to individualization of VEN's pharmacotherapy, offering to clinicians the ability to better predict and manage pharmacological treatments to maximize the drug effectiveness. Thus, this review provides an extensive discussion of the pharmacokinetics of VEN focusing in particular on metabolism issues, without forgetting the clinically relevant sources of pharmacokinetics variability (mainly the genetic sources) and aiming on the identification of phenotypic and/or genetic biomarkers for therapy optimization.

First MEPS/HPLC assay for the simultaneous determination of venlafaxine and O-desmethylvenlafaxine in human plasma

Background: A new high-performance liquid chromatography–fluorescence detection assay based on microextraction by packed sorbent as sample preparation approach is described to quantify venlafaxine (VEN) and its main metabolite [O-desmethylvenlafaxine (ODV)]in human plasma. Methods & results: Chromatographic separation of the target analytes (VEN and ODV) and internal standard (licarbazepine) was achieved in less than 6 min on a reverse-phase C18 column using isocratic elution. Calibration curves were linear in the ranges of 10–1000 ng ml-1 for VEN and 20–1000 ng ml-1 for ODV. The method was successfully applied to real plasma samples. Conclusion: This microextraction by packed sorbent/high-performance liquid chromatography–fluorescence detection assay offers a cost-effective tool that can be applied for therapeutic drug monitoring and also support other pharmacokinetic-based studies in humans.

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.

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.