A case report of a poor metabolizer of CYP2D6 presented with unusual responses to nortriptyline medication

Genes, Cognition, and Their Interplay in Methamphetamine Use Disorder

Methamphetamine use disorder is a pressing global health issue, often accompanied by significant cognitive deficits that impair daily functioning and quality of life and complicate treatment. Emerging evidence highlights the potential role of genetic factors in methamphetamine use disorder, particularly in association with cognitive function. This review examines the key genetic and cognitive dimensions and their interplay in methamphetamine use disorder. There is converging evidence from several studies that genetic polymorphisms in BDNF, FAAH, SLC18A1, and SLC18A2 are associated with protection against or susceptibility to the disorder. In addition, people with methamphetamine use disorder consistently displayed impairments in cognitive flexibility and inhibitory control compared with people without the disorder. These cognitive domains were associated with reactivity to methamphetamine cues that were positively correlated with total years of methamphetamine use history. Emerging research also suggests that inhibitory control is negatively correlated with lower blood FAAH mRNA levels, while cognitive flexibility positively correlates with higher blood SLC18A2 mRNA levels, highlighting how genetic and cognitive dimensions interact in methamphetamine use disorder. We also include some future directions, emphasizing potential personalized therapeutic strategies that integrate genetic and cognitive insights. By drawing attention to the interplay between genes and cognition, we hope to advance our understanding of methamphetamine use disorder and inform the development of targeted interventions.

Prescribed Doses of CYP2D6-Metabolized Drugs and Hemodynamic Responses in Relation to CYP2D6 Genotype Among Older Patients Exposed to Polypharmacy

Background

Many drugs with dose-dependent effects on hemodynamic variables are metabolized by cytochrome P450 2D6 (CYP2D6). The aim of this study was to compare prescribed dosages and hemodynamic responses of such drugs in relation to pharmacogenetic variability in CYP2D6 metabolism among patients aged ≥ 70 years exposed to polypharmacy.

Materials and Methods

We included 173 patients with detailed information about drug use. The patients were retrospectively subjected to CYP2D6 genotyping, which comprised the most common variant alleles encoding reduced, absent, or increased CYP2D6 metabolism. In order to compare dosages across different CYP2D6-metabolized drugs, all prescribed daily doses were harmonized to the ‘percent of a daily defined dose’ (DDD). The mean harmonized DDD was compared between genotype-predicted normal metabolizers (NMs) and patients with reduced or absent CYP2D6 enzyme activity, defined as intermediate or poor metabolizers (IMs/PMs). Blood pressure, pulse, and patient proportions with orthostatism and bradycardia were also compared between genotype subgroups.

Results

The genotype-predicted phenotype subgroups comprised 79 NMs (45.7%), 75 IMs (43.4%), and 16 PMs (9.2%). There were no differences in dosing of CYP2D6 substrates between NMs and IMs/PMs (p = 0.76). A higher proportion of CYP2D6 IMs/PMs experienced orthostatism (p = 0.03), while there were no significant subgroup differences for the other hemodynamic variables.

Conclusion

In this real-life clinical setting of patients aged ≥ 70 years, dosing of CYP2D6 substrates were not adjusted according to genotype-predicted CYP2D6 metabolism. The increased occurrence of orthostatism in patients with reduced/absent CYP2D6 metabolism may indicate that individualized dosing based on genotype has the potential to prevent adverse effects in these vulnerable patients.

Electronic supplementary material

The online version of this article (10.1007/s40266-020-00763-0) contains supplementary material, which is available to authorized users.

Risk assessment of accidental nortriptyline poisoning: the importance of cytochrome P450 for nortriptyline elimination investigated using a population-based pharmacokinetic simulator

It is not possible to make a prospective clinical study that reveals the importance of the nortriptyline metabolising cytochrome P450 (CYP) isoforms (CYP1A2, CYP2C19, CYP2D6, and CYP3A4) in relation to attaining potential toxic nortriptyline concentrations with a possibly fatal outcome. Therefore to study this we have applied the population based pharmacokinetic simulator Simcyp. The objective was to estimate how important CYP2C19 and CYP2D6 phenotype status, hepatic activity of CYP3A4, body weight, CYP2D6 phenotype dose adjustment, and drug-drug interactions are with regard to accidental poisoning in a virtual population receiving a daily dose of 100mg nortriptyline. Accidental poisoning is here defined as intake of a normal dose which because of slow metabolism may lead to potentially toxic concentrations. The input parameters values for Simcyp were based on average literature in vitro and in vivo data. The Simcyp simulations of nortriptyline pharmacokinetics reflected reported clinical concentration-time profiles, therapeutic drug monitoring data, and the consequence of CYP2D6 poor metaboliser (PM) and ultrarapid metaboliser status. Of the investigated factors, the simulations indicate that having CYP2D6 PM status is a major risk factor for attaining high concentrations and thereby possibly becoming poisoned by nortriptyline. Of the CYP2D6 PM subjects 16% would attain plasma concentrations exceeding the toxic limit. Individuals with the combination of CYP2D6 PM status and 10% of the average liver CYP3A4 expression had a 90% risk of becoming poisoned. The results point towards the combination of low CYP3A4 activity and CYP2D6 PM status of major importance for attaining possibly toxic nortriptyline concentrations. In a forensic toxicological context, the results indicate that both the activity of CYP3A4, information on possible drug-drug interactions, and the genotype of CYP2D6 are needed in order to elucidate whether an individual might have been accidentally poisoned because of slow metabolism. In a clinical context, the simulations suggest that precise individual dose adjustment of nortriptyline requires information regarding the activity of both CYP3A4 and CYP2D6. This underlines the value of therapeutic drug monitoring for nortriptyline. Population based pharmacokinetic simulations are considered useful tools for risk assessment in clinical and forensic toxicology.

Cytochrome P450 loss-of-function polymorphism genotyping on the Agilent Bioanalyzer and clinical application

Responses to toxins and drugs, even to standard medical drug treatment regimens, can vary significantly between individuals. Similar dosages can have divergent results due to polymorphisms in the genes that code for the enzymes responsible for the metabolism of drugs. The focus of this report is to describe our exploration of the personalized medicine approach for patient care at Sydney West Area Health Service. We would like to demonstrate the importance of this approach as it is the subject of debate in the medical and scientific community. The critical points in this debate are the cost of testing, laboratory space required and clinical application. We have shown that a simple approach and instruments like the Agilent Bioanalyzer could be cost effective for laboratory operation. The Agilent Bioanalyzer (Agilent Technologies, CA, USA) can be used for proteins, DNA and cell studies. Hence, reduced cost of instruments, laboratory space requirements, maintenance and operational costs are great advantages of this technology, especially for development and research laboratories.

Prospective use of CYP pharmacogenetics and medication analysis to facilitate improved therapy - a pilot study

OBJECTIVES

To assess the efficacy of cytochrome P450 (CYP) pharmacogenetic testing and medication interaction analysis in a controlled environment for reduction of events, stays in hospital, extra care and required extra doctors visits to the patients.

METHODS

A prospective cohort study of 28 patients in a geriatric care facility with multimedication and at least one report of an event was performed over a period of 7 months. In the first phase of the study the patients were closely monitored twice a day by the care staff, recording all potential events, regardless of association with the indication or not, requirement for extra care, requirement for an unplanned site visit from a physician and days in hospital. In a 1-month period, the patients were genotyped for the cytochromes CYP2C9, CYP2C19 and CYP2D6, and their medication analyzed for interactions, using a proprietary computer program. Recommendations for medication change based upon genetics and/or medication interaction analysis were made to the care physicians. In a second 3-month phase the patients were monitored as in Phase I. The data comparing Phase I with Phase II was analyzed using two way ANOVA.

RESULTS

Of the 28 patients in the study in both phases, 16 (55%) had genetic and/or medication interaction problems that required change of medication. A total of 11 out of 16 (69%) of the patients did have their medication altered by the care physician. Of the 11 patients, five (45%) demonstrated some betterment in the number of reported events after alteration of their medication. Of these five patients, three had improvements when their medication was altered for their genetics. A further three (one patient had improvements due to both effects) had improvements when their medication was altered after a medication interaction analysis.

CONCLUSION

Although an exploratory pilot study, this cohort study shows the possibilities and potential of pharmacogenetic testing for CYP alterations combined with medication interaction analysis of patients in a geriatric care facility.

Translating pharmacogenomics: challenges on the road to the clinic

Pharmacogenomics is one of the first clinical applications of the postgenomic era. It promises personalized medicine rather than the established "one size fits all" approach to drugs and dosages. The expected reduction in trial and error should ultimately lead to more efficient and safer drug therapy. In recent years, commercially available pharmacogenomic tests have been approved by the Food and Drug Administration (FDA), but their application in patient care remains very limited. More generally, the implementation of pharmacogenomics in routine clinical practice presents significant challenges. This article presents specific clinical examples of such challenges and discusses how obstacles to implementation of pharmacogenomic testing can be addressed.