Response to CYP2D6 substrate antidepressants is predicted by a CYP2D6 composite phenotype based on genotype and comedications with CYP2D6 inhibitors

Cytochrome P450 2D6 profiles and anti-relapse efficacy of tafenoquine against Plasmodium vivax in Australian Defence Force personnel

Plasmodium vivax infections and relapses remain a major health problem for malaria-endemic countries, deployed military personnel, and travelers. Presumptive anti-relapse therapy and radical cure using the 8-aminoquinoline drugs primaquine and tafenoquine are necessary to prevent relapses. Although it has been demonstrated that the efficacy of primaquine is associated with Cytochrome P450 2D6 (CYP2D6) activity, there is insufficient data on the role of CYP2D6 in the anti-relapse efficacy of tafenoquine. We investigated the relationship between CYP2D6 activity status and tafenoquine efficacy in preventing P. vivax relapses retrospectively using plasma samples collected from Australian Defence Force personnel deployed to Papua New Guinea and Timor-Leste who participated in clinical trials of tafenoquine during 1999-2001. The CYP2D6 gene was amplified from plasma samples and fully sequenced from 92 participant samples, comprised of relapse (n = 31) and non-relapse (n = 61) samples, revealing 14 different alleles. CYP2D6 phenotypes deduced from combinations of CYP2D6 alleles predicted that among 92 participants 67, 15, and 10 were normal, intermediate, and poor metabolizers, respectively. The deduced CYP2D6 phenotype did not correlate with the corresponding participant's plasma tafenoquine concentrations that were determined in the early 2000s by high-performance liquid chromatography or liquid chromatography-mass spectrometry. Furthermore, the deduced CYP2D6 phenotype did not associate with P. vivax relapse outcomes. Our results indicate that CYP2D6 does not affect plasma tafenoquine concentrations and the efficacy of tafenoquine in preventing P. vivax relapses in the assessed Australian Defence Force personnel.

CYP1A2 expression rather than genotype is associated with olanzapine concentration in psychiatric patients

Olanzapine is a commonly prescribed atypical antipsychotic agent for treatment of patients with schizophrenia and bipolar disorders. Previous in vitro studies using human liver microsomes identified CYP1A2 and CYP2D6 enzymes being responsible for CYP-mediated metabolism of olanzapine. The present work focused on the impact of CYP1A2 and CYP2D6 genetic polymorphisms as well as of CYP1A2 metabolizing capacity influenced by non-genetic factors (sex, age, smoking) on olanzapine blood concentration in patients with psychiatric disorders (N = 139). CYP2D6 genotype-based phenotype appeared to have negligible contribution to olanzapine metabolism, whereas a dominant role of CYP1A2 in olanzapine exposure was confirmed. However, CYP1A2 expression rather than CYP1A2 genetic variability was demonstrated to be associated with olanzapine concentration in patients. Significant contribution of - 163C > A (rs762551), the most common SNP (single nucleotide polymorphism) in CYP1A2 gene, to enhanced inducibility was confirmed by an increase in CYP1A2 mRNA expression in smokers carrying - 163A, and smoking was found to have appreciable impact on olanzapine concentration normalized by the dose/bodyweight. Furthermore, patients' olanzapine exposure was in strong association with CYP1A2 expression; therefore, assaying CYP1A2 mRNA level in leukocytes can be an appropriate tool for the estimation of patients' olanzapine metabolizing capacity and may be relevant in optimizing olanzapine dosage.

Pharmacogenetics and phenoconversion: the influence on side effects experienced by psychiatric patients

Introduction: Preventing side effects is important to ensure optimal psychopharmacotherapy and therapeutic adherence among psychiatric patients. Obtaining the pharmacogenetic profile of CYP2C19 and CYP2D6 can play an important role in this. When the genotype-predicted phenotype shifts because of the use of co-medication, this is called phenoconversion. The aim was to study the influence of the pharmacogenetic (PGx) profile and phenoconversion on side effects experienced by psychiatric patients. Methods: A retrospective cohort study was performed using data from 117 patients from a psychiatric outpatient clinic. Patients were genotyped with a psychiatric PGx panel and side effects were evaluated using the Udvalg for Kliniske Undersølgelser side effects rating scale (UKU). Results: Of all patients, 10.3% and 9.4% underwent phenoconversion (any shift in predicted phenotype) for CYP2C19 and CYP2D6 respectively. No significant associations were found between the phenotype and UKU-score. 75% of the patients with an Intermediate metabolizer (IM) or Poor metabolizer (PM) phenoconverted phenotype of CYP2C19 experienced nausea and vomiting compared to 9.1% of the Normal metabolizer (NM) and Ultrarapid metabolizer (UM) patients (p = 0.033). 64% of the patients with an IM or PM phenoconverted phenotype of CYP2D6 experienced the side effect depression compared to 30.4% NMs and UMs (p = 0.020). CYP2D6 IM and PM patients had a higher concentration-dose ratio than NM patients (p < 0.05). Discussion: This study underlines the importance to consider phenoconversion when looking at a patient's genotype. This is important for a better prediction of the phenotype and preventing possible side effects under a specific psychopharmacotherapy.

Pharmacokinetic Markers of Clinical Outcomes in Severe Mental Illness: A Systematic Review

The term severe mental illness (SMI) encompasses those psychiatric disorders exerting the highest clinical burden and socio-economic impact on the affected individuals and their communities. Pharmacogenomic (PGx) approaches hold great promise in personalizing treatment selection and clinical outcomes, possibly reducing the burden of SMI. Here, we sought to review the literature in the field, focusing on PGx testing and particularly on pharmacokinetic markers. We performed a systematic review on PUBMED/Medline, Web of Science, and Scopus. The last search was performed on the 17 September 2022, and further augmented with a comprehensive pearl-growing strategy. In total, 1979 records were screened, and after duplicate removal, 587 unique records were screened by at least 2 independent reviewers. Ultimately, forty-two articles were included in the qualitative analysis, eleven randomized controlled trials and thirty-one nonrandomized studies. The observed lack of standardization in PGx tests, population selection, and tested outcomes limit the overall interpretation of the available evidence. A growing body of evidence suggests that PGx testing might be cost-effective in specific settings and may modestly improve clinical outcomes. More efforts need to be directed toward improving PGx standardization, knowledge for all stakeholders, and clinical practice guidelines for screening recommendations.

Cranberry Ingestion Modulated Drug Transporters and Metabolizing Enzymes: Gefitinib Used as a Probe Substrate in Rats

Cranberry, a polyphenol-rich functional food, is commonly used for the prophylaxis of urinary tract infections. Gefitinib, an anticancer agent clinically prescribed to treat non-small-cell lung cancer, is a substrate of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), and metabolized mainly by cytochrome P450 (CYP) 3A4 and CYP2D6. This study used gefitinib as a probe substrate to investigate the modulation of cranberry on P-gp, BCRP, CYP3A4 and CYP2D6. Rats were administered gefitinib with and without 5.0 g/kg of cranberry as juice (CJ). The concentration of gefitinib in serum was determined by LC-MS/MS. The results showed that CJ significantly increased the C_max and AUC_0-t of gefitinib by 28% and 55%, respectively. Mechanism studies indicated that CJ activated P-gp, and cranberry metabolites (CM) inhibited CYP2D6. Moreover, the protein level of P-gp in rat enterocytes was decreased, whereas that in hepatocytes was increased. In addition, the protein levels of BCRP, CYP3A4 and CYP2D6 in enterocytes and hepatocytes were decreased. In conclusion, CJ ingestion affected the activities and protein levels of P-gp, BCRP, CYP3A4 and CYP2D6.

Therapeutic Drug Monitoring of Second- and Third-Generation Antipsychotic Drugs-Influence of Smoking Behavior and Inflammation on Pharmacokinetics

Both inflammation and smoking can influence a drug’s pharmacokinetic properties, i.e., its liberation, absorption, distribution, metabolism, and elimination. Depending on, e.g., pharmacogenetics, these changes may alter treatment response or cause serious adverse drug reactions and are thus of clinical relevance. Antipsychotic drugs, used in the treatment of psychosis and schizophrenia, should be closely monitored due to multiple factors (e.g., the narrow therapeutic window of certain psychotropic drugs, the chronicity of most mental illnesses, and the common occurrence of polypharmacotherapy in psychiatry). Therapeutic drug monitoring (TDM) aids with drug titration by enabling the quantification of patients’ drug levels. Recommendations on the use of TDM during treatment with psychotropic drugs are presented in the Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology; however, data on antipsychotic drug levels during inflammation or after changes in smoking behavior—both clinically relevant in psychiatry—that can aid clinical decision making are sparse. The following narrative review provides an overview of relevant literature regarding TDM in psychiatry, particularly in the context of second- and third-generation antipsychotic drugs, inflammation, and smoking behavior. It aims to spread awareness regarding TDM (most pronouncedly of clozapine and olanzapine) as a tool to optimize drug safety and provide patient-tailored treatment.

Therapeutic Drug Monitoring of Second- and Third-Generation Antipsychotic Drugs—Influence of Smoking Behavior and Inflammation on Pharmacokinetics

Both inflammation and smoking can influence a drug’s pharmacokinetic properties, i.e., its liberation, absorption, distribution, metabolism, and elimination. Depending on, e.g., pharmacogenetics, these changes may alter treatment response or cause serious adverse drug reactions and are thus of clinical relevance. Antipsychotic drugs, used in the treatment of psychosis and schizophrenia, should be closely monitored due to multiple factors (e.g., the narrow therapeutic window of certain psychotropic drugs, the chronicity of most mental illnesses, and the common occurrence of polypharmacotherapy in psychiatry). Therapeutic drug monitoring (TDM) aids with drug titration by enabling the quantification of patients’ drug levels. Recommendations on the use of TDM during treatment with psychotropic drugs are presented in the Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology; however, data on antipsychotic drug levels during inflammation or after changes in smoking behavior—both clinically relevant in psychiatry—that can aid clinical decision making are sparse. The following narrative review provides an overview of relevant literature regarding TDM in psychiatry, particularly in the context of second- and third-generation antipsychotic drugs, inflammation, and smoking behavior. It aims to spread awareness regarding TDM (most pronouncedly of clozapine and olanzapine) as a tool to optimize drug safety and provide patient-tailored treatment.

Therapeutic Drug Monitoring of Second- and Third-Generation Antipsychotic Drugs-Influence of Smoking Behavior and Inflammation on Pharmacokinetics

Both inflammation and smoking can influence a drug's pharmacokinetic properties, i.e., its liberation, absorption, distribution, metabolism, and elimination. Depending on, e.g., pharmacogenetics, these changes may alter treatment response or cause serious adverse drug reactions and are thus of clinical relevance. Antipsychotic drugs, used in the treatment of psychosis and schizophrenia, should be closely monitored due to multiple factors (e.g., the narrow therapeutic window of certain psychotropic drugs, the chronicity of most mental illnesses, and the common occurrence of polypharmacotherapy in psychiatry). Therapeutic drug monitoring (TDM) aids with drug titration by enabling the quantification of patients' drug levels. Recommendations on the use of TDM during treatment with psychotropic drugs are presented in the Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology; however, data on antipsychotic drug levels during inflammation or after changes in smoking behavior-both clinically relevant in psychiatry-that can aid clinical decision making are sparse. The following narrative review provides an overview of relevant literature regarding TDM in psychiatry, particularly in the context of second- and third-generation antipsychotic drugs, inflammation, and smoking behavior. It aims to spread awareness regarding TDM (most pronouncedly of clozapine and olanzapine) as a tool to optimize drug safety and provide patient-tailored treatment.

Cytochrome P450 2D6 profiles and their relationship with outcomes of primaquine anti-relapse therapy in Australian Defence Force personnel deployed to Papua New Guinea and East Timor

Background

Primaquine, an 8-aminoquinoline with anti-hypnozoite activity against Plasmodium vivax, is metabolized by human cytochrome P450 2D6 (CYP2D6) to its active metabolite. Human CYP2D6 activities may influence the metabolism of primaquine and the risk of experiencing Plasmodium relapses following primaquine anti-relapse therapies (PART). In this study, the CYP2D6 profile and its relationship with outcomes of PART in Australian Defence Force (ADF) personnel is retrospectively investigated.

Methods

Genomic DNA was isolated from stored and de-identified serum or blood samples from ADF personnel deployed on peacekeeping duties to Papua New Guinea (PNG) (1999) and East Timor (1999–2000) who received PART before returning to Australia and after experiencing relapses. CYP2D6 allelic type was determined by PCR and Sanger sequencing. CYP2D6 allele frequency, predicted phenotypes and activity scores were compared among personnel who did not experience P. vivax (ADF-NR, n = 48) and those who experience at least one (ADF-R, n = 109) relapse, as well as between those who experienced 1 (n = 79), 2 (n = 21) and 3–5 (n = 9) relapses within the ADF-R group.

Results

16 CYP2D6 alleles were observed in 157 ADF personnel. Alleles *1, *4, *2 and *41 were major alleles (> 5%). The CYP2D6 allele frequency profile in the ADF-NR group matched that of a European population. There was an increased proportion of non-functional CYP2D6 alleles in the ADF-R group compared to the European population and ADF-NR group. However, frequencies of predicted CYP2D6 phenotype and activity score were not different between the ADF-R and ADF-NR groups, nor among sub-groups experiencing multiple relapses within the ADF-R group.

Conclusions

CYP2D6 phenotype or activity score based on the allele classification was not a major contributor to P. vivax relapse in this ADF cohort. Other factors such as adherence and/or parasite tolerance to primaquine are likely contributing factors to P. vivax relapses in this cohort.

Pharmacokinetic-Pharmacodynamic interaction associated with venlafaxine-XR remission in patients with major depressive disorder with history of citalopram / escitalopram treatment failure

BACKGROUND

The purpose of this study was to identify specific pharmacokinetic (PK) and pharmacodynamics (PD) factors that affect the likelihood of treatment remission with a serotonin norepinephrine reuptake inhibitor (SNRI) in depressed patients whose initial selective serotonin reuptake inhibitor (SSRI) failed.

METHODS

Multiple logistic regression modeling of PK and PD variation hypothesized to contribute to SNRI (i.e. duloxetine or venlafaxine) treatment remission in prior SSRI (i.e. citalopram or escitalopram) failure was conducted on 139 subjects from the Pharmacogenomics Research Network (PGRN) and Sequenced Treatment Alternatives to Relieve Depression (STAR*D) studies. Depressive symptoms were assessed with the Quick Inventory of Depressive Symptomatology Clinician-rated (QIDS-C₁₆).

RESULTS

Venlafaxine-XR remission was associated with a significant interaction between CYP2D6 ultra-rapid metabolizer (URM) phenotype and SLC6A4 5-HTTLPR L/L genotype. A similar significant interaction effect was observed between CYP2D6 URM and SLC6A2 G1287A GA genotype. Stratifying by transporter genotypes, venlafaxine-XR remission was associated with CYP2D6 URM in patients with SLC6A4 L/L (p = 0.001) and SLC6A2 G1287A GA genotypes.

LIMITATIONS

The primary limitation of this post hoc study was small sample size.

CONCLUSION

Our results suggest that CYP2D6 ultra-rapid metabolizer status contributes to venlafaxine-XR treatment remission in MDD patients; in particular, there is a PK-PD interaction with treatment remission associated with CYP2D6 URM phenotype and SLC6A4 5-HTTLPR L/L or SLC6A2 G1287A G/A genotype, respectively. These preliminary data are encouraging and support larger pharmacogenomics studies differentiating treatment response to mechanistically different antidepressants in addition to further PK-PD interactive analyses.

Cytochrome P450 2C19 Poor Metabolizer Phenotype in Treatment Resistant Depression: Treatment and Diagnostic Implications

Background: Pharmacogenomic testing, specifically for pharmacokinetic (PK) and pharmacodynamic (PD) genetic variation, may contribute to a better understanding of baseline genetic differences in patients seeking treatment for depression, which may further impact clinical antidepressant treatment recommendations. This study evaluated PK and PD genetic variation and the clinical use of such testing in treatment seeking patients with bipolar disorder (BP) and major depressive disorder (MDD) and history of multiple drug failures/treatment resistance.

Methods: Consecutive depressed patients evaluated at the Mayo Clinic Depression Center over a 10-year study time frame (2003–2013) were included in this retrospective analysis. Diagnoses of BP or MDD were confirmed using a semi-structured diagnostic interview. Clinical rating scales included the Hamilton Rating Scale for Depression (HRSD₂₄), Generalized Anxiety Disorder 7-item scale (GAD-7), Patient Health Questionnaire-9 (PHQ-9), and Adverse Childhood Experiences (ACE) Questionnaire. Clinically selected patients underwent genotyping of cytochrome P450 CYP2D6/CYP2C19 and the serotonin transporter SLC6A4. PK and PD differences and whether clinicians incorporated test results in providing recommendations were compared between the two patient groups.

Results: Of the 1795 patients, 167/523 (31.9%) with BP and 446/1272 (35.1%) with MDD were genotyped. Genotyped patients had significantly higher self-report measures of depression and anxiety compared to non-genotyped patients. There were significantly more CYP2C19 poor metabolizer (PM) phenotypes in BP (9.3%) vs. MDD patients (1.7%, p = 0.003); among participants with an S-allele, the rate of CYP2C19 PM phenotype was even higher in the BP (9.8%) vs. MDD (0.6%, p = 0.003). There was a significant difference in the distribution of SLC6A4 genotypes between BP (l/l = 28.1%, s/l = 59.3%, s/s = 12.6%) and MDD (l/l = 31.4%, s/l = 46.1%, s/s = 22.7%) patients (p < 0.01).

Conclusion: There may be underlying pharmacogenomic differences in treatment seeking depressed patients that potentially have impact on serum levels of CYP2C19 metabolized antidepressants (i.e., citalopram / escitalopram) contributing to rates of efficacy vs. side effect burden with additional potential risk of antidepressant response vs. induced mania. The evidence for utilizing pharmacogenomics-guided therapy in MDD and BP is still developing with a much needed focus on drug safety, side effect burden, and treatment adherence.

An economic model of the cost-utility of pre-emptive genetic testing to support pharmacotherapy in patients with major depression in primary care

The pharmacokinetics of many antidepressants (tricyclic antidepressants (TCA) or selective serotonin re-uptake inhibitors (SSRI)) are influenced by the highly polymorphic CYP2D6 enzyme. Therefore, pharmacogenetics could play an important role in the treatment of depressive patients. The potential cost-utility of screening patients is however still unknown. Therefore, a Markov model was developed to compare the strategy of screening for CYP2D6 and subsequently adjust antidepressant treatment according to a patient's metabolizer profile of poor, extensive, or ultra metabolizer, with the strategy of no screening ('one size fits all' principle). Each week a patient had a probability of side effects, which was followed by dosage titration or treatment switching. After 6 weeks treatment effect was evaluated followed by treatment adjustments if necessary, with a total time horizon of the model of 12 weeks. The analysis was performed from a societal perspective. The strategy of screening compared with no screening resulted in incremental costs of €91 (95 percentiles: €39; €152) more expensive but also more effect with 0.001 quality adjusted life years (QALYs) (95 percentiles: 0.001; 0.002) gain. The incremental cost-effectiveness ratio (ICER) was therefore €77,406 per QALY gained, but varied between €22,500 and €377,500 depending on the price of screening and productivity losses. According to our model, we cannot unequivocally conclude that screening for CYP2D6 in primary care patients using antidepressants is be cost-effective, as the results are surrounded by large uncertainty. Therefore, information from ongoing studies should be used to reduce these uncertainties.

Association between CYP2D6 Genotypes and the Risk of Antidepressant Discontinuation, Dosage Modification and the Occurrence of Maternal Depression during Pregnancy

Importance: Polymorphic expression of drug metabolizing enzymes affects the metabolism of antidepressants, and thus can contribute to drug response and/or adverse events. Pregnancy itself can affect CYP2D6 activity with profound variations determined by CYP2D6 genotype. Objective: To investigate the association between CYP2D6 genotype and the risk of antidepressant discontinuation, dosage modification, and the occurrence of maternal CYP2D6, Antidepressants, Depression during pregnancy. Setting: Data from the Organization of Teratology Information Specialists (OTIS) Antidepressants in Pregnancy Cohort, 2006-2010, were used. Women were eligible if they were within 14 completed weeks of pregnancy at recruitment and exposed to an antidepressant or having any exposures considered non-teratogenic. Main Outcomes and Measures: Gestational antidepressant usage was self-reported and defined as continuous/discontinued use, and non-use; dosage modification was further documented. Maternal depression and anxiety were measured every trimester using the telephone interviewer-administered Edinburgh Postnatal Depression Scale and the Beck Anxiety Inventory, respectively. Saliva samples were collected and used for CYP2D6 genotype analyses. Logistic regression models were used to calculate crude and adjusted odds ratios (OR) with 95% confidence intervals. Results: A total of 246 pregnant women were included in the study. The majority were normal metabolizers (NM, n = 204, 83%); 3.3% (n = 8) were ultrarapid metabolizers (UM), 5.7% (n = 14) poor metabolizers (PM), and 8.1% (n = 20) intermediate metabolizers (IM). Among study subjects, 139 women were treated with antidepressants at the beginning of pregnancy, and 21 antidepressant users (15%) discontinued therapy during pregnancy. Adjusting for depressive symptoms, and other potential confounders, the risk of discontinuing antidepressants during pregnancy was nearly four times higher in slow metabolizers (poor or intermediate metabolizers) compared to those with a faster metabolism rate (normal or ultrarapid metabolizers), aOR = 3.57 (95% CI: 1.15-11.11). Predicted CYP2D6 metabolizer status did not impact dosage modifications. Compared with slow metabolizers, significantly higher proportion of women in the fast metabolizer group had depressive symptom in the first trimester (19.81 vs. 5.88%, P = 0.049). Almost 21% of treated women remained depressed during pregnancy (14.4% NM-UM; 6.1% PM-IM). Conclusions and Relevance: Prior knowledge of CYP2D6 genotype may help to identify pregnant women at greater risk of antidepressant discontinuation. Twenty percent of women exposed to antidepressants during pregnancy remained depressed, indicating an urgent need for personalized treatment of depression during pregnancy.

A Model Based Cost-Effectiveness Analysis of Routine Genotyping for CYP2D6 among Older, Depressed Inpatients Starting Nortriptyline Pharmacotherapy

OBJECTIVE

Genotyping for CYP2D6 has the potential to predict differences in metabolism of nortriptyline. This information could optimize pharmacotherapy. We determined the costs and effects of routine genotyping for old aged Dutch depressed inpatients.

METHODS

With a decision-tree, we modelled the first 12 weeks of nortriptyline therapy. Direct costs of genotyping, hospitalization, therapeutic drug monitoring and drugs were included. Based on genotype, patients could be correctly, sub-, or supratherapeutically dosed. Improvement from sub- or supratherapeutically dosed patients to correctly dosed patients was simulated, assuming that genotyping would prevent under- or overdosing of patients. In the base case, this improvement was assumed to be 35%. A probabilistic sensitivity analysis (PSA) was performed to determine uncertainty around the incremental cost-effectiveness ratio (ICER).

RESULTS

In the base case analysis, costs for genotyping were assumed €200 per test with a corresponding ICER at €1 333 000 per QALY. To reach a €50 000 per QALY cut-off, genotyping costs should be decreased towards €40 per test. At genotyping test costs < €35 per test, genotyping was dominant. At test costs of €17 per test there was a 95% probability that genotyping was cost-effective at €50 000 per QALY.

CONCLUSIONS

CYP2D6 genotyping was not cost-effective at current genotyping costs at a €50 000 per QALY threshold, however at test costs below €40, genotyping could be costs-effective.

Raising the Minimum Effective Dose of Serotonin Reuptake Inhibitor Antidepressants: Adverse Drug Events

This review focuses on the dose-response of serotonin reuptake inhibitor (SRI) antidepressants for efficacy and for adverse drug events (ADEs). Dose-response is identified by placebo-controlled, double-blind, fixed-dose clinical trials comparing various doses for efficacy and for ADEs. Reports from the great majority of clinical trials have consistently found that the minimum SRI effective dose is usually optimal for efficacy in the treatment of depression disorders, even though most American medical practitioners raise the dose when early antidepressant treatment results are negative or partial. To better understand this issue, the medical literature was comprehensively reviewed to ascertain the degree to which SRI medications resulted in a flat dose response for efficacy and then to identify specific ADEs that are dose-dependent. Strong evidence from fixed-dose trial data for the efficacy of nonascendant, minimum effective doses of SRIs was found for the treatment of both major depression and anxiety disorders. Particularly important was the finding that most SRI ADEs have an ascending dose-response curve. These ADEs include sexual dysfunction, hypertension, cardiac conduction risks, hyperglycemia, decreased bone density, sweating, withdrawal symptoms, and agitation. Thus, routinely raising the SRI dose above the minimum effective dose for efficacy can be counter-productive.

Pharmacokinetic Pharmacogenetic Prescribing Guidelines for Antidepressants: A Template for Psychiatric Precision Medicine

Antidepressants are commonly prescribed medications in the United States, and there is increasing interest in individualizing treatment selection for more than 20 US Food and Drug Administration-approved treatments for major depressive disorder. Providing greater precision to pharmacotherapeutic recommendations for individual patients beyond the large-scale clinical trials evidence base can potentially reduce adverse effect toxicity profiles and increase response rates and overall effectiveness. It is increasingly recognized that genetic variation may contribute to this differential risk to benefit ratio and thus provides a unique opportunity to develop pharmacogenetic guidelines for psychiatry. Key studies and concepts that review the rationale for cytochrome P450 2D6 (CYP2D6) and cytochrome P450 2C19 (CYP2C19) genetic testing can be delineated by serum levels, adverse events, and clinical outcome measures (eg, antidepressant response). In this article, we report the evidence that contributed to the implementation of pharmacokinetic pharmacogenetic guidelines for antidepressants primarily metabolized by CYP2D6 and CYP2C19.

Liver Function Test Abnormalities in Depressed Patients Treated with Antidepressants: A Real-World Systematic Observational Study in Psychiatric Settings

Background

Concerning the risk of antidepressant induced liver injury, it is not clear whether psychiatrists perform a liver function test (LFT) and whether an increase in aminotransferase levels should contraindicate antidepressant treatment.

Aim

To evaluate LFT availability, the prevalence of LFT abnormalities and the probable cause of an altered LFT in patients with a major depressive episode (MDE) requiring an antidepressant drug.

Methods

We studied LFT evaluation in a real world psychiatric setting, in a sample of 321 consecutive patients with a current major depressive episode (MDE) requiring an antidepressant drug treatment, but without current alcohol or drug dependence or unstable medical disease.

Results

An LFT is performed in 36.1% (116/321) of depressed patients. One fifth of antidepressant-treated patients who had an LFT evaluation had abnormal results. The most frequent causes of LFT abnormalities were: NAFLD (nonalcoholic fatty liver disease) (7/321; 2.1%), acute alcohol consumption (4/321; 1.2%), antidepressant-induced liver injury (3/321; 0.9%), hepatitis C virus infection (2/321; 0.6%) and heart failure (1/321; 0.3%). The cause of LFT abnormalities was unknown in 32% of patients (8/25) due to the absence of etiological investigations.

Conclusion

These results demonstrate that an LFT is infrequently performed by psychiatrists in depressed patients requiring an antidepressant drug. Baseline LFT assessment and observations during the first six months of antidepressant treatment may be useful for detection of patients with pre-existing liver disease such as NAFLD, and early identification of cases of antidepressant-induced liver injury. An increase in aminotransferase levels may be related to an underlying liver disease, but does not contraindicate antidepressant treatment.

Atomoxetine: A Review of Its Pharmacokinetics and Pharmacogenomics Relative to Drug Disposition

Atomoxetine is a selective norepinephrine (NE) reuptake inhibitor approved for the treatment of attention-deficit/hyperactivity disorder (ADHD) in children (≥6 years of age), adolescents, and adults. Its metabolism and disposition are fairly complex, and primarily governed by cytochrome P450 (CYP) 2D6 (CYP2D6), whose protein expression varies substantially from person to person, and by race and ethnicity because of genetic polymorphism. These differences can be substantial, resulting in 8-10-fold differences in atomoxetine exposure between CYP2D6 poor metabolizers and extensive metabolizers. In this review, we have attempted to revisit and analyze all published clinical pharmacokinetic data on atomoxetine inclusive of public access documents from the new drug application submitted to the United States Food and Drug Administration (FDA). The present review focuses on atomoxetine metabolism, disposition, and genetic polymorphisms of CYP2D6 as they specifically relate to atomoxetine, and provides an in-depth discussion of the fundamental pharmacokinetics of the drug including its absorption, distribution, metabolism, and excretion in pediatric and adult populations. Further, a summary of relationships between genetic variants of CYP2D6 and to some degree, CYP2C19, are provided with respect to atomoxetine plasma concentrations, central nervous system (CNS) pharmacokinetics, and associated clinical implications for pharmacotherapy. Lastly, dosage adjustments based on pharmacokinetic principles are discussed.

Personalizing supportive care in oncology patients using pharmacogenetic-driven treatment pathways

Cancer patients frequently suffer from disease- and treatment-related pain, nausea and depression, which severely reduces patients' quality of life. It is critical that clinicians are aware of drug-gene interactions and recognize the utility of applying pharmacogenetic information to personalize and improve supportive care. Pharmacogenetic-based algorithms may enhance clinical outcomes by allowing the clinician to select the 'least genetically vulnerable' drug. This review summarizes clinically relevant drug-gene interactions and presents pharmacogenetic-driven treatment pathways for depression, nausea/vomiting and pain. Ideally, this review provides a resource for clinicians to consult when selecting pharmacotherapy for a patient who presents with limited pharmacogenetic test results, with the hope of better controlling burdensome symptoms and improving the quality of life for cancer patients.

CYP450 genotype and pharmacogenetic association studies: a critical appraisal

Despite strong pharmacological support, association studies using genotype-predicted phenotype as a variable have yielded conflicting or inconclusive evidence to promote personalized pharmacotherapy. Unless the patient is a genotypic poor metabolizer, imputation of patient's metabolic capacity (or metabolic phenotype), a major factor in drug exposure-related clinical response, is a complex and highly challenging task because of limited number of alleles interrogated, population-specific differences in allele frequencies, allele-specific substrate-selectivity and importantly, phenoconversion mediated by co-medications and inflammatory co-morbidities that modulate the functional activity of drug metabolizing enzymes. Furthermore, metabolic phenotype and clinical outcomes are not binary functions; there is large intragenotypic and intraindividual variability. Therefore, the ability of association studies to identify relationships between genotype and clinical outcomes can be greatly enhanced by determining phenotype measures of study participants and/or by therapeutic drug monitoring to correlate drug concentrations with genotype and actual metabolic phenotype. To facilitate improved analysis and reporting of association studies, we propose acronyms with the prefixes ‘g’ (genotype-predicted phenotype) and ‘m’ (measured metabolic phenotype) to better describe this important variable of the study subjects. Inclusion of actually measured metabolic phenotype, and when appropriate therapeutic drug monitoring, promises to reveal relationships that may not be detected by using genotype alone as the variable.

[Economic evaluation of desvenlafaxine in the treatment of major depressive disorder in Spain]

INTRODUCTION

The objective of this analysis was to evaluate the clinical and economic value of the use of 50mg-desvenlafaxine compared to the usual care (mix of duloxetine and venlafaxine) in the outpatient treatment of major depressive disorder after first line treatment failure (relapse) in Spain.

MATERIALS AND METHODS

A Markov model was used to follow up a cohort of major depressive disorder patients for one year after failure of first-line treatment with a serotonin-specific reuptake inhibitor and estimate outcome measures (percentage remission and depression-free days) and accrued and direct costs incurred during outpatient treatment of major depressive disorder. In order to obtain the efficacy data related to the treatment alternatives, a literature review of clinical trials was performed. A panel of clinical experts validated the use of clinical resources employed in the estimation of economic outcomes together with model assumptions. The analysis was performed in 2014 from the perspective of the National Health System.

RESULTS

Due to fewer discontinuations, initiating second line treatment with desvenlafaxine was associated with more depression-free days and a higher percentage of patients in remission versus usual care: 1.7 days and 0.5%, respectively. This was translated into lower drug and events management costs, and an overall cost reduction of €108 for the National Health System.

CONCLUSIONS

In patients who have not responded to a first-line serotonin-specific reuptake inhibitor therapy, desvenlafaxine-50mg was clinically similar in effectiveness, but a less costly option, compared with a weighted average of duloxetine and venlafaxine for the second-line treatment of major depressive disorder patients from a payer (National Health System) perspective in Spain.

Inflammation-induced phenoconversion of polymorphic drug metabolizing enzymes: hypothesis with implications for personalized medicine

Phenoconversion transiently converts genotypic extensive metabolizers (EMs) into phenotypic poor metabolizers (PMs) of drugs, potentially with corresponding changes in clinical response. This phenomenon, typically resulting from coadministration of medications that inhibit certain drug metabolizing enzymes (DMEs), is especially well documented for enzymes of the cytochrome P450 family. Nonclinical evidence gathered over the last two decades also strongly implicates elevated levels of some proinflammatory cytokines, released during inflammation, in down-regulation of drug metabolism, especially by certain DMEs of the P450 family, thereby potentially causing transient phenoconversion. Clinically, phenoconversion of NAT2, CYP2C19, and CYP2D6 has been documented in inflammatory conditions associated with elevated cytokines, such as human immunodeficiency virus infection, cancer, and liver disease. The potential of other inflammatory conditions to cause phenoconversion has not been studied but experimental and anecdotal clinical evidence supports infection-induced down-regulation of CYP1A2, CYP3A4, and CYP2C9 as well. Collectively, the evidence supports a hypothesis that certain inflammatory conditions associated with elevated proinflammatory cytokines may cause phenoconversion of certain DMEs. Since inflammatory conditions associated with elevated levels of proinflammatory cytokines are highly prevalent, phenoconversion of genotypic EM patients into transient phenotypic PMs may be more frequent than appreciated. Since drug pharmacokinetics, and therefore the clinical response, is influenced by DME phenotype rather than genotype per se, phenoconversion (whatever its cause) can have a significant impact on the analysis and interpretation of genotype-focused clinical outcome association studies. There is a risk that focusing on genotype alone may miss important associations between clinical outcomes and DME phenotypes, thus compromising future prospects of personalized medicine.