Therapeutic Drug Monitoring of Venlafaxine in an Everyday Clinical Setting: Analysis of Age, Sex and Dose Concentration Relationships

Developing a machine learning model for predicting venlafaxine active moiety concentration: a retrospective study using real-world evidence

BACKGROUND

Venlafaxine is frequently prescribed for patients with depression. To control the concentration of venlafaxine within the therapeutic window for the best treatment effect, a model to predict venlafaxine concentration is necessary.

AIM

Our objective was to develop a prediction model for venlafaxine concentration using real-world evidence based on machine learning and deep learning techniques.

METHOD

Patients who underwent venlafaxine treatment between November 2019 and August 2022 were included in the study. Important variables affecting venlafaxine concentration were identified using a combination of univariate analysis, sequential forward selection, and machine learning techniques. Predictive performance of nine machine learning and deep learning algorithms were assessed, and the one with the optimal performance was selected for modeling. The final model was interpreted using SHapley Additive exPlanations.

RESULTS

A total of 330 eligible patients were included. Five influential variables that affect venlafaxine concentration were venlafaxine daily dose, sex, age, hyperlipidemia, and adenosine deaminase. The venlafaxine concentration prediction model was developed using the eXtreme Gradient Boosting algorithm (R2 = 0.65, mean absolute error = 77.92, root mean square error = 93.58). In the testing cohort, the accuracy of the predicted concentration within ± 30% of the actual concentration was 73.49%. In the subgroup analysis, the prediction accuracy was 69.39% within the recommended therapeutic range of venlafaxine concentration within ± 30% of the actual value.

CONCLUSION

The XGBoost model for predicting blood concentration of venlafaxine using real-world evidence was developed, guiding the adjustment of regimen in clinical practice.

Multiplexed quantification of venlafaxine and metabolites in human plasma by liquid chromatography-tandem mass spectrometry

BACKGROUND

Venlafaxine (VEN) and its O-demethylated metabolite, O-desmethylvenlafaxine (ODV), are commonly prescribed serotonin-norepinephrine reuptake inhibitors, approved for the treatment of depression and anxiety. Both are metabolized to inactive metabolites via cytochrome P450 enzymes. While previous studies have focused on quantifying VEN and ODV, bioanalytical methods for the simultaneous measurement of all metabolites are needed to fully characterize the pharmacology of VEN and ODV.

METHODS

K2EDTA plasma was spiked with VEN, ODV, N-desmethylvenlafaxine (NDV), N,O-didesmethylvenlafaxine (NODDV), and N,N-didesmethylvenlafaxine (NNDDV). Drugs and metabolites were extracted via protein precipitation and quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The multiplexed assay was validated in accordance with regulatory recommendations, and evaluated in remnant plasma samples from persons prescribed venlafaxine.

RESULTS

The analytical measuring range for venlafaxine and all four metabolites was 5-800 ng/mL. Standard curves were generated via weighted quadratic (NNDDV) or linear (VEN, ODV, NDV, NODDV) regression of calibrators. Inter-assay imprecision was between 1.9-9.3% for all levels of all analytes. Minor matrix effects were observed, and both recovery efficiency and process efficiency were >96% for all analytes. All other assay validation assessments met acceptance criteria. Drug concentrations measured from remnant plasma specimens obtained from patients with current venlafaxine prescriptions (37.5-450 mg/day) yielded NDDV, NDV, and NODDV metabolite concentrations in 6/21, 14/21, and 20/21 samples, respectively. The ratio of active to inactive analytes ranged from 0.74 to 14.5, with a median of 6.39.

CONCLUSIONS

An efficient and accurate LC-MS/MS method was developed and validated for the quantification of VEN, ODV, and all three inactive metabolites in plasma. The assay met all acceptance criteria, and may be used in future studies of the pharmacokinetics of these drugs.

Therapeutic Drug Monitoring in Psychiatry: Enhancing Treatment Precision and Patient Outcomes

Psychiatric disorders often require pharmacological interventions to alleviate symptoms and improve quality of life. However, achieving an optimal therapeutic outcome is challenging due to several factors, including variability in the individual response, inter-individual differences in drug metabolism, and drug interactions in polytherapy. Therapeutic drug monitoring (TDM), by measuring drug concentrations in biological samples, represents a valuable tool to address these challenges, by tailoring medication regimens to each individual. This review analyzes the current landscape of TDM in psychiatric practice, highlighting its significance in optimizing drug dosages, minimizing adverse effects, and improving therapeutic efficacy. The metabolism of psychiatric medications (i.e., mood stabilizers, antipsychotics, antidepressants) often exhibits significant inter-patient variability. TDM can help address this variability by enhancing treatment personalization, facilitating early suboptimal- or toxic-level detection, and allowing for timely interventions to prevent treatment failure or adverse effects. Furthermore, this review briefly discusses technological advancements and analytical methods supporting the implementation of TDM in psychiatric settings. These innovations enable quick and cost-effective drug concentration measurements, fostering the widespread adoption of TDM as a routine practice in psychiatric care. In conclusion, the integration of TDM in psychiatry can improve treatment outcomes by individualizing medication regimens within the so-called precision medicine.

Age of onset for increased dose-adjusted serum concentrations of antidepressants and association with sex and genotype: An observational study of 34,777 individuals

PURPOSE

The aim of this study was to examine the age of onset for increased dose-adjusted serum concentrations (C/D ratio) of common antidepressant drugs and to explore the potential association with sex and CYP2C19/CYP2D6 genotype.

METHODS

Serum concentrations and prescribed daily doses for citalopram, escitalopram, sertraline, venlafaxine and mirtazapine, and CYP genotypes, were obtained from a therapeutic drug monitoring (TDM) service. Segmented linear regression analysis was used to examine the relationship between age and antidepressant log C/D ratio in (i) all individuals, (ii) men and women, and (iii) CYP2D6/CYP2C19 normal metabolizers (NMs) and CYP2D6/CYP2C19 intermediate or poor metabolizers (IMs/PMs).

RESULTS

A total of 34,777 individuals were included in the study; CYP genotype was available for 21.3%. An increase in C/D ratio started at 44‒55 years of age. Thereafter, the increase progressed more rapidly for citalopram and escitalopram than for venlafaxine and mirtazapine. A doubled C/D ratio was estimated to occur at 79 (citalopram), 81 (escitalopram), 86 (venlafaxine), and 90 years (mirtazapine). For sertraline, only modest changes in C/D ratio were observed. For escitalopram and venlafaxine, the observed increase in C/D ratio started earlier in women than in men. The results regarding CYP genotype were inconclusive.

CONCLUSION

The age-related increase in C/D ratio starts in middle-aged adults and progresses up to more than twofold higher C/D ratio in the oldest old. Sertraline seems to be less prone to age-related changes in C/D ratio than the other antidepressants.

Venlafaxine's therapeutic reference range in the treatment of depression revised: a systematic review and meta-analysis

INTRODUCTION

The selective serotonin and norepinephrine reuptake inhibitor venlafaxine is among the most prescribed antidepressant drugs worldwide and, according to guidelines, its dose titration should be guided by drug-level monitoring of its active moiety (AM) which consists of venlafaxine (VEN) plus active metabolite O-desmethylvenlafaxine (ODV). This indication of therapeutic drug monitoring (TDM), however, assumes a clear concentration/effect relationship for a drug, which for VEN has not been systematically explored yet.

OBJECTIVES

We performed a systematic review and meta-analysis to investigate the relationship between blood levels, efficacy, and adverse reactions in order to suggest an optimal target concentration range for VEN oral formulations for the treatment of depression.

METHODS

Four databases (MEDLINE (PubMed), PsycINFO, Web of Science Core Collection, and Cochrane Library) were systematically searched in March 2022 for relevant articles according to a previously published protocol. Reviewers independently screened references and performed data extraction and critical appraisal.

RESULTS

High-quality randomized controlled trials investigating concentration/efficacy relationships and studies using a placebo lead-in phase were not found. Sixty-eight articles, consisting mostly of naturalistic TDM studies or small noncontrolled studies, met the eligibility criteria. Of them, five cohort studies reported a positive correlation between blood levels and antidepressant effects after VEN treatment. Our meta-analyses showed (i) higher AM and (ii) higher ODV concentrations in patients responding to VEN treatment when compared to non-responders (n = 360, k = 5). AM concentration-dependent occurrence of tremor was reported in one study. We found a linear relationship between daily dose and AM concentration within guideline recommended doses (75-225 mg/day). The population-based concentration ranges (25-75% interquartile) among 11 studies (n = 3200) using flexible dosing were (i) 225-450 ng/ml for the AM and (ii) 144-302 ng/ml for ODV. One PET study reported an occupancy of 80% serotonin transporters for ODV serum levels above 85 ng/ml. Based on our findings, we propose a therapeutic reference range for AM of 140-600 ng/ml.

CONCLUSION

VEN TDM within a range of 140 to 600 ng/ml (AM) will increase the probability of response in nonresponders. A titration within the proposed reference range is recommended in case of non-response at lower drug concentrations as a consequence of VEN's dual mechanism of action via combined serotonin and norepinephrine reuptake inhibition. Drug titration towards higher concentrations will, however, increase the risk for ADRs, in particular with supratherapeutic drug concentrations.

Automated Interlaboratory Comparison of Therapeutic Drug Monitoring Data and Its Use for Evaluation of Published Therapeutic Reference Ranges

Therapeutic drug monitoring is a tool for optimising the pharmacological treatment of diseases where the therapeutic effect is difficult to measure or monitor. Therapeutic reference ranges and dose-effect relation are the main requirements for this drug titration tool. Defining and updating therapeutic reference ranges are difficult, and there is no standardised method for the calculation and clinical qualification of these. The study presents a basic model for validating and selecting routine laboratory data. The programmed algorithm was applied on data sets of antidepressants and antipsychotics from three public hospitals in Denmark. Therapeutic analytical ranges were compared with the published therapeutic reference ranges by the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) and in additional literature. For most of the drugs, the calculated therapeutic analytical ranges showed good concordance between the laboratories and to published therapeutic reference ranges. The exceptions were flupentixol, haloperidol, paroxetine, perphenazine, and venlafaxine + o-desmethyl-venlafaxine (total plasma concentration), where the range was considerably higher for the laboratory data, while the calculated range of desipramine, sertraline, ziprasidone, and zuclopenthixol was considerably lower. In most cases, we identified additional literature supporting our data, highlighting the need of a critical re-examination of current therapeutic reference ranges in Denmark. An automated approach can aid in the evaluation of current and future therapeutic reference ranges by providing additional information based on big data from multiple laboratories.

The pharmacogenetics of CYP2D6 and CYP2C19 in a case series of antidepressant responses

Pharmacogenetics has potential for optimizing use of psychotropics. CYP2D6 and CYP2C19 are two clinically relevant pharmacogenes in the prescribing of antidepressants. Using cases recruited from the Understanding Drug Reactions Using Genomic Sequencing (UDRUGS) study, we aimed to evaluate the clinical utility of genotyping CYP2D6 and CYP2C19 in antidepressant response. Genomic and clinical data for patients who were prescribed antidepressants for mental health disorders, and experienced adverse reactions (ADRs) or ineffectiveness, were extracted for analysis. Genotype-inferred phenotyping of CYP2D6 and CYP2C19 was carried out as per Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines. A total of 52 patients, predominantly New Zealand Europeans (85%) with a median age (range) of 36 years (15-73), were eligible for analysis. Thirty-one (60%) reported ADRs, 11 (21%) ineffectiveness, and 10 (19%) reported both. There were 19 CYP2C19 NMs, 15 IMs, 16 RMs, one PM and one UM. For CYP2D6, there were 22 NMs, 22 IMs, four PMs, three UMs, and one indeterminate. CPIC assigned a level to each gene-drug pair based on curated genotype-to-phenotype evidence. We analyzed a subgroup of 45 cases, inclusive of response type (ADRs/ineffectiveness). Seventy-nine (N = 37 for CYP2D6, N = 42 for CYP2C19) gene-drug/antidepressant-response pairs with CPIC evidence levels of A, A/B, or B were identified. Pairs were assigned as 'actionable' if the CYP phenotypes potentially contributed to the observed response. We observed actionability in 41% (15/37) of CYP2D6-antidepressant-response pairs and 36% (15/42) of CYP2C19-antidepressant-response pairs. In this cohort, CYP2D6 and CYP2C19 genotypes were actionable for a total of 38% pairs, consisting of 48% in relation to ADRs and 21% in relation to drug ineffectiveness.

Joint population pharmacokinetic modeling of venlafaxine and O-desmethyl venlafaxine in healthy volunteers and patients to evaluate the impact of morbidity and concomitant medication

Introduction: Venlafaxine (VEN) is a widely used dual selective serotonin/noradrenaline reuptake inhibitor indicated for depression and anxiety. It undergoes first-pass metabolism to its active metabolite, O-desmethyl venlafaxine (ODV). The aim of the present study was to develop a joint population pharmacokinetic (PPK) model to characterize their pharmacokinetic characters simultaneously. Methods: Plasma concentrations with demographic and clinical data were derived from a bioequivalence study in 24 healthy subjects and a naturalistic TDM setting containing 127 psychiatric patients. A parent-metabolite PPK modeling was performed with NONMEM software using a non-linear mixed effect modeling approach. Goodness of fit plots and normalized prediction distribution error method were used for model validation. Results and conclusion: Concentrations of VEN and ODV were well described with a one-compartment model incorporating first-pass metabolism. The first-pass metabolism was modeled as a first-order conversion. The morbid state and concomitant amisulpride were identified as two significant covariates affecting the clearance of VEN and ODV, which may account for some of the variations in exposure. This model may contribute to the precision medication in clinical practice and may inspire other drugs with pre-system metabolism.

Current Status of Therapeutic Drug Monitoring in Mental Health Treatment: A Review

Therapeutic drug monitoring (TDM) receives growing interest in different psychiatric clinical settings (emergency, inpatient, and outpatient services). Despite its usefulness, TDM remains underemployed in mental health. This is partly due to the need for evidence about the relationship between drug serum concentration and efficacy and tolerability, both in the general population and even more in subpopulations with atypical pharmacokinetics. This work aims at reviewing the scientific literature published after 2017, when the most recent guidelines about the use of TDM in mental health were written. We found 164 pertinent records that we included in the review. Some promising studies highlighted the possibility of correlating early drug serum concentration and clinical efficacy and safety, especially for antipsychotics, potentially enabling clinicians to make decisions on early laboratory findings and not proceeding by trial and error. About populations with pharmacokinetic peculiarities, the latest studies confirmed very common alterations in drug blood levels in pregnant women, generally with a progressive decrease over pregnancy and a very relevant dose-adjusted concentration increase in the elderly. For adolescents also, several drugs result in having different dose-related concentration values compared to adults. These findings stress the recommendation to use TDM in these populations to ensure a safe and effective treatment. Moreover, the integration of TDM with pharmacogenetic analyses may allow clinicians to adopt precise treatments, addressing therapy on an individual pharmacometabolic basis. Mini-invasive TDM procedures that may be easily performed at home or in a point-of-care are very promising and may represent a turning point toward an extensive real-world TDM application. Although the highlighted recent evidence, research efforts have to be carried on: further studies, especially prospective and fixed-dose, are needed to replicate present findings and provide clearer knowledge on relationships between dose, serum concentration, and efficacy/safety.

Treatment of depression: Are psychotropic drugs appropriately dosed in women and in the elderly? Dosages of psychotropic drugs by sex and age in routine clinical practice

BACKGROUND

Several researchers have shown higher concentration-dose ratios of psychotropic drugs in women and the elderly. Therefore, lower dosages of psychotropic drugs may be recommended in women and the elderly. This study describes sex- and age-related dosage of psychotropic drugs prescribed to patients with major depressive disorder (MDD) in routine clinical practice.

METHOD

Influence of sex and age on dosages are analysed for the 10 most commonly prescribed drugs in our dataset consisting of 32,082 inpatients with MDD. Data stems from the European drug safety program "Arzneimittelsicherheit in der Psychiatrie". The observed sex and age differences in prescriptions are compared to differences described in literature on age- and gender-related pharmacokinetics.

RESULTS

Among patients over 65 years, a statistically significant decrease in dosages with increasing age (between 0.65% and 2.83% for each increasing year of age) was observed, except for zopiclone. However, only slight or no influence of sex-related adjustment of dosage in prescriptions was found.

CONCLUSION

Age appears to influence adjustment of dosage in most psychotropic drugs, but to a lower extent than data on age-related pharmacokinetics suggests. Although literature also suggests that lower dosages of psychotropic drugs may be appropriate for females, this study found women are usually prescribed the same dosage as men.

Dose-Dependent Inhibition of CYP2D6 by Bupropion in Patients With Depression

PURPOSE

The aim of this study was to investigate the potential dose-dependent CYP2D6 inhibition by bupropion (BUP) in patients with depression.

METHODS

Patients combining BUP with venlafaxine were included from a therapeutic drug monitoring (TDM) database at the Diakonhjemmet Hospital (Oslo, Norway). The O/N-desmethylvenlafaxine metabolic ratio measured in TDM samples was used as a biomarker for CYP2D6 phenotype and was compared between patients treated with BUP 150 mg/d and 300 mg/d or greater. In addition, reference groups of venlafaxine-treated patients genotyped as CYP2D6 poor metabolizers (PMs, no CYP2D6 activity) and normal metabolizers (NMs, fully functional CYP2D6 activity) were included.

FINDINGS

A total of 221 patients were included in the study. The median O/N-desmethylvenlafaxine metabolic ratio was significantly higher in patients treated with BUP 150 mg/d (n = 59) versus 300 mg/d or greater (n = 34, 1.77 vs 0.96, P < 0.001). In CYP2D6 NMs (n = 62) and PMs (n = 66), the median metabolic ratios were 40.55 and 0.48, respectively. For patients treated with BUP 150 mg/d, 11 (19%) of the 59 patients were phenoconverted to PMs, whereas this was the case for 17 (50%) of the 34 patients treated with BUP 300 mg/d or greater.

CONCLUSIONS

Bupropion exhibits a clear dose-dependent CYP2D6 inhibitory effect during treatment of patients with depression. This finding is of clinical relevance when adjusting dosing of CYP2D6 substrates during comedication with BUP. Half of the patients treated with high-dose BUP are converted to CYP2D6 PM phenotype. Because of the variability in CYP2D6 inhibition, TDM of CYP2D6 substrates should be considered to provide individualized dose adjustments during comedication with BUP.

Higher venlafaxine serum concentrations necessary for clinical improvement? Time to re-evaluate the therapeutic reference range of venlafaxine

BACKGROUND

The therapeutic reference range for venlafaxine in antidepressant treatment has been defined as 100 to 400 ng/mL. However, in an everyday setting active moiety concentrations above the therapeutic reference range were often reported.

AIM

The aim of this study was to re-evaluate the therapeutic reference range of venlafaxine.

METHODS

In-patients (⩽60 years) with major depressive episodes receiving antidepressant monotherapy with venlafaxine during routine clinical treatment were included in this observational study. Depressive symptom severity was evaluated on a weekly basis using the Hamilton Depression Rating Scale (HAMD-21), and therapeutic drug monitoring analyses were performed. Resting electrocardiograms were analyzed in week 3, week 5 and week 7 of study participation.

RESULTS

Clinical improvement from baseline to week 4 was significantly associated with increasing serum concentrations of the active moiety of venlafaxine (N = 23, Pearson correlation, p = 0.009), but not with the dose of venlafaxine. Patients achieving remission showed significantly higher serum concentrations than patients achieving response/non-response (Kruskal-Wallis test, p = 0.019). Moreover, in patients with serum concentrations above 400 ng/mL time to remission and time to response was significantly shorter than in patients with concentrations below 400 ng/mL (Mantel-COX test, p = 0.001; p = 0.010). QTc time was below the upper limit of a normal QTc time (450 ms) for all patients.

CONCLUSION

The serum concentration of the active moiety and not the dose determined the effect of venlafaxine. Shorter remission times without ECG alterations in patients with serum concentrations above the therapeutic reference range suggest a re-evaluation of the therapeutic reference range for venlafaxine in larger studies.

Therapeutic Drug Monitoring of Venlafaxine and Impact of Age, Gender, BMI, and Diagnosis

Depression is a common mental disorder affecting more than 264 million people in the world and 5.1% of the Slovak population. Although various antidepressant approaches have been used; still, about 40% of patients do not respond to a first-choice drug administration and one third of patients do not achieve total remission. Therapeutic drug monitoring (TDM) is a method used for quantification and interpreting the drug concentrations in plasma in order to optimize the pharmacotherapy. The aim of this study was to measure the plasma concentrations of venlafaxine, the fourth most prescribed antidepressant in Slovakia, as well as its active metabolite and interpret them with the relevant patients’ characteristics.

The study was of retrospective nature and 28 adult patients in total were included. The concentrations of venlafaxine and its active metabolite O-desmethylvenlafaxine (ODV) in plasma were quantified using the validated UHPLC-MS/MS method. The effects of potential influencing factors were evaluated by a multivariate linear regression model.

Only 39% of patients reached the venlafaxine active moiety concentrations within the recommended therapeutic range. Plasma concentrations were dependent on age, gender, and duration of the therapy. Venlafaxine metabolism expressed as a metabolite-to-parent concentrations ratio was influenced by a combination of age, gender, and body mass index (BMI). We did not observe any significant difference in plasma concentrations between the patients with a single and recurrent diagnosis of depression. Combining variables made an additive effect on plasma concentrations, for example, active moiety plasma concentrations were higher in older women. In contrast, drug metabolism was higher in older men and men with lower BMI. TDM of venlafaxine is recommended in clinical practice, especially in the elderly when beginning the pharmacotherapy.

Use of Antidepressants in Older People during a 10-Year Period: An Observational Study on Prescribed Doses and Serum Levels

Background

According to previous studies, older patients frequently have serum concentrations of antidepressant medication above the recommended reference range.

Objective

The aim of this study was to investigate whether prescribed doses of antidepressants and the proportion of individuals with serum concentrations above the recommended reference range in older individuals (≥ 65 years) have changed over a 10-year period in Norway.

Methods

Serum concentration measurements and prescribed daily doses of antidepressants in 2007 and 2017 were extracted from a therapeutic drug monitoring (TDM) database at the Center for Psychopharmacology, Diakonhjemmet Hospital, Oslo, Norway. The database contains routine follow-up serum concentration measurements of psychotropic drugs for patients from all parts of the country. For citalopram, escitalopram, sertraline, mirtazapine and venlafaxine, the differences between 2007 and 2017 in mean prescribed doses and the proportion of patients with at least one serum concentration above the reference range, according to the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) guidelines, were compared. For the proportion of patients with serum concentrations above the recommended reference range, differences between individuals aged 65–79 and ≥ 80 years were also examined.

Results

The analyses of prescribed doses included 806 patients from 2007 and 1932 patients from 2017, with 972 and 2441 TDM samples, respectively. Between 2007 and 2017, modest reductions in prescribed daily doses were observed for citalopram (20 vs. 17 mg/day) and escitalopram (11 vs. 10 mg/day), but the proportion of patients with serum concentrations above the recommended reference range was unchanged for both drugs, i.e. 11.5% vs. 12.4% for citalopram and 3.6% vs. 2.9% for escitalopram. For mirtazapine and venlafaxine, prescribed doses were reduced from 28 to 25 mg/day and 150 to 125 mg/day, respectively. A significant reduction in the proportion of individuals with serum concentrations above the recommended reference range was observed for mirtazapine (27.1% vs. 11.5%) and for individuals aged ≥ 80 years using venlafaxine (60.0% vs. 30.0%). For sertraline, no differences in prescribed doses or serum concentrations above the recommended reference range were observed.

Conclusions

Over a 10-year period, prescribed doses of antidepressants have been slightly reduced in older Norwegian patients, but a considerable proportion is still exposed to high serum concentrations of antidepressants.

Electronic supplementary material

The online version of this article (10.1007/s40266-020-00784-9) contains supplementary material, which is available to authorized users.

Effect of venlafaxine dosage, valproic acid concentration, sex, and age on steady state dose-corrected concentrations of venlafaxine and O-desmethylvenlafaxine: A retrospective analysis of therapeutic drug monitoring data in a Chinese population

PURPOSE

This study aimed to investigate the influence of diagnosis, body weight, sex, age, smoking, formulations, and concomitant drugs on steady-state dose-corrected serum concentrations (C/D) of venlafaxine (VEN) and O-desmethylvenlafaxine (ODV).

METHODS

A retrospective analysis of therapeutic drug monitoring (TDM) was carried out. Patients' demographic data, therapeutic regimens, and concentrations were collected.

RESULTS

We included 91 verified samples from 80 patients. Females had by average 13% smaller body weight, 50% higher C/D of VEN, and VEN + ODV and 25% smaller ODV/VEN than males. Patients >60 years had by average 33-59% higher C/D levels of ODV and VEN + ODV than younger patients. The concomitant use of valproic acid caused an average 51% higher C/D of ODV and a 2.2-fold larger ODV/VEN, while clozapine was related with 40% smaller ratio of ODV/VEN and 38% lower C/D levels of ODV. Positive correlations were detected between valproic acid concentrations and the C/D of VEN and VEN + ODV. In a multiple linear regression analysis, variance in the C/D of VEN + ODV was partly attributed to the daily dose of VEN, sex, age and valproic acid concentration.

CONCLUSION

Our results suggested daily dose of VEN, sex, age, and valproic acid as indicators for the C/D of VEN + ODV in Chinese patients. TDM as a valuable tool was suggested in elderly female patients and patients receiving polypharmacy.

Analysis of smoking behavior on the pharmacokinetics of antidepressants and antipsychotics: evidence for the role of alternative pathways apart from CYP1A2

Smoking is common among psychiatric patients and has been shown to accelerate the metabolism of different drugs. We aimed to determine the effect of smoking on the serum concentrations of psychopharmacological drugs in a naturalistic clinical setting. Dose-corrected, steady-state serum concentrations of individual patients were analyzed retrospectively by linear regression including age, sex, and smoking for amitriptyline (n=503), doxepin (n=198), mirtazapine (n=572), venlafaxine (n=534), clozapine (n=106), quetiapine (n=182), and risperidone (n=136). Serum levels of amitriptyline (P=0.038), clozapine (P=0.02), and mirtazapine (P=0.002) were significantly lower in smokers compared with nonsmokers after correction for age and sex. In addition, the ratios of nortriptyline/amitriptyline (P=0.001) and nordoxepin/doxepin (P=0.014) were significantly higher in smokers compared with nonsmokers. Smoking may not only induce CYP1A2, but may possibly also affect CYP2C19. Furthermore, CYP3A4, UGT1A3, and UGT1A4 might be induced by tobacco smoke. Hence, a different dosing strategy is required among smoking and nonsmoking patients. Nevertheless, the clinical relevance of the results remained unclear.

Point-of-care companion diagnostic tests for personalizing psychiatric medications: fulfilling an unmet clinical need

Over the last decade stable isotope-labeled substrates have been used as probes for rapid, point-of-care, non-invasive and user-friendly phenotype breath tests to evaluate activity of drug metabolizing enzymes. These diagnostic breath tests can potentially be used as companion diagnostics by physicians to personalize medications, especially psychiatric drugs with narrow therapeutic windows, to monitor the progress of disease severity, medication efficacy and to study in vivo the pharmacokinetics of xenobiotics. Several genotype tests have been approved by the FDA over the last 15 years for both cytochrome P450 2D6 and 2C19 enzymes, however they have not been cleared for use in personalizing medications since they fall woefully short in identifying all non-responders to drugs, especially for the CYP450 enzymes. CYP2D6 and CYP2C19 are among the most extensively studied drug metabolizing enzymes, involved in the metabolism of approximately 30% of FDA-approved drugs in clinical use, associated with large individual differences in medication efficacy or tolerability essentially due to phenoconversion. The development and commercialization via FDA approval of the non-invasive, rapid (<60 min), in vivo, phenotype diagnostic breath tests to evaluate polymorphic CYP2D6 and CYP2C19 enzyme activity by measuring exhaled ¹³CO₂ as a biomarker in breath will effectively resolve the currently unmet clinical need for individualized psychiatric drug therapy. Clinicians could personalize treatment options for patients based on the CYP2D6 and CYP2C19 phenotype by selecting the optimal medication at the right initial and subsequent maintenance dose for the desired clinical outcome (i.e. greatest efficacy and minimal side effects).