Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology: Update 2017

Therapeutic drug monitoring (TDM) is the quantification and interpretation of drug concentrations in blood to optimize pharmacotherapy. It considers the interindividual variability of pharmacokinetics and thus enables personalized pharmacotherapy. In psychiatry and neurology, patient populations that may particularly benefit from TDM are children and adolescents, pregnant women, elderly patients, individuals with intellectual disabilities, patients with substance abuse disorders, forensic psychiatric patients or patients with known or suspected pharmacokinetic abnormalities. Non-response at therapeutic doses, uncertain drug adherence, suboptimal tolerability, or pharmacokinetic drug-drug interactions are typical indications for TDM. However, the potential benefits of TDM to optimize pharmacotherapy can only be obtained if the method is adequately integrated in the clinical treatment process. To supply treating physicians and laboratories with valid information on TDM, the TDM task force of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) issued their first guidelines for TDM in psychiatry in 2004. After an update in 2011, it was time for the next update. Following the new guidelines holds the potential to improve neuropsychopharmacotherapy, accelerate the recovery of many patients, and reduce health care costs.

TDM in psychiatry and neurology: A comprehensive summary of the consensus guidelines for therapeutic drug monitoring in neuropsychopharmacology, update 2017; a tool for clinicians<sup/>

OBJECTIVES

Therapeutic drug monitoring (TDM) combines the quantification of drug concentrations in blood, pharmacological interpretation and treatment guidance. TDM introduces a precision medicine tool in times of increasing awareness of the need for personalized treatment. In neurology and psychiatry, TDM can guide pharmacotherapy for patient subgroups such as children, adolescents, pregnant women, elderly patients, patients with intellectual disabilities, patients with substance use disorders, individuals with pharmacokinetic peculiarities and forensic patients. Clear indications for TDM include lack of clinical response in the therapeutic dose range, assessment of drug adherence, tolerability issues and drug-drug interactions.

METHODS

Based upon existing literature, recommended therapeutic reference ranges, laboratory alert levels, and levels of recommendation to use TDM for dosage optimization without specific indications, conversion factors, factors for calculation of dose-related drug concentrations and metabolite-to-parent ratios were calculated.

RESULTS

This summary of the updated consensus guidelines by the TDM task force of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie offers the practical and theoretical knowledge for the integration of TDM as part of pharmacotherapy with neuropsychiatric agents into clinical routine.

CONCLUSIONS

The present guidelines for TDM application for neuropsychiatric agents aim to assist clinicians in enhancing safety and efficacy of treatment.

Blood Levels to Optimize Antipsychotic Treatment in Clinical Practice: A Joint Consensus Statement of the American Society of Clinical Psychopharmacology and the Therapeutic Drug Monitoring Task Force of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie

OBJECTIVE

The quantification of antipsychotic levels in blood, also known as therapeutic drug monitoring (TDM), is a potentially useful tool of modern personalized therapy that can be applied to augment antipsychotic use and dosing decisions. The application of TDM for antipsychotics can be helpful in numerous challenging clinical scenarios, such as lack of therapeutic response, relapse, or adverse drug reactions (ADRs) related to antipsychotic treatment. The benefits of TDM may be particularly evident in the treatment of highly vulnerable patient subgroups, such as children, adolescents, pregnant women, and the elderly. The main aim of this article is to aid clinicians who routinely prescribe antipsychotics to successfully apply TDM in routine clinical practice in order to help optimize the efficacy and safety of those antipsychotics.

PARTICIPANTS

Participants were clinicians and researchers, members of the American Society of Clinical Psychopharmacology, and the Therapeutic Drug Monitoring Task Force of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (Association of Neuropsychopharmacology and Pharmacopsychiatry).

EVIDENCE

TDM literature on antipsychotics was critically reviewed to provide a condensed clinical decision-making algorithm with therapeutic reference ranges for blood antipsychotic levels, within which patients are most likely to respond and tolerate treatment, although TDM is not equally recommended/supported for all antipsychotics.

CONSENSUS PROCESS

A preliminary draft was prepared and circulated to the writing group members. Consensus was achieved in all cases, and resulting recommendations focused on following areas: steady-state and sampling time, levels of recommendations, indications, therapeutic reference ranges and laboratory alert levels, practical issues, and interpretation, as well as limitations.

CONCLUSIONS

The utilization of TDM as a tool for problem solving in antipsychotic treatment offers a unique method to improve safety and efficacy. This consensus statement summarizes essential information on the routine use of TDM for antipsychotics and encourages clinicians to perform TDM with the appropriate indications as part of the clinical decision-making process.

Cariprazine, a new, orally active dopamine D2/3 receptor partial agonist for the treatment of schizophrenia, bipolar mania and depression

Cariprazine is a novel drug with partial agonist activity at dopamine D2/3 receptors and six- to eightfold higher affinity for human dopamine D3 over D2 receptors. Results from several placebo-controlled Phase II/III trials in patients with a The Diagnostic and Statistical Manual of Mental Disorders IV diagnosis of schizophrenia or bipolar I disorder suggest that cariprazine is superior to placebo with respect to antipsychotic and antimanic activity. Reports concerning safety and tolerability of cariprazine are mainly favorable, although the rates of treatment-associated adverse events, which most commonly included akathisia and extrapyramidal symptom, are rather high. However, only minor alterations of clinical laboratory values, prolactin concentrations and ECG parameters are reported in cariprazine-treated patients. A new drug application to the U.S. F DA for cariprazine for the treatment of both schizophrenia and manic or mixed episodes associated with bipolar I disorder was submitted in November 2012. A more precise assessment of the clinical properties of this new drug will require additional studies, aimed to compare and contrast cariprazine with other antipsychotic agents.

Opiate-induced dopamine release is modulated by severity of alcohol dependence: an [(18)F]fallypride positron emission tomography study

BACKGROUND

Preclinical data implicate the reinforcing effects of alcohol to be mediated by interaction between the opioid and dopamine systems of the brain. Specifically, alcohol-induced release of β-endorphins stimulates μ-opioid receptors (MORs), which is believed to cause dopamine release in the brain reward system. Individual differences in opioid or dopamine neurotransmission have been suggested to be responsible for enhanced liability to abuse alcohol. In the present study, a single dose of the MOR agonist remifentanil was administered in detoxified alcohol-dependent patients and healthy control subjects to mimic the β-endorphin-releasing properties of ethanol and to assess the effects of direct MOR stimulation on dopamine release in the mesolimbic reward system.

METHODS

Availability of D(2/3) receptors was assessed before and after single-dose administration of the MOR agonist remifentanil in 11 detoxified alcohol-dependent patients and 11 healthy control subjects with positron emission tomography with the radiotracer [(18)F]fallypride. Severity of dependence as assessed with the Alcohol Use Disorders Identification Test was compared with remifentanil-induced percentage change in [(18)F]fallypride binding (Δ%BP(ND)).

RESULTS

The [(18)F]fallypride binding potentials (BP(ND)s) were significantly reduced in the ventral striatum, dorsal putamen, and amygdala after remifentanil application in both patients and control subjects. In the patient group, ventral striatum Δ%BP(ND) was correlated with the Alcohol Use Disorders Identification Test score.

CONCLUSIONS

The data provide evidence for a MOR-mediated interaction between the opioid and the dopamine system, supporting the assumption that one way by which alcohol unfolds its rewarding effects is via a MOR-(γ-aminobutyric acid)-dopamine pathway. No difference in dopamine release was found between patients and control subjects, but evidence for a patient-specific association between sensitivity to MOR stimulation and severity of alcohol dependence was found.

Body mass index (BMI) but not body weight is associated with changes in the metabolism of risperidone; A pharmacokinetics-based hypothesis

OBJECTIVE

We sought to unravel the influence of body weight and body mass index (BMI), both consistently reported as pharmacokinetic relevant parameters, on metabolism of risperidone in a naturalistic sample.

METHODS

Conducting non parametrical tests we sought for correlations between plasma concentrations of RIS, 9-OH-RIS and AM and body weight and BMI in patients out of a therapeutic drug monitoring (TDM) database. Further, we stratified patients to three groups based upon BMI values and compared drug concentrations between groups.

RESULTS

Although body weight failed to correlate with pharmacokinetic parameters, BMI was positively correlated with plasma concentrations of the active metabolite (9-OH-RIS) (r_s=0.121, p=0.002) and active moiety (sum of RIS+9-OH-RIS) (r_s=0.128, p=0.001) as well as dose adjusted plasma concentrations of the active moiety (r_s=0.08, p=0.04). The comparison of pharmacokinetic parameters between different BMI groups yielded lower plasma concentrations of 9-OH-RIS in patients with low BMI (<20kg/m²) and higher plasma concentrations of the active moiety in obese patients (BMI ≥30kg/m²) when compared with the control group (30>BMI≥20kg/m²). By comparing low vs. high BMI patients, the latter group showed higher 9-OH-RIS plasma concentrations.

CONCLUSIONS AND LIMITATIONS

Considerable alterations in metabolism of risperidone were detected when comparing obese and cachectic patients with the control group in alignment with the positive correlation between BMI values and plasma concentrations of the active metabolite and active moiety as well as dose adjusted plasma concentrations of the active moiety. We suggest changes in CYP2D6 or CYP3A4 activity or differences in P-glycoprotein function in obese patients with greater BMI as a plausible mechanism underlying these alterations.

Elevated Clozapine Concentrations in Clozapine-Treated Patients with Hypersalivation

BACKGROUND AND OBJECTIVE

Hypersalivation is a common, clozapine-related adverse drug reaction with a serious impact on quality of life. Pharmacokinetic correlates of clozapine-related hypersalivation have evaded attention. The purpose of this study was to compare pharmacokinetic parameters between clozapine-treated patients with vs. without hypersalivation from a large therapeutic drug monitoring database.

METHODS

Out of a large therapeutic drug monitoring dataset of clozapine-treated patients, we compared a group of patients with hypersalivation (n = 72) and a control group of patients without any adverse reactions in this regard (n = 323). Comparisons included plasma concentrations and concentrations-by-dose as well as demographic characteristics between groups. Post-hoc analyses were performed separately in smokers and non-smokers. We used the non-parametric Mann-Whitney U test and the chi-square test, while effects of confounders were assessed using a bootstrapping analysis of covariance.

RESULTS

Patients with hypersalivation had higher clozapine plasma concentrations and concentrations-by-dose (p < 0.001 for the Mann-Whitney U test in both cases). Groups did not differ regarding demographic characteristics except for clozapine daily dose and percentage of smokers (p = 0.005 for the Mann-Whitney U test and p = 0.028 for the chi-square test, respectively). There were fewer smokers across patients with hypersalivation compared with patients without and daily doses were higher in patients with hypersalivation. After analysis of covariance, differences remained for both plasma concentrations and concentrations-by-dose (p < 0.001 for both). Post hoc analyses in smokers and non-smokers separately reported similar findings.

CONCLUSIONS

Elevated clozapine plasma concentrations and higher concentrations-by-dose were observed in patients with hypersalivation. A potential role for therapeutic drug monitoring in the prevention or management of clozapine-related hypersalivation is suggested.

The impact of pregnancy on the pharmacokinetics of antidepressants: a systematic critical review and meta-analysis

Introduction: Pregnancy-related physiological changes exert a crucial impact on the pharmacokinetics of antidepressants; however, the current evidence presents inconsistencies. A clearer understanding of pregnancy-related effects on antidepressant disposition may facilitate the development of guidelines for appropriate dose adjustments during the course of pregnancy based on therapeutic drug monitoring.Areas covered: We systematically reviewed studies comparing antidepressant levels in the same individuals during pregnant and non-pregnant states. Using dose-adjusted plasma concentration measurements, we estimated alteration ratios between the 3rd trimester and baseline (before or after pregnancy). Additionally, we performed a meta-analysis for changes in dose-adjusted concentrations to estimate mean differences.Expert opinion: Data for several antidepressants display clear alteration patterns during pregnancy. On the basis of the alteration ratios trimipramine, fluvoxamine, and nortriptyline show a prominent decrease in dose-adjusted levels, especially in the 3rd trimester. Clomipramine, imipramine, citalopram, and paroxetine show smaller decreases in dose-adjusted concentrations in the third trimester. For escitalopram, venlafaxine and fluoxetine, changes are considered negligible. For sertraline, there was a tendency toward increased dose-adjusted concentrations in pregnancy. Available evidence suffers from major limitations and factors affecting pharmacokinetics have been insufficiently addressed. Further research is required to promote knowledge on pregnancy effects on antidepressant pharmacokinetics.

Effect of fluvoxamine augmentation and smoking on clozapine serum concentrations

BACKGROUND

Clozapine (CLZ) is metabolized via cytochrome P450 CYP1A2 to N-desmethylclozapine (NCLZ). Smoking induces CYP1A2 thereby increasing clozapine metabolism whereas fluvoxamine inhibits CYP1A2. Studies suggest that the beneficial effect of fluvoxamine augmentation in raising serum clozapine concentrations also occurs when serum concentrations are low due to smoking. Yet, little is known about the influence of fluvoxamine augmentation on clozapine serum concentrations in smoking versus non-smoking patients.

METHODS

A TDM database was analyzed. Serum concentrations of CLZ, NCLZ, dose-adjusted serum concentrations (C/D) and metabolite-to-parent ratios (MPR) were compared using non-parametrical tests in four groups: clozapine-monotherapy in non-smokers (V_NS, n = 28) and smokers (V_S, n = 43); combined treatment with clozapine and fluvoxamine in non-smokers (V_NS+F, n = 11) and smokers (V_S+F, n = 43).

RESULTS

The CLZ monotherapy smoking group showed lower values of C/D CLZ of -38.6% (p < 0.001), C/D NCLZ -35.6% (p < 0.001) and a higher MPR (p = 0.021) than in the non-smoking group. The combination of CLZ and fluvoxamine in non-smoking patients led to higher C/D values: C/D CLZ +117.9% (p < 0.001), C/D NCLZ +60.8% (p = 0.029) while the MPR did not differ between groups (p = 0.089). Changes were comparable to fluvoxamine augmentation in the smoking group with increased C/D CLZ of +120.1% (p < 0.001), C/D NCLZ of +85.8% (p < 0.001) and lower MPR (p = 0.006).

CONCLUSIONS

Smoking in clozapine monotherapy reduced median dose-adjusted serum concentrations more than a third. Combined treatment with fluvoxamine and clozapine led to higher median C/D values in both, smokers and non-smokers. The opposing effects of CYP1A2 induction by smoking and inhibition by fluvoxamine on clozapine serum concentrations balanced out.

Sertraline in pregnancy - Therapeutic drug monitoring in maternal blood, amniotic fluid and cord blood

RATIONALE

This study is the first to measure and correlate sertraline concentrations in maternal blood, amniotic fluid and umbilical cord blood and account for distribution of the drug between these three compartments.

METHODS

Concentrations of sertraline were measured in six mother infant pairs at the time of delivery. Data are provided as median values, first and third quartiles as well as ranges. To account for the penetration ratio into amniotic fluid and cord blood, the concentration of sertraline in both environments was divided by the concentration in maternal serum. Daily doses were correlated with maternal serum- and umbilical cord blood-concentrations, and serum levels were correlated with levels in amniotic fluid.

RESULTS

The median daily dose of sertraline was 75mg (Q1: 43.75mg, Q3: 100mg; range 25-100mg). Amniotic fluid concentrations of sertraline strongly correlated with the daily dose (r=0.833, p=0.039) while neither maternal serum concentrations nor cord blood concentrations correlated with the daily dose (p>0.05). The median penetration ratio for sertraline into amniotic fluid was 0.57 (Q1: 0.28, Q3: 0.75; range: 0.22-0.88). The median penetration ratio into the fetal circulation, calculated on the basis of umbilical cord blood-concentrations, was found to be 0.36 (Q1: 0.28, Q3: 0.49; range: 0.17-0.65).

CONCLUSIONS

Sertraline concentrations in amniotic fluid gave evidence that maternally administered sertraline is constantly accessible to the fetus via amniotic fluid in a manner not previously appreciated. A relatively low penetration into fetal circulation may contribute to a sufficient safety profile of sertraline during pregnancy although in our study APGAR Scores were relatively low in three infants. Our data support the important role of therapeutic drug monitoring in maintaining the safety of pregnant women and exposed infants.

Pharmacokinetics of risperidone in different application forms - Comparing long-acting injectable and oral formulations

We aimed to explore the differences in the pharmacokinetics of risperidone between oral and long-acting injectable (LAI) formulations using a large database of therapeutic drug monitoring (TDM). Plasma concentrations of risperidone (RIS), its active metabolite (9-OH-RIS) and the active moiety (AM) (RIS+9-OH-RIS), their concentration-to-dose (C/D) ratios and ratio of RIS/9-OH-RIS (an index of CYP2D6 metabolic activity) were used to compare patients receiving risperidone orally (n = 851) and those treated with LAI RIS (n = 63). Patients taking CYP inducers or inhibitors or with liver/renal impairment were eliminated. Our study demonstrated that patients on LAI RIS, despite slightly higher RIS doses in the oral group, showed no significant differences in total AM or 9-OH-RIS. Conversely, RIS concentration, RIS C/D ratio and total C/D ratio were slightly higher in the LAI RIS group, reaching significance due to the large sample size. More importantly, the median ratio of RIS/9-OH-RIS was 0.52 in LAI RIS vs. 0.25 in the oral group, providing a significant difference (p < 0.001). After controlling for confounding factors, we replicated the RIS/9-OH-RIS ratio increases in patients with LAI RIS, probably reflecting a decrease in first-pass metabolism. More studies are required to establish the clinical use of TDM for patients on LAI RIS.

Clinically Significant Drug-Drug Interactions with Agents for Attention-Deficit/Hyperactivity Disorder

This article provides an overview of the pharmacokinetic drug-drug interactions (DDIs) for agents prescribed for attention-deficit/hyperactivity disorder (ADHD). Polypharmacy in the treatment of patients with ADHD leads to high exposures to DDIs and possibly adverse safety outcomes. We performed a systematic search of DDI reports for ADHD agents in Embase and Medline. We also searched for agents in the pharmacological pipeline, which include (1) mazindol, molindone and viloxazine, which were previously prescribed for other indications; (2) centanafadine and AR-08, never before approved; and (3) two extracts (Polygala tenuifolia extract and the French maritime pine bark extracts). The identified literature included case reports, cross-sectional, cross-over and placebo-controlled studies of patient cohorts and healthy volunteers. The DDIs were classified as follows: ADHD agents acting as perpetrators, i.e., affecting the clearance of co-prescribed agents (victim drugs), or ADHD agents being the victim drugs, being affected by other agents. Ratios for changes in pharmacokinetic parameters before and after the DDI were used as a rough estimate of the extent of the DDI. Alcohol may increase plasma dextroamphetamine concentrations by presystemic effects. Until studies are done to orient clinicians regarding dosing changes, clinicians need to be aware of the potential for cytochrome P450 (CYP) 2D6 inhibitors to increase amphetamine levels, which is equivalent to increasing dosages. Atomoxetine is a wide therapeutic window drug. The CYP2D6 poor metabolizers who do not have CYP2D6 activity had better atomoxetine response, but also an increased risk of adverse effects. CYP2D6 inhibitors have been used to increase atomoxetine response in CYP2D6 extensive metabolizers. Guanfacine is mainly metabolized by CYP3A4, which can be induced and inhibited. The package insert recommends that in guanfacine-treated patients, after adding potent CYP3A4 inducers, the guanfacine dose should be doubled; after adding potent CYP3A4 inhibitors the guanfacine dose should be halved. Based on a phenobarbital case report and our experience with CYP3A4-metabolized antipsychotics, these correction factors may be too low. According to two case reports, carbamazepine is a clinically relevant inducer of methylphenidate (MPH). A case series study suggested that MPH may be associated with important elevations in imipramine concentrations. Due to the absence of or limitations in the data, no comments for clinicians can be provided on the pharmacokinetic DDIs for clonidine, centanafadine, mazindol, molindone, AR-08, P. tenuifolia extract and the French maritime pine bark extracts. According to currently available data, clinicians should not expect that ADHD drugs modify each other's serum concentrations. A summary table for clinicians provides our current recommendations on pharmacokinetic DDIs of ADHD agents based on our literature review and the package inserts; whenever it was possible, we provide information on serum concentrations and dose correction factors. There will be a need to periodically update these recommendations and these correction factors as new knowledge becomes available.

The role of striatal dopamine D2/3 receptors in cognitive performance in drug-free patients with schizophrenia

OBJECTIVE

A considerable body of research links cognitive function to dopaminergic transmission in the prefrontal cortex, but less is known about cognition in relation to striatal dopamine D_2/3 receptors in unmedicated patients with psychosis.

METHODS

We investigated this association by obtaining PET recordings with the high-affinity D_2/3 antagonist ligand [¹⁸F] fallypride in 15 medication-free patients with schizophrenia and 11 healthy controls. On the day of PET scanning, we undertook comprehensive neuropsychological testing and assessment of psychopathology using the Positive and Negative Syndrome Scale (PANSS).

RESULTS

The patients' performance in cognitive tests was significantly impaired in almost all domains. Irrespective of medication history, the mean [¹⁸F] fallypride binding potential (BP_ND) in the patient group tended to be globally 5-10% higher than that of the control group, but without reaching significance in any brain region. There were significant positive correlations between individual patient performance in the Trail Making Test (TMT(A) and TMT(B)) and Digit-Symbol-Substitution-Test with regional [¹⁸F] fallypride BP_ND, which remained significant after Bonferroni correction for the TMT(A) in caudate nucleus (CN) and for the TMT(B) in CN and putamen. No such correlations were evident in the control group.

DISCUSSION

The association between better cognitive performance and greater BP_ND in schizophrenia patients may imply that relatively lower receptor occupancy by endogenous dopamine favors better sparing of cognitive function. Absence of comparable correlations in healthy controls could indicate a greater involvement of signaling at dopamine D_2/3 receptors in certain cognitive functions in schizophrenia patients than in healthy controls.

Differences in Duloxetine Dosing Strategies in Smoking and Nonsmoking Patients: Therapeutic Drug Monitoring Uncovers the Impact on Drug Metabolism

BACKGROUND

For certain psychotropic drugs, such as clozapine or olanzapine, the influence of smoking on drug metabolism is well studied. Tobacco smoke increases the metabolism of drugs that are substrates for cytochrome P450 (CYP) 1A2 due to CYP induction. The antidepressant duloxetine, acting as a serotonin-norepinephrine reuptake inhibitor, is mainly metabolized via CYP1A2. To date, little is known about the influence of smoking on serum duloxetine concentrations.

METHODS

A therapeutic drug monitoring database consisting of plasma concentrations of duloxetine collected from January 2013 to June 2017 was analyzed. A group of nonsmoking patients undergoing treatment with duloxetine (n = 89) was compared to a group of active smokers also receiving duloxetine (n = 36). Serum concentrations of duloxetine and dose-adjusted serum concentrations were compared using non-parametric tests.

RESULTS

Groups did not differ concerning sex (P = .063), but the group of active smokers was younger (P < .001) and received higher daily doses of duloxetine (P = .001). Smokers showed significantly lower median serum duloxetine concentrations (38.4% lower, P = .002) and 53.6% lower dose-adjusted serum concentrations (0.325 [ng/mL]/[mg/d] in smokers vs 0.7 [ng/mL]/[mg/d] in nonsmokers, P < .001).

CONCLUSIONS

Despite higher daily doses, smokers had considerably lower serum duloxetine concentrations. The induction of CYP1A2 by tobacco smoke is a clinically relevant factor for drugs that are substrates for CYP1A2. Clinicians should actively assess smoking status, inform patients about the effect of smoking on duloxetine metabolism, and anticipate higher serum concentrations in the case of smoking cessation. Therapeutic drug monitoring ensures treatment efficacy by enabling the personalizing of treatment, as smokers need higher duloxetine doses to target serum concentrations within the therapeutic reference range.

Effect of smoking on risperidone pharmacokinetics - A multifactorial approach to better predict the influence on drug metabolism

PURPOSE

To disentangle an association between tobacco smoking, smoking habits and pharmacokinetic patterns such as plasma concentrations of risperidone (RIS), its active metabolite 9-hydroxyrisperidone (9-OH-RIS) and the active moiety, AM, (RIS+9-OH-RIS) in a naturalistic sample.

METHODS

Plasma concentrations, dose adjusted plasma concentrations (C/D) of RIS, 9-OH-RIS and AM in patients out of a therapeutic drug monitoring (TDM) database were compared between smokers (n=401) and non-smokers (n=292).

RESULTS

Daily dosage of risperidone differed significantly with smokers receiving higher doses than patients in the control group (p=0.001). No differences were detected in plasma concentrations of the active moiety, RIS and 9-OH-RIS (p=0.8 for AM, p=0.646 for RIS and p=0.538 for 9-OH-RIS). However, dose corrected concentrations (C/D) of metabolite (C/D 9-OH-RIS) and active moiety (C/D AM) differed between significantly between groups (p=0.002 and p=0.007). After stratifying smokers to a group of moderate smokers (<20cigarettes/day) (RS1, n=109) and a group of heavy smokers (≥20cigarettes/day) (RS2, n=135), the comparison between non-smokers and both groups only showed lower values of C/D for 9-OH-RIS (p=0.011) for the group of moderate smokers while other pharmacokinetic parameters did not differ.

CONCLUSIONS

Apart from the well-known induction of CYP1A2 activity by polycyclic aromatic hydrocarbons, smoking might exert an effect on other CYP isoenzymes as well. A possible interpretation proposes a slight inducing effect of smoking on risperidone metabolism most likely via CYP3A4.

Therapeutic Reference Range for Aripiprazole in Schizophrenia Revised: a Systematic Review and Metaanalysis

RATIONALE

While one of the basic axioms of pharmacology postulates that there is a relationship between the concentration and effects of a drug, the value of measuring blood levels is questioned by many clinicians. This is due to the often-missing validation of therapeutic reference ranges.

OBJECTIVES

Here, we present a prototypical meta-analysis of the relationships between blood levels of aripiprazole, its target engagement in the human brain, and clinical effects and side effects in patients with schizophrenia and related disorders.

METHODS

The relevant literature was systematically searched and reviewed for aripiprazole oral and injectable formulations. Population-based concentration ranges were computed (N = 3,373) and pharmacokinetic influences investigated.

RESULTS

Fifty-three study cohorts met the eligibility criteria. Twenty-nine studies report blood level after oral, 15 after injectable formulations, and nine were positron emission tomography studies. Conflicting evidence for a relationship between concentration, efficacy, and side effects exists (assigned level of evidence low, C; and absent, D). Population-based reference ranges are well in-line with findings from neuroimaging data and individual efficacy studies. We suggest a therapeutic reference range of 120-270 ng/ml and 180-380 ng/ml, respectively, for aripiprazole and its active moiety for the treatment of schizophrenia and related disorders.

CONCLUSIONS

High interindividual variability and the influence of CYP2D6 genotypes gives a special indication for Therapeutic Drug Monitoring of oral and long-acting aripiprazole. A starting dose of 10 mg will in most patients result in effective concentrations in blood and brain. 5 mg will be sufficient for known poor metabolizers.

Antidepressant transfer into amniotic fluid, umbilical cord blood & breast milk: A systematic review & combined analysis

OBJECTIVE

Data regarding the ability of antidepressants to enter fetal, newborn and infant fluids have become gradually available, but mechanisms of antidepressant transfer remain poorly understood. Here we calculated penetration ratios in an array of matrices from combined samples of pregnant/breastfeeding women taking antidepressants.

METHOD

We performed a systematic literature search of PubMed and EMBASE to identify studies with concentrations of antidepressants from maternal blood, amniotic fluid, umbilical cord blood and/or breast milk. Penetration ratios were calculated by dividing the concentrations in amniotic fluid, umbilical cord plasma or breast milk by the maternal plasma concentration. When data from multiple studies were available, we calculated combined penetration ratios, weighting the study mean by study size.

RESULTS

Eighty-five eligible studies were identified. For amniotic fluid, the highest penetration ratios were estimated for venlafaxine (mean 2.77, range 0.43-4.70 for the active moiety) and citalopram (mean 2.03, range 0.35-6.97), while the lowest ratios were for fluvoxamine (mean 0.10) and fluoxetine (mean 0.11, range 0.02-0.20 for the active moiety). For umbilical cord plasma, nortriptyline had the highest ratio (mean 2.97, range 0.25-26.43) followed by bupropion (mean 1.14, range 0.3-5.08). For breast milk, the highest ratios were observed for venlafaxine (mean 2.59, range 0.85-4.85), mianserin (mean 2.22, range 0.80-3.64) and escitalopram (mean 2.19, range 1.68-3.00).

CONCLUSION

We observed considerable variability across antidepressants regarding their ability to enter fetal, newborn and infant fluids. Measuring antidepressant concentrations in a maternal blood sample can provide a reliable estimate of fetal/infant exposure, although further evidence for concentration-dependent effects is required.

Pregnancy exposure to quetiapine - Therapeutic drug monitoring in maternal blood, amniotic fluid and cord blood and obstetrical outcomes

RATIONALE

This prospective study is the first to measure and correlate quetiapine concentrations in maternal blood, amniotic fluid and umbilical cord blood to account for the distribution of quetiapine.

METHODS

Concentrations of quetiapine are quantified in seven mother infant pairs at the time of delivery. Data are provided as median values, first (Q1) and third (Q3) quartiles and ranges. To account for the penetration ratio, the concentration of quetiapine in amniotic fluid and cord blood was divided by maternal concentrations. Correlations between daily dosage, maternal serum and umbilical cord blood concentrations were computed for seven patients while calculations for amniotic fluid were only available for six mother-infant pairs.

RESULTS

The median daily dosage of quetiapine was 300mg (Q1: 300mg, Q3: 600mg, range 200-800mg). There was a strong and significant correlation between maternal serum and cord blood concentrations (r=0.893, p=0.007). The median penetration ratio into fetal circulation was 0.18 (Q1: 0.16, Q3: 0.32; range 0.13-0.42), suggesting a low penetration. The median penetration ratio into amniotic fluid was 0.44 (Q1: 0.15, Q3: 0.96; range 0.09-1.70).

CONCLUSIONS

Quetiapine concentrations in amniotic fluid and cord blood give evidence that quetiapine is constantly accessible to the fetus with a relatively low penetration ratio. A high correlation between maternal serum and umbilical cord blood concentrations highlights a predictive role of quantifying drug concentrations in maternal serum for assessing drug concentrations in fetal circulation. Findings support the important role of therapeutic drug monitoring in supporting the efficacy and safety of psychopharmacological treatment strategies in highly vulnerable populations.

Pharmacokinetic considerations in the treatment of hypertension in risperidone-medicated patients - thinking of clinically relevant CYP2D6 interactions

BACKGROUND

Treatment of arterial hypertension in patients with severe mental illnesses often results in polypharmacy, potentially leading to drug-drug interactions. The objective of the study was to analyse the in vivo inhibitory potential of two antihypertensive drugs, amlodipine and metoprolol on CYP2D6 catalysed 9-hydroxylation of risperidone (RIS).

METHODS

A therapeutic drug monitoring database with plasma concentrations of RIS and 9-hydroxyrisperidone (9-OH-RIS) of 1584 patients was analysed. Three groups were considered; a group of patients receiving RIS without a potentially cytochrome influencing co-medication (control group, R0, n=852), a group co-medicated with amlodipine (RA, n=27) and a group, co-medicated with metoprolol (RM, n=41). Plasma concentrations, concentration-to-dose ratios (C/Ds) of RIS, 9-OH-RIS and the active moiety (AM), as well as the metabolic ratios were computed and compared using the Kruskal-Wallis test, the Mann-Whitney U test and the Jonckheere-Terpstra test to determine the means and different patterns of distribution of plasma concentrations as well as the concentration-to-dose ratios.

RESULTS

The median daily dosage of RIS did not differ between the groups (p=0.708). No differences were found in median plasma concentrations of RIS, 9-OH-RIS and AM. However, concentration-to-dose ratios for RIS, 9-OH-RIS and AM were significantly higher in the amlodipine group (p=0.025, p=0.048 and p=0.005). In the metoprolol group, the concentration-to-dose ratio for RIS was significantly higher than in the control group (p=0.017), while the C/D for 9-OH-RIS and AM was not.

CONCLUSIONS AND LIMITATIONS

Our data show a potential pharmacokinetic interaction, most likely via CYP3A4 between amlodipine and RIS, reflected in significantly different C/Ds for RIS, 9-OH-RIS and AM. Although the interaction did not result in significantly higher plasma levels, changes in C/Ds and their distribution with regard to the median concentrations were observed.