Optimisation of pharmacotherapy in psychiatry through therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests: focus on antipsychotics.

BACKGROUND: For psychotic disorders (i.e. schizophrenia), pharmacotherapy plays a key role in controlling acute and long-term symptoms. To find the optimal individual dose and dosage strategy, specialized tools are used. Three tools have been proven useful to personalize drug treatments: therapeutic drug monitoring (TDM) of drug levels, pharmacogenetic testing (PG), and molecular neuroimaging. METHODS: In these Guidelines, we provide an in-depth review of pharmacokinetics, pharmacodynamics, and pharmacogenetics for 50 antipsychotics. Over 30 international experts in psychiatry selected studies that have measured drug concentrations in the blood (TDM), gene polymorphisms of enzymes involved in drug metabolism, or receptor/transporter occupancies in the brain (positron emission tomography (PET)). RESULTS: Study results strongly support the use of TDM and the cytochrome P450 (CYP) genotyping and/or phenotyping to guide drug therapies. Evidence-based target ranges are available for titrating drug doses that are often supported by PET findings. CONCLUSION: All three tools discussed in these Guidelines are essential for drug treatment. TDM goes well beyond typical indications such as unclear compliance and polypharmacy. Despite its enormous potential to optimize treatment effects, minimize side effects and ultimately reduce the global burden of diseases, personalized drug treatment has not yet become the standard of care in psychiatry.

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.

Concentrations of escitalopram in blood of patients treated in a naturalistic setting: focus on patients with alcohol and benzodiazepine use disorder.

The selective serotonin reuptake inhibitor escitalopram (ESC) is indicated for the treatment of major depressive disorder (MDD) and of generalized anxiety disorder (GAD). Monitoring of blood levels (BLs) is strongly indicated due to ESC's high interindividual pharmacokinetic variability. The aim of this study was to analyse clinical efficacy and pharmacokinetic influences on ESC BLs, in patients with depressive disorder alone and with comorbid alcohol or benzodiazepine use disorder. Data were collected from patients treated under naturalistic conditions for whom Therapeutic Drug Monitoring (TDM) was requested to guide antidepressant drug therapy and analysed retrospectively. Particular emphasis was given to patients with alcohol or benzodiazepine use disorder. Responders according to the clinical global impression (CGI) scale were compared with nonresponders for their ESC blood level (BL). The patient sample included 344 patients from 16 psychiatric hospitals in Germany. Influencing factors that could explain 22% of ESC BLs were dose, sex and age. Variability was high between individuals, and doses up to 40 mg were common in real-world settings. Patients treated with ESC monotherapy who responded showed a trend towards higher BLs compared to nonresponders with a concentration of 15 ng/mL separating both groups. Pathological changes in liver function (indicated by elevated GGT in combination with an AST/ALT ratio ≥ 1) resulted in higher dose-corrected ESC concentrations. Influencing factors that could explain 22% of ESC blood levels were dose, sex, and age. Our findings confirm the currently recommended lower threshold level and support the need for standard TDM analyses in everyday clinical practice. The ICD 10 diagnosis alcohol dependence alone does not lead to pharmacokinetic changes in the metabolism of ESC, but altered liver function does.

Tools for optimising pharmacotherapy in psychiatry (therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests): focus on antidepressants.

Objectives: More than 40 drugs are available to treat affective disorders. Individual selection of the optimal drug and dose is required to attain the highest possible efficacy and acceptable tolerability for every patient.Methods: This review, which includes more than 500 articles selected by 30 experts, combines relevant knowledge on studies investigating the pharmacokinetics, pharmacodynamics and pharmacogenetics of 33 antidepressant drugs and of 4 drugs approved for augmentation in cases of insufficient response to antidepressant monotherapy. Such studies typically measure drug concentrations in blood (i.e. therapeutic drug monitoring) and genotype relevant genetic polymorphisms of enzymes, transporters or receptors involved in drug metabolism or mechanism of action. Imaging studies, primarily positron emission tomography that relates drug concentrations in blood and radioligand binding, are considered to quantify target structure occupancy by the antidepressant drugs in vivo. Results: Evidence is given that in vivo imaging, therapeutic drug monitoring and genotyping and/or phenotyping of drug metabolising enzymes should be an integral part in the development of any new antidepressant drug.Conclusions: To guide antidepressant drug therapy in everyday practice, there are multiple indications such as uncertain adherence, polypharmacy, nonresponse and/or adverse reactions under therapeutically recommended doses, where therapeutic drug monitoring and cytochrome P450 genotyping and/or phenotyping should be applied as valid tools of precision medicine.

Genetic structure and admixture in sheep from terminal breeds in the United States.

Selection for performance in diverse production settings has resulted in variation across sheep breeds worldwide. Although sheep are an important species to the United States, the current genetic relationship among many terminal sire breeds is not well characterized. Suffolk, Hampshire, Shropshire and Oxford (terminal) and Rambouillet (dual purpose) sheep (n = 248) sampled from different flocks were genotyped using the Applied Biosystems Axiom Ovine Genotyping Array (50K), and additional Shropshire sheep (n = 26) using the Illumina Ovine SNP50 BeadChip. Relationships were investigated by calculating observed heterozygosity, inbreeding coefficients, eigenvalues, pairwise Wright's FST estimates and an identity by state matrix. The mean observed heterozygosity for each breed ranged from 0.30 to 0.35 and was consistent with data reported in other US and Australian sheep. Suffolk from two different regions of the United States (Midwest and West) clustered separately in eigenvalue plots and the rectangular cladogram. Further, divergence was detected between Suffolk from different regions with Wright's FST estimate. Shropshire animals showed the greatest divergence from other terminal breeds in this study. Admixture between breeds was examined using admixture, and based on cross-validation estimates, the best fit number of populations (clusters) was K = 6. The greatest admixture was observed within Hampshire, Suffolk, and Shropshire breeds. When plotting eigenvalues, US terminal breeds clustered separately in comparison with sheep from other locations of the world. Understanding the genetic relationships between terminal sire breeds in sheep will inform us about the potential applicability of markers derived in one breed to other breeds based on relatedness.

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.

[Genetic tests for controlling treatment with antidepressants]. / Genetische Tests zur Steuerung der Behandlung mit Antidepressiva.

In clinical practice, there is a need for a more individualized selection of antidepressants and adequate dosage. The investigation of pharmacokinetically relevant genes is a promising approach to assist this selection. In the past 2 years, two commercially available tests have been subject of advertisement, a test from Stada, which analyses variants of the cytochrome P450 isoenzymes CYP2D6 and CYP2C19 and a test from HMNC Brain Health, which analyses variants of the ABCB1 gene. The costs for both kits are not covered by the statutory health insurance and it is therefore proposed that the patients are invoiced directly in the form of individual healthcare payment. The companies claim that by applying the tests antidepressant treatment failure can be avoided and that patients will respond faster to the antidepressant used. These claims are not based on appropriate clinical trials, which are either lacking or reveal conflicting results. Hence, the routine use of these tests is not recommended. In accordance with the German S3 Guideline for unipolar depression, therapeutic drug monitoring (TDM) of serum levels should be carried out in cases of non-response to an antidepressant with adequate dosage and duration. As a rule the costs for TDM are covered by the statutory health insurance. Cytochrome P450 genotyping is only indicated when the serum level is not within the expected range and other reasons to explain this discrepancy are excluded. Many laboratories provide these analyses and in individual cases the costs are reimbursed by the statutory health insurance. Further research should be carried out to investigate the importance of the ABCB1 gene for the treatment with antidepressants.

Retrospective pilot study for analysis of antidepressant serum concentrations of citalopram and venlafaxine during inflammation.

INTRODUCTION: Inflammation-mediated changes in drug metabolism may increase drug levels in blood and lead to intoxications. The objective of this study was to find out whether elevated serum levels of C-reactive protein (CRP) are associated with increased serum concentrations of the antidepressants citalopram and venlafaxine. METHODS: Therapeutic drug monitoring request forms of psychiatric patients were screened retrospectively. The serum concentrations in relation to the daily doses [(C/D) (ng/ml/mg)] and the metabolic ratios (metabolite/drug) were compared intraindividually under normal (<5 mg/l) and pathological (>5 mg/l) condition by the Wilcoxon signed-rank test. RESULTS: Elevated levels of CRP were not associated with a significant (P>0.05) increase in C/D for citalopram (2.4 ng/ml/mg vs. 2.85 ng/ml/mg, N=15) or in C/D for the active moiety of venlafaxine (1.76 ng/ml/mg vs. 1.68 ng/ml/mg, N=39), compared with normal CRP serum levels. No significant difference in the metabolic ratio was observed in both groups. DISCUSSION: There was no major effect of inflammation on the metabolism of citalopram and venlafaxine. Because of the broad therapeutic indices of these 2 drugs, the drugs seem to be a good choice for the treatment of depression, even if an infection occurs.

Steady-state serum concentrations of venlafaxine in patients with late-life depression. Impact of age, sex and BMI.

Diagnosis of late-life depression is given when depressive symptoms emerge in persons older than 65 years. Great care is needed when elderly patients receive psychopharmacotherapy due to altered pharmacokinetic status. As a consequence, age is considered to have a significant effect on serum concentrations of antidepressant drugs. The magnitudes of age-dependent changes, however, are uncertain. By utilizing a large therapeutic drug monitoring (TDM) database, this cross-sectional study aimed to retrospectively assess pharmacotherapy in elderly patients in comparison with their younger counterparts, when treated with venlafaxine, which is widely used to treat late-life depression. In addition, the influence of sex and body mass index (BMI) was evaluated. Serum concentrations of venlafaxine and its active metabolite O-desmethylvenlafaxine requested during routine TDM in two University Medical Centers in Germany were analyzed. Patients with concomitant CYP2D6 inhibiting drugs as co-medication were excluded. In total, 1,417 samples were available for the analysis. Elderly patients had by average 42% higher dose-adjusted serum concentrations (ng/mL/mg) of the active moiety (venlafaxine plus O-desmethylvenlafaxine) than younger patients. In addition, our study demonstrated that the difference between age groups is independent of sex and BMI. However, age groups only explain 4.5% of the total dose-adjusted serum concentration variation of the venlafaxine active moiety. Dose adjustments for venlafaxine are recommended in patients aged 65 years or older, particularly in elderly female patients who are exceptionally vulnerable to high serum concentrations of venlafaxine. TDM is recommended during venlafaxine pharmacotherapy.

Risk of bleeding related to selective and non-selective serotonergic antidepressants: a case/non-case approach using data from two pharmacovigilance databases.

INTRODUCTION: There is increasing evidence for an association between treatment with selective serotonin reuptake inhibitors (SSRI) and an increased risk of bleeding events. The most important underlying mechanism appears to be inhibition of serotonin uptake in platelets, an effect that is also present in antidepressants with non-selective serotonin-reuptake inhibition (NSRI). Accordingly, also NSRI may be associated with an increased risk of bleeding. However, there is little data in this regard. METHODS: Based on data (spontaneous reports of adverse drug reactions) from 2 pharmacovigilance databases (WHO-database/Vigibase™; BfArM/AkdÄ-database in Germany) we used a case/non-case approach and calculated reporting odds ratios (ROR) as measures for disproportionality regarding the association of treatment with an agent of the group SSRI/NSRI and haemorrhages. RESULTS: Whereas both positive control agents (ASS and diclofenac) were statistically associated with haemorrhages in both databases (ASS: BfArM/AkdÄ, ROR 13.62 [95% CI 12.76-14.53]/WHO, ROR 12.96 [95% CI 12.75-13.16]; diclofenac: BfArM/AkdÄ, ROR 3.01 [95% CI 2.71-3.21]/WHO, ROR 2.11 [95% CI 2.05-2.16]), none of the agents of the group SSRI (ROR<1) was associated with haemorrhages. In group NSRI, only St. John's wort/hypericum was associated with haemorrhages (WHO-database, ROR 1.31 [95% CI 1.06-1.63]). DISCUSSION: Signal detectioning in 2 pharmacovigilance databases suggest that serotonin reuptake inhibition is not associated with an increased risk of bleeding. However, underreporting may have accounted for the evaluated absent associations, particularly concerning SSRI. Regarding the detected increased risk of bleeding associated with hypericum, pharmacokinetic drug-drug interactions may be relevant independent of serotonin reuptake inhibition.

Influence of concomitant medications on the total clearance and the risk for supra-therapeutic plasma concentrations of Citalopram. A population-based cohort study.

INTRODUCTION: The main objective of this study was to investigate the influence of the use of multiple medications and other risk factors on citalopram plasma concentrations. METHODS: A retrospective cohort study with a naturalistic population of 957 patients for whom routine therapeutic drug monitoring (TDM) of citalopram had been requested between 2006 and 2013 was conducted. RESULTS: Concomitant drugs inhibiting at least 2 different CYP subtypes involved in the metabolism of citalopram decreased statistically significantly the total clearance (Clt). Compared to younger patients over 64-year-old patients had on average a 4.5 times higher risk rate of supra-therapeutic plasma concentrations. However, binary logistic regression showed that age, sex and co-medication accounted only for 26% of the inter-individual variability of citalopram plasma concentrations. DISCUSSION: Due to pharmacokinetic interactions, citalopram plasma concentrations are often higher than expected with a given dose. Especially in geriatric and often multimorbid patients who are usually prescribed high numbers of concomitant drugs and are at higher risk for adverse drug reactions (ADR), restriction of the maximal dose of citalopram is not sufficient to prevent supra-therapeutic plasma concentrations.

Prediction of antidepressant response to venlafaxine by a combination of early response assessment and therapeutic drug monitoring.

INTRODUCTION: Early assessment of a therapeutic response is a central goal in antidepressant treatment. The present study examined the potential for therapeutic drug monitoring and symptom rating to predict venlafaxine treatment efficacy (measured by overall patient response and remission). METHODS: 88 patients were uptitrated homogenously to 225 mg/day venlafaxine. Serum concentrations of venlafaxine (VEN) and its active metabolite O-desmethylvenlafaxine (ODV) were measured at week 2. Continuous psychopathometric ratings were measured for up to 6 weeks by independent study raters. RESULTS: An early improvement was significantly more common in venlafaxine responders than non-responders (χ(2); p=0.007). While ODV serum levels were significantly higher in responders (t test; p=0.006), VEN serum levels, sum level of VEN+ODV and the ratio of ODV/VEN levels were not. Moreover, patients who showed an early response combined with an ODV serum level above the median of 222 ng/mL were significantly more likely to achieve full response (binary logistic model; p<0.01). Sensitivity (84% for early response) and specificity (81% for combination of early response and therapeutic drug monitoring) were sufficient to qualify as a reasonable screening instrument. CONCLUSION: Our results indicate that early improvement and ODV serum concentration are predictive of therapeutic outcome and can thus be used to guide use of the antidepressant venlafaxine.

[New facts of long-term prophylaxis for bipolar affective disorder]. / Neue Fakten zur Phasenprophylaxe der bipolar affektiven Erkrankung.

Lithium and with restrictions, carbamazepine, valproic acid, lamotrigine, olanzapine, aripiprazole and quetiapine, are approved in Germany for maintenance treatment of bipolar disorder. Lithium is the only drug that (I) proved to be effective for the prevention of depressive as well as manic episodes in state-of-the-art studies without an enriched design and that (II) is approved for the maintenance treatment of bipolar disorders without restrictions. It (III) is also the only drug which is recommended for maintenance treatment by the current German S3 guidelines on bipolar disorders with the highest degree of recommendation (A) and (IV) is the only drug with a well proven suicide preventive effect. Hence, lithium is the mood stabilizer of first choice. No patient should be deprived of lithium without a specific reason. Side effects and risks are manageable if both the physician and the patient are well informed. Detailed and practical information on a safe use of lithium can be found in the S3 guidelines on bipolar disorders. For patients who do not respond sufficiently to lithium, have contraindications or non-tolerable side effects, other mood stabilizers should be used. Restrictions in their respective approval as well as specific side effects and risks have to be taken into account. Because maintenance treatment is a long-term treatment, particular concern should be paid to drugs with the potential risk of a metabolic syndrome, particularly atypical antipsychotics.

Therapeutic drug monitoring of zuclopenthixol in a double-blind placebo-controlled discontinuation study in adults with intellectual disabilities and aggressive behaviour.

The trial was a double-blind, placebo-controlled comparison with a discontinuation design. 49 mentally retarded patients with aggressive behaviour were treated with zuclopenthixol at a dose of 2-20 mg/d. At each visit the clinical effect was evaluated. Correlations between dose, serum concentration, and efficacy measures were calculated. The mean dose was 10.0 mg/day (±5.17); the mean serum concentration 4.19 ng/mL (±3.16). Associations of dosage, serum concentration and clinical efficiency did not result in coherent patterns. Correlations with clinical efficiency measures appeared to be contradictory for dosage and serum concentrations, respectively. As no consistent associations between dosage, serum concentration, and clinical efficiency measures were found, different hypotheses explaining the results are discussed.

[Therapeutic drug monitoring in psychiatry. A brief summary of the new consensus paper by the task force on TDM of the AGNP]. / Therapeutisches Drug-Monitoring in der Psychiatrie. Kurze Zusammenfassung des neuen Konsensuspapiers der Arbeitsgruppe TDM der AGNP.

In October 2011 the Task Force Therapeutic Drug Monitoring of the Association for Neuropsychopharmacology and Pharmacopsychiatry (AGNP) published an update (Pharmacopsychiatry 2011, 44: 195-235) of the first version of the consensus paper on therapeutic drug monitoring (TDM) published in 2004. This article summarizes the essential statements to make them accessible to a wider readership in German speaking countries.

Early improvement and serum concentrations of citalopram to predict antidepressant drug response of patients with major depression.

INTRODUCTION: Post hoc analyses of clinical trials have shown that early improvement around day 14 is highly predictive for later response. More-over, evidence has been given that sufficiently high concentrations of antidepressant drugs in blood are required to attain response. In this study, we determined cut-off levels for citalopram serum concentrations and clinical improvement during the early phase of treatment to predict later response and the predictive power of these measures either alone or in combination. METHODS: Inpatients with depressive disorder according to ICD-10 who received citalopram were included. Psychopathology was assessed by the 17-item Hamilton Depression (HAMD-17) rating scale, and serum concentrations of citalopram were measured in weekly intervals. RESULTS: The analysis included 55 inpatients. Receiver operating characteristics analysis revealed for citalopram a serum concentration of 53 ng/ml on day 7 and a clinical improvement of 24% on the HAMD-17 scale on day 14 as significant cut-off values to predict response after 5 weeks of treatment. Both measures taken together predicted response on week 5 with 73% sensitivity and 85% specificity with an odds ratio of 14.6. DISCUSSION: It is concluded that treatment with citalopram should be guided by symptom rating at baseline and on day 14 and serum concentration determination on day 7.

Agomelatine and hepatotoxicity: implications of cumulated data derived from spontaneous reports of adverse drug reactions.

Considering the antidepressant agomelatine (AGM) there is a discrepancy between the widespread knowledge of the potential of AGM to cause hepatotoxic adverse drug reactions (ADR) and the availability of corresponding published data. This impedes an adequate assessment of the hepatotoxicity profile of AGM. We conducted a query of the database of a German Medical Regulatory Body (BfArM) and analyzed spontaneous reports of hepatotoxic ADR. We identified n=58 cases of AGM-related hepatotoxic ADR. Most frequent ADR was asymptomatic increase of liver enzymes (79%); n=6 patients (10%) with AGM-related toxic hepatitis were reported. Characteristics of patients: female sex (69%), age > 50 years (mean 54 years), polypharmacy (57%), and presence of cardiovascular risk factors (58.5%). Most of the hepatotoxic ADR (90%) were reported to have improved/recovered after discontinuation of AGM. Our evaluation suggests that AGM features a potential to cause severe forms of hepatotoxicity and emphasizes that a pre-existing liver disease is a contraindication for treatment with AGM. Secondly, increased age, female sex and polypharmacy may be risk factors for the development of AGM-related hepatotoxic ADR.

Pharmacodynamic effects of aripiprazole and ziprasidone with respect to p-glycoprotein substrate properties.

INTRODUCTION: Aripiprazole, an atypical antipsychotic drug with mixed antagonism and agonism on dopamine D2 and serotonin receptors, is a substrate of the efflux transporter P-glycoprotein (P-gp). Here we tested the pharmacodynamic consequences of these properties in a P-gp deficient mouse model by studying the effects of aripiprazole and of ziprasidone on motor coordination. METHODS: The motor behaviour of wild-type (WT) and P-gp deficient [abcb1ab(-/-)] mice was investigated on a RotaRod. Mice received acute injections of either aripirazole or ziprasidone. For comparison, the dopamine receptor antagonist haloperidol and serotonin receptor ligands buspirone and ketanserin were also applied. RESULTS: Pharmacokinetic analyses revealed P-gp activity for aripiprazole and ziprasidone. This was indicated by 3.1- and 1.9-fold higher ratios of brain to plasma concentrations of drugs in knock-out to WT animals. Acute doses of ariprazole or ziprasidone impaired motor behaviour on the RotaRod. Effects were similar after injection of haloperidol, whereas the serotonin receptor ligands buspirone and ketanserin enhanced RotaRod performance. Genotype dependent differences of motor performance were found for aripiprazole but not for ziprasidone. DISCUSSION: Evidence was given that P-gp substrate properties have pharmacodynamic consequences for aripiprazole but not for ziprasidone and thus affect dopamine receptor related motor behaviour.