"There is no dose-response relationship in psychopharmacotherapy" vs "pharmacotherapy in psychiatry is based on ligand-receptor interaction": a unifying hypothesis and the need for plasma concentration based clinical trials

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.

Concentration-Effect Relationships of Psychoactive Drugs and the Problem to Calculate Therapeutic Reference Ranges

BACKGROUND

Despite the obvious potential of Therapeutic Drug Monitoring (TDM) as a tool to optimize psychopharmacotherapy, especially treatment with mood-stabilizing, antidepressant and antipsychotic drugs, acceptance of TDM as a routine tool is still limited. A serious scientific argument against the regular use of TDM is the lack of evidence for a concentration-dependent clinical effect. The aim of this review was to highlight methodological problems leading to poor or even negative concentration-effect relationships and to show how therapeutically effective concentrations of psychoactive drugs can be determined using routine TDM databases.

METHODS

Reports on concentration-effect relationships of psychoactive drugs were analyzed with regard to applied methods. From routine TDM databases of patients who had been treated with antidepressant or antipsychotic drugs and whose improvement was measured by the clinical global impressions scale, mean and median drug concentrations were calculated and compared with reference ranges recommended by TDM guidelines.

RESULTS

Few fixed-dose studies with adequate design and data analysis demonstrated a correlation between drug concentration and clinical effect for psychoactive drugs. Most studies, however, mostly retrospective analyses of TDM databases, failed to find significant concentration-effect relationships because of flexible dosing. They were not suitable for the determination of therapeutically effective drug concentrations. Using TDM databases of antidepressant and antipsychotic drug concentrations in blood of patients who were categorized as responders by the clinical global impressions score, the interquartile ranges of drug concentrations (25th-75th percent range) can be shown to be very close to the therapeutic reference ranges recommended in guidelines for TDM in psychiatry.

CONCLUSIONS

This review provides a discussion on why simple correlation analyses of psychoactive drug concentrations in blood and clinical effects are obsolete for flexible-dose studies or TDM databases. TDM databases, however, can and should be used to calculate drug concentrations in blood of patients who had responded to the drugs. Interquartile ranges can be regarded and used as preliminary therapeutic reference ranges.

Changes in psychopathology in schizophrenia patients starting treatment with new-generation antipsychotics: therapeutic drug monitoring in a naturalistic treatment setting

Previous studies on the relationship between plasma levels of new-generation antipsychotics (NGAs) and clinical response did not account for inter- and intra-individual variability in drug levels. Therefore, the present study calculated the ratio of observed versus expected NGA plasma levels and investigated its relationship with changes in the Positive and Negative Syndrome Scale (PANSS). Data of patients starting monotherapy with a NGA were collected 2, 4, 8, and 12 weeks after initiation of treatment. Next to the assessment of changes in psychopathology (PANSS) the ratio of observed versus expected plasma level was calculated. A total number of 221 ratios were eligible for analysis. About half of them ranged from 0.5-2 and were considered "normal", whereas the others were considered either "too low" or "too high". Psychopathological symptoms improved over the course of treatment, but changes in PANSS from baseline did not correlate significantly with the ratios of observed versus expected plasma levels at any assessment. The lack of linear correlation can be explained by the fact that 92% of the observed NGA plasma levels were at ≥ 50% of the lower limit of the therapeutic reference range, i.e., within the asymptote of the logistic plasma level-effect relationship. Accordingly, our findings indicate that the great majority of patients were treated with NGA doses that led to optimal plasma levels, based on the clinical impression of the treating psychiatrist only. Thus, calculating the ratio of observed versus expected plasma level may not be necessary in a routine clinical setting.

Therapeutic reference range for plasma concentrations of paroxetine in patients with major depressive disorders

BACKGROUND

We investigated the relationship between plasma concentrations of paroxetine and the therapeutic effect of the drug, and we evaluated the therapeutic reference range for plasma concentration of paroxetine in patients with major depressive disorders (MDD).

METHODS

In this study, 120 patients with MDD were treated with 10-40 mg/d of paroxetine for 6 weeks, and 89 patients completed the protocol. The Montgomery-Asberg Depression Rating Scale (MADRS) was used to evaluate the patients at 0, 1, 2, 4, and 6 weeks. At the 6-week treatment time point, the patients were divided into 7 groups according to their paroxetine plasma concentrations in increments of 20 ng/mL. We used an analysis of variance and a χ test to define the therapeutic reference range for plasma paroxetine concentrations.

RESULTS

We used 50% as the cutoff values for the percentage of MADRS improvement to determine the responder rates, and we defined remitters as patients with MADRS scores <10 at the 6-week treatment time point. We analyzed the responder and remitter rates of the patients according to their plasma paroxetine concentrations: 20 ng/mL, 40 ng/mL, and 60 ng/mL using the χ test. According to the results of the χ test in the responder rates, the 20-60 ng/mL plasma paroxetine group showed the highest effect size.

CONCLUSIONS

The results of this study suggested that a range of 20-60 ng/mL is the therapeutic reference range for concentrations of paroxetine in plasma in patients with MDD.

The influence of 5-HTTLPR genotype on the association between the plasma concentration and therapeutic effect of paroxetine in patients with major depressive disorder

INTRODUCTION

The efficacy of treatment with selective serotonin reuptake inhibitors in patients with major depressive disorder (MDD) can differ depending on the patient's serotonin transporter-linked polymorphic region (5-HTTLPR) genotype, and the effects of varying plasma concentrations of drugs can also vary. We investigated the association between the paroxetine plasma concentration and clinical response in patients with different 5-HTTLPR genotypes.

METHODS

Fifty-one patients were enrolled in this study. The Montgomery-Asberg Depression Rating Scale (MADRS) was used to evaluate patients at 0, 1, 2, 4, and 6 weeks. The patients' paroxetine plasma concentrations at week 6 were measured using high-performance liquid chromatography. Additionally, their 5-HTTLPR polymorphisms (alleles S and L) were analyzed using a polymerase chain reaction with specific primers. We divided the participants into two groups based on their L haplotype: the SS group and the SL and LL group. We performed single and multiple regression analyses to investigate the associations between MADRS improvement and paroxetine plasma concentrations or other covariates for each group.

RESULTS

There were no significant differences between the two groups with regard to demographic or clinical data. In the SS group, the paroxetine plasma concentration was significantly negatively correlated with improvement in MADRS at week 6. In the SL and LL group, the paroxetine plasma concentration was significantly positively correlated with improvement in MADRS at week 6 according to the results of the single regression analysis; however, it was not significantly correlated with improvement in MADRS at week 6 according to the results of the multiple regression analysis.

CONCLUSION

Among patients with MDD who do not respond to paroxetine, a lower plasma concentration or a lower oral dose of paroxetine might be more effective in those with the SS genotype, and a higher plasma concentration might be more effective in those with the SL or LL genotype.