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.

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.

Doxepin plasma concentrations: is there really a therapeutic range?

Despite the introduction of numerous new agents, tricyclic antidepressants remain an important option for the treatment of depression. Doxepin is still in wide use, and determining its concentration is a standard procedure in many psychiatric clinics. Some widely cited reviews indicate a therapeutic range from 150 to 250 ng/mL (parent plus desmethyl metabolite). The vast majority of the authors' patients fell short of these concentrations under customary doses. To resolve this issue, the authors' serum-level databank was analyzed, a questionnaire was sent to U.S. and German psychiatric university departments and laboratories, and the literature was reviewed. The main results were the following: (1) Only 9% of all samples analyzed (N = 217) displayed plasma levels (high-performance liquid chromatography) between 150 and 250 ng/mL; 88% were subtherapeutic. The mean doxepin + desmethyldoxepin steady-state serum concentration was 89+/-75 ng/mL (N = 32, doxepin >3 weeks). The mean daily dose was 143+/-30 mg. There was no correlation between concentrations and improvement. (2) A wide variety of recommendations is given by the different university departments (10-1,000 ng/mL). (3) According to the studies published to date, there is not enough evidence for recommending a therapeutic range. The preliminary suggestions given in some influential reviews have been widely adopted without critical re-evaluation. Compared with the concentrations found in the original studies, the therapeutic ranges suggested are too high. A methodologically sound study to determine a therapeutic range is required for the rational monitoring of this drug. Meanwhile, a preliminary working range of 50 to 250 ng/mL is proposed on the basis of critical reassessment of published data.

Pharmacogenetics: a new diagnostic tool in the management of antidepressive drug therapy

Pharmacogenetics studies the genetic basis of an individual's ability to respond to pharmacotherapy. Variability of this response is a major problem. Fatal adverse drug reactions have been reported to be the fourth leading cause of death in the US. In depression, 30-40% of all patients do not respond sufficiently to the initial treatment and it can take up to 6 weeks for them to be identified. Much knowledge has been gathered throughout the last 3 decades about the genetic basis of pharmacokinetic variability. Genetic tests suitable for the routine laboratory are now available for some important metabolizing enzymes (e.g., CYP2D6, CYP2C19) identifying those individuals who are slow or fast metabolizers of certain drugs, many of which are widely used in the treatment of depression (e.g., tricyclic antidepressants). The possible use of these tests in the clinical practice of monitoring antidepressant therapy is discussed in relation to older phenotyping methods and therapeutic drug monitoring.Less well studied than the genetics of pharmacokinetics is the genetic basis of pharmacodynamic variability. As selective serotonin reuptake inhibitors (SSRI) have a wide therapeutic index, pharmacokinetic variability usually does not explain insufficient response to therapy. Recently, some excitement was caused by reports on serotonin transporter gene polymorphisms and their influence on the response to antidepressive therapy with SSRIs as this could provide an interesting diagnostic tool in assessing the chances of response to the most popular group of antidepressants at present. Current knowledge in this young field of research is summarized.

Effect of adjunctive paroxetine on serum levels and side-effects of tricyclic antidepressants in depressive inpatients

RATIONALE

Previous studies showed that adjunctive paroxetine increases tricyclic antidepressant (TCA) serum levels by inhibiting cytochrome P4502D6. This effect has, however, been examined only in experimental studies using low doses of TCAs in healthy volunteers.

OBJECTIVE

The present study investigated TCA serum level changes and side-effects after the addition of paroxetine in depressed patients treated with doses customarily used for inpatients.

METHODS

14 patients who had a moderate or severe depressive episode according to ICD-10 and who had not sufficiently responded (< or = 25% reduction of the Hamilton depression scale) to 3-week monotherapy with amitriptyline (n = 9) or imipramine (n = 5) with daily doses between 125 and 200 mg/day, received 20 mg/day paroxetine additionally under steady state conditions.

RESULTS

After 2 weeks the serum levels of the metabolites nortriptyline (from 88 +/- 49 ng/ml to 176 +/- 57 ng/ml) and desipramine (from 152 +/- 78 ng/ml to 338 +/- 104 ng/ml) had risen to a significantly greater extent than those of the parent compounds amitriptyline (123 +/- 50 ng/ml to 195 +/- 128 ng/ml) and imipramine (from 75 +/- 36 ng/ml to 98 +/- 51 ng/ml). It is noteworthy that, with the exception of one case of incipient delirium, the combination therapy was well tolerated despite high TCA serum level rises.

CONCLUSION

The higher increase of the metabolites as compared with the parent compounds can be explained by a paroxetine-induced inhibition of the liver enzyme cytochrome P4502D6, which catalyses the second step of the TCA metabolism, i.e. the hydroxylation of the metabolites. Blood levels should be meticulously monitored, if TCAs are combined with paroxetine.

Intoxication due to negative canrenone interference in digoxin drug monitoring

Canrenone and spironolactone caused falsely low readings in a common assay for digoxin (AxSym MEIA) due to negative cross-reactivity. Misleading subtarget concentrations were repeatedly reported, and falsely guided drug dosing resulted in a case of digoxin intoxication.

Performance and specificity of monoclonal immunoassays for cyclosporine monitoring: how specific is specific?

BACKGROUND

Immunoassays designed for the selective measurement of cyclosporin A (CsA) inadvertently show cross-reactivity for CsA metabolites. The extent and clinical significance of the resulting overestimation is controversial. A comprehensive assessment of old and new methods in clinical specimens is needed.

METHODS

In a comprehensive evaluation, CsA was analyzed in 145 samples with the new CEDIA assay and compared with the Emit assay with the old and new pretreatments, the TDx monoclonal and polyclonal assays, the AxSYM, and HPLC. All samples were from patients with liver and/or kidney transplants.

RESULTS

The CEDIA offered the easiest handling, followed by the AxSYM, which showed the longest calibration stability. The TDx monoclonal assay provided the lowest detection limit and the lowest CVs. The mean differences compared with HPLC were as follows: Emit, 9-12%; CEDIA, 18%; AxSYM, 29%; and TDx monoclonal, 57%. The CycloTrac RIA paralleled the Emit results. In contrast to the mean differences, substantial (>200%) and variable overestimations of the CsA concentration were observed in individual patient samples. Metabolic ratios, estimates of the overall concentrations of several cross-reacting metabolites (nonspecific TDx polyclonal/specific reference method), correlated with the apparent biases of the various monoclonal assays. Metabolic ratios varied up to 10-fold, which translated into biases for individual samples between -7% and +174%. The higher the cross-reactivity of an assay was, the higher was the range of biases observed. The interindividual differences markedly exceeded other factors of influence (organ transplanted, hepatic function).

CONCLUSION

Because assay bias cannot be predicted in individual samples, substantially erratic CsA dosing can result. The specificity of CsA assays for parent CsA remains a major concern.

[Influence of anatomical variations of the pancreatic artery on the surgical technic of segmental pancreas transplantation in dogs]

The surgical technique in clinical pancreas transplantation is still not standardized. Animal experimentation should allow a reproducible and reliable model by choosing the cervical region in dogs as the site of segmental grafting. A goal of the experiments was to determine the influence of preservation, operation technique, duct occlusion, immunosuppression, and gastrointestinal hormones (Somatostatin, Cyclosporin A). 50 grafts have been transplanted. It could be clearly demonstrated that in 54% the vascularization of the left lobe of the canine pancreas differs extremely from man. Successful results are to expect being aware of the anatomical variations. The varieties of the arterial blood supply indicate which technique has to be performed to avoid ischemic grafts due to inadequate preservation.