Trimipramine pharmacokinetics after intravenous and oral administration in carriers of CYP2D6 genotypes predicting poor, extensive and ultrahigh activity

Pharmacogenetic Dose Modeling Based on CYP2C19 Allelic Phenotypes

Pharmacogenetic variability in drug metabolism leads to patient vulnerability to side effects and to therapeutic failure. Our purpose was to introduce a systematic statistical methodology to estimate quantitative dose adjustments based on pharmacokinetic differences in pharmacogenetic subgroups, addressing the concerns of sparse data, incomplete information on phenotypic groups, and heterogeneity of study design. Data on psychotropic drugs metabolized by the cytochrome P450 enzyme CYP2C19 were used as a case study. CYP2C19 activity scores were estimated, while statistically assessing the influence of methodological differences between studies, and used to estimate dose adjustments in genotypic groups. Modeling effects of activity scores in each substance as a population led to prudential predictions of adjustments when few data were available ('shrinkage'). The best results were obtained with the regularized horseshoe, an innovative Bayesian approach to estimate coefficients viewed as a sample from two populations. This approach was compared to modeling the population of substance as normally distributed, to a more traditional "fixed effects" approach, and to dose adjustments based on weighted means, as in current practice. Modeling strategies were able to assess the influence of study parameters and deliver adjustment levels when necessary, extrapolated to all phenotype groups, as well as their level of uncertainty. In addition, the horseshoe reacted sensitively to small study sizes, and provided conservative estimates of required adjustments.

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.

The anaesthetist, opioid analgesic drugs, and serotonin toxicity: a mechanistic and clinical review

Most cases of serotonin toxicity are provoked by therapeutic doses of a combination of two or more serotonergic drugs, defined as drugs affecting the serotonin neurotransmitter system. Common serotonergic drugs include many antidepressants, antipsychotics, and opioid analgesics, particularly fentanyl, tramadol, meperidine (pethidine), and methadone, but rarely morphine and other related phenanthrenes. Symptoms of serotonin toxicity are attributable to an effect on monoaminergic transmission caused by an increased synaptic concentration of serotonin. The serotonin transporter (SERT) maintains low serotonin concentrations and is important for the reuptake of the neurotransmitter into the presynaptic nerve terminals. Some opioids inhibit the reuptake of serotonin by inhibiting SERT, thus increasing the plasma and synaptic cleft serotonin concentrations that activate the serotonin receptors. Opioids that are good inhibitors of SERT (tramadol, dextromethorphan, methadone, and meperidine) are most frequently associated with serotonin toxicity. Tramadol also has a direct serotonin-releasing action. Fentanyl produces an efflux of serotonin, and binds to 5-hydroxytryptamine (5-HT)_1A and 5-HT_2A receptors, whilst methadone, meperidine, and more weakly tapentadol, bind to 5-HT_2A but not 5-HT_1A receptors. The perioperative period is a time where opioids and other serotonergic drugs are frequently administered in rapid succession, sometimes to patients with other serotonergic drugs in their system. This makes the perioperative period a relatively risky time for serotonin toxicity to occur. The intraoperative recognition of serotonin toxicity is challenging as it can mimic other serious syndromes, such as malignant hyperthermia, sepsis, thyroid storm, and neuroleptic malignant syndrome. Anaesthetists must maintain a heightened awareness of its possible occurrence and a readiness to engage in early treatment to avoid poor outcomes.

Inhibitory potencies of trimipramine and its main metabolites at human monoamine and organic cation transporters

RATIONALE

The antidepressant trimipramine shows an atypical pharmacological profile and its mechanism of action is still obscure.

OBJECTIVES

The present study investigated whether trimipramine and three of its metabolites interact with targets of other antidepressants, namely, the human monoamine transporters for noradrenaline (hNAT), serotonin (hSERT), and dopamine (hDAT), and with the human organic cation transporters (hOCT1, hOCT2, and hOCT3) which are expressed in the brain and are known to be involved in the uptake of monoamines.

METHODS

HEK293 cells heterologously expressing the abovementioned transporters were used to determine the inhibition of [(3)H]MPP(+) uptake by trimipramine and its main metabolites.

RESULTS

At concentrations up to 30 μM, all transporters, except hOCT3, were inhibited by all examined substances. With IC(50) values between 2 and 10 μM, trimipramine inhibited hSERT, hNAT, hOCT1, and hOCT2, whereas clearly higher concentrations were needed for half-maximal inhibition of hDAT. Desmethyl-trimipramine showed about the same potencies as trimipramine, whereas 2-hydroxy-trimipramine was less potent at hNAT, hSERT, and hOCT1. Trimipramine-N-oxide preferentially inhibited hSERT.

CONCLUSIONS

Neither trimipramine nor its metabolites are highly potent inhibitors of the examined monoamine transporters. However, since at a steady state the sum of the concentrations of the parent compound and its active metabolites is almost two times higher than the plasma concentration of trimipramine and since it is known that tricyclic antidepressants accumulate in the brain (up to tenfold), at least partial inhibition by trimipramine and its metabolites of hSERT and hNAT (but not of hOCT3) may contribute to the antidepressant action of trimipramine.

Genetic polymorphisms of cytochrome P450 enzymes and antidepressant metabolism

INTRODUCTION

The cytochrome P450 (CYP) enzymes are the major enzymes responsible for Phase I reactions in the metabolism of several substances, including antidepressant medications. Thus, it has been hypothesized that variants in the CYP network may influence antidepressant efficacy and safety. Nonetheless, data on this field are still contradictory. The authors aim to give an overview of the published studies analyzing the influence of CYP highly polymorphic loci on antidepressant treatment in order to translate the acquired knowledge to a clinical level.

AREAS COVERED

The authors collected and compared experimental works and reviews published from the 1980s to the present and included in the Medline database. The included studies pertain to the effects of CYP gene polymorphisms on antidepressant pharmacokinetic parameters and clinical outcomes (response and drug-related adverse effects), with a focus on applications in clinical practice. The authors focused mainly on in vivo studies in humans (patients or healthy volunteers).

EXPERT OPINION

Great variability in antidepressant metabolism among individuals has been demonstrated. Thus, with the current interest in individualized medicine, several genetic tests to detect CYP variants have been produced. They provide a potentially useful way to anticipate some clinical outcomes of antidepressant treatment, although they will only be extensively used in clinical practice if precise and specific treatment options and guidelines based on genetic tests can be provided.

Paracetamol metabolism and related genetic differences

Paracetamol (acetaminophen) is a worldwide used analgesic and antipyretic drug. It is metabolised via several metabolic pathways, including glucuronidation, sulfation, oxidation, hydroxylation, and deacetylation: Hepatic and other organ damage may occur, especially in overdose, because of the accumulation of a toxic metabolite. Intersubject and ethnic differences have been reported in paracetamol metabolism activation, suggesting possible differences in susceptibility to toxicity and in pain alleviation, linked to different pharmacogenetic profiles. This article aims at reviewing, in the literature, the links between paracetamol metabolism and enzyme genotypes in the context of toxic side effects and efficacy of paracetamol in therapeutics.

Outcome in delusional depression comparing trimipramine monotherapy with a combination of amitriptyline and haloperidol--a double-blind multicenter trial

BACKGROUND

Patients with delusional depression are difficult to treat. The atypical antidepressant trimipramine was effective in a previous 4-week open label pilot study in patients with this disorder. The major neurobiological effect of trimipramine is the inhibition of the hypothalamic-pituitary-adrenocortical (HPA) system. In delusional depression HPA overactivity is more distinct than in other subtypes of depression. HPA suppression is thought to contribute to the action of trimipramine.

METHODS

In a double-blind, randomized, placebo controlled multicenter trial we compared the effects of trimipramine monotherapy versus a combination of amitriptyline and haloperidol. Dosage was increased stepwise from 100mg up to 400mg trimipramine and from 100mg up to 200mg amitriptyline combined with 2mg up to 7.5mg haloperidol. The average dose of trimipramine was higher than that of amitriptyline throughout the trial. During sixth week mean dosage (+/-standard deviation) were 356.1+/-61.2mg trimipramine, 184.0+/-23.6 mg amitriptyline and 6.3+/-1.8 mg haloperidol. During six weeks psychometric assessments were performed weekly. For HPA monitoring a dexamethasone/corticotropin-releasing hormone (Dex/CRH) test was performed before active medication and at the end of treatment. Additionally tolerability was monitored by ECG, EEG assessment of extrapyramidal symptoms and akathisia, clinical laboratory routine and recording of blood pressure and heart rate. Adverse events were documented.

RESULTS

94 patients were enclosed into the study. The per protocol sample consisted of 33 patients of the trimipramine group and of 24 patients of the amitriptyline/haloperidol group. The decrease of the Hamilton depression (HAMD) score (24 items) showed non-inferiority of trimipramine compared to amitriptyline/haloperidol. Twenty-eight patients (84.84%) in the trimipramine arm and 17 patients (70.83%) in the amitriptyline/haloperidol arm were responders (HAMD <or=50%). Remission (HAMD<8) was found in 18 (54.55%) patients after trimipramine and in 11 (45.83%) patients after amitriptyline/haloperidol. No significant differences were found concerning response and remission. The cortisol and ACTH response in the Dex/CRH test decreased between days 1 and 42 in both groups. Serious side effects were not reported.

CONCLUSION

In all, trimipramine monotherapy appears to be an effective treatment in delusional depression.

Serum concentrations of antidepressant drugs in a naturalistic setting: compilation based on a large therapeutic drug monitoring database

A compilation of therapeutic drug monitoring data for 15 antidepressant drugs in a naturalistic routine clinical setting is presented. A substantial number of serum concentrations, at different daily doses, are outlined, and the intraindividual and overall serum concentration coefficient of variation for a respective substance is presented. Also, concentration comparisons between women and men, and patients older or younger than 65 years are made. The drugs included are amitriptyline (n = 394), citalopram (n = 5457), clomipramine (n = 400), escitalopram (n = 3066), fluoxetine (n = 793), fluvoxamine (n = 165), mianserin (n = 1063), mirtazapine (n = 1427), moclobemide (n = 200), nortriptyline (n = 206), paroxetine (n = 1677), reboxetine (n = 85), sertraline (n = 2998), trimipramine (n = 158), and venlafaxine (n = 1781). Of the 9 drugs exhibiting linear (first order) kinetics, all but reboxetine gave a significant negative dose-to-dose-normalized correlation with concentrations, that is an increased clearance with higher dose. When dose was correlated to the metabolite:parent substance ratio for drugs exhibiting linear kinetics, citalopram and mianserin gave a positive slope, contrary to a negative slope shown for sertraline and venlafaxine. The intraindividual variations of the serum concentrations were lower than the overall variations, and the intraindividual variation of the metabolite:parent substance ratio was lower than the intraindividual variation of respective parent substance (except clomipramine and mianserin). Women had significantly higher serum concentrations than men (significant for citalopram, escitalopram, mianserin, mirtazapine, and venlafaxine), and patients older than 65 years had higher serum concentrations than the younger ones for all drugs except amitriptyline, moclobemide, and trimipramine. By presenting a comprehensive compilation of therapeutic drug monitoring data for each drug, a reference tool is created, in addition to improved pharmacokinetic knowledge of antidepressant drugs.

[Expanding therapeutic reference ranges using dose-related reference ranges]

Evidence-based therapeutic drug monitoring (TDM), which may be successfully employed to guide drug therapy in clinical routine, supplies all the information from laboratory determination of a drug concentration in a patient's blood specimen. This value is interpreted first of all in relation to a therapeutic reference range that must be established according to the same rules that are generally accepted for clinical studies aimed to license a new drug. The drug concentration may be furthermore interpreted in reference to a dose-related reference range. Thereby a signal is created to alert for individual abnormalities such as drug/drug interactions, gene polymorphisms that give rise to slow/rapid metabolizers, altered function of the excretion organs liver and kidneys by age and/or disease, compliance problems, a missing pharmacokinetic steady state, and even signal overlay in the laboratory analysis. We return all information available and clinical pharmacological comments to physicians who send specimens to our laboratory.

The pharmacogenetics of analgesia

Genomic variations influencing response to pharmacotherapy of pain are under investigation. Candidate genes such as (opioid)-receptors, transporters and other molecules important for pharmacotherapy are discussed. Drug metabolising enzymes represent a further major target of ongoing research in order to identify associations between an individual's genetic profile and drug response (pharmacogenetics). Polymorphisms of the cytochrome P450 enzymes influence analgesic efficacy of codeine, tramadol and tricyclic antidepressants (CYP2D6). Blood levels of some NSAIDs are dependent on CYP2C9 activity, whereas opioid-receptor polymorphisms are discussed for differences in opioid mediated analgesia and side effects. Pharmacogenetics as a diagnostic tool has the potential to improve patient therapy and care, and it is hoped that pharmacogenetics will individualise drug treatment to a greater extent in the near future.

Genetic factors in pain and its treatment

PURPOSE OF REVIEW

Genomic variations influencing basal pain sensitivity, the likelihood of developing chronic pain diseases as well as the response to pharmacotherapy of pain are currently under investigation Here, we review examples of promising approaches to diagnose genetic predisposition from recently published studies.

RECENT FINDINGS

Candidate genes such as those for catechol-O-methyltransferase, melanocortin-1 receptor, guanosine triphosphate cyclohydrolase and mu-opioid receptor have been intensively investigated, and associations were found with sensitivity to pain as well as with analgesic requirements in states of acute and chronic pain. In contrast, the impact of genetic variants of drug-metabolizing enzymes on the response to pharmacotherapy is generally well described. Polymorphisms of the cytochrome P450 enzymes influence the analgesic efficacy of codeine, tramadol, tricyclic antidepressants and nonsteroidal antiinflammatory drugs. Together with further candidate genes, they are major targets of ongoing research in order to identify associations between an individual's genetic profile and drug response (pharmacogenetics).

SUMMARY

The article reviews recent studies on genetic variables influencing pain and pharmacotherapy. Examples of promising candidate genes have been intensively studied during recent years. Although the number of subjects investigated is often small, published data and current advances in genotyping and study design suggest valid and clinically relevant results to date and even more in the future.

The impact of CYP allelic variation on antidepressant metabolism: a review

Psychiatric diseases that are treated with antidepressants are the leading causes of morbidity and mortality in humankind. Although antidepressants are generally well tolerated and widely available, they are not equally effective in all patients and only 35 - 45% of patients treated for depression with these drugs recover to premorbid levels of functioning. There is a need for an effective, individualized approach to antidepressant selection. One promising lead in the development of personalized medicine is the emerging field of pharmacogenomics, whereby pharmacologic agents are selected on the basis of the genotype of patients, with particular attention to drug targets and phase I- and phase II-metabolizing enzymes. This review article focuses on phase I antidepressant-metabolizing enzymes (e.g., relevant CYP enzymes). The authors first briefly review CYP nomenclature, the relevant members of the CYP superfamily and their alleles, the metabolic categories and CYP antidepressant substrates, inhibitors and inducers. The literature on the impact of CYP polymorphisms on antidepressant metabolism are also reviewed.

Concentrations of tramadol and O-desmethyltramadol enantiomers in different CYP2D6 genotypes

The influence of CYP2D6 genotype and CYP2D6 inhibitors on enantiomeric plasma levels of tramadol and O-desmethyltramadol as well as response to tramadol was investigated. One hundred and seventy-four patients received one hundred intravenous tramadol 3 mg/kg for postoperative analgesia. Blood samples drawn 30, 90, and 180 min after administration were analyzed for plasma concentrations of the enantiomers (+)-, (-)tramadol and (+)-, (-)O-desmethyltramadol by liquid chromatography-tandem mass spectrometry. Different CYP2D6 genotypes displaying zero (poor metabolizer (PM)), one (heterozygous individual (HZ)/intermediate metabolizer (IM)), two extensive metabolizer (EM), and three (ultra rapid metabolizer (UM)) active genes were compared. Concentrations of O-desmethyltramadol differed in the four genotype groups. Median (1/3 quartile) area under the concentration-time curves for (+)O-desmethyltramadol were 0 (0/11.4), 38.6 (15.9/75.3), 66.5 (17.1/118.4), and 149.7 (35.4/235.4) ng x h/ml for PMs, HZ/IMs, EMs, and UMs (P<0.001). Comedication with CYP2D6 inhibitors decreased (+) O-desmethyltramadol concentrations (P<0.01). In PMs, non-response rates to tramadol treatment increased fourfold compared with the other genotypes (P<0.001). In conclusion, CYP2D6 genotype determined concentrations of O-desmethyltramadol enantiomers and influenced efficacy of tramadol treatment.

Pharmacokinetics of mirtazapine: enantioselective effects of the CYP2D6 ultra rapid metabolizer genotype and correlation with adverse effects

Enantiomerically pure drugs and genotyping are promising approaches to achieve optimization in antidepressant therapy. Mirtazapine is a mixed noradrenergic serotoninergic antidepressant used as a racemate. We analyzed pharmacokinetics of its enantiomers in relation to CYP2D6 genotype and in relation to its adverse effects. Mirtazapine was enantioselectively absorbed from the gut with a rate constant of 0.2 min-1 for S+, but 0.08 min-1 for R- mirtazapine. Kinetics of R- mirtazapine was only marginally dependent on CYP2D6 genotype, but total clearance of the S+ enantiomer were 1.3, 2.3, and 3.4 L min-1 in poor, extensive, and ultrarapid metabolizers of CYP2D6 substrates with apparent substantial first-pass metabolism in rapid and ultrarapid metabolizers. Mirtazapine effects on heart rate and blood pressure correlated much more strongly with R- then with S+ concentrations, whereas sedation correlated similarly with both enantiomers. At least concerning some adverse effects, it might be worthwhile to study further mirtazapine enantiospecifically.

Genetik, Schmerz und Analgesie

Genomic variations influencing nociceptive sensitivity and susceptibility to pain conditions, as well as responses to pharmacotherapy of pain are currently under investigation. Candidate genes involved in pain perception, pain processing and pain management such as (opioid) receptors, transporters and other targets of pharmacotherapy are discussed. Drug metabolizing enzymes represent a further major target of ongoing research in order to identify associations between an individual's genetic profile and drug response (pharmacogenetics). Polymorphisms of the cytochrome P 450 enzymes influence analgesic efficacy of codeine, tramadol and tricyclic antidepressants (CYP2D6). Blood levels of some non-steroidal anti-inflammatory drugs (NSAIDs) are dependent on CYP2C9 activity, whereas opioid receptor polymorphisms are discussed with respect to differences in opioid-mediated analgesia and side-effects. Pharmacogenetics is seen as a potential diagnostic tool for improving patient therapy and care and will contribute to a more individualized drug treatment in the future.

Drug disposition of chiral and achiral drug substrates metabolized by cytochrome P450 2D6 isozyme: case studies, analytical perspectives and developmental implications

The concepts of drug development have evolved over the last few decades. Although number of novel chemical entitities belonging to varied classes have made it to the market, the process of drug development is challenging, intertwined as it is with complexities and uncertainities. The intention of this article is to provide a comprehensive review of novel chemical entities (NCEs) that are substrates to cytochrome P450 (CYP) 2D6 isozyme. Topics covered in this review aim: (1) to provide a framework of the importance of CYP2D6 isozyme in the biotransformation of NCEs as stand-alones and/or in conjunction with other CYP isozymes; (2) to provide several case studies of drug disposition of important drug substrates, (3) to cover key analytical perspectives and key assay considerations to assess the role and involvement of CYP2D6, and (4) to elaborate some important considerations from the development point of view. Additionally, wherever applicable, special emphasis is provided on chiral drug substrates in the various subsections of the review.

[Does genomics determine efficacy of analgesics?]

Recent advances in knowledge about gene structure derived from the human genome project has also revealed data on genomic variation and their possible impact on complex and acute diseases as well as pharmacotherapy. The hypothesis of a genetic predisposition for complex diseases such as pain syndromes, side effects, and adverse outcomes challenging the clinician is ready to be tested by advanced genetic-epidemiologic study designs employing the latest genotyping technology. In pain therapy, the genetic background of the efficacy of analgesics, especially of opioids, is of particular interest. Genetic differences in drug kinetics and dynamics, e.g., differences in metabolism or genetic variations of the drug target (e.g., receptors) will be of importance in the future. Pharmacogenetics can individualize pharmacotherapy and improve care by predicting the optimal dose and avoiding side effects and toxicity in individual patients.

Pharmacogenomics Education: International Society of Pharmacogenomics Recommendations for Medical, Pharmaceutical, and Health Schools Deans of Education

Pharmacogenomics would be instrumental for the realization of personalized medicine in coming decades. Efforts are evident to clarify the potential bioethical, societal, and legal implications of key pharmacogenomics-based technologies projected to be soon introduced into the core practice of medicine. In sharp contrast, a lack of sufficient attention to educational aspects of pharmacogenomics, both for professionals and for society at large, is evident. In order to contribute to this discussion, a 'Pharmacogenomics Education Forum' was held on October 2, 2004 during the 3rd Annual Meeting of the International Society of Pharmacogenomics (ISP) at Santorini, Greece. The participants, members of the ISP Pharmacogenomics Education Forum, after deliberate discussions, proposed a document of 'Background Statement' and 'Recommendations and Call for Action' addressed to Deans of Education at Medical, Pharmaceutical, and Health Schools globally. This document has been considered by the education committee of the International Society of Pharmacogenomics and the result is presented here. We hope that this call would be listened to, and soon followed by beneficial action, ultimately leading to enhanced implementation of personalized medicine into core medical education and practice.

Psychiatric genetics--the new era: genetic research and some clinical implications

Impressive advances in the last decade have been made in the genetics and neuroscience of neuropsychiatric illness. Synergies between complex genetics, elaboration of intermediate phenotypes (Egan et al. (2004) Schizophrenia. London: Blackwell) and novel applications in neuroimaging (Bookheimer et al. (2000) N Engl J Med, 343, 450-456) are revealing the effects of positively associated disease alleles on aspects of neurological function. Genes such as NRG-1, DISC1, RGS4, COMT, PRODH, DTNBP1, G72, DAAO, GRM3 (Harrison and Weinberger (2005) Mol Psychiatry, 10, 40-68) and others have been implicated in schizophrenia along with 5-HTTPR (Ogilvie et al. (1996) Lancet, 347, 731-733; Caspi et al. (2003) Science, 301, 386-389) and BDNF (Geller et al. (2004) Am J Psychiatry, 161, 1698-1700) in affective disorders. As the genetics and complex neurocircuits of these and disorders are being untangled, parallel applications in pharmacogenomics and gene-based drug metabolism are shaping a drive for personalized medicine. Genetic research and pharmacogenomics suggest that the subcategorization of individuals based on various sets of susceptibility alleles will make the treatment of neuropsychiatric and other illnesses more predictable and effective.

Pharmacogenetics of antidepressants and antipsychotics: the contribution of allelic variations to the phenotype of drug response

Genetic factors contribute to the phenotype of drug response. We systematically analyzed all available pharmacogenetic data from Medline databases (1970-2003) on the impact that genetic polymorphisms have on positive and adverse reactions to antidepressants and antipsychotics. Additionally, dose adjustments that would compensate for genetically caused differences in blood concentrations were calculated. To study pharmacokinetic effects, data for 36 antidepressants were screened. We found that for 20 of those, data on polymorphic CYP2D6 or CYP2C19 were found and that in 14 drugs such genetic variation would require at least doubling of the dose in extensive metabolizers in comparison to poor metabolizers. Data for 38 antipsychotics were examined: for 13 of those CYP2D6 and CYP2C19 genotype was of relevance. To study the effects of genetic variability on pharmacodynamic pathways, we reviewed 80 clinical studies on polymorphisms in candidate genes, but those did not for the most part reveal significant associations between neurotransmitter receptor and transporter genotypes and therapy response or adverse drug reactions. In addition associations found in one study could not be replicated in other studies. For this reason, it is not yet possible to translate pharmacogenetic parameters fully into therapeutic recommendations. At present, antidepressant and antipsychotic drug responses can best be explained as the combinatorial outcome of complex systems that interact at multiple levels. In spite of these limitations, combinations of polymorphisms in pharmacokinetic and pharmacodynamic pathways of relevance might contribute to identify genotypes associated with best and worst responders and they may also identify susceptibility to adverse drug reactions.