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.

Analysis of GTP-binding proteins, phosphoproteins, and cytosolic calcium in functional heterogeneous human blood platelet subpopulations.

The biochemical basis for the functional heterogeneity of human blood platelets was investigated in terms of protein phosphorylation, cytoplasmic calcium ([Ca2+]i), the ratio of 46 and 50 kDa vasodilator-stimulated protein (VASP), and GTP-binding proteins (G-proteins). Platelets were fractionated by density. Comparing resting low-density platelets (LDP) to high-density platelets (HDP) revealed higher phosphorylation of proteins in the 47, 31, and 24 kDa ranges. A higher phosphorylation of the 20 kDa protein in LDP compared to HDP was related to an enhanced [Ca2+]i, an increased ADP-ribosylation of the inhibitory G-protein (G(i alpha1-3)) and rhoA, and a decreased ADP-ribosylation of the stimulatory G-protein (G(s alpha)). The differences in the ribosylation patterns of the subpopulations were not influenced by thrombin stimulation or exposure to prostaglandin E1 (PGE1). An 18 kDa phosphoprotein was more highly phosphorylated in resting HDP than in LDP. Thrombin exposure caused dephosphorylation of the 18 kDa phosphoprotein in the HDP, but generally increased phosphorylation of both HDP and LDP in the 47, 31, 24, and 20 kDa bands. Preincubation with prostaglandin E1 or sodium nitroprusside diminished the subsequent thrombin-induced increase in phosphorylation, particularly in HDP. In unstimulated HDP, the 50 kDa VASP phospho form was enhanced, whereas in unstimulated LDP the 46 kDa VASP dephospho form was increased. Our findings suggest that the functional heterogeneity of platelets is partly derived from differences in signal transduction mechanisms reflected in varying phosphoprotein patterns and G-protein properties of platelet stimulatory and inhibitory pathways.

Circadian and seasonal rhythms of 5-HT receptor subtypes, membrane anisotropy and 5-HT release in hippocampus and cortex of the rat.

Specific serotonin binding (5-HT1, 5-HT1A, and 5-HT2 subtypes) and membrane anisotropy were measured at 2 h intervals over a 24 h period in the hippocampus and cortex of Wistar WU rats, housed under a 12 h light-dark cycle, with lights on at 07.00. All experiments were performed both in March and December. In the hippocampus significant circadian rhythms could be ascertained for 5-HT1 binding sites in March and December while for 5-HT1A (subtype of 5-HT1) binding sites the circadian rhythm was only significant in March. The membrane anisotropy also showed significant variations only in March. Circadian rhythms were also found in the cortex for 5-HT1 (December) and 5-HT2 (March and December) binding sites as well as for the membrane anisotropy (December). A correlation was found between membrane anisotropy and 5-HT1 and 5-HT2 binding sites in hippocampus and cortex, respectively. A circadian rhythmicity was also observed for serotonin release as measured by in vivo voltammetry in both brain areas. The results obtained on the diurnal variations of serotonin receptor subtypes and serotonin release and the probable inverse relationship of these two parameters may be relevant in understanding the coupling of pre- and postsynaptic activity.

Stress-induced changes of extracellular 5-hydroxyindoleacetic acid concentrations followed in the nucleus raphe dorsalis and the frontal cortex of the rat.

In the present paper, the effect of different stressors on extracellular 5-hydroxyindoleacetic acid (5-HIAA) concentrations in the frontal cortex and the N. raphe dorsalis (NRD) of the rat were studied. The following stressful procedures were used: Immobilization, 10 min, cold, 20 min, and forced exercise in a rotating wheel, 2h. These procedures were compared with a handling procedure, 10 min. The extracellular 5-HIAA concentration was followed by in vivo voltammetry with carbon multifibre electrodes in the awake animal. Handling had no significant effect on extracellular 5-HIAA concentrations neither in the frontal cortex nor the NRD, whereas immobilization and cold evoked significant increases in both brain areas. During and after forced exercise a significant increase was measurable only in the frontal cortex, while extracellular 5-HIAA concentrations were unchanged in the NRD. Since it is very likely that the modulation of the activity of the central serotoninergic system under stressful conditions is closely connected with changes in behaviour and temperature regulation, we compared our findings on extracellular 5-HIAA levels during stress with the effect of the 5-HT1A agonist (+)-8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT), a substance known to reduce body temperature. The i.p. injection of a low dose decrease significantly both, the extracellular 5-HIAA concentration in the NRD and body temperature. Our results suggest that the serotoninergic activation in the frontal cortex may prove to be a general response to stress which could function perhaps as a part of the central coping mechanism, whereas serotonin (5-HT) in the NRD may modulate specific regulatory responses such as body temperature.

The effect of adrenergic drugs on serotonin metabolism in the nucleus raphe dorsalis of the rat, studied by in vivo voltammetry.

The serotonin (5-HT) and norepinephrine (NE) system participate in the control of behavioural functions. The experiments were aimed at the question whether the NE system of the locus coeruleus interferes with the 5-HT activity of the nucleus raphe dorsalis and of which receptors are possibly involved. The alpha 1- and beta-adrenoceptor agonists methoxamine and isoproterenol, as well as a high dose (600 micrograms/kg i.p.) of the alpha 2-adrenoceptor agonist clonidine, increased extraneuronal 5-hydroxyindoleacetic acid (5-HIAA) levels in the nucleus raphe dorsalis as measured by in vivo voltammetry. In contrast, a low dose (60 micrograms/kg i.p.) of clonidine and the alpha 1-, alpha 2- and beta-adrenoceptor antagonists, prazosin, piperoxane, and atenolol, reduced the 5-HIAA concentration. In the locus coeruleus, the origin of NE projections to the nucleus raphe dorsalis, clonidine decreased whereas piperoxane enhanced extracellular 3,4-dihydroxyphenylacetic acid (DOPAC), an index of NE metabolism in the locus coeruleus. The results suggest that 5-HT neurotransmission in the nucleus raphe dorsalis is stimulated by the NE system of the locus coeruleus and that adrenoceptor drugs may affect 5-HT neuronal activity in addition to NE neurotransmission.

Functional studies on monoaminergic transmitter release in parkinsonism.

1. In vivo pulse voltammetry and apomorphine induced circling behaviour were used to study the effect of antiparkinsonian drugs and neurotoxins on striatal, extraneuronal dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations which are a measure of dopamine (DA) release/DA metabolism and serotonin (5-HT) release, respectively. 2. The DA precursor dihydroxyphenylalanine (DOPA, i.p.) increased extraneuronal DOPAC and reduced 5-HIAA levels whereas the opposite effect was induced by the 5-HT precursor 5-hydroxytryptophan (5-HTP, i.p.). Tryptophan, i.p., decreased the extraneuronal DOPAC levels without significant effect on 5-HT release. 3. The monoamine oxidase (MAO) inhibitors pargyline, i.p., and deprenyl, i.p., as well as the DA agonist apomorphine, i.p., decreased the catechol signal. The DA antagonist haloperidol, i.p., increased extraneuronal DOPAC. 4. In longterm studies unilateral application of the neurotoxins 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetra-hydroxypyridine (MPTP), and 1-methyl-4-phenylpyridinium cation (MPP+) into the substantia nigra pars compacta abolished the DOPAC signal in the striatum at the lesioned side. This effect can be partially or fully restored by DOPA depending on the time elapsed after neurotoxin administration. 5. In accordance with the voltammetric recorded unilateral lesion of the dopaminergic system the apomorphine stimulated circling behaviour was significantly enhanced in MPTP and MPP+ treated rats as compared with controls. 6. The results obtained indicate that antiparkisonian drugs and neurotoxins besides their effect on total catecholamine and 5-HT concentrations change specifically the extraneuronal levels of the transmitter (metabolites). Moreover the results suggest that neurotoxin-treated rats can be used as a model to study Parkinson-like effects with regard to the pathogenesis and treatment of this disease.

In vivo studies on the effects of memantine on dopamine metabolism in the striatum and n. accumbens of the rat.

The action of the amantadine derivative memantine on the dopamine metabolism in the striatum and the n. accumbens of the rat was studied in vivo with different voltammetrical techniques. It was shown by differential pulse voltammetry that memantine enhanced extracellular levels of dopamine (DA) in the striatum of the anaesthetized rat, whereas an increase of 3,4 dihydroxyphenylacetic acid (DOPAC) could be observed only under freely moving conditions using square wave voltammetry. Under chloral hydrate anaesthesia the effect of memantine on extracellular DOPAC levels in the striatum and the n. accumbens was compared with MK-801, a well-known non-competitive NMDA-antagonist. Memantine did not affect striatal DOPAC concentrations under these conditions whereas MK-801 reduced the DOPAC signal. In the n. accumbens memantine enhanced the levels of extracellular DOPAC, while after MK-801 the signal was only slightly different from control. These findings suggest that in addition to its NMDA receptor antagonism, memantine affects dopaminergic transmission also by other mechanisms.

Biochemical lesions of the nigrostriatal system by TaClo (1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline) and derivatives.

In vivo voltammetry with carbon fibre electrodes was used to study the effects of highly halogenated tetrahydro-beta-carbolines on the striatal dopamine (DA) metabolism of the rat. As representatives of chloral-derived heterocycles, "TaClo" (1-trichloro-1,2,3,4-tetrahydro-beta-carboline) and its N-methylated derivative. "N-methyl-TaClo", were investigated. After intranigral injection of 10 micrograms TaClo, the DA activity in the ipsilateral striatum was reduced compared with the intact side. Application of N-methyl-TaClo (10 micrograms) resulted in a nearly total reduction of the DOPAC signal. Furthermore, also "TaBro" (1-tribromomethyl-1,2,3,4-tetrahydro-beta-carboline), the bromal-derived analogue of TaClo, was tested. The impairment of the DA metabolism in rats achieved with 10 micrograms TaBro was found to be between that observed after application of TaClo and N-methyl-TaClo, respectively. The results demonstrate the toxic potential of chloral- and bromal-derived beta-carbolines towards dopaminergic neurons.

Effect of lazaroid U-74389G on iron-induced reduction of striatal dopamine metabolism.

The substantia nigra of parkinsonian brains is reported to contain increased amounts of iron as compared with age-matched controls. Since iron might be cytotoxic via radical mechanisms, we analyzed the effect of intranigral iron infusion on the dopaminergic activity in the striatum of the rat. The striatal dopamine metabolism of the rat was followed 1, 3, and 6 weeks after unilateral intranigral iron (III) (1.5 micrograms) application. A progressive decrease of extraneuronal 3,4-dihydroxyphenylacetic acid (DOPAC) levels was observed in the ipsilateral striatum by means of in vivo pulse voltammetry. The significant reduction of the DOPAC signal could be attenuated by pretreatment of the animals with the lazaroid U-74389G, applied ip 20 minutes before unilateral intranigral iron application. Our data indicate that a single iron application into the substantia nigra leads to a progressive loss of dopaminergic activity in the striatum, also observed in Parkinson patients. Furthermore, the Lazaroid U-74389G seems to be beneficial in this model of Parkinson's disease.

[Atypical neuroleptics in child- and adolescent psychiatry]. / Atypische Neuroleptika in der Kinder- und Jugendpsychiatrie.

Atypical neuroleptic drugs have enriched our treatment programs, especially in childhood and adolescent schizophrenia. Reviewed here is the use of atypical neuroleptics in children and adolescents with a schizophrenic disorder. The receptor binding profile and pharmacological properties, indications, side effects, clinical application, and trials of atypical neuroleptic drugs are compared to the classical neuroleptic drug haloperidol in the treatment of adolescent schizophrenia. Special attention is paid to the most common atypical neuroleptics clozapine, olanzapine and risperidone since most studies are carried out with these compounds, most often with clozapine. More clinically controlled trials have to be conducted since only one has been performed to date. The place of atypical neuroleptic drugs is discussed and further studies are necessary in order to differentiate, and eventually broaden the spectrum of the indications tested thus far.

Mode of action of cupping--local metabolism and pain thresholds in neck pain patients and healthy subjects.

OBJECTIVES: Cupping worldwide has been part of traditional medicine systems and is in the western world used as CAM therapy mainly for treating pain syndromes. The mode of action is up to now unclear. In order to investigate its mechanism we measured in parallel metabolic changes in the tissue under the cupping glass and pressure pain thresholds. DESIGN AND INTERVENTIONS: In 12 volunteers (6 healthy subjects and 6 patients with chronic neck pain) a microdialysis system was implanted subcutaneously on both sides (left and right) above the trapezius muscle. After baseline measures cupping was performed at one randomly selected side (left or right), the other side served as control. Every 20 min during baseline measures and for 280 min after cupping, microdialysis probes for detection of lactate, pyruvate, glucose and glycerin were taken. In addition, pain thresholds were measured before and after cupping with algometry. RESULTS: Cupping resulted in a strong increase of lactate (beginning 160 min after cupping until the end of the measurements) and the lactate/pyruvate ratio, indicating an anaerobe metabolism in the surrounding tissue. Baseline pain thresholds were non-significantly lower in neck pain patients compared to healthy controls and slightly increased immediately after cupping (p<0.05 compared to baseline close to the area of cupping in healthy subjects and on the foot in neck pain patients). After 280 min no more significant changes of pain thresholds were detected. CONCLUSIONS: Cupping induces >280 min lasting anaerobe metabolism in the subcutaneous tissue and increases immediate pressure pain thresholds in some areas.

Impact of drugs approved for treating ADHD on the cell survival and energy metabolism: an in-vitro study in human neuronal and immune cells.

The oxidative and antioxidative properties of psychostimulants such as methylphenidate and amphetamine are discussed controversially. The aim of the present study was to evaluate the impact of psychostimulants and atomoxetine in different concentrations between 31.25 and 5000 ng/ml on the survival of human neuronal (neuroblastoma SH-SY5Y) and immune (monocytic U-937) cells and the impact of psychostimulants and atomoxetine in different concentrations between 500 and 5000 ng/ml on energy metabolism (adenosine triphosphate [ATP] content) in SH-SY5Y cells. Statistical analysis revealed that incubation for 24 h with amphetamine led to a significantly enhanced cell survival in both cell lines after treatment with various (32.5, 125, 250 and 1250 ng/ml) concentrations. Methylphenidate and atomoxetine induced a significantly enhanced cell survival at lower concentrations in the SH-SY5Y cell line, whereas in the U-937 cell line higher concentrations increased the cell survival. Incubation with the highest concentration of methylphenidate (5000 ng/ml) caused a significant reduction of cell survival in both cell types. Measurement of ATP contents in the neuronal cell line revealed no significant effects of the investigated compounds. Our results show that the examined substances exert concentration-dependent effects on cell survival in both applied cell lines.

Effects of quetiapine, risperidone, 9-hydroxyrisperidone and ziprasidone on the survival of human neuronal and immune cells in vitro.

Because there are reports on cytotoxic and cytoprotective effects of antipsychotics, the aim of the present study was to evaluate the impacts of different concentrations (1.6-50 microg/mL) of atypical antipsychotics on the survival of human neuronal (neuroblastoma SH-SY5Y) and immune (monocytic U-937) cells and on energy metabolism (ATP level after the incubation with antipsychotics in the concentration of 25 microg/mL). Statistical analysis showed that incubation for 24 h with the antipsychotics quetiapine, risperidone, 9-hydroxyrisperidone and ziprasidone led to a significantly enhanced cell survival in both cell lines in the lower concentrations. Higher concentrations exerted in part cytotoxic effects with the exception of quetiapine, but therapeutically relevant concentrations of the drugs were not cytotoxic in our experiments. Measurement of ATP contents in the neuronal cell line showed significantly increased levels after a 24-h treatment with 25 microg/mL risperidone and 9-hydroxyrisperidone. The other substances produced no effects. Our results show that the antipsychotic substances under investigation exert concentration-dependent effects on cell survival in both cell lines examined.

Effects of antipsychotics and vitamin C on the formation of reactive oxygen species.

There is evidence that reactive oxygen species (ROS) are involved in the pathophysiology of psychiatric disorders such as schizophrenia. Indirect biochemical alterations of ROS formation have been shown for patients treated with antipsychotics as well as for untreated patients. Only one study measured directly the ROS formation after treatment with antipsychotics by using electron spin resonance spectroscopy. The aim of the present examination was to demonstrate the effects of haloperidol, clozapine and olanzapine in concentrations of 18, 90 and 180 µg/mL on the formation of ROS in the whole blood of rats by using electron spin resonance spectroscopy after incubation for 30 min. To test the protective capacity of vitamin C we incubated the highest concentration of each drug with vitamin C (1 mM). Under all treatment conditions, olanzapine led to a significantly higher formation of ROS compared with control conditions, whereas in the cases of haloperidol and clozapine the two higher concentrations induced a significantly enhanced formation of ROS. Vitamin C reduced the ROS production of all drugs tested and for haloperidol and clozapine the level of significance was reached. Our study demonstrated that antipsychotics induce the formation of ROS in the whole blood of rats, which can be reduced by the application of vitamin C.

Therapeutic drug monitoring of quetiapine in adolescents with psychotic disorders.

INTRODUCTION: There are developmental and age-dependent differences in the pharmacokinetics and the pharmacodynamics of drugs in children and adolescents. Therefore, there is a need to carry out standardised studies to find out therapeutic ranges of plasma/serum concentrations in psychopharmacotherapy of children and adolescents. The aim of this prospective study was to examine the relationship between quetiapine serum concentration, treatment response, and side effects in a clinical setting to elucidate the age-specific therapeutic range of quetiapine in adolescents. METHODS: Over a period of two years, therapeutic drug monitoring (TDM) was routinely performed in 21 adolescents (mean age was 15.9+/-1.5 years, 57% male) with psychotic disorders according to the guidelines of the AGNP TDM expert group. The psychopathology was assessed by using the Clinical Global Impression Scale (CGI) and the Brief Psychiatric Rating Scale (BPRS). Side effects were assessed by using the Dose Record and Treatment Emergent Symptom Scale (DOTES). Trough quetiapine concentrations were determined under steady state conditions after multiple-dose regimes (median 600 mg/day; range 100-800 mg/day). RESULTS: There was a marked variability of the serum concentrations, ranging from 19-877 ng/ml. 40.8% of the determined values were below and 24.5% above the therapeutic range (70-170 ng/ml) recommended for adults. None of the patients had severe side effects. We found a weak correlation between dose and serum concentration of quetiapine and no relationship between serum concentration and treatment response. DISCUSSION: There are several limitations of this study, and our results should therefore be interpreted with caution. Notwithstanding, differences in the ontogenesis of pharmacokinetics and pharmacodynamics may be the reason for the difference in the relationship between blood concentrations and therapeutic response to psychopharmaca in children, adolescents and adults. Further studies using larger samples, baseline assessment of psychopathology, definition of the treatment interval and investigation of clinically relevant interactions with various co-medications are warranted to improve the limitations of this pilot study.

Effect of lazaroid pretreatment on dopamine-induced impairment of the rat nigrostriatal system.

Oxidative stress induced by enhanced catecholamine metabolism may subsequently cause damages to the nervous system. We used in vivo-pulse voltammetry to study an enhanced brain dopamine (metabolism) induced either by intranigral dopamine (DA) injection or reduction of cerebral blood flow. One week after intranigral injection of 10 microg DA or unilateral occlusion of one carotid the DA activity in the ipsilateral striatum was decreased as compared to the contralateral side. Three weeks after DA application and carotid clamping the DA activity was restored to normal. The significant reduction of 3,4-dihydroxyphenylacetic acid (DOPAC) after one week was attenuated by pretreatment with the lazaroid U-74389G, injected 20 min before surgery. The results are in accordance with the view that radical mechanisms play a crucial role in the impairment of the nigrostriatal system induced by oligemia.

Serotonin-norepinephrine interactions: a voltammetric study on the effect of serotonin receptor stimulation followed in the N. raphe dorsalis and the Locus coeruleus of the rat.

In vivo voltammetry with carbon fibre electrodes was used to study the effect of the serotoninergic (5-HT) neuronal system on the noradrenergic (NE) system in the Locus coeruleus of the rat. The voltammetric DOPAC signal in the Locus coeruleus, used as a measure of NE neuronal activity, was increased after systemic application of the 5-HT1B agonist CGS-12066B, the 5-HT2 antagonist ritanserin, and, to a lesser extent, by ipsapirone, a 5-HT1A agonist. The findings suggest that the NE neuronal system of the Locus coeruleus is stimulated by 5-HT1A and 5-HT1B receptor activation and inhibited by 5-HT2 receptors. Likewise the 5-HT releaser and uptake inhibitor fenfluramine increased the DOPAC level in the Locus coeruleus. In contrast to the 5-HT1 agonists, which reduced 5-hydroxyindoleacetic acid (5-HIAA) in the Nucleus raphe dorsalis, ritanserin increased the 5-HIAA signal in this nucleus. This finding could help to explain the action of ritanserin as sleep-modulating substance.

Blood biogenic amines during clozapine treatment of early-onset schizophrenia.

The aims of this investigation were to evaluate long-term and short-term effects of clozapine-treatment on plasma biogenic amines and psychopathology measures in adolescents with schizophrenia (DSM-III-R criteria). The long-term study was conducted in a study sample of 40 young patients (age 14-22 years) following a mean of 3.4 years of neuroleptic treatment. During the study, 20 patients received clozapine, and the other 20 patients were treated with standard neuroleptic medications. At the beginning of the open clinical trials, the patients had already been receiving clozapine treatment for 24 +/- 15 months. Assessment of the biochemical and psychopathological measures was performed on six occasions at consecutive 6-week intervals during maintenance treatment with clozapine or conventional neuroleptics. Blood levels of serotonin, 3-methoxy-4-hydroxy-phenylglycol (MHPG), norepinephrine, and epinephrine were significantly higher in clozapine-treated patients than in conventionally treated patients. During long-term treatment, higher serotonin levels were associated with significantly fewer negative symptoms of schizophrenia, whereas higher MHPG levels were correlated with less depression. The short-term effects of clozapine were assessed in a second and independent study sample. After failing on conventional neuroleptics in clinical trials lasting a mean of 1.6 years, 15 inpatients (aged 11-20 years) received clozapine. Weekly ratings of psychopathological symptoms using standard rating scales were performed in parallel to blood samplings for measurements of biogenic amines and serum levels of clozapine. These measures were obtained for 6 weeks during conventional neuroleptic treatment and for 6 weeks during the open-label clozapine trial. Serum levels of serotonin and plasma norepinephrine levels were significantly higher during treatment with clozapine than during pretreatment with typical neuroleptics. A comparison of plasma epinephrine levels in responders (n = 7) and nonresponders (n = 8) to clozapine revealed that response to clozapine can be predicted by epinephrine levels prior to initiation of treatment with clozapine (responders ranging from 32.2 to 90.3 pg/ml; nonresponders ranging from 92.5 to 473.5 pg/ml). Additionally, subjects who responded to clozapine showed increased mean plasma concentrations of MHPG and epinephrine during treatment with this drug in comparison to the levels measured during pretreatment with typical neuroleptic medication. Nonresponders to clozapine failed to show this increase. Finally, in responders to clozapine a negative linear relationship between negative symptoms of schizophrenia and the concentrations of plasma norepinephrine and serum serotonin were observed. In conclusion, our results demonstrate that plasma epinephrine levels prior to initiation of clozapine therapy predict response to this atypical neuroleptic. Our findings derived from short-term and maintenance treatment with clozapine suggest involvement of norepinephrine, epinephrine and serotonin in the therapeutic actions of the atypical neuroleptic clozapine.