Biotransformation of post-clozapine antipsychotics: pharmacological implications

Comorbidities and the right dose: antipsychotics

INTRODUCTION

The effects of antipsychotic drugs are dose-dependent, which is particularly true for their efficacy, each antipsychotic having a specific dose-response curve. This may justify individualizing doses for these agents.

AREAS COVERED

We review the pharmacokinetic profiles of seven oral antipsychotics: haloperidol, risperidone, olanzapine, clozapine, quetiapine, ziprasidone, and aripiprazole. Their main indications are psychotic and affective disorders. They are prescribed in a very large population which may have comorbidities. Hence, we analyze the impact of the latter on the pharmacokinetic profiles of these antipsychotics, focusing on renal and hepatic impairment. Reviews and clinical trials were discussed based on a systematic literature search (PubMed) ranging from 1995 to 2022.

EXPERT OPINION

Factors liable to impact antipsychotic dosage are numerous and their subsequent effects often hard to predict, due to multi-level interactions and compensatory phenomena. In clinical practice, physicians must be aware of these potential effects, but base their decisions on monitoring antipsychotic plasma levels.

CYP2D6 Genotyping and Antipsychotic-Associated Extrapyramidal Adverse Effects in a Randomized Trial of Aripiprazole Versus Quetiapine Extended Release in Children and Adolescents, Aged 12-17 Years, With First Episode Psychosis

PURPOSE/BACKGROUND

The aim of this study was to examine the association between genetically predicted CYP2D6 phenotypes and extrapyramidal symptoms (EPSs).

METHODS/PROCEDURES

Data from the Tolerability and Efficacy of Antipsychotics trial of adolescents with first-episode psychosis randomized to aripiprazole versus quetiapine extended release were studied. Extrapyramidal symptom assessments included the Simpson-Angus Scale and the Barnes Akathisia Rating Scale. Patients were CYP2D6 genotyped. Plasma concentrations of antipsychotics and antidepressants were analyzed.

FINDINGS/RESULTS

One hundred thirteen youths (age, 12-17 years; males, 30%; antipsychotic naive, 51%) were enrolled. Poor metabolizers had a significantly higher dose-adjusted aripiprazole plasma concentration (±SD) compared with normal metabolizers at week 4 (24.30 ± 6.40 ng/mL per milligram vs 14.85 ± 6.15 ng/mL per milligram; P = 0.019), but not at week 12 (22.15 ± 11.04 ng/mL per milligram vs 14.32 ± 4.52 ng/mL per milligram; P = 0.067). This association was not found in the quetiapine extended release group. No association between CYP2D6 genotype groups and global Barnes Akathisia Rating Scale score or Simpson-Angus Scale score was found in any of the treatment arms.

IMPLICATIONS/CONCLUSIONS

Our results do not support routine use of CYP2D6 testing as a predictor of drug-induced parkinsonism or akathisia risk in clinical settings. Further studies with larger samples of CYP2D6 poor metabolizers are needed.

Nose to brain delivery of tailored clozapine nanosuspension stabilized using (+)-alpha-tocopherol polyethylene glycol 1000 succinate: Optimization and in vivo pharmacokinetic studies

Clozapine is widely used to treat schizophrenia as an atypical antipsychotic. Low solubility, poor dissolution rate, degradation in the gastrointestinal tract, high hepatic first-pass metabolism, and eventually less drug transfer in the brain are all issues with oral clozapine administration. On account of this poor pharmacokinetic parameters, the authors aimed to develop clozapine nanosuspension using (+)-alpha-tocopherol polyethylene glycol 1000 succinate (TPGS) and polyvinylpyrrolidone K-30 (PVP K-30) and deliver it through the intranasal route. The nanosuspension was prepared by the high-speed homogenization method with 3² full factorial design for optimization of the product. Quality Target Product Profile (QTPP) was enlisted before the product development. The amount of TPGS and speed of homogenizer were selected as independent variables whereas, particle size and drug permeation profile after 24 h (Y₂, %) were selected as dependent variables. As per the results of optimization, amount of TPGS and speed of homogenizer were chosen as 0.1% and 7000 rpm, respectively. The particle size of the optimized nanosuspension of clozapine was found to be 281 nm. The conversion of clozapine crystals to an amorphous form was verified by characterization studies (XRD and DSC). The drug permeability study showed 96.15% and 41.12% clozapine release after 24 h from nanosuspension and conventional suspension, respectively. The study of nasal cilio-toxicity (histopathological studies) demonstrated the appropriateness of nanosuspension for intranasal purposes. The single-dose in vivo pharmacokinetic analysis in the rat model showed a substantial increase in the therapeutic concentration of clozapine in the brain tissue in the case of intranasal nanosuspension (dose = 0.05 mg drug/0.1 mL, C_max = 8.62 ± 0.45 μg/g, t_max = 1 h) compared to conventional oral clozapine suspension (dose = 26.43 mg drug/0.158 mL, C_max = 1.14 ± 0.12 μg/g, t_max = 1 h).Ultimately, in the case of an intranasal route, a 3.56-fold increase in brain drug concentration was observed with a 528-fold lower drug dose compared with oral administration. The results suggest that clozapine nanosuspension may be used for successful nose-to-brain delivery.

Combination of amisulpride and olanzapine in treatment-resistant schizophrenic psychoses

Treatment-resistant schizophrenia often leads to combined application of antipsychotic drugs. We report first experience with the combination of olanzapine and amisulpride. Improvement of psychopathological state and side effects could be achieved, and drug doses were lower than under monotherapy. We thus conclude that this approach represents a useful therapeutic option.

The use of ziprasidone in clinical practice: Analysis of pharmacokinetic and pharmacodynamic aspects from data of a drug monitoring survey

This study related clinical effects to daily doses and serum concentrations of ziprasidone by retrospective analysis of data from a therapeutic drug monitoring (TDM) survey established for patients treated with the new antipsychotic drug. In the total sample of 463 patients ziprasidone doses ranged between 20 and 320 mg/d and correlated significantly (r2 = 0.093, P < 0.01) with serum concentrations. The latter were highly variable within and between individual patients (between patients median 67 ng/ml, 25–75th percentile 40–103 ng/ml). Pharmacokinetic interactions with comedication played a minor role. According to the clinical global impressions (CGI) scale most of the 348 patients who were under antipsychotic monotherapy with ziprasidone were either much or very much improved (43.3 and 17.3%, respectively). The previously proposed therapeutic range of 50–130 ng/ml ziprasidone in serum or plasma, which can in effect be used interchangeable, was confirmed. In patients who were at least much improved and defined as “responders” mean serum concentrations of ziprasidone were 80 ng/ml and 78 ng/ml in patients who did not reach this improvement score. In patients with serum levels above or below 50 ng/ml, the number of responders was 66 or 63%, respectively. The difference between the two groups was not significant (P = 0.375), and improvement or side effects did not correlate significantly (P > 0.05) with doses or serum levels. It is concluded that TDM of ziprasidone may be useful for treatment optimization because of highly variable serum concentrations resulting under therapeutically recommended doses of the drug.

The blood-brain barrier in psychosis

Blood-brain barrier pathology is recognised as a central factor in the development of many neurological disorders, but much less is known about the role of the blood-brain barrier in psychiatric disorders. We review post-mortem, serum-biomarker, CSF-biomarker, and neuroimaging studies that have examined blood-brain barrier structure and function in schizophrenia and related psychoses. We consider how blood-brain barrier dysfunction could relate to glutamatergic and inflammatory abnormalities, which are increasingly understood to play a part in the pathogenesis of psychosis. Mechanisms by which the blood-brain barrier and its associated solute transporters moderate CNS availability of antipsychotic drugs are summarised. We conclude that the complex nature of blood-brain barrier dysfunction in psychosis might be relevant to many aspects of disrupted neuronal and synaptic function, increased permeability to inflammatory molecules, disrupted glutamate homoeostasis, impaired action of antipsychotics, and development of antipsychotic resistance. Future research should address the longitudinal course of blood-brain barrier alterations in psychosis, to determine whether blood-brain barrier dysfunction is a cause or consequence of the pathology associated with the disorder.

Olanzapine: a 5-year perspective

Olanzapine is a novel antipsychotic, approved for the acute and maintenance treatment of schizophrenia and bipolar I disorder. Despite the publicity regarding reported adverse events with the novel antipsychotics, such as weight gain and Type II diabetes mellitus, olanzapine remains a useful and important medicine. It is a selective monoaminergic antagonist with high-affinity binding to a number of receptors thought to be implicated in some psychotic and mood symptoms. The complex pharmacology of olanzapine has lead to studies exploring its use in treating substance abuse, aggression/violence, borderline personality disorder, schizotypal personality disorder, obsessive-compulsive disorder and as a neuroprotective agent in schizophrenia. As the pharmacology of olanzapine and other novel antipsychotics becomes better understood, future effective treatment strategies are likely to match an individual's genetic makeup and receptor profiles to the most compatible agent.

Safety and pharmacokinetics of atypical antipsychotics in children and adolescents

Pediatric behavioral and affective disorders often require antipsychotic therapy, in combination with psychotherapeutic interventions, for their treatment and stabilization. Although pharmacotherapy can include either typical or atypical antipsychotics, the latter are generally preferred because of their apparently lower risk of adverse effects. Recent controlled trials have demonstrated the efficacy of some of these agents (including aripiprazole, clozapine, olanzapine, paliperidone, quetiapine, risperidone, ziprasidone) in adolescent schizophrenia and children or adolescent bipolar mania, or to treat severe aggression and self-injury in the context of autism in children and adolescents. Although few studies have systematically monitored their short- and, more importantly, long-term safety, current evidence indicates that sedation, hyperprolactinemia, and metabolic abnormalities such as excess weight gain, diabetes, and related cardiovascular effects were clinically relevant adverse effects in young patients, with the individual agents differing in their propensity to induce these effects. When prescribing antipsychotics for children and adolescents, physicians should therefore be aware of the specific adverse effect profiles and patients should be closely monitored for the short- and long-term development of adverse events. In pediatric patients, the starting dose, titration plan, and maintenance dose of antipsychotics must be based on their pharmacokinetics and metabolism, as in adults. Because there are significant individual differences in drug and active metabolite(s) pharmacokinetics and metabolism, which may be further affected by a number of confounding factors (including demographic variables, phenotype and drug interactions), therapeutic drug monitoring may be a valid tool for individualizing dosage, but its interpretation should also take account of changes in pharmacodynamic sensitivity with the development during childhood and adolescence.

Plasma amisulpride in relation to prescribed dose, clozapine augmentation, and other factors: data from a therapeutic drug monitoring service, 2002-2010

OBJECTIVE

This study aimed to investigate the effect of dose and other factors on plasma amisulpride concentrations in clinical practice.

METHOD

Amisulpride therapeutic drug monitoring data 2002-2010 have been studied.

RESULTS

There were 296 samples (196 adult patients). Amisulpride was not detected in 10% of samples. In the remainder, the mean plasma amisulpride in relation to the prescribed dose (mg/day) was as follows: 100-200 (111 µg/L), 201-400 (254 µg/L), 400-800 (421 µg/L), and 800-1200 (494 µg/L). For prescribed doses up to 800 mg/day, only 51% of results were within 100-319 µg/L. There were no significant sex differences in mean plasma amisulpride or mean dose. The mean plasma amisulpride, but not the dose, was significantly higher in smokers. Linear regression analysis showed that dose explained only 42% of the variation in plasma amisulpride after log(10) transformation of both variables. There was no significant difference in the mean dose or mean plasma amisulpride in patients co-prescribed clozapine as compared with the remaining samples.

CONCLUSION

In practice, dose is a poor predictor of plasma amisulpride concentration. Therapeutic drug monitoring may not only help assess adherence, but also guide dosage.

Critical appraisal of lurasidone in the management of schizophrenia

Lurasidone is a new atypical antipsychotic in the benzoisothiazoles class of chemicals. Like most second-generation antipsychotics it is a full antagonist at dopamine D(2) and serotonin 5-HT(2A) receptors, and is a partial agonist at 5-HT(1A) receptors, a property shared by some but not all older agents. It has much greater affinity for 5-HT(7) subtype receptors than other atypical antipsychotics. Pharmacokinetic studies showed that lurasidone is reasonably rapidly absorbed, with bioavailability appearing to be increased by food. Lurasidone undergoes extensive metabolism to a number of metabolites, some of which retain pharmacological activities. Metabolism is mainly by CYP3A4, resulting in steady-state concentrations that vary between individuals and are potentially affected by strong inducers and inhibitors of this enzyme. Short-term clinical trials have demonstrated the efficacy of lurasidone in acute schizophrenia, with doses of 40 and 80 mg/day giving significant improvements from baseline in the PANSS and BPRS scores. The most common adverse events are nausea, vomiting, akathisia, dizziness, and sedation, with minimal increases in the risk of developing metabolic syndrome. Lurasidone did not raise the risk of QTc interval prolongation, although additional studies are required. Long-term trials are also needed to assess the risk of new-onset diabetes. Ongoing trials in patients with bipolar disorder are being completed but, again, efficacy and safety have been investigated only in a few short-term clinical trials.

Relationship between P-glycoprotein and second-generation antipsychotics

The membrane transport protein P-glycoprotein (P-gp) is an interesting candidate for individual differences in response to antipsychotics. To present an overview of the current knowledge of P-gp and its interaction with second-generation antipsychotics (SGAs), an internet search for all relevant English original research articles concerning P-gp and SGAs was conducted. Several SGAs are substrates for P-gp in therapeutic concentrations. These include amisulpride, aripiprazole, olanzapine, perospirone, risperidone and paliperidone. Clozapine and quetiapine are not likely to be substrates of P-gp. However, most antipsychotics act as inhibitors of P-gp, and can therefore influence plasma and brain concentrations of other substrates. No information was available for sertindole, ziprasidone or zotepine. Research in animal models demonstrated significant differences in antipsychotic brain concentration and behavior owing to both P-gp knockout and inhibition. Results in patients are less clear, as several external factors have to be accounted for. Patients with polymorphisms which decrease P-gp functionality tend to perform better in clinical settings. There is some variability in the findings concerning adverse effects, and no definitive conclusions can be drawn at this point.

Pharmacokinetics and metabolism update for some recent antipsychotics

INTRODUCTION

The search for drugs that reduce psychotic symptoms, with minimal adverse effects, has led to the development of new agents that act somewhat differently from their older antipsychotic counterparts. These agents, which include aripiprazole, lurasidone and perospirone, act by targeting both D₂ and 5-HT(1A) receptors, in addition to other characteristic receptors.

AREAS COVERED

This article covers the pharmacokinetics and metabolism of aripiprazole, perospirone, lurasidone and cariprazine. The review also describes the effects of physiological and pathological variables on these drugs as well as potential drug interactions. The author provides the reader with knowledge of the fundamental pharmacokinetic characteristics and metabolic pathways of these new antipsychotics, emphasizing the clinically important common features and differences compared to other older agents.

EXPERT OPINION

Aripiprazole, perospirone, lurasidone and cariprazine share some of the pharmacokinetic characteristics of older, lipophilic antipsychotics and, like these, each has some distinct pharmacokinetic features that are clinically beneficial and some that are not. We await the results of future practical effectiveness trials of these new antipsychotics and their follow-on derivatives to learn more about their benefit/risk profile compared with established antipsychotics. It is hoped that some of these newer antipsychotics will not only increase the range of pharmacotherapeutic options, but decisively improve the expectations of psychotherapy for schizophrenia.

Genome-wide pharmacogenomic analysis of response to treatment with antipsychotics

Schizophrenia is an often devastating neuropsychiatric illness. Understanding the genetic variation affecting response to antipsychotics is important to develop novel diagnostic tests to match individual schizophrenia patients to the most effective and safe medication. In this study, we use a genome-wide approach to detect genetic variation underlying individual differences in response to treatment with the antipsychotics olanzapine, quetiapine, risperidone, ziprasidone and perphenazine. Our sample consisted of 738 subjects with DSM-IV schizophrenia who took part in the Clinical Antipsychotic Trials of Intervention Effectiveness. Subjects were genotyped using the Affymetrix 500 K genotyping platform plus a custom 164 K chip to improve genome-wide coverage. Treatment outcome was measured using the Positive and Negative Syndrome Scale. Our criterion for genome-wide significance was a prespecified threshold that ensures that, on an average, only 10% of the significant findings are false discoveries. The top statistical result reached significance at our prespecified threshold and involved a single-nucleotide polymorphism (SNP) in an intergenic region on chromosome 4p15. In addition, SNPs in Ankyrin Repeat and Sterile Alpha Motif Domain-Containing Protein 1B (ANKS1B) and in the Contactin-Associated Protein-Like 5 gene (CNTNAP5), which mediated the effects of olanzapine and risperidone on Negative symptoms, were very close to our threshold for declaring significance. The most significant SNP in CNTNAP5 is nonsynonymous, giving rise to an amino-acid substitution. In addition to highlighting our top results, we provide all P-values for download as a resource for investigators with the requisite samples to carry out replication. This study demonstrates the potential of genome-wide association studies to discover novel genes that mediate the effects of antipsychotics, which could eventually help to tailor drug treatment to schizophrenic patients.

Efficacy, safety and tolerability of Symbyax for acute-phase management of treatment-resistant depression

Treatment resistance is frequently encountered during the long-term care of patients with major depression. A number of 'next step' therapeutic options exist in such cases, including switching to an alternative antidepressant, combining antidepressants from different pharmacological classes, adding evidence-supported psychotherapies to ongoing antidepressant treatment and augmentation with a nonantidepressant drug. Augmenting antidepressants with atypical antipsychotic drugs has generated considerable clinical interest. Three atypical antipsychotics (aripiprazole, quetiapine and olanzapine) have received regulatory approval for adjunctive use with antidepressants for treatment-resistant major depression (TRD) in adults. Symbyax (olanzapine-fluoxetine combination or OFC), the combination of olanzapine and the selective serotonin-reuptake inhibitor fluoxetine, is also approved for this indication. The short-term effectiveness of OFC for TRD is supported by results of five published randomized, controlled, acute-phase studies of generally similar design. In each study, OFC was associated with rapid reduction in depressive symptoms. In two studies, significantly greater improvement in depressive symptoms occurred in OFC-treated patients at study end point compared with those who received antidepressant monotherapy. These effects appeared to be strongest in cases where antidepressant failure was established during the current depressive episode. Although OFC was well-tolerated, increases in body weight and prolactin concentration were greater with OFC than antidepressant monotherapy, and were similar to olanzapine monotherapy. Increases in random total cholesterol levels were greatest for OFC, and were significantly greater than those of olanzapine and antidepressant monotherapy. The long-term efficacy and tolerability of OFC for TRD has not been investigated, and the comparative effectiveness of OFC versus other next-step options is unknown. As such, the exact place of OFC among the available therapeutic options for TRD is not fully understood at this time.

New atypical antipsychotics for schizophrenia: iloperidone

The optimal treatment of schizophrenia poses a challenge to develop more effective treatments and safer drugs, to overcome poor compliance, discontinuation and frequent switching with available antipsychotics. Iloperidone is a new dopamine type 2/serotonin type 2A (D(2)/5-HT(2A)) antagonist structurally related to risperidone, expected to give better efficacy with less extrapyramidal symptoms than D(2) receptor antagonist antipsychotics. In double-blind phase III trials iloperidone reduced the symptoms of schizophrenia at oral doses from 12 to 24 mg. It was more effective than placebo in reducing positive and negative syndrome total score and Brief Psychiatric Rating scale scores; it was as effective as haloperidol and risperidone in post-hoc analysis. Its long-term efficacy was equivalent to that of haloperidol. The most common adverse events were dizziness, dry mouth, dyspepsia and somnolence, with few extrapyramidal symptoms and metabolic changes in short- and long-term studies in adults. Akathisia was rare, but prolongation of the corrected QT (QTc) interval was comparable to haloperidol and ziprasidone, which is of particular concern. Further comparative studies are needed to clarify the benefit/risk profile of iloperidone and its role in the treatment of schizophrenia.

Antipsychotic Drug Treatment for Patients with Schizophrenia: Theoretical Background, Clinical Considerations and Patient Preferences

The cornerstone in treatment of psychosis is antipsychotic drugs. Treatment options have increased over the years; newer antipsychotic drugs with a proposed increased efficacy regarding negative and cognitive symptoms, but also a shift in side-effects from neurological side-effects to metabolic side-effects have arisen as the new challenge. The basis of successful pharmacological treatment is a fundamental understanding of the mechanisms of action, the desired effects and side-effects of antipsychotic drugs, a good relationship with the patient and a thorough monitoring of the patient before and during treatment. The clinically relevant aspects of antipsychotic drug treatment are reviewed; mechanism of antipsychotic drug action, clinical considerations in treatment, switching antipsychotic drugs, polypharmacy, safety and patient preference.

Amisulpride doses and plasma levels in different age groups of patients with schizophrenia or schizoaffective disorder

Because of a unique pharmacodynamic profile, amisulpride seems appropriate for treatment of elderly patients with schizophrenia. In a large-scale naturalistic therapeutic drug monitoring study, daily amisulpride dose, trough and dose-corrected amisulpride plasma levels, co-medication, clinical effectiveness (CGI) and side effects (UKU) were compared between age groups in 395 patients with schizophrenia or schizoaffective disorder (46% women; mean age 39.1 +/- 14.2 years, range 18-83 years) under amisulpride therapy. Mean amisulpride doses (574 +/- 269 mg/day), plasma levels (304 +/- 274 ng/mL), dose-corrected amisulpride plasma levels (C/D ratios, 0.52 +/- 0.41 ng/mL:mg), clinical response (at least moderate improvement, 71.6%), and side effects (any side effect, 32.2%; extrapyramidal symptoms, 14.9%) were comparable between age groups (P > 0.25). At higher age, significantly more benzodiazepines (P = 0.04), non-benzodiazepine hypnotics (P = 0.004) and non-psychotropic medications (P < 0.0001) were prescribed. The naturalistic study showed higher C/D ratios in women (P = 0.019) and a slight increase of C/D ratios with age (P = 0.026), but no substantial age-dependent effects on amisulpride doses or plasma levels. In patients above 60 years, clinical response was associated with lower amisulpride plasma levels (P = 0.016) at comparable doses. Neither the age-dependent decrease of amisulpride clearance nor the significantly higher prevalence of co-morbidity and co-medication seem to be the reasons for definite clinical concerns against amisulpride treatment of elderly if contraindications are seriously taken.

Genetic polymorphism in cytochrome P450 2D6 (CYP2D6): Population distribution of CYP2D6 activity

Cytochrome P-450 2D6 (CYP2D6) is involved in the metabolism of many therapeutic drugs even though the enzyme represents a small proportion of the total CYP content of human liver. In vivo phenotyping with probe drug substrates such as debrisoquine and dextromethorphan showed a clear separation between poor metabolizers (PM) and extensive metabolizers (EM). This polymorphism may affect susceptibility to environmental disease, as suggested by molecular epidemiologic studies that found an association between CYP2D6 metabolizer phenotype and cancer risk; however, this association is not consistent. There are only a few examples of CYP2D6 involvement in toxicant mechanism of action, but this has not been extensively studied. Gene probe studies documented a number of genetic polymorphisms that underlie CYP2D6 metabolizer phenotypes. The EM group carries the wild-type (*1) or active (*2) variant alleles, while the PM group carries the *3, *4, *5, or *6 alleles, all of which code for a protein that has lower or null CYP2D6 activity. The current analysis characterizes (a) influence of genotype on phenotype based upon in vivo metabolism studies of probe drugs and (b) frequency of the major genotypes in different population groups is also characterized. These data were then incorporated into Monte Carlo modeling to simulate population distributions of CYP2D6 activity. This analysis reproduced the bimodal distributions commonly seen in phenotyping studies of Caucasians and found extensive population variability in enzyme activity, as indicated by the 9- to 56-fold difference between the PM modal median and the total population median CYP2D6 activity. This substantial degree of interindividual variability in CYP function indicates that assessments involving CYP2D6 substrates need to consider the full distribution of enzyme activity in refining estimates of internal dose in health assessments of xenobiotics.

Update on the management of symptoms in schizophrenia: focus on amisulpride

Amisulpride is an atypical antipsychotic drug with a unique receptor pharmacology which is dose dependent. It is a standard treatment in dysthymia as well as in psychosis. Amisulpride is efficacious, effective and well tolerated in positive symptoms of schizophrenia: there is extensive evidence that it treats negative symptoms when given in low doses, although relative lack of EPS and an antidepressant effect may contribute. In first-episode patients amisulpride is an option, although there is little comparative work available. Amisulpride has the best evidence as an effective adjunct to clozapine treatment. Regarding intellectual function, amisulpride appears cognitive sparing but the clinical relevance of this remains obscure. There is evidence that amisulpride can improve social function but again there is little comparative work to demonstrate any particular advantages. Regarding the current conventional versus atypical antipsychotic controversy, amisulpride did better in switching studies and meta-analyses than in the single large pragmatic randomized trial reported to date. It is a versatile drug, and may offer advantages over other atypical antipsychotic drugs in the treatment of negative and depressive symptoms, and tolerability advantages such as the avoidance of weight gain. Essentially it rests with the treating clinician to employ a rational psychopharmacological approach towards the individual patient: there will be few circumstances in which amisulpride will not be a likely contender as a treatment choice.

Iloperidone: a new benzisoxazole atypical antipsychotic drug. Is it novel enough to impact the crowded atypical antipsychotic market?

Iloperidone is a new-generation atypical antipsychotic agent, acting as a serotonin/dopamine (5-HT(2A)/D(2)) antagonist, under development by Vanda Pharmaceuticals for the treatment of schizophrenia, bipolar disorder and other psychiatric conditions. Chemically, iloperidone is a benzisoxazole, like risperidone, and shows a multiple receptor binding profile, sharing this feature with the other atypical antipsychotic agents. Administered orally, the drug is highly bound to plasma proteins and extensively metabolised. Several clinical trials have been carried out, to check efficacy, safety and side effects. In order to introduce iloperidone as an agent for the treatment of schizophrenia, a short overview of the disease and of the most important antipsychotic drugs available or under development will be reported. Iloperidone pharmacokinetics and pharmacodynamics are presented herein, together with an evaluation of clinical safety and efficacy results.

Clinical Pharmacokinetics of Atypical Antipsychotics

In the past, the information about the dose-clinical effectiveness of typical antipsychotics was not complete and this led to the risk of extrapyramidal adverse effects. This, together with the intention of improving patients' quality of life and therapeutic compliance, resulted in the development of atypical or second-generation antipsychotics (SGAs). This review will concentrate on the pharmacokinetics and metabolism of clozapine, risperidone, olanzapine, quetiapine, amisulpride, ziprasidone, aripiprazole and sertindole, and will discuss the main aspects of their pharmacodynamics. In psychopharmacology, therapeutic drug monitoring studies have generally concentrated on controlling compliance and avoiding adverse effects by keeping long-term exposure to the minimal effective blood concentration. The rationale for using therapeutic drug monitoring in relation to SGAs is still a matter of debate, but there is growing evidence that it can improve efficacy, especially when patients do not respond to therapeutic doses or when they develop adverse effects. Here, we review the literature concerning the relationships between plasma concentrations of SGAs and clinical responses by dividing the studies on the basis of the length of their observation periods. Studies with clozapine evidenced a positive relationship between plasma concentrations and clinical response, with a threshold of 350-420 ng/mL associated with good clinical response. The usefulness of therapeutic drug monitoring is well established because high plasma concentrations of clozapine can increase the risk of epileptic seizures. Plasma clozapine concentrations seem to be influenced by many factors such as altered cytochrome P450 1A4 activity, age, sex and smoking. The pharmacological effects of risperidone depend on the sum of the plasma concentrations of risperidone and its 9-hydroxyrisperidone metabolite, so monitoring the plasma concentrations of the parent compound alone can lead to erroneous interpretations. Despite a large variability in plasma drug concentrations, the lack of studies using fixed dosages, and discrepancies in the results, it seems that monitoring the plasma concentrations of the active moiety may be useful. However, no therapeutic plasma concentration range for risperidone has yet been clearly established. A plasma threshold concentration for parkinsonian side effects has been found to be 74 ng/mL. Moreover, therapeutic drug monitoring may be particularly useful in the switch between the oral and the long-acting injectable form. The reviewed studies on olanzapine strongly indicate a relationship between clinical outcomes and plasma concentrations. Olanzapine therapeutic drug monitoring can be considered very useful in assessing therapeutic efficacy and controlling adverse events. A therapeutic range of 20-50 ng/mL has been found. There is little evidence in favour of the existence of a relationship between plasma quetiapine concentrations and clinical responses, and an optimal therapeutic range has not been identified. Positron emission tomography studies of receptor blockade indicated a discrepancy between the time course of receptor occupancy and plasma quetiapine concentrations. The value of quetiapine plasma concentration monitoring in clinical practice is still controversial. Preliminary data suggested that a therapeutic plasma amisulpride concentration of 367 ng/mL was associated with clinical improvement. A therapeutic range of 100-400 ng/mL is proposed from non-systematic clinical experience. There is no direct evidence concerning optimal plasma concentration ranges of ziprasidone, aripiprazole or sertindole.

Clozapin-Augmentation mit atypischen Antipsychotika

Typical antipsychotic medications have considerably improved clinical outcome of patients suffering from schizophrenic psychoses, but up to 40% of the cases show treatment resistant symptoms. Even therapy with atypical antipsychotic drugs such as risperidone, quetiapine, olanzapine, sulpiride, amisulpride, and ziprasidone often fails to reach complete remission due to resistant, positive or negative symptoms or dose-limiting side effects. As this also holds true in the case of monotherapy with clozapine, a substance known to be effective against treatment-resistant schizophrenia, increasing numbers of patients receive atypical antipsychotic drugs in addition to clozapine. This review systematically evaluates case reports and clinical investigations on the use of clozapine combined with risperidone, olanzapine, quetiapine, sulpiride, amisulpride, or ziprasidone. Details on indication, methodology, and effects of the investigations are summarized. Only one double blind, placebo-controlled trial on the combination with sulpiride exists within a number of altogether 31 publications about 1182 treatments. Favorable effects on positive and/or negative symptoms or improvements of clozapine-induced side effects were described for every combination approach. In some cases pharmacokinetic interactions or serious unfavorable effects occurred. In conclusion it might be accepted that most of the combination therapies follow a neurobiological rational. There a major differences in the level of evidence that they are safe, tolerable and effective. We discuss criteria for the indication for augmenting clozapine therapy and the differential indication for existing alternatives. Additional randomized prospective trials are needed in order to evaluate these strategies systematically.

Quetiapine serum concentrations in psychiatric patients: the influence of comedication

Steady-state serum concentrations of quetiapine were recorded in 62 psychiatric patients under routine conditions. Doses were administered twice daily, and serum quetiapine levels were measured in the morning about 12 hours after the last dose. Eight patients were in monotherapy, whereas the rest received various additional psychotropic drugs. For the whole group, the concentration-to-dose ratio (C/D) varied 238-fold, with a median value of 0.41 nmol/L/(mg/24 h). For the administered dose range (37.5-1200 mg/24 h), the serum concentrations ranged from below the detection limit (10 nmol/L) to 999 nmol/L. With the exception of 2 subjects receiving carbamazepine and patients receiving quetiapine outside the recommended dose interval, 80% of the rest had serum levels within the range 50 to 650 nmol/L, which may serve as an orienting interval for serum concentrations observed under routine treatment conditions. Patients (n = 38) comedicated with drugs competing for metabolism by CYP3A4 displayed a median C/D value of 0.48 nmol/L/(mg/24 h), which was 70% higher than the C/D value of the monotherapy group [0.28 nmol/L/(mg/24 h)], in contrast to patients receiving drugs metabolized by CYP2D6 with a median C/D of 0.23 nmol/L/(mg/24 h). None of the comedicated groups were significantly different from the monotherapy group. Two subjects comedicated with carbamazepine had very low C/D values [0.02-0.04 nmol/L/(mg/24 h)].

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.

[Pharmacological treatment of psychosis in epilepsy]

Epilepsy is one of the main causes of functional disability, and it is usually associated to psychiatric comorbidity, such as psychosis of epilepsy (POE). POE requires more careful pharmacological treatment, considering the propensity of the antipsychotics (AP) to provoke seizures and the risk of pharmacokinetic interaction with anti-epileptic drugs (AEDs). We discussed the classification and the main types of POE, as well as some characteristics of AP typical and atypical, its potential to decrease the epileptogenic threshold (ET) and possible interactions between AP and AED. Atypical AP, except clozapine, disclosed smaller influence on ET than typical AP. Regarding pharmacokinetic interactions, AEDs are related with a significant increase of the AP metabolism. Therefore, in spite of the risk for AP induced convulsions be dose-dependent, higher doses of AP can be necessary in the treatment of POE.

Use of perospirone for obesity and diabetes mellitus in patients with schizophrenia: three case reports

We report that perospirone may have had positive effects on the obesity of three patients with schizophrenia and on the fasting blood sugar (FBS) and HbA1C of two of them who had type 2 diabetes mellitus.

Metabolic drug interactions with new psychotropic agents

New psychotropic drugs introduced in clinical practice in recent years include new antidepressants, such as selective serotonin reuptake inhibitors (SSRI) and 'third generation' antidepressants, and atypical antipsychotics, i.e. clozapine, risperidone, olanzapine, quetiapine, ziprasidone and amisulpride. These agents are extensively metabolized in the liver by cytochrome P450 (CYP) enzymes and are therefore susceptible to metabolically based drug interactions with other psychotropic medications or with compounds used for the treatment of concomitant somatic illnesses. New antidepressants differ in their potential for metabolic drug interactions. Fluoxetine and paroxetine are potent inhibitors of CYP2D6, fluvoxamine markedly inhibits CYP1A2 and CYP2C19, while nefazodone is a potent inhibitor of CYP3A4. These antidepressants may be involved in clinically significant interactions when coadministered with substrates of these isoforms, especially those with a narrow therapeutic index. Other new antidepressants including sertraline, citalopram, venlafaxine, mirtazapine and reboxetine are weak in vitro inhibitors of the different CYP isoforms and appear to have less propensity for important metabolic interactions. The new atypical antipsychotics do not affect significantly the activity of CYP isoenzymes and are not expected to impair the elimination of other medications. Conversely, coadministration of inhibitors or inducers of the CYP isoenzymes involved in metabolism of the various antipsychotic compounds may alter their plasma concentrations, possibly leading to clinically significant effects. The potential for metabolically based drug interactions of any new psychotropic agent may be anticipated on the basis of knowledge about the CYP enzymes responsible for its metabolism and about its effect on the activity of these enzymes. This information is essential for rational prescribing and may guide selection of an appropriate compound which is less likely to interact with already taken medication(s).

Significant dose effect of carbamazepine on reduction of steady-state plasma concentration of haloperidol in schizophrenic patients

A reduction in haloperidol concentration induced by carbamazepine coadministration has been consistently reported. However, the degree of this reduction is very different among individuals treated with various doses of carbamazepine. Thus, we investigated dose effect of carbamazepine on the steady-state plasma concentration of haloperidol. Eleven excited schizophrenic inpatients, despite receiving haloperidol 12 mg/d, were treated with incremental doses of carbamazepine for 6 weeks (100, 300, 600 mg/d for 2 weeks each). Plasma drug concentrations were monitored together with clinical assessments before and after each phase of the 3 carbamazepine doses. Mean haloperidol concentrations during coadministration of carbamazepine 100, 300, and 600 mg/d were 75%, 39%, and 15%, respectively, of corresponding variables before carbamazepine coadministration. Negative linear correlations were observed between dose or plasma concentration of carbamazepine and the degree of reduction in haloperidol concentration. Mean carbamazepine dose and plasma carbamazepine concentrations at 50% reduction of haloperidol concentration were 240 mg/d and 3.5 microg/mL, respectively. Scores in total and excitement symptoms were significantly reduced after carbamazepine coadministration, whereas no changes were observed in other clinical symptoms or any of the subgroup side effects. Therefore, this study indicates that carbamazepine decreases plasma haloperidol concentration in a dose-dependent or concentration-dependent manner, and that reduction in haloperidol concentration is apparent even at subtherapeutic dose of carbamazepine.

Carbonic anhydrase activators. The selective serotonin reuptake inhibitors fluoxetine, sertraline and citalopram are strong activators of isozymes I and II

The selective serotonin reuptake inhibitors (SSRI) fluoxetine, sertraline and citalopram have been investigated for their ability to activate two carbonic anhydrase (CA) isozymes, hCA I and hCA II, in parallel with two standard activators for which the X-ray structure (in complex with isozyme II) has been resolved: histamine and phenylalanine. All three SSRI activated both isozymes with potencies comparable to that of the standards although the profile was different: for hCA I, best activators were fluoxetine and histamine, with citalopram and sertraline showing weaker activity. For hCA II, the best activators were phenylalanine and citalopram, and the weakest histamine and sertraline, whereas fluoxetine showed an intermediate behavior. These results suggest that SSRI efficacy in major depression complicating Alzheimer's disease may be partly due to their ability to activate CA isozymes and may lead to the development of potent activators for the therapy of diseases associated with significant decreases in brain CA activity.

Fatalities associated with therapeutic use and overdose of atypical antipsychotics

Since 1989, several novel antipsychotic drugs have become available for use including clozapine, risperidone, olanzapine, quetiapine and ziprasidone. These agents represent a substantial improvement in the treatment of schizophrenia and related disorders and are considered to have a favourable adverse effect profile relative to traditional antipsychotics. Nonetheless, in rare cases, people have died as a result of taking atypical antipsychotic drugs at therapeutic and supratherapeutic doses. Toxic doses of atypical antipsychotics are highly variable: some patients have died while taking therapeutic doses and others have survived massive overdoses. Toxicity may be increased by coingestion of other agents, particularly drugs with similar metabolic pathways. Atypical antipsychotics are metabolised predominantly by cytochrome p450 (CYP) isoenzymes, particularly CYP1A2 (clozapine and olanzapine), CYP3A4 (clozapine, quetiapine and ziprasidone) and CYP2D6 (olanzapine and risperidone). Concurrent prescription of other drugs that inhibit these isoenzymes may increase the probability of adverse events in patients taking atypical antipsychotics. Deaths due to atypical antipsychotic toxicity are often related to cardiovascular complications, but pulmonary, neurological, endocrine and gastrointestinal complications have also caused fatalities. Prevention and management of atypical antipsychotic overdose are of increased clinical relevance as prescription of these drugs increases.

Role of the smoking-induced cytochrome P450 (CYP)1A2 and polymorphic CYP2D6 in steady-state concentration of olanzapine

This study investigated whether the smokinginducible cytochrome P450 (CYP) 1A2 and the polymorphic CYP2D6 play significant roles in the metabolism of olanzapine and its clinical effects at steady-state treatment. Caffeine and debrisoquine were used as measures of CYP1A2 and CYP2D6, respectively. After drug therapy for 15 days, the effect of olanzapine on the activities of CYP1A2 and CYP2D6 was also examined. Seventeen psychiatric patients (9 men and 8 women) were orally administered olanzapine, at a mean +/- standard deviation (SD) dosage of 10 mg/d for all smokers (n = 8) and 7.5 +/- 2.5 mg/d (range, 5-10 mg) for nonsmokers (n = 9;p <0.01). The plasma concentration-to-dose (C:D) ratio was closely correlated to the CYP1A2 activity ( s = -0.89;p <0.0001). The mean urinary caffeine indexes of nonsmokers and smokers were 17 +/- 8 and 101 +/- 44, respectively, indicating that smoking had induced a sixfold higher CYP1A2 activity (p <0.0001). Likewise, the olanzapine plasma C:D ratio (ng.mL.mg) was about fivefold lower in smokers (7.9 +/- 2.6) than in nonsmokers (1.56 +/- 1.1;p <0.0001). On day 15 of the antipsychotic therapy, the percentage decrease in Brief Psychiatric Rating Scale (BPRS) total score relative to the predosing score (in the drug-free period) was higher for nonsmokers than for smokers (30.4 +/- 10% vs. 12.5 +/- 14%;p <0.01). Six nonsmokers and three smokers experienced side effects with olanzapine. After 15 days of drug treatment, olanzapine had caused significant (p <0.0001) and substantial CYP1A2 inhibition (by 50%) in comparison with predosing values, and such inhibition can contribute to adverse drug interactions. In conclusion, smoking-induced increased CYP1A2 activity significantly diminished plasma olanzapine concentrations and the antipsychotic effect of the drug. The performance of a simple caffeine test may assist in individualization of the olanzapine dosage.

Ziprasidone Mesylate for Injection

Each month, subscribers to The Formulary Monograph Service receive five to six well-documented monographs on drugs that are newly released or are in late Phase III trials. The monographs are targeted to your Pharmacy and Therapeutics Committee. Subscribers also receive monthly one-page summary monographs on the agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation (DUE) is also provided each month. The monographs are published in printed form and on diskettes that allow customization. Subscribers to the The Formulary Monograph Service also receive access to a pharmacy bulletin board, The Formulary Information Exchange (The F.I.X.). All topics pertinent to clinical and hospital pharmacy are discussed on The F.I.X.

Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800–322–4349. The November 2002 monograph topics are adefovir dipivoxil, ximelagatran, agalsidase alfa and agalsidase beta, pemetrexed, and emtricitabine. The DUE is on adefovir dipivoxil.

Antiepileptic-antipsychotic drug interactions: a critical review of the evidence

The potential for drug-drug interactions in psychiatry and patients with epilepsy is very high. Moreover, antiepileptic drugs are widely used outside epilepsy as psychotropic agents and their spectrum of activity on behavior is of considerable interest to psychopharmacology. In both neurologic and psychiatric practice, pharmacotherapy combinations are commonly used to treat comorbid psychiatric and neurologic disorders, to reduce or control the adverse effects of a medication or to increase its efficacy. This paper focuses on the metabolic pharmacokinetic interactions between two classes of psychotropic drugs: antiepileptic and antipsychotic drugs. The degree of documentation varies for many interactions from clinical case-report experiences to well established research outcomes. The evidence and the clinical significance of these interactions are reviewed. In general, it is better to use as few drugs as possible, as multicolored politherapies increase the possible adverse effects of drug interactions and reduce patient compliance.

Cytochrome p450 phenotyping/genotyping in patients receiving antipsychotics: useful aid to prescribing?

Many antipsychotics, including perphenazine, zuclopenthixol, thioridazine, haloperidol and risperidone, are metabolised to a significant extent by the polymorphic cytochrome P450 (CYP) 2D6, which shows large interindividual variation in activity. Significant relationships between CYP2D6 genotype and steady-state concentrations have been reported for perphenazine, zuclopenthixol, risperidone and haloperidol when used in monotherapy. Other CYPs, especially CYP1A2 and CYP3A4, also contribute to the interindividual variability in the kinetics of antipsychotics and the occurrence of drug interactions. For many antipsychotics, the role of the different CYPs at therapeutic drug concentrations remains to be clarified. Some studies have suggested that poor metabolisers for CYP2D6 would be more prone to oversedation and possibly parkinsonism during treatment with classical antipsychotics, whereas other, mostly retrospective, studies have been negative or inconclusive. For the newer antipsychotics, such data are lacking. Whether phenotyping or genotyping for CYP2D6 or other CYPs can be used to predict an optimal dose range has not been studied so far. Genotyping or phenotyping can today be recommended as a complement to plasma concentration determination when aberrant metabolic capacity (poor or ultrarapid) of CYP2D6 substrates is suspected. The current rapid developments in molecular genetic methodology and pharmacogenetic knowledge can in the near future be expected to provide new tools for prediction of the activity of the various drug-metabolising enzymes. Further prospective clinical studies in well-defined patient populations and with adequate evaluation of therapeutic and adverse effects are required to establish the potential of pharmacogenetic testing in clinical psychiatry.

In vitro P-glycoprotein affinity for atypical and conventional antipsychotics

The transmembrane transporter P-glycoprotein (P-gp) is an ATP-dependent efflux pump for a wide range of drugs. P-gp potentially limits access to brain tissue of psychoactive substrates, but little is known about its specificity for antipsychotics. The objective of this study was to assess the affinity of some atypical antipsychotic drugs in vitro for P-gp as indicative of their potential as P-gp substrates in vivo. The activity of P-gp towards four atypical and two conventional antipsychotics and a proven substrate, verapamil, was examined by their P-gp ATPase activity, a putative measure of P-gp affinity. The Michaelis-Menten equation was fitted to the data. The rank order of the ratio V(max) / K(m) was: verapamil (2.6) > quetiapine (1.7) > risperidone (1.4) > olanzapine (0.8) > chlorpromzaine (0.7) > haloperidol (0.3) = clozapine (0.3). The atypical antipsychotics quetiapine and risperidone were relatively good P-gp substrates, although their affinities were not as high as verapamil. Olanzapine showed intermediate affinity and clozapine showed the least affinity of the drugs studied. These results suggest that P-gp is likely to influence the access to the brain of all of the atypical antipsychotics studied to various degrees. In vivo studies are needed to confirm these findings.

Amisulpride: a review of its use in the management of schizophrenia

Amisulpride, a substituted benzamide derivative, is a second-generation (atypical) antipsychotic. At low doses, it enhances dopaminergic neurotransmission by preferentially blocking presynaptic dopamine D2/D3 autoreceptors. At higher doses, amisupride antagonises postsynaptic dopamine D2 and D3 receptors, preferentially in the limbic system rather than the striatum, thereby reducing dopaminergic transmission. In patients with acute exacerbations of schizophrenia, the recommended dosage of amisulpride is 400 to 800 mg/day, although dosages < or =1200 mg/day may be administered. In comparative trials, amisulpride administered within this range (400 to 1200 mg/day) was as effective as haloperidol 5 to 40 mg/day, flupenthixol 25 mg/day and risperidone 8 mg/day in patients with acute exacerbations of schizophrenia with predominantly positive symptoms. Amisulpride was more effective than haloperidol but equally effective as risperidone in controlling negative symptoms. Amisulpride 400 to 800 mg/day was more effective than haloperidol, risperidone and flupenthixol in controlling affective symptoms in these patients. In randomised, double-blind trials involving patients with predominantly negative symptoms of schizophrenia, amisulpride 50 to 300 mg/day was more effective than placebo. Amisulpride is effective as maintenance therapy in patients with chronic schizophrenia. Long-term treatment with amisulpride was associated with improvements in quality of life and social functioning. Amisulpride is generally well tolerated. In well-controlled trials, the neurological tolerability profile (including ratings on extrapyramidal symptom scales) of amisulpride 400 to 1200 mg/day was superior to that of the conventional antipsychotics (haloperidol or flupenthixol), but was similar to that of the atypical antipsychotic risperidone. At low dosages of amisulpride (< or =300 mg/day), the incidence of adverse events (including extrapyramidal symptoms) reported with amisulpride was similar to that with placebo.

CONCLUSION

In comparative trials, amisulpride 400 to 1200 mg/day showed efficacy in reducing overall symptomatology and positive symptoms similar to that of conventional antipsychotics and newer atypical antipsychotics in patients with acute exacerbations of schizophrenia. Moreover, its effective alleviation of negative and affective symptoms, its lower association with extrapyramidal symptoms and loss of cognitive function than conventional antipsychotics and its long-term efficacy justifies consideration of the use of higher dosages of amisulpride in this group of patients. Consequently, the dosage of amisulpride that is recommended in patients with acute exacerbations of schizophrenia is 400 to 800 mg/day, although dosages < or =1200 mg/day may be administered. Lower dosages of amisulpride (50 to 300 mg/day) should be considered for the management of patients with negative symptoms of schizophrenia. Amisulpride is a first-line treatment option in the management of schizophrenia in the acute phase and for the maintenance of treatment response.

Cytochrome P450 polymorphisms and response to antipsychotic therapy

Antipsychotic drugs are used for the treatment of schizophrenia and other related psychotic disorders. The antipsychotics currently available include older or classical compounds and newer or atypical agents. Most antipsychotic drugs are highly lipophilic compounds and undergo extensive metabolism by cytochrome P450 (CYP) enzymes in order to be excreted. There is a wide interindividual variability in the biotransformation of antipsychotic drugs, resulting in pronounced differences in steady-state plasma concentrations and, possibly, in therapeutic and toxic effects, during treatment with fixed doses. Many classical and some newer antipsychotics are metabolized to a significant extent by the polymorphic CYP2D6, which shows large interindividual variation in activity. Other CYPs, especially CYP1A2 and CYP3A4, also contribute to the interindividual variability in the kinetics of antipsychotics and occurrence of drug interactions. No relationship between CYP2D6 genotype or activity and therapeutic effects of classical antipsychotic drugs has been found in the few studies performed. On the other hand, some investigations suggest that poor metabolizers (PMs) of CYP2D6 would be more prone to over-sedation and, possibly, Parkinsonism during treatment with classical antipsychotics, while other studies, mostly retrospective, have been negative or inconclusive. For the newer antipsychotics, such data are lacking. To date, CYP2D6 phenotyping and genotyping appear, therefore, to be clinically useful for dose predicting only in special cases and for a limited number of antipsychotics, while their usefulness in predicting clinical effects must be further explored.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Olanzapine: a review of its use in the treatment of bipolar I disorder

Olanzapine, a thienobenzodiazepine derivative, is a psychotropic agent that has shown efficacy in the treatment of patients with bipolar I disorder. Olanzapine has a multireceptorial binding profile including a greater affinity for serotonin 5-HT(2A) than for dopamine D(2) receptors. Olanzapine 5 to 20 mg/day demonstrated significantly greater antimanic efficacy than placebo in two double-blind, randomised 3- or 4-week trials of patients with bipolar I disorder of either manic or mixed episodes, with or without psychotic features. Additionally, in one of these trials, improvements in cognitive function and hostility were superior with olanzapine. In cohorts of severely depressed and rapid cycling patients, improvements in manic and depressive symptoms and in manic symptoms only, were superior with olanzapine compared with placebo. Significant improvements from baseline in symptoms of mania, depression, cognitive functioning and hostility were seen with olanzapine in a 49-week extension phase study. In double-blind trials, olanzapine 10 mg/day appeared to have similar antimanic efficacy to oral lithium 400mg twice daily in the treatment of patients with pure mania (4-week small study). In patients with acute manic or mixed episodes olanzapine 5 to 20 mg/day appeared to be more effective than oral valproate semisodium (divalproex sodium) 500 to 2500 mg/day (3-week study) and at least as effective as oral haloperidol 3 to 15 mg/day (12-week study). Preliminary results from a large 6-week placebo-controlled study suggest that olanzapine 5 to 20 mg/day in combination with mood stabilisers (lithium or valproate semisodium) provides effective augmentation of antimanic treatment of patients with bipolar I disorder, with benefits seen in the first week. Adverse events reported significantly more often with olanzapine than with placebo were somnolence, dry mouth, dizziness and bodyweight gain, and in comparison with valproate semisodium were somnolence, dry mouth, increased appetite and bodyweight gain. Olanzapine was generally well tolerated with no clinically relevant abnormalities in laboratory tests, vital signs or electrocardiogram results.

CONCLUSION

Olanzapine demonstrated superior efficacy compared with placebo in the short-term treatment of patients with bipolar I disorder with manic or mixed episodes, with or without psychotic features, and was generally well tolerated. According to preliminary data the antimanic efficacy of olanzapine appears similar to that of haloperidol and better than that of valproate semisodium in patients with bipolar I disorder experiencing a manic or mixed episode; among nonpsychotic patients with manic or mixed episodes olanzapine appears to be superior to haloperidol. Available data support the choice of olanzapine as an option in the short-term management of mania in patients with bipolar I disorder with manic or mixed episodes, with or without psychotic features.

Focus on amisulpride

Amisulpride is a second-generation antipsychotic, a substituted benzamide. It appears to be an effective agent in treating schizophrenia for what are characterised as positive and negative symptoms. The recommended doses are between 400 mg/day and 800 mg/day. Amisulpride demonstrates a good global safety profile, particularly when compared with first-generation antipsychotics, such as haloperidol. There are interesting studies that point towards amisulpride's antidepressant effect in dysthymia speculative on possible roles in affective psychoses and chronic fatigue syndrome.