Investigation of the potential of clozapine to cause torsade de pointes

Overcoming clozapine's adverse events: a narrative review of systematic reviews and meta-analyses

INTRODUCTION

Clozapine is the gold standard treatment for treatment-resistant schizophrenia, however adverse events remain a clinical challenge.

AREAS COVERED

This review presents a narrative synthesis of systematic reviews and meta-analyses that have reported the onset, incidence, prevalence, and management of clozapine's adverse events. We conducted a systematic literature search using PubMed, Embase, PsycINFO, OvidMEDLINE, CINAHL, and the Cochrane Database of Systematic Reviews from inception to April 2024.

EXPERT OPINION

Effective management of clozapine's adverse events necessitates multi-faceted, individualized, and shared-decision strategies. Despite a lack of high-quality systematic evidence, expert inter-disciplinary solutions are provided to help address a critical need for clinical guidance. This 35-year update offers an evidence-based framework to assist clinicians, patients, and caregivers navigate the adverse events associated with clozapine therapy.

Prevalence and predictors of QTc prolongation in patients seen in a clozapine clinic in a real-world setting in Australia

BACKGROUND

Many antipsychotic drugs have been associated with QTc prolongation, which is a risk factor for sudden death. We studied the prevalence and predictors of QTc prolongation in treatment-resistant schizophrenia patients who were receiving clozapine in a real-world setting.

METHODS

Data were extracted from the records of all schizophrenia patients aged 18-65 years, enrolled in a clozapine clinic in metropolitan Australia during October 2020 to April 2022, for whom ECG data were available.

RESULTS

There were 104 eligible patients. The mean age of the sample was 42 years. The sample was 56 % male. About a third of patients were receiving antipsychotic and antidepressant drugs in addition to clozapine. The mean (standard deviation) QTc was 437.0 (24.8) ms in men and 445.8 (28.5) ms in women. QTc prolongation was present in 36.5 % of the sample. In univariate analysis, higher heart rate and higher clozapine levels were significantly associated with QTc prolongation; in multivariable logistic regression analysis, nonsignificant statistical trends were observed for male sex, higher heart rate, and higher serum clozapine level.

CONCLUSIONS

QTc prolongation may be common in schizophrenia patients who receive clozapine in real world settings; this is a matter of much concern. Potential predictors of QTc prolongation need to be identified and these predictors and their interactions require to be explored in studies with greater statistical power.

The atypic antipsychotic clozapine inhibits multiple cardiac ion channels

Clozapine is an atypical neuroleptic used to manage treatment-resistant schizophrenia which is known to inhibit cardiac hERG/K_V11.1 potassium channels, a pharmacological property associated with increased risk of potentially fatal Torsades de Pointes (TdP) and sudden cardiac death (SCD). Yet, the long-standing clinical practice of clozapine does not show a consistent association with increased incidence of TdP, although SCD is considerably higher among schizophrenic patients than in the general population. Here, we have established the inhibitory profile of clozapine at the seven cardiac ion currents proposed by the ongoing comprehensive in vitro pro-arrhythmia (CiPA) initiative to better predict new drug cardio-safety risk. We found that clozapine inhibited all CiPA currents tested with the following rank order of potency: K_V11.1 > Na_V1.5 _{(late current)} ≈ Ca_V1.2 ≈ Na_V1.5 _{(peak current)} ≈ K_V7.1 > K_V4.3 > K_ir2.1 _{(outward current)}. Half-maximal inhibitory concentrations (IC₅₀) at the repolarizing K_V11.1 and K_V7.1 channels, and at the depolarizing Ca_V1.2 and Na_V1.5 channels fell within a narrow half-log 3-10 µM concentration range, suggesting that mutual compensation could explain the satisfactory arrhythmogenic cardio-safety profile of clozapine. Although the IC₅₀ values determined herein using an automated patch-clamp (APC) technique are at the higher end of clozapine plasmatic concentrations at target therapeutic doses, this effective antipsychotic appears prone to distribute preferentially into the cardiac tissue, which supports the clinical relevance of our in vitro pharmacological findings.

QT interval prolongation noted in one percent of 2553 Asian patients with schizophrenia: Findings from the REAP-AP survey

Although the association between antipsychotic use and corrected QT interval (QTc) prolongation has been repeatedly confirmed, the relationship has been rarely studied in a practical setting. Using data from the Research on Asian Psychotropic Prescription Patterns for Antipsychotics (REAP-AP) survey, our study aimed to investigate the prevalence and clinical correlates of QTc prolongation in 2553 Asian patients with schizophrenia. After adjusting for the potential effect of confounding factors, the baseline and clinical characteristics of the schizophrenia patients with and without QTc prolongation were compared using analyses of covariance and binary logistic analyses. In addition, a binary logistic analysis model with a forward selection method was used to identify the distinctive clinical correlates of QTc prolongation. QTc prolongation was noted in 1.1% of Asian patients with schizophrenia. Schizophrenia patients were characterized by lower proportions of disorganized speech and negative symptoms; higher use of amisulpride and clozapine; and higher proportions of rigidity, hypercholesterolemia, and sedation than those without QTc prolongation. Finally, a binary logistic mode showed that amisulpride, clozapine, rigidity, and hypercholesterolemia might be the distinctive clinical correlates of QTc prolongation in Asian patients with schizophrenia. These findings indicate the clinical implications that the uses of amisulpride and clozapine and the occurrences of rigidity and hypercholesterolemia may be potential risk factors for QTc prolongation of schizophrenia patients.

British Heart Rhythm Society Clinical Practice Guidelines on the Management of Patients Developing QT Prolongation on Antipsychotic Medication

The British Heart Rhythm Society’s Clinical Practice Guidelines on the Management of Patients Developing QT Prolongation on Antipsychotic Medication are written for heart rhythm consultants, primary care physicians, specialist registrars, nurses and physiologists who may be requested to review ECGs or advise on cases where antipsychotic-induced QT prolongation is suspected or proven. The guidance is adapted from the latest Maudsley Prescribing Guidelines in Psychiatry, published in 2018.

Twenty-Four-Hour Measures of Heart Rate-Corrected QT Interval, Peak-to-End of the T-Wave, and Peak-to-End of the T-Wave/Corrected QT Interval Ratio During Antipsychotic Treatment

PURPOSE/BACKGROUND

Prolonged ventricular repolarization, measured by heart rate-corrected QT interval (QTc) prolongation, might be a biomarker for risk of torsade de pointes (TdP) and sudden cardiac death. However, the predictive value of QTc has been challenged, and a component of QTc, peak-to-end of the T-wave (Tpe), and a high Tpe/QT ratio might be superior biomarkers because they better reflect increased transmural dispersion of ventricular myocyte repolarization, which can lead to TDP. The purpose of this pilot study was to provide the first measurements of heart rate, QTc, Tpe, Tpe/QTc, and their variability over 24 hours in medication-free patients with schizophrenia, during treatment with ziprasidone or other antipsychotic drugs, and healthy controls.

METHODS

Subjects included 12 patients treated with ziprasidone, 30 treated with other antipsychotic drugs, 3 unmedicated patients, and 15 normal controls. Subjects underwent 24-hour analog Holter recording, and the recordings were digitized. A cardiologist blind to treatment selected multiple 10-cycle segments throughout each recording and measured the electrocardiogram metrics.

RESULTS

Variability in QTc, Tpe, and Tpe/QTc over the 24 hours was present in all groups; 91.1% of patients and 100% of controls had 1 or more QTc values of 450 milliseconds or greater. Mean QTc length was significantly greater in the ziprasidone-treated than the non-ziprasidone-treated patients (P = 0.02). Mean Tpe was not elevated in the ziprasidone patients, whereas mean Tpe/QTc was lower (P < 0.01).

CONCLUSIONS

The large variability in QTc, Tpe, and Tpe/QTc observed supports the need for 24-hour electrocardiogram recordings to provide an accurate assessment of risk of TdP. Heart rate-corrected QT interval alone does not capture the risk of TdP.

Safety of antipsychotics for the treatment of schizophrenia: a focus on the adverse effects of clozapine

Clozapine, a dibenzodiazepine developed in 1961, is a multireceptorial atypical antipsychotic approved for the treatment of resistant schizophrenia. Since its introduction, it has remained the drug of choice in treatment-resistant schizophrenia, despite a wide range of adverse effects, as it is a very effective drug in everyday clinical practice. However, clozapine is not considered as a top-of-the-line treatment because it may often be difficult for some patients to tolerate as some adverse effects can be particularly bothersome (i.e. sedation, weight gain, sialorrhea etc.) and it has some other potentially dangerous and life-threatening side effects (i.e. myocarditis, seizures, agranulocytosis or granulocytopenia, gastrointestinal hypomotility etc.). As poor treatment adherence in patients with resistant schizophrenia may increase the risk of a psychotic relapse, which may further lead to impaired social and cognitive functioning, psychiatric hospitalizations and increased treatment costs, clozapine adverse effects are a common reason for discontinuing this medication. Therefore, every effort should be made to monitor and minimize these adverse effects in order to improve their early detection and management. The aim of this paper is to briefly summarize and provide an update on major clozapine adverse effects, especially focusing on those that are severe and potentially life threatening, even if most of the latter are relatively uncommon.

Management of psychosis and agitation in medical-surgical patients who have or are at risk for prolonged QT interval

We review the literature on management of psychosis and agitation in medical-surgical patients who have or are at risk for prolonged QT interval, a risk factor for torsade de pointes (TdP), and we describe our protocols for treating these patients. We searched PubMed and PsycInfo for relevant studies and found few papers describing options for treating psychosis and agitation in these patients. Prolonged QTc interval has been more often associated with low-potency phenothiazines such as thioridazine; however, it may occur with high potency typical antipsychotics such as fluphenazine and haloperidol as well as with atypical antipsychotics such as quetiapine, risperidone, olanzapine, iloperidone, and particularly ziprasidone. Antipsychotics for which no association with prolonged QTc interval has been shown include lurasidone, clozapine, and aripiprazole. For patients who have risk factors for prolonged QTc interval but whose electrocardiograms do not show this, reasonable first choices include oral or intramuscular olanzapine or aripiprazole, followed by risperidone and quetiapine or oral or intramuscular haloperidol. For those who have prolonged QTc but that measures less than 500 ms, we limit the use of antipsychotics to aripiprazole, olanzapine, risperidone, or quetiapine. Finally, for patients who have a QTc of 500 ms or greater, we rely on aripiprazole, valproate, trazodone, and benzodiazepines.

QTc prolongation, torsades de pointes, and psychotropic medications

BACKGROUND

Prolongation of the corrected QT (QTc) interval is a key issue for patients who receive psychotropic medications. Such patients may have baseline clinical risk factors for QTc prolongation, and many psychotropic medications may further prolong this interval. This has great clinical relevance, as QTc prolongation is linked with dangerous arrhythmias, especially torsades de pointes (TdP).

METHODS

We summarize current literature regarding appropriate methods of calculating the QTc interval, the association of the QTc interval with TdP, and risk factors for QTc prolongation. We then review connections between psychiatric medications and QTc prolongation, with a specific focus on antidepressants and antipsychotics.

RESULTS

QTc interval prolongation is an established, though imperfect, risk marker for TdP. There are no well-controlled studies that assess the risk of TdP associated with psychotropic agents. There are limited data that selective serotonin reuptake inhibitors (SSRIs) as a class are linked to QTc prolongation; citalopram appears more likely than others to induce this phenomenon. Among antipsychotics, thioridazine remains the agent most associated with QTc prolongation; intravenous haloperidol also appears to carry an increased risk. Of the atypical antipsychotics, ziprasidone appears most likely to prolong the QTc interval.

CONCLUSIONS

The majority of patients in need of psychotropic medications display few risk factors for QTc prolongation and should be considered to be at low risk for TdP. The frequency of cardiac monitoring for patients receiving psychiatric medications should be individually determined, based on the prescribed agent(s) and additional risk factors for TdP.

Overdose of atypical antipsychotics: clinical presentation, mechanisms of toxicity and management

Historically, treatment for schizophrenia focused on sedation. The advent of the typical antipsychotics resulted in treatment aimed specifically at the underlying disease, but these agents were associated with numerous adverse effects, and were not particularly effective at treatment of the negative symptoms of schizophrenia. As a result, numerous atypical agents have been developed over the past 2 decades, including several agents within the past 5 years. Overdose of antipsychotics remains quite common in Western society. In 2010, poison control centres in the US received nearly 43,000 calls related to atypical antipsychotics alone. Due to underreporting, the true incidence of overdose with atypical antipsychotics is likely much greater. Following overdose of an atypical antipsychotic, the clinical effects observed, such as CNS depression, tachycardia and orthostasis are largely predictable based on the unique receptor binding profile of the agent. This article, which focuses on the atypical antipsychotics commonly used in the treatment of schizophrenia, discusses the features commonly encountered in overdose. Specifically, agents that result in QT prolongation and the corresponding potential for torsades de pointes, as well as unique features encountered with the various medications are discussed. The diagnosis of this overdose is largely based on history. Routine use of drug screens is unlikely to be beneficial. The primary goal of management is aggressive supportive care. Patients with significant CNS depression with associated loss of airway reflexes and respiratory failure need advanced airway management. Hypotension should be treated first with intravenous fluids, with the use of direct acting vasopressors reserved for persistent hypotension. Benzodiazepines should be used for seizures, with barbiturates used for refractory seizures. Intravenous magnesium can be administered for patients with a corrected QT interval exceeding 500 milliseconds.

The comparative sensitivity of three in vitro safety pharmacology models for the detection of lidocaine-induced cardiac effects

INTRODUCTION

In the current ICH S7B guideline, in vitro evaluation of proarrhythmic liability is limited to the risk of QT interval prolongation, whilst the effect of new chemical entities on cardiac conductivity is often overlooked. The aim of this work was to compare the effects of the sodium channel blocker, lidocaine in three in vitro safety pharmacology models: hNa(v)1.5 channel test, atrial action potential (AP) and Purkinje fiber AP and to identify the most sensitive model for detecting cardiac conduction slowing.

METHODS

Whole-cell patch-clamp methods were used to record the sodium current (I(Na)) encoded by hNa(v)1.5 in stably transfected HEK293 cells at ambient temperature. Transmembrane APs were recorded in rabbit Purkinje fibers and rabbit and guinea-pig left stimulated atria at physiological temperature. Parameters involved in depolarization or repolarization were reported.

RESULTS

Lidocaine (from 10 to 1000 μM) decreased the amplitude of I(Na) (IC(50): 256±37 μM) in a concentration-dependent manner. In the Purkinje fiber assay, lidocaine (10, 30 and 100 μM) had no effects on maximal upstroke velocity (Vmax), but shortened AP duration at 90% repolarization (APD(90)). At 30 and 100 μM, lidocaine also increased AP triangulation. In guinea-pig atria, lidocaine decreased Vmax starting from 30 μM and conduction velocity (CV) at 100 μM, but had no effects on other parameters. In rabbit atria, lidocaine decreased Vmax and CV at 100 μM without affecting APD(90). The effects of 100 μM lidocaine on Vmax and CV were more marked in rabbit than in guinea-pig atria.

CONCLUSION

Rabbit atria are more sensitive than rabbit Purkinje fibers or guinea-pig atria for detecting lidocaine-induced cardiac conduction slowing. These data suggest that isolated rabbit atria in addition to the hNa(v)1.5 channel assay could be relevant models to predict drug-induced conduction slowing.

Cardiac Safety Implications of hNav1.5 Blockade and a Framework for Pre-Clinical Evaluation

The human cardiac sodium channel (hNav1.5, encoded by the SCN5A gene) is critical for action potential generation and propagation in the heart. Drug-induced sodium channel inhibition decreases the rate of cardiomyocyte depolarization and consequently conduction velocity and can have serious implications for cardiac safety. Genetic mutations in hNav1.5 have also been linked to a number of cardiac diseases. Therefore, off-target hNav1.5 inhibition may be considered a risk marker for a drug candidate. Given the potential safety implications for patients and the costs of late stage drug development, detection, and mitigation of hNav1.5 liabilities early in drug discovery and development becomes important. In this review, we describe a pre-clinical strategy to identify hNav1.5 liabilities that incorporates in vitro, in vivo, and in silico techniques and the application of this information in the integrated risk assessment at different stages of drug discovery and development.

QTc prolongation by psychotropic drugs and the risk of Torsade de Pointes

INTRODUCTION

Many psychotropic drugs can delay cardiac repolarization and thereby prolong the rate-corrected QT interval (QTc). A prolonged QTc often arouses concern in clinical practice, as it can be followed, in rare cases, by the life-threatening polymorphic ventricular tachyarrhythmia called torsade de pointes (TdP).

METHOD

We searched PubMed for pertinent literature on the risk of QTc prolongation and/or TdP associated with commonly used psychotropic drugs.

RESULTS

Thioridazine and ziprasidone confer the highest risk of QTc prolongation and/or TdP. There is also a clinically significant risk associated with haloperidol given intravenously in high doses. TdP has been reported in a few cases in association with the use of newer antipsychotic drugs (mainly quetiapine and amisulpride), most of the tri- and tetracyclic antidepressants, and the selective monoamine reuptake inhibitors citalopram, fluoxetine, paroxetine, and venlafaxine. As a rule, however, QTc prolongation and/or TdP occur only in the presence of multiple additional risk factors, such as age over 65 years, pre-existing cardiovascular disease, bradycardia, female sex, hypokalemia, hypomagnesemia, a supratherapeutic or toxic serum concentration, or the simultaneous administration of other drugs that delay repolarization or interfere with drug metabolism.

CONCLUSION

Before prescribing a psychotropic drug, the physician should carefully assess its risks and benefits to avoid this type of adverse reaction, particularly when additional risk factors are present. The ECG and electrolytes should be regularly monitored in patients taking psychotropic drugs.

Sex difference in QTc prolongation in chronic institutionalized patients with schizophrenia on long-term treatment with typical and atypical antipsychotics

OBJECTIVE

The rate-corrected electrocardiographic QT (QTc) interval may significantly increase in patients with schizophrenia taking antipsychotics. The objective of this naturalistic study was to assess the prevalence of prolonged QTc interval in a large population of inpatients with chronic schizophrenia and to explore QTc relationship with demographic variables and prescribed treatments.

MATERIALS AND METHODS

Electrocardiograms were obtained from age- and sex-matched 456 controls and 1,006 inpatients with schizophrenia (male/female = 689/317) taking antipsychotics. QTc prolongation was defined as a mean value of two standard deviations above the controls. The adjusted relative risk was calculated using logistic regression analysis.

RESULTS

QTc prolongation was present in 45 (4.5%) of 1,006 patients overall. Fewer men (3.2%, 22 of 689) than women (7.3%, 23 of 317) displayed QTc prolongation (p < 0.004). Moreover, QTc intervals were shorter in male (391 ± 31 ms) than female subjects (400 ± 37 ms) (p < 0.001). Clozapine was found to produce a longer QTc intervals compared to risperidone and typical antipsychotics. Furthermore, multiple regression analysis showed that significant predictors for QTc prolongation were comorbid cardiovascular disease, antipsychotic types, sex, and age (all p < 0.01).

CONCLUSION

Our present findings suggest that there are sex differences in the prevalence of QTc prolongation and QTc lengthening in schizophrenia. Antipsychotic types are risk factors for QTc prolongation, and risks are substantially higher for clozapine.

Assessing QT interval prolongation and its associated risks with antipsychotics

Several antipsychotics are associated with the ventricular tachycardia torsade de pointes (TdP), which may lead to sudden cardiac death (SCD), because of their inhibition of the cardiac delayed potassium rectifier channel. This inhibition extends the repolarization process of the ventricles of the heart, illustrated as a prolongation of the QT interval on a surface ECG. SCD in individuals receiving antipsychotics has an incidence of approximately 15 cases per 10,000 years of drug exposure but the exact association with TdP remains unknown because the diagnosis of TdP is uncertain. Most patients manifesting antipsychotic-associated TdP and subsequently SCD have well established risk factors for SCD, i.e. older age, female gender, hypokalaemia and cardiovascular disease. QT interval prolongation is the most widely used surrogate marker for assessing the risk of TdP but it is considered somewhat imprecise, partly because QT interval changes are subject to measurement error. In particular, drug-induced T-wave changes (e.g. flattening of the T-wave) may complicate the measurement of the QT interval. Furthermore, the QT interval depends on the heart rate and a corrected QT (QTc) interval is often used to compensate for this. Several correction formulas have been suggested, with Bazett's formula the most widely used. However, Bazett's formula overcorrects at a heart rate above 80 beats per minute and, therefore, Fridericia's formula is considered more appropriate to use in these cases. Several other surrogate markers for TdP have been developed but none of them is clinically implemented yet and QT interval prolongation is still considered the most valid surrogate marker. Although automated QT interval determination may offer some assistance, QT interval determination is best performed by a cardiologist skilled in its measurement. A QT interval >500 ms markedly increases the risk for TdP and SCD, and should lead to discontinuation of the offending drug and, if present, correction of underlying electrolyte disturbances, particularly serum potassium and magnesium derangements. Before prescribing antipsychotics that may increase the QTc interval, the clinician should ask about family and personal history of SCD, presyncope, syncope and cardiac arrhythmias, and recommend cardiology consultation if history is positive.

The 2009 schizophrenia PORT psychopharmacological treatment recommendations and summary statements

In light of the large number of studies published since the 2004 update of Schizophrenia Patient Outcomes Research Team psychopharmacological treatment recommendations, we conducted an extensive literature review to determine whether the current psychopharmacological treatment recommendations required revision and whether there was sufficient evidence to warrant new treatment recommendations for prespecified outcomes of interest. We reviewed over 400 articles, which resulted in 16 treatment recommendations: the revision of 11 previous treatment recommendations and 5 new treatment recommendations. Three previous treatment recommendations were eliminated. There were 13 interventions and/or outcomes for which there was insufficient evidence for a treatment recommendation, and a statement was written to summarize the current level of evidence and identify important gaps in our knowledge that need to be addressed. In general, there was considerable consensus among the Psychopharmacology Evidence Review Group and the expert consultants. Two major areas of contention concerned whether there was sufficient evidence to recommend specific dosage ranges for the acute and maintenance treatment of first-episode and multi-episode schizophrenia and to endorse the practice of switching antipsychotics for the treatment of antipsychotic-related weight gain. Finally, there continue to be major gaps in our knowledge, including limited information on (1) the use of adjunctive pharmacological agents for the treatment of persistent positive symptoms or other symptom domains of psychopathology, including anxiety, cognitive impairments, depressive symptoms, and persistent negative symptoms and (2) the treatment of co-occurring substance or medical disorders that occur frequently in individuals with schizophrenia.

Secondary effects of antipsychotics: women at greater risk than men

CONTEXT

The health burden of antipsychotic medication is well known, but the disproportionate effect on women as compared with men is underappreciated.

OBJECTIVE

The goal of this article is preventive--to better inform clinicians so that the risks to women and to their offspring can be diminished.

METHOD

All PubMed sources in which the search term gender (or sex) was linked to a side effect of antipsychotic medication were reviewed.

RESULT

There is general agreement in the literature on women's increased susceptibility to weight gain, diabetes, and specific cardiovascular risks of antipsychotics, with less consensus on malignancy risks and risks to the fetus. Cardiovascular death, to which men are more susceptible than women, is disproportionately increased in women by the use of antipsychotics. Sedating antipsychotics raise the risk of embolic phenomena during pregnancy, and postpartum. Prolactin-elevating drugs suppress gonadal hormone secretion and may enhance autoimmune proclivity.

CONCLUSIONS

Clinicians need to be aware of the differential harm that women (and their offspring) can incur from the side effects of antipsychotics.

Potential causes of higher mortality in elderly users of conventional and atypical antipsychotic medications

OBJECTIVES

To investigate the potential mechanisms through which conventional antipsychotic medication (APM) might act, the specific causes of death in elderly patients newly started on conventional APM were compared with those of patients taking atypical APM.

DESIGN

Cohort study.

SETTING

Community.

PARTICIPANTS

All British Columbia residents aged 65 and older who initiated a conventional or atypical APM between 1996 and 2004.

MEASUREMENTS

Cox proportional hazards models were used to compare risks of developing a specific cause of death within 180 days of APM initiation. Potential confounders were adjusted for using traditional multivariable, propensity-score, and instrumental-variable adjustments.

RESULTS

The study cohort included 12,882 initiators of conventional APM and 24,359 initiators of atypical APM. Of 3,821 total deaths within the first 180 day of use, cardiovascular (CV) deaths accounted for 49% of deaths. Initiators of conventional APM had a significantly higher adjusted risk of all CV death (hazard ratio (HR)=1.23, 95% confidence interval (CI)=1.10-1.36) and out-of-hospital CV death (HR=1.36, 95% CI=1.19-1.56) than initiators of atypical APM. Initiators of conventional APM also had a higher risk of death due to respiratory diseases, nervous system diseases, and other causes.

CONCLUSION

These data suggest that greater risk of CV deaths might explain approximately half of the excess mortality in initiators of conventional APM. The risk of death due to respiratory causes was also significantly higher in conventional APM use.

In silico risk assessment for drug-induction of cardiac arrhythmia

The main components of repolarization reserve for the ventricular action potential (AP) are the rapid (I(Kr)) and slow (I(Ks)) delayed outward K(+) currents. While many drugs block I(Kr) and cause life-threatening arrhythmias including torsades de pointes, the frequency of arrhythmias varies between different I(Kr)-blockers. Different types of block of I(Kr) cause distinct phenotypes of prolongation of action potential duration (APD), increase in transmural dispersion of repolarization (TDR) and, accordingly, occurrence of torsades de pointes. Therefore the assessment of a drug's proarrhythmic risk requires a method that provides quantitative and comprehensive comparison of the effects of different forms of I(Kr)-blockade upon APDs and TDR. However, most currently available methods are not adapted to such an extensive comparison. Here, we introduce I(Kr)-I(Ks) two-dimensional maps of APD and TDR as a novel risk-assessment method. Taking the kinetics of I(Kr)-blockade into account, APDs can be calculated upon a ventricular AP model which systematically alters the magnitudes of I(Kr) and I(Ks). The calculated APDs are then plotted on a map where the x axis represents the conductance of I(Kr) while the y axis represents that of I(Ks). TDR is simulated with models corresponding to APs in epicardial, midcardial and endocardial myocardium. These two-dimensional maps of APD and TDR successfully account for differences in the risk resulting from three distinct types of I(Kr)-blockade which correspond to the effects of dofetilide, quinidine and vesnarinone. This method may be of use to assess the arrhythmogenic risk of various I(Kr)-blockers.

PRECLINICAL ELECTROPHYSIOLOGY ASSAYS OF MITEMCINAL (GM-611), A NOVEL PROKINETIC AGENT DERIVED FROM ERYTHROMYCIN

Mitemcinal (GM-611) is a novel erythromycin-derived prokinetic agent that acts as an agonist at the motilin receptor. Erythromycin has shown QT prolongation and torsades de pointes (TdP) in humans and cisapride, a second class of prokinetic agents typified by the 5-HT(4) receptor agonist, has been terminated due to TdP. In this study an extended series of safety pharmacology protocols and evaluations have been undertaken to assess the potential risk of mitemcinal on QT prolongation or proarrhythmic effects. Mitemcinal and its metabolites, GM-577 and GM-625, inhibited the human ether-a-go-go-related gene (HERG) tail current in a concentration-dependent manner with IC(50) values of 20.2, 41.7, and 55.0 microM, respectively. Administration of 10 mg/kg mitemcinal in anesthetized guinea pigs resulted in a slight prolongation of the monophasic action potential (MAP) duration during atrial pacing at the plasma concentration of mitemcinal 1.1 microM, with low maximum increases in MAPD(70) (6.6%) and MAPD(90) (4.6%) relative to vehicle. A 10-min infusion of 20 mg/kg of mitemcinal in a proarrhythmic rabbit model did not evoke TdP even when QT and corrected QT (QTc) intervals were significantly prolonged. In this study, the Cmax plasma-free concentration of mitemcinal indicates that the prolongation was more than 400-fold that of the therapeutic dose. Our findings of a wide safety margin and the absence of TdP within this margin suggest that mitemcinal may provide sufficient safety in clinical use.

Blinded validation of the isolated arterially perfused rabbit ventricular wedge in preclinical assessment of drug-induced proarrhythmias

BACKGROUND

The development of preclinical models with high predictive value for the identification of drugs with a proclivity to induce Torsade de Pointes (TdP) in the clinic has long been a pressing goal of academia, industry and regulatory agencies alike. The present study provides a blinded appraisal of drugs, in an isolated arterially-perfused rabbit ventricular wedge preparation, with and without the potential to produce TdP.

METHODS AND RESULTS

Thirteen compounds were tested for their potential for TdP using the rabbit left ventricular wedges. All investigators were blinded to the names, concentrations and molecular weights of the drugs. The compounds were prepared by the study sponsor and sent to the investigator as 4 sets of 13 stock solutions with the order within each set being assigned by a random number generator. Each compound was scored semi-quantitatively for its relative potential for TdP based on its effect on ventricular repolarization measured as QT interval, dispersion of repolarization measured as T(p-e)/QT ratio and early afterdepolarizations. Disclosure of the names and concentrations after completion of the study revealed that all compounds known to be free of TdP risk received a score of less or equal to 0.25, whereas those with known TdP risk received a score ranging from 1.00 to 7.25 at concentrations less than 100X their free therapeutic plasma C(max).

CONCLUSIONS

Our study provides a blinded evaluation of the isolated arterially-perfused rabbit wedge preparation demonstrating both a high sensitivity and specificity in the assessment of 13 agents with varying propensity for causing TdP.

Antipsychotikainduzierte QT-Verlängerung

Prolongation of myocardial repolarisation, i.e. lengthening of the QT interval on surface electrocardiogram, has been recognised as a side effect of many drugs, including antipsychotics. In predisposed individuals, abnormal excessive QT prolongation and severe ventricular arrhythmias (the ventricular tachycardia type 'torsade de pointes', or TdP) may occur. In almost all cases, additional factors are present that increase the propensity of patients to develop TdP, such as serum hypokalemia, the combination of drugs prolonging repolarisation, overdosing, intoxication, and factors interfering with drug metabolism and excretion. Serum hypokalemia and/or bradycardia may induce TdP alone, in the absence of drugs prolonging the QT interval. Experimental studies demonstrate that prolongation of myocardial repolarisation is a class effect of neuroleptics. Clinically, the extent to which individual drugs prolong the QT interval varies. Among the antipsychotics, thioridazine has the greatest propensity to induce abnormal QT prolongations and TdP. Case reports of TdP with other antipsychotics have been published. Physicians prescribing physicians these drugs must be aware that they can induce proarrhythmia in individual cases. They should also be aware of the circumstances which are necessary for abnormal QT prolongation and TdP to develop. Patients should be monitored with regard to these risk factors before and during drug treatment.

Are hERG channel inhibition and QT interval prolongation all there is in drug-induced torsadogenesis? A review of emerging trends

Contemporary preclinical in vitro and in vivo methods have been imperfect in predicting drug-induced Torsades de Pointes (TdP) in humans. A better understanding of additional relevant factors in the genesis of drug-induced TdP is necessary. New sophisticated in vitro techniques, such as arterially perfused ventricular wedge preparations or isolated perfused hearts, potentially offer a better understanding of torsadogenic mechanisms and a refinement of drug testing. Of particular interest are the dispersion of repolarization and the refractoriness of different cell types across the ventricular wall, triangulation of the action potential, reverse use dependence and instability of the action potential duration. In vivo models are currently refined by establishing parameters such as beat-to-beat variability and T-wave morphology as derived from the in vitro proarrhythmia indices. Animal models of proarrhythmia are to date not recommended for routine evaluation. A pharmacodynamic interaction with combinations of torsadogenic compounds is another area to be considered. Little is known about channel/receptor cross talk, although considerable evidence exists that cardiac G protein-coupled receptors can modulate hERG channel function. More investigations are necessary to further evaluate the role of altered gene expression, mutations, and polymorphisms in drug-induced TdP. A novel mechanism of drug-induced torsadogenesis is the reduced expression of hERG channel protein on the plasma membrane due to a trafficking defect. Pharmacokinetic and metabolism data are crucial for calculating the risk of a torsadogenic potential in man. Consideration of intracardiac accumulation can help in delineating pharmacokinetic-pharmacodyamic relationships. In silico virtual screening procedures with new chemical entities to predict hERG block may develop as a promising tool. The role of in silico modeling of TdP arrhythmia is likely to become increasingly important for organizing and integrating the vast amount of generated data. At present, however, in silico methods cannot replace existing preclinical in vitro and in vivo models.

Prediction of the risk of Torsade de Pointes using the model of isolated canine Purkinje fibres

Torsade de Pointes (TdP) is a well-described major risk associated with various kinds of drugs. However, prediction of this risk is still uncertain both in preclinical and clinical trials. We tested 45 reference compounds on the model of isolated canine Purkinje fibres. Of them, 22 are clearly associated and/or labelled with a risk of TdP, and 13 others are drugs with published clinical evidence of QT prolongation, with only one or two exceptional cases of TdP. The 10 remaining drugs are without reports of TdP and QT prolongation. The relevance of different indicators such as APD(90) increase, reverse use dependency, action potential triangulation or effect on V(max) was evaluated by comparison with available clinical data. Finally, a complex algorithm called TDPscreen and based on two subalgorithms corresponding to particular electrophysiological patterns was defined. This latter algorithm enabled a clear separation of drugs into three groups: (A) drugs with numerous or several reports (>2 cases) of TdP, (B) drugs causing QT prolongation and/or TdP only, the latter at a very low frequency (< or =2 cases), (C) drugs without reports of TdP or QT prolongation. The use of such an algorithm combined with a database accrued from reference compounds with available clinical data is suggested as a basis for testing new candidate drugs in the early stages of development for proarrhythmic risk prediction.

Atypical antipsychotics: from potassium channels to torsade de pointes and sudden death

Syncope and sudden death are features of schizophrenia that can be attributed to ischaemic heart disease, the use of antipsychotics (because of proarrhythmia or other reasons such as pharyngeal dyskinesia) or the psychiatric disease itself. Cases have been described with most antipsychotics and have led to the withdrawal, temporary suspension from the market or restricted use of antipsychotics, such as sultopride, droperidol, sertindole or thioridazine. Reviewing the available data shows that all antipsychotics tested affect the cardiac potassium channel, with the concentration that produces 50% inhibition (IC50) ranging from 1 nmol/L (haloperidol) to 6 micromol/L (olanzapine). Experimental in vitro or in vivo electrophysiological studies have shown a dose-dependent increase in the duration of the action potential with various degrees of indicators of serious arrhythmogenicity. However, this does not always translate clinically into an increased duration of the QT interval or increased risk of torsade de pointes or sudden death in clinical trials or pharmacoepidemiological studies. In turn, QT prolongation in clinical trials does not always translate to an increased risk of torsade de pointes or sudden death. The reasons for these apparent discrepancies are unclear and could be related to insufficiently powered field studies, low plasma and tissue drug concentrations with reference to in vitro data or drug effects on other receptors or ion channels that have a protective effect. Alternatively, risks that were not apparent from preclinical or clinical data could be related to the use of the drug in high-risk patients, metabolic interactions or other factors that would only be encountered in large postmarketing populations. The assessment of cardiovascular safety, both preclinical and during premarketing clinical trials, needs to be supported by appropriately powered pharmacoepidemiology studies.

Adverse cardiac effects associated with clozapine

OBJECTIVE

To review the published literature on serious adverse cardiac events associated with the atypical antipsychotic agent, clozapine, and to make recommendations for cardiac assessment of candidates for clozapine treatment and for monitoring of cardiac status after treatment is initiated.

DATA SOURCES

We searched the PubMed and MEDLINE databases for articles published from 1970 to 2004 that contain the keywords "clozapine and myocarditis," "clozapine and cardiomyopathy," "clozapine and cardiotoxicity," "clozapine and sudden death" or "clozapine and mortality." We also manually searched the bibliographies of these articles for related sources.

STUDY SELECTION

We reviewed the 30 case reports, case series, laboratory and clinical trials, data mining studies, and previous reviews identified by this search.

DATA SYNTHESIS

Recent evidence suggests that clozapine is associated with a low (0.015% to 0.188%) risk of potentially fatal myocarditis or cardiomyopathy. The drug is not known to be independently associated with pathologic prolongation of the QTc interval, but it may contribute to pathologic QTc prolongation in patients with other risk factors for this condition.

CONCLUSIONS

The low risk of a serious adverse cardiac event should be outweighed by a reduction in suicide risk for most patients taking clozapine. We provide recommendations for assessing and monitoring cardiac status in patients prior to and after initiation of treatment with clozapine.