QT-interval prolongation by non-cardiac drugs: lessons to be learned from recent experience

Advantages of azithromycin over erythromycin in improving the gastric emptying half-time in adult patients with gastroparesis

Background/Aims

Current therapy for gastroparesis with prokinetic agents is limited by options and side effects. One macrolide, erythromycin (ERY), is associated with possible sudden cardiac death from QT prolongation due to P450 iso-enzyme inhibition. An alternative, azithromycin (AZI), lacks P450 inhibition. We compared the effect on gastric emptying half-times (t½) between AZI and ERY in patients diagnosed with gastroparesis by gastric emptying scintigraphy.

Methods

Patients stopped medications known to affect gastric emptying prior to the study, and then ingested 1 scrambled egg meal labeled with 18.5-37 MBq of technetium-99m sulfur colloid followed by continuous imaging for 120 minutes, at 1 minute per frame. A simple linear fit was applied to the rate of gastric emptying, and gastric emptying t½ was calculated (normal = 45-90 minutes). At 75-80 minutes, if the stomach had clearly not emptied, patients were given either ERY (n = 60) or AZI (n = 60) 250 mg IV and a new post-treatment gastric emptying t½ was calculated.

Results

Comparison of gastric emptying t½ showed a similar positive effect (mean gastric emptying t½ for AZI = 10.4 ± 7.2 minutes; mean gastric emptying t½ for ERY = 11.9 ± 8.4 minutes; p = 0.30).

Conclusions

AZI is equivalent to ERY in accelerating the gastric emptying of adult patients with gastroparesis. Given the longer duration of action, better side effect profile and lack of P450 interaction for AZI as compared with ERY, further research should evaluate the long term effectiveness and safety of AZI as a gastroparesis treatment.

Prolonged QTc interval in cancer therapeutic drug development: defining arrhythmic risk in malignancy

Anticancer therapy drug development is an arduous task, taking 10 to 15 years to complete, requiring approximately 1 billion dollars, and rarely leads to Food and Drug Administration approval. Methods to predict unacceptable drug-induced toxicity, such as a prolonged QTc interval/risk of torsade de pointes, should be highly informative to quickly and accurately determine if further resources should be allocated in the continued development of an agent. Expert consensus has established guidelines to ascertain the ability of a new drug to prolong the QTc interval. Although QTc measurement is the best way to assess arrhythmic risk, it is imprecise for a variety of reasons. In addition, oncology patients have multiple risk factors for QTc prolongation at baseline. Competing interests involved in assessing arrhythmic risk of a new oncology agent include inability to precisely follow published guidelines for QTc assessment, patients' concomitant medical problems interfering with drug assessment and therefore clinical trial enrollment, patient safety concerns, general public safety concerns regarding toxicity assessment, need for discovery of more curative drug therapies, and individual patient perception of therapeutic risk vs benefit. Oncology patients are concerned about access to experimental agents, as well as early abandonment of a potentially beneficial agent because of a low estimated risk of toxicity, even if the event is catastrophic. We review the issues involved in evaluating the QTc interval-prolonging risk in new anticancer agents.

Anticancer drugs and cardiotoxicity: Insights and perspectives in the era of targeted therapy

Drug-induced cardiotoxicity is emerging as an important issue among cancer survivors. For several decades, this topic was almost exclusively associated with anthracyclines, for which cumulative dose-related cardiac damage was the limiting step in their use. Although a number of efforts have been directed towards prediction of risk, so far no consensus exists on the strategies to prevent and monitor chemotherapy-related cardiotoxicity. Recently, a new dimension of the problem has emerged when drugs targeting the activity of certain tyrosine kinases or tumor receptors were recognized to carry an unwanted effect on the cardiovascular system. Moreover, the higher than expected incidence of cardiac dysfunction occurring in patients treated with a combination of old and new chemotherapeutics (e.g. anthracyclines and trastuzumab) prompted clinicians and researchers to find an effective approach to the problem. From the pharmacological standpoint, putative molecular mechanisms involved in chemotherapy-induced cardiotoxicity will be reviewed. From the clinical standpoint, current strategies to reduce cardiotoxicity will be critically addressed. In this perspective, the precise identification of the antitarget (i.e. the unwanted target causing heart damage) and the development of guidelines to monitor patients undergoing treatment with cardiotoxic agents appear to constitute the basis for the management of drug-induced cardiotoxicity.

Quantitative analysis of T-wave morphology increases confidence in drug-induced cardiac repolarization abnormalities: evidence from the investigational IKr inhibitor Lu 35-138

This study investigates repolarization changes induced by a new candidate drug to determine whether a composite electrocardiographic (ECG) measure of T-wave morphology could be used as a reliable marker to support the evidence of abnormal repolarization, which is indicated by QT interval prolongation. Seventy-nine healthy subjects were included in this parallel study. After a baseline day during which no drug was given, 40 subjects received an I(Kr)-blocking antipsychotic compound (Lu 35-138) on 7 consecutive days while 39 subjects received placebo. Resting ECGs were recorded and used to determine a combined measure of repolarization morphology (morphology combination score [MCS]), based on asymmetry, flatness, and notching. Replicate measurements were used to determine reliable change and study power for both measures. Lu 35-138 increased the QTc interval with corresponding changes in T-wave morphology as determined by MCS. For subjects taking Lu 35-138, T-wave morphology was a more reliable indicator of I(Kr) inhibition than QTcF (chi(2) = 20.3, P = .001). At 80% study power for identifying a 5-millisecond placebo-adjusted change from baseline for QTcF, the corresponding study power for MCS was 93%. As a covariate to the assessment of QT interval liability, MCS offered important additive information to the effect of Lu 35-138 on cardiac repolarization.

[Promotility drugs use in critical care: indications and limits?]

Enteral feeding is often limited by gastric and intestinal motility disturbances in critically ill patients, particularly in patients with shock. So, promotility agents are frequently used to improve tolerance to enteral nutrition. This review summaries the pathophysiology, presents the available pharmacological strategies, the clinical data, the counter-indications and the principal limits. The clinical data are poor. No study demonstrates a positive effect on clinical outcomes. Metoclopramide and erythromycin seems to be the more effective. Considering the risk of antibiotic resistance, the first line use of erythromycin should be avoided in favor of metoclopramide.

hERG-related drug toxicity and models for predicting hERG liability and QT prolongation

BACKGROUND

hERG K(+) channels have been recognized as a primary antitarget in safety pharmacology. Their blockade, caused by several drugs with different therapeutic indications, may lead to QT prolongation and, eventually, to potentially fatal arrhythmia, namely torsade de pointes. Therefore, a number of preclinical models have been developed to predict hERG liability early in the drug development process.

OBJECTIVE

The aim of this review is to outline the present state of the art on drug-induced hERG blockade, providing insights on the predictive value of in vitro and in silico models for hERG liability.

METHODS

On the basis of latest reports, high-throughput preclinical models have been discussed outlining advantages and limitations.

CONCLUSION

Although no single model has an absolute value, an integrated risk assessment is recommended to predict the pro-arrhythmic risk of a given drug. This prediction requires expertise from different areas and should encompass emerging issues such as interference with hERG trafficking and QT shortening.

Collation, assessment and analysis of literature in vitro data on hERG receptor blocking potency for subsequent modeling of drugs' cardiotoxic properties

The assessment of the torsadogenic potency of a new chemical entity is a crucial issue during lead optimization and the drug development process. It is required by the regulatory agencies during the registration process. In recent years, there has been a considerable interest in developing in silico models, which allow prediction of drug-hERG channel interaction at the early stage of a drug development process. The main mechanism underlying an acquired QT syndrome and a potentially fatal arrhythmia called torsades de pointes is the inhibition of potassium channel encoded by hERG (the human ether-a-go-go-related gene). The concentration producing half-maximal block of the hERG potassium current (IC(50)) is a surrogate marker for proarrhythmic properties of compounds and is considered a test for cardiac safety of drugs or drug candidates. The IC(50) values, obtained from data collected during electrophysiological studies, are highly dependent on experimental conditions (i.e. model, temperature, voltage protocol). For the in silico models' quality and performance, the data quality and consistency is a crucial issue. Therefore the main objective of our work was to collect and assess the hERG IC(50) data available in accessible scientific literature to provide a high-quality data set for further studies.

Management of the critically poisoned patient

BACKGROUND

Clinicians are often challenged to manage critically ill poison patients. The clinical effects encountered in poisoned patients are dependent on numerous variables, such as the dose, the length of exposure time, and the pre-existing health of the patient. The goal of this article is to introduce the basic concepts for evaluation of poisoned patients and review the appropriate management of such patients based on the currently available literature.

METHODS

An unsystematic review of the medical literature was performed and articles pertaining to human poisoning were obtained. The literature selected was based on the preference and clinical expertise of authors.

DISCUSSION

If a poisoning is recognized early and appropriate testing and supportive care is initiated rapidly, the majority of patient outcomes will be good. Judicious use of antidotes should be practiced and clinicians should clearly understand the indications and contraindications of antidotes prior to administration.

Torsades de Pointes with QT prolongation related to donepezil use

An 83-year-old female, who had a history of anterior myocardial infarction, was treated for Alzheimer's disease with donepezil. She suffered from repeated diarrhea and vomiting, and experienced syncope. She was admitted to our hospital and was diagnosed with acute colitis and syncope. On admission, her heart rate was 54 beats/min with regular rhythm. Laboratory data showed a low plasma potassium level. Electrocardiogram (ECG) showed poor R progression, ST elevation, negative T in precordial leads, and marked QT prolongation. Transthoracic echocardiogram showed the enlargement of the left atrium and aneurysmal area at the apex. Torsades de Pointes (TdP) with syncope and convulsion were confirmed on ECG monitoring twice after admission. We treated her with potassium chloride and started magnesium sulfate and lidocaine, and then added isoprenaline injection. After these treatments, her heart rate increased and we did not detect TdP again. With the aging population in Japan, prescriptions for donepezil are increasing. We have to be vigilant for syncope in patients taking donepezil, which is possibly related to QT prolongation and TdP.

Unintended consequences of reducing QT-alert overload in a computerized physician order entry system

PURPOSE

After complaints of too many low-specificity drug-drug interaction (DDI) alerts on QT prolongation, the rules for QT alerting in the Dutch national drug database were restricted in 2007 to obviously QT-prolonging drugs. The aim of this virtual study was to investigate whether this adjustment would improve the identification of patients at risk of developing Torsades de Pointes (TdP) due to QT-prolonging drug combinations in a computerized physician order entry system (CPOE) and whether these new rules should be implemented.

METHODS

During a half-year study period, inpatients with overridden DDI alerts regarding QT prolongation and with an electrocardiogram recorded before and within 1 month of the alert override were included if they did not have a ventricular pacemaker and did not use the low-risk combination cotrimoxazole and tacrolimus. QT-interval prolongation and the risk of developing TdP were calculated for all patients and related to the number of patients for whom a QT-alert would be generated in the new situation with the restricted database.

RESULTS

Forty-nine patients (13%) met the inclusion criteria. In this study population, knowledge base-adjustment would reduce the number of alerts by 53%. However, the positive predictive value of QT alerts would not change (31% before and 30% after) and only 47% of the patients at risk of developing TdP would be identified in CPOEs using the adjusted knowledge base.

CONCLUSION

The new rules for QT alerting would result in a poorer identification of patients at risk of developing TdP than the old rules. This is caused by the many non-drug-related risk factors for QT prolongation not being incorporated in CPOE alert generation. The partial contribution of all risk factors should be studied and used to create clinical rules for QT alerting with an acceptable positive predictive value.

Quinazolin-4-piperidin-4-methyl sulfamide PC-1 inhibitors: alleviating hERG interactions through structure based design

PC-1 (NPP-1) inhibitors may be useful as therapeutics for the treatment of CDDP (calcium pyrophosphate dehydrate) deposition disease and osteoarthritis. We have identified a series of potent quinazolin-4-piperidin-4-ethyl sulfamide PC-1 inhibitors. The series, however, suffers from high affinity binding to hERG potassium channels, which can cause drug-induced QT prolongation. We used a hERG homology model to identify potential key interactions between our compounds and hERG, and the information gained was used to design and prepare a series of quinazolin-4-piperidin-4-methyl sulfamides that retain PC-1 activity but lack binding affinity for hERG.

Psychotropic drugs associated with corrected QT interval prolongation

AIMS

To study whether listed putative corrected QT (QTc)-prolonging psychotropic drugs indeed prolong the QTc interval under everyday circumstances and to evaluate whether this is a class effect or an individual drug effect, we conducted a prospective population-based cohort study.

METHODS

This study was conducted as part of the Rotterdam Study and included 3377 men and 4845 women (>or=55 years) who had triennial electrocardiograms (ECGs). The primary end points of the study were the length of the QTc interval at each ECG, the difference in QTc interval between consecutive ECGs within one person, and the risk of an abnormally prolonged QTc interval. Drug use at the index date was obtained from automated dispensing records. The associations were examined by means of a repeated measurement analysis, adjusted for age, sex, diabetes mellitus, hypertension, myocardial infarction, heart failure, and use of class 1 QTc-prolonging drugs.

RESULTS

Of the 8222 participants, 813 participants (9.9%) developed QTc prolongation during follow-up and 492 participants (74.4% women) used psychotropic drugs at the time of an ECG. Starting tricyclic antidepressants increased the QTc interval significantly with 6.9 milliseconds (95% confidence interval [CI], 3.1-10.7 milliseconds) between consecutive ECGs in comparison with consecutive ECGs of participants not using tricyclic antidepressants, in particular starting amitriptyline (8.5 milliseconds; 95% CI, 2.8-14.2 milliseconds), maprotiline (13.9 milliseconds; 95% CI, 3.6-24.3 milliseconds), and nortriptyline (35.3 milliseconds; 95% CI, 8.0-62.6 milliseconds). Starting lithium also increased the QTc interval significantly (18.6 milliseconds; 95% CI, 4.8-32.4 milliseconds).

CONCLUSIONS

In this population-based prospective cohort study, we confirmed the importance of antidepressants and antipsychotics as potential contributors to QTc prolongation. Especially, starting tricyclic antidepressant drugs (as a class) is associated with a significant intraindividual increase in the QTc interval in comparison to the change in nonusers. The tricyclic antidepressants seem to prolong the QTc interval as a class effect.

Atypical antipsychotic drugs and the risk of sudden cardiac death

BACKGROUND

Users of typical antipsychotic drugs have an increased risk of serious ventricular arrhythmias and sudden cardiac death. However, less is known regarding the cardiac safety of the atypical antipsychotic drugs, which have largely replaced the older agents in clinical practice.

METHODS

We calculated the adjusted incidence of sudden cardiac death among current users of antipsychotic drugs in a retrospective cohort study of Medicaid enrollees in Tennessee. The primary analysis included 44,218 and 46,089 baseline users of single typical and atypical drugs, respectively, and 186,600 matched nonusers of antipsychotic drugs. To assess residual confounding related to factors associated with the use of antipsychotic drugs, we performed a secondary analysis of users of antipsychotic drugs who had no baseline diagnosis of schizophrenia or related psychoses and with whom nonusers were matched according to propensity score (i.e., the predicted probability that they would be users of antipsychotic drugs).

RESULTS

Current users of typical and of atypical antipsychotic drugs had higher rates of sudden cardiac death than did nonusers of antipsychotic drugs, with adjusted incidence-rate ratios of 1.99 (95% confidence interval [CI], 1.68 to 2.34) and 2.26 (95% CI, 1.88 to 2.72), respectively. The incidence-rate ratio for users of atypical antipsychotic drugs as compared with users of typical antipsychotic drugs was 1.14 (95% CI, 0.93 to 1.39). Former users of antipsychotic drugs had no significantly increased risk (incidence-rate ratio, 1.13; 95% CI, 0.98 to 1.30). For both classes of drugs, the risk for current users increased significantly with an increasing dose. Among users of typical antipsychotic drugs, the incidence-rate ratios increased from 1.31 (95% CI, 0.97 to 1.77) for those taking low doses to 2.42 (95% CI, 1.91 to 3.06) for those taking high doses (P<0.001). Among users of atypical agents, the incidence-rate ratios increased from 1.59 (95% CI, 1 .03 to 2.46) for those taking low doses to 2.86 (95% CI, 2.25 to 3.65) for those taking high doses (P=0.01). The findings were similar in the cohort that was matched for propensity score.

CONCLUSIONS

Current users of typical and of atypical antipsychotic drugs had a similar, dose-related increased risk of sudden cardiac death.

Exposure to antibacterial agents with QT liability in 14 European countries: trends over an 8-year period

AIMS

(i) To classify antibacterial agents with QT liability on the basis of the available evidence, and (ii) to assess trends in their consumption over an 8-year period (1998-2005) in 14 European countries.

METHODS

Current published evidence on QT liability of antibiotics was retrieved through MEDLINE search and joined to official warnings from regulatory agencies. Each drug was classified according to an already proposed algorithm based on the strength of evidence: from group A (any evidence) to group E (clinical reports of torsades de pointes and warnings on QT liability). Consumption data were provided by the European Surveillance of Antibacterial Consumption (ESAC) project and were expressed as defined daily doses per 1000 inhabitants per day (DID).

RESULTS

Among 21 detected compounds, nine [six fluoroquinolones (FQs) and three macrolides (MACs)] belonged to group E. Use of group E drugs ranged from 1.3 (Sweden) to 4.1 DID (Italy) in 1998 and from 1.2 (Sweden) to 6.5 DID (Italy) in 2005. Significant exposure was observed in Italy and Spain (6.5 and 3.8 DID, respectively, in 2005). Only Denmark, Sweden and UK showed a slight decrease in use. Exposure to clarithromycin increased in 10 out of 14 countries, with a marked increment in Italy (3 DID in 2005).

CONCLUSIONS

Notwithstanding regulatory measures, in 2005 there was still significant exposure to antibacterials with strong evidence of QT liability and, in most countries, it was even increased. This warrants further investigation of appropriateness of use and suggests closer monitoring of group E drugs. Physicians should be aware when prescribing them to susceptible patients.

Long QT syndrome and torsade de pointes after anthracycline chemotherapy

Anthracycline chemotherapy, which represents the treatment of choice for many hematologic and metastatic cancers, unfortunately carries with it the possibility of both early cardiotoxic phenomena, occuring during chemotherapy, and also late cardiotoxic manifestations, occuring even months or years from the completion of treatment.

The clinical manifestations of early cardiotoxicity commonly include: ventricular premature beats, supraventricular tachycardia, cardiomyopathy and sudden death.

This study confirms the necessity for close cardiac monitoring of patients undergoing anthracycline therapy. Such monitoring should not only comprise echocardiographic monitoring for left ventricular systo-diastolic dysfunction, but also electrocardiographic monitoring (QTc) in order to exclude electrophysiological changes possibly related to life threatening arrhythmias (10).

Clinically relevant QTc prolongation due to overridden drug-drug interaction alerts: a retrospective cohort study

AIMS

To investigate whether, in patients in whom drug-drug interaction (DDI) alerts on QTc prolongation were overridden, the physician had requested an electrocardiogram (ECG), and if these ECGs showed clinically relevant QTc prolongation.

METHODS

For all patients with overridden DDI alerts on QTc prolongation during 6 months, data on risk factors for QT prolongation, drug class and ECGs were collected from the medical record. Patients with ventricular pacemakers, patients treated on an outpatient basis, and patients using the low-risk combination of cotrimoxazole and tacrolimus were excluded. The magnitude of the effect on the QTc interval was calculated if ECGs before and after overriding were available. Changes of the QTc interval in these cases were compared with those of a control group using one QTc-prolonging drug.

RESULTS

In 33% of all patients with overridden QTc alerts an ECG was recorded within 1 month. ECGs were more often recorded in patients with more risk factors for QTc prolongation and with more QTc overrides. ECGs before and after the QTc override were available in 29% of patients. Thirty-one percent of patients in this group showed clinically relevant QTc prolongation with increased risk of torsades de pointes or ventricular arrhythmias. The average change in QTc interval was +31 ms for cases and -4 ms for controls.

CONCLUSIONS

Overriding the high-level DDI alerts on QTc prolongation rarely resulted in the preferred approach to subsequently record an ECG. If ECGs were recorded before and after QTc overrides, clinically relevant QTc prolongation was found in one-third of cases. ECG recording after overriding QTc alerts should be encouraged to prevent adverse events.

Critical care toxicology

Emergency physicians are regularly called on to care for critically poisoned patients. This article reviews the general approach and management of the critically poisoned patient. Specific clinical characteristics are identified that may clue the clinician into a specific toxin class as a diagnosis. Appropriate testing in the poisoned patient is reviewed. Complications of poisoning that may bring a rapid demise of the critically ill poisoned patient are highlighted and the management of those complications is discussed.

Optimization and structure-activity relationship of a series of 1-phenyl-1,8-naphthyridin-4-one-3-carboxamides: identification of MK-0873, a potent and effective PDE4 inhibitor

A SAR study of a series of 1-phenyl-1,8-naphthyridin-4-one-3-carboxamides is described. Optimization of the series was based on in vitro potency against PDE4, inhibition of the LPS-induced production of TNF-alpha in human whole blood and minimizing affinity for the hERG potassium channel. From these studies, compounds 18 and 20 (MK-0873) were identified as optimized PDE4 inhibitors with good overall in vitro and in vivo profiles and selected as development candidates.

The hERG K+ channel: target and antitarget strategies in drug development

The human ether-à-go-go related gene (hERG) K+ channel is of great interest for both basic researchers and clinicians because its blockade by drugs can lead to QT prolongation, which is a risk factor for torsades de pointes, a potentially life-threatening arrhythmia. A growing list of agents with "QT liability" have been withdrawn from the market or restricted in their use, whereas others did not even receive regulatory approval for this reason. Thus, hERG K+ channels have become a primary antitarget (i.e. an unwanted target) in drug development because their blockade causes potentially serious side effects. On the other hand, the recent identification and functional characterization of hERG K+ channels not only in the heart, but also in several other tissues (e.g. neurons, smooth muscle and cancer cells) may have far reaching implications for drug development for a possible exploitation of hERG as a target, especially in oncology and cardiology.

Newer fluoroquinolones in the treatment of acute exacerbations of COPD

Acute exacerbations of COPD are a major cause of morbidity and mortality. Bacteria are implicated in about half of all cases. The frequency of exacerbations is related to decline in lung function and poorer quality of life. 25% of patients with COPD have bacterial colonization of the lower airways in stable state whereas non-smokers without COPD have airways that are sterile. The significance of the colonization is unclear, but there is emerging evidence that it may be detrimental. Much of the data recommending antibiotic treatment are based on findings more than 10 years old and do not take into account emerging bacterial resistance. This article reviews these data and that from newer antibiotic trials. It also reviews current antibiotic prescribing guidelines from major respiratory societies around the world. Recent antibiotic trials have compared fluoroquinolones with “standard” antibiotics and found, in the main, longer exacerbation-free intervals and better bacterial eradication rates in those treated with fluoroquinolones.

The application of discovery toxicology and pathology towards the design of safer pharmaceutical lead candidates

Toxicity is a leading cause of attrition at all stages of the drug development process. The majority of safety-related attrition occurs preclinically, suggesting that approaches to identify 'predictable' preclinical safety liabilities earlier in the drug development process could lead to the design and/or selection of better drug candidates that have increased probabilities of becoming marketed drugs. In this Review, we discuss how the early application of preclinical safety assessment--both new molecular technologies as well as more established approaches such as standard repeat-dose rodent toxicology studies--can identify predictable safety issues earlier in the testing paradigm. The earlier identification of dose-limiting toxicities will provide chemists and toxicologists the opportunity to characterize the dose-limiting toxicities, determine structure-toxicity relationships and minimize or circumvent adverse safety liabilities.

Activation of ERG2 potassium channels by the diphenylurea NS1643

Three members of the ERG potassium channel family have been described (ERG1-3 or Kv 11.1-3). ERG1 is by far the best characterized subtype and it constitutes the molecular component of the cardiac I(Kr) current. All three channel subtypes are expressed in neurons but their function remains unclear. The lack of functional information is at least partly due to the lack of specific pharmacological tools. The compound NS1643 has earlier been reported as an ERG1 channel activator. We found that NS1643 also activates the ERG2 channel; however, the molecular mechanism of the activation differs between the ERG1 and ERG2 channels. This is surprising since ERG1 and ERG2 channels have very similar biophysical and structural characteristics. For ERG2, NS1643 causes a left-ward shift of the activation curve, a faster time-constant of activation and a slower time-constant of inactivation as well as an increased relative importance for the fast component of deactivation to the total deactivation. In contrast, for ERG1, NS1643 causes a right-ward shift in the voltage-dependent release from inactivation but does not affect time-constants of deactivation. Because of these differences in the responses of ERG1 and ERG2 to NS1643, NS1643 can be used as a pharmacological tool to address ERG channel function. It may be useful for revealing physiological functions of ERG channels in neuronal tissue as well as to elucidate the structure-function relationships of the ERG channels.

Modeling Promiscuity Based on in vitro Safety Pharmacology Profiling Data

This study describes a method for mining and modeling binding data obtained from a large panel of targets (in vitro safety pharmacology) to distinguish differences between promiscuous and selective compounds. Two naïve Bayes models for promiscuity and selectivity were generated and validated on a test set as well as publicly available drug databases. The model shows a higher score (lower promiscuity) for marketed drugs than for compounds in early development or compounds that failed during clinical development. Such models can be used in triaging high-throughput screening data or for lead optimization.

Understanding hERG inhibition with QSAR models based on a one-dimensional molecular representation

Blockage of the potassium channel encoded by the human ether-a-go-go related gene (hERG) is well understood to be the root cause of the cardio-toxicity of numerous approved and investigational drugs. As such, a cascade of in vitro and in vivo assays have been developed to filter compounds with hERG inhibitory activity. Quantitative structure activity relationship (QSAR) models are used at the very earliest part of this cascade to eliminate compounds that are likely to have this undesirable activity prior to synthesis. Here a new QSAR technique based on the one-dimensional representation is described in the context of the development of a model to predict hERG inhibition. The model is shown to perform close to the limits of the quality of the data used for model building. In order to make optimal use of the available data, a general robust mathematical scheme was developed and is described to simultaneously incorporate quantitative data, such as IC50 = 50 nM, and qualitative data, such as inactive or IC50 > 30 microM into QSAR models without discarding any experimental information.

Cardiovascular Safety of Gadoterate Meglumine (Gd-DOTA)

OBJECTIVES

Gadolinium complexes are not considered to be a drug class at high risk for prolonging cardiac repolarization, which can lead to potentially life-threatening arrhythmias such as torsade de pointes. However, only limited robust data are available on these compounds despite their extensive use as contrast enhancers in magnetic resonance imaging. We present an overview of recent cardiovascular safety data obtained on gadoterate meglumine (Gd-DOTA).

MATERIALS AND METHODS

Cardiovascular safety was evaluated by "state-of-the-art" nonclinical ex vitro (dog Purkinje fibers) and in vivo studies in both normal (dogs) and sensitized animal models (rabbits) and in patients with various diseases in a specific clinical trial.

RESULTS

In all of these studies, Gd-DOTA did not show any direct deleterious effect on cardiac electrophysiology and especially on ventricular repolarization.

CONCLUSION

These results confirmed the good safety profile of Gd-DOTA derived from postmarketing evaluations. Nonspecific gadolinium complexes used for magnetic resonance contrast enhancement do not constitute a class-at-risk for drug-related arrhythmias.

QTc-interval abnormalities in a forensic population

BACKGROUND

Antipsychotic drugs have been linked to sudden death among psychiatric patients, with a suggestion that prolongation of the QT-interval detectable on a standard electrocardiogram may be linked to fatal cardiac arrhythmias in these circumstances. Patients in secure forensic psychiatric facilities may be particularly likely to be on high-dose antipsychotic medication, and yet, as far as the authors are aware, no study of QT-intervals among such patients has been reported.

AIM

To investigate the prevalence of QT-interval abnormalities and associated known risk factors for fatal cardiac arrhythmias in a sample of forensic patients.

METHOD

Participants had a 12-lead electrocardiogram taken at 50 mm/s. Information was collected on their age, gender, psychiatric diagnosis, history of cardiovascular, liver and kidney diseases, and smoking, on all medications and on history of seclusion over the previous 12 months. Analysis was carried out using binary logistic regression.

RESULTS

Lower rates of QT-interval abnormalities than might be expected for this population were found. It was also found that a high dose of antipsychotics was associated with QTc prolongation (Adjusted OR = 9.5, 95% CI 2.6-34.2), a result consistent with previous literature.

CONCLUSION

Forensic patients need not be at increased risk of QTc abnormality provided risk factors are properly managed. A high dose of antipsychotic medication increases the risk of QTc prolongation.

Post-Marketing Surveillance of the Safety of Levofloxacin in Japan

BACKGROUND

Central nervous system reactions to new quinolones, such as convulsions due to interaction with nonsteroidal anti-inflammatory drugs (NSAIDS), have attracted increased attention in Japan.

METHODS

The safety of levofloxacin (LVX) was investigated in Japan by post-marketing surveillance and reviewing spontaneous reports.

RESULTS

Post-marketing surveillance was performed in 16,117 patients between 1994 and 1996. The incidence of adverse reactions was 1.3% (203/16,117), being comparable with that for ofloxacin or that shown by phase II/III studies. Among 4,977 patients receiving concomitant NSAID treatment, the overall incidence of adverse reactions and the incidence of neurological reactions (including convulsions) did not significantly differ from those in patients without anti-inflammatory therapy. Review of the spontaneous reports on convulsions showed that patients with nephropathy, patients over 75 years and patients with a history of convulsive diseases were more likely to develop convulsions during LVX therapy.

CONCLUSION

LVX should be used cautiously in patients with the above risk factors.

Antimicrobial-associated QT interval prolongation: pointes of interest

Until recently, cardiac toxicity manifesting in the form of arrhythmias related to QT interval prolongation was uncommonly appreciated within the antimicrobial class of drugs, but it was well described among antiarrhythmic agents. Antimicrobials that are associated with QT prolongation include the macrolides/ketolides, certain fluoroquinolones and antimalarials, pentamidine, and the azole antifungals. Although, in most cases, mild delays in ventricular repolarization caused by these drugs are clinically unnoticeable, they may serve to amplify the risk for torsades de pointes (TdP) when prescribed in the setting of other risk factors. Conditions or variables that influence proarrhythmic risk include sex, age, electrolyte derangements, structural heart disease, pharmacokinetic/pharmacodynamic interactions, and genetic predisposition. It is important that clinicians be knowledgeable about drugs with QT liability, as well as the risk factors that increase the probability of TdP. Additionally, because TdP remains a difficult-to-measure adverse event, we must rely upon multiple data sources to determine the risk versus the benefit for newly approved drugs.

Mallotoxin is a novel human ether-a-go-go-related gene (hERG) potassium channel activator

Human ether-a-go-go-related gene (hERG) encodes a rapidly activating delayed rectifier potassium channel that plays important roles in cardiac action potential repolarization. Although many drugs and compounds block hERG channels, activators of the channel have only recently been described. Three structurally diverse synthetic compounds have been reported to activate hERG channels by altering deactivation or inactivation or by unidentified mechanisms. Here, we describe a novel, naturally occurring hERG channel activator, mallotoxin (MTX). The effects of MTX on hERG channels were investigated using the patch-clamp technique. MTX increased both step and tail hERG currents with EC(50) values of 0.34 and 0.52 microM, respectively. MTX leftward shifted the voltage dependence of hERG channel activation to less depolarized voltages ( approximately 24 mV at 2.5 microM). In addition, MTX increased hERG deactivation time constants. MTX did not change the half-maximal inactivation voltage of the hERG channel, but it reduced the slope of the voltage-dependent inactivation curve. All of these factors contribute to the enhanced activity of hERG channels. During a voltage-clamp protocol using prerecorded cardiac action potentials, 2.5 microM MTX increased the total potassium ions passed through hERG channels by approximately 5-fold. In conclusion, MTX activates hERG channels through distinct mechanisms and with significantly higher potency than previously reported hERG channel activators.

Computer-based analysis of dynamic QT changes: toward high precision and individual rate correction

BACKGROUND

New strategies are needed to improve the results of automatic measurement of the various parts of the ECG signal and their dynamic changes.

METHODS

The EClysis software processes digitally-recorded ECGs from up to 12 leads at 500 Hz, using strictly defined algorithms to detect the PQRSTU points and to measure ECG intervals and amplitudes. Calculations are made on the averaged curve of each sampling period (beat group) or as means +/- SD for beat groups, after being analyzed at the individual beat level in each lead. Resulting data sets can be exported for further statistical analyses. Using QT and R-R measured on beat level, an individual correction for the R-R dependence can be performed.

RESULTS

EClysis assigns PQRSTU points and intervals in a sensitive and highly reproducible manner, with coefficients of variation in ECG intervals corresponding to ca. 2 ms in the simulated ECG. In the normal ECG, the CVs are 2% for QRS, 0.8% for QT, and almost 6% for PQ intervals. EClysis highlights the increase in QT intervals and the decrease of T-wave amplitudes during almokalant infusion versus placebo. Using the observed linear or exponential relationships to adjust QT for R-R dependence in healthy subjects, one can eliminate this dependence almost completely by individualized correction.

CONCLUSIONS

The EClysis system provides a precise and reproducible method to analyze ECGs.

Genetic polymorphisms in KCNQ1, HERG, KCNE1 and KCNE2 genes in the Chinese, Malay and Indian populations of Singapore

AIMS

To determine the genetic variability of long QT syndrome (LQTS)-associated genes (KCNQ1, HERG, KCNE1 and KCNE2) among three distinct ethnic groups in the Singapore population.

METHODS

Genomic DNA samples from up to 265 normal healthy Chinese, 118 Malay and 139 Indian volunteer subjects were screened for genetic variations in the coding region of the LQTS-associated genes using denaturing high-performance liquid chromatography and sequencing analyses.

RESULTS

In total, 37 single nucleotide polymorphisms (SNPs) were identified in the coding exons of the LQTS-associated potassium ion channel genes, seven of which were novel nonsynonymous polymorphisms. SNPs 356G-->A (exon 1 of KCNQ1), 2624C-->T and 2893G-->A (exon 11 of HERG), 3164G-->A, 3322C-->G and 3460G-->A (exon 14 of HERG), and 79C-->T (exon 3 of KCNE2) resulted in Gly119Asp, Thr875Met, Gly965Arg, Arg1055Gln, Leu1108Val, Gly1154Ser and Arg27Cys amino acid substitutions, respectively. In addition, 16 intronic variants were detected. The functional consequence of these variants has not been studied and their association with risk of LQTS is unclear.

CONCLUSIONS

There exist multiple genetic polymorphisms of the LQTS-associated genes in the three distinct Asian populations. Though the functional significance of many of these SNPs is unknown, this interindividual and interethnic genetic variability may underlie the different susceptibilities of individuals to developing LQTS.

ILSI-HESI cardiovascular safety subcommittee initiative: Evaluation of three non-clinical models of QT prolongation

INTRODUCTION

Drugs that delay cardiac repolarization pose potential safety risks to patients and cause serious regulatory concern because of the link between QT interval prolongation and the potentially fatal arrhythmia torsades de pointes (TdP). Predicting which drugs will cause TdP is an inexact and difficult science. The utility of non-clinical assays was not well understood due in part to variability in methods, species, and consistency in the assays reported in the literature. The Health and Environmental Sciences Institute of the International Life Sciences Institute (ILSI/HESI) outlined a set of studies to determine how well selected commonly used non-clinical assays identified compounds known to cause TdP and prolong QT interval in humans.

METHODS

Compounds known to prolong ventricular repolarization and compounds considered safe by years of clinical use were tested in three assays: HERG ionic current, Purkinje fiber repolarization, and in vivo QT studies in conscious telemeterized dogs.

RESULTS

The data from each of these assays demonstrate that compounds that may pose a proarrhythmia risk for patients can be distinguished from those that are considered safe.

DISCUSSION

Taken collectively, the in-vitro and in-vivo preclinical results can be integrated to develop an accurate preclinical risk assessment to support clinical safety.

Bicyclo[3.1.0]hexyl urea melanin concentrating hormone (MCH) receptor-1 antagonists: Impacting hERG liability via aryl modifications

Herein, we report the discovery of an effective strategy to modulate liabilities related to affinity of previously disclosed bicyclohexane MCHR-1 antagonists for the hERG channel. This paper describes one of several strategies incorporated to limit hERG binding via modifications of a terminal aryl group in an otherwise promising bicyclohexyl urea series.

Frequency of high-risk use of QT-prolonging medications

PURPOSE

Prolongation of the QT interval has been associated with increased risk of torsades de pointes and death. Concurrent use of more than one QT-prolonging drug or a QT-prolonging drug with a drug that alters its pharmacokinetic profile is an important risk factor for adverse outcomes.

METHODS

Using a representative sample of 2 million health plan members from 10 health maintenance organizations with pharmacy benefits between January 1999 and July 2001, we identified potential drug interactions involving QT-prolonging medications. Prescription claims overlapping by at least 7 days for either 2 or more QT-prolonging drugs or a QT-prolonging drug with a drug that alters its clearance were considered potential drug interactions. We determined the number of drug interactions overall and the number of these interactions involving patients with other risk factors for torsades de pointes.

RESULTS

A total of 48 465 potential drug interactions were identified in 10 415 (4.6%) of the 228 550 patients with at least one prescription for a QT-prolonging drug. Amitriptyline was involved in 37 859 (78.1%) of the drug interactions. Of all potential drug interactions, 43 689 (90.1%) occurred in patients with at least one other risk factor for torsades de pointes, and 1053 (2.2%) were listed as a contraindicated combination in product labeling.

CONCLUSION

Potential drug interactions involving currently marketed QT-prolonging drugs occurred in 4.6% of patients who had a prescription for a QT-prolonging medication. The findings suggest several areas for targeted interventions to decrease the potential risk from QT-prolonging medications.