The thorough QT/QTc study 4 years after the implementation of the ICH E14 guidance

Fetal QT Interval Estimation Using Sequential Hypothesis Testing

Objective: Recent studies utilizing fetal magnetocardiography have demonstrated the efficacy of corrected QT interval (QTc) measurement for in utero diagnosis and prognosis of long QT syndrome, a leading cause of sudden death in early life. The objective of the study was to formulate and test a novel statistical estimation method to detect the end of the fetal T-wave and thereby improve the accuracy of fetal QT interval measurement. Methods: To detect the end of the T-wave, we apply a sequential composite hypothesis test to decide when the T-wave has returned to baseline. The method uses the generalized likelihood ratio test in conjunction with a low-rank spatiotemporal model that exploits the repetitive nature of cardiac signals. The unknown model parameters are determined using maximum likelihood estimation. Results: In realistic simulations, the detector was shown to be accurate to within 10 ms (95% prediction interval), even at noise-to-signal ratios as high as 6. When applied to real data from normal fetuses, the detector agreed well with measurements made by cardiologists ( 1.4 6.9 ms). Conclusions: The method was effective and practical. Detector performance was excellent despite the continual presence of strong maternal interference. Significance: This detector serves as a valuable adjunct to traditional measurement based on subjective assessment.Objective: Recent studies utilizing fetal magnetocardiography have demonstrated the efficacy of corrected QT interval (QTc) measurement for in utero diagnosis and prognosis of long QT syndrome, a leading cause of sudden death in early life. The objective of the study was to formulate and test a novel statistical estimation method to detect the end of the fetal T-wave and thereby improve the accuracy of fetal QT interval measurement. Methods: To detect the end of the T-wave, we apply a sequential composite hypothesis test to decide when the T-wave has returned to baseline. The method uses the generalized likelihood ratio test in conjunction with a low-rank spatiotemporal model that exploits the repetitive nature of cardiac signals. The unknown model parameters are determined using maximum likelihood estimation. Results: In realistic simulations, the detector was shown to be accurate to within 10 ms (95% prediction interval), even at noise-to-signal ratios as high as 6. When applied to real data from normal fetuses, the detector agreed well with measurements made by cardiologists ( 1.4 6.9 ms). Conclusions: The method was effective and practical. Detector performance was excellent despite the continual presence of strong maternal interference. Significance: This detector serves as a valuable adjunct to traditional measurement based on subjective assessment.

Why Can dl-Sotalol Prolong the QT Interval In Vivo Despite Its Weak Inhibitory Effect on hERG K(+) Channels In Vitro? Electrophysiological and Pharmacokinetic Analysis with the Halothane-Anesthetized Guinea Pig Model

In order to bridge the gap of action of dl-sotalol between the human ether-a-go-go-related gene (hERG) K(+) channel inhibition in vitro and QT-interval prolongation in vivo, its electropharmacological effect and pharmacokinetic property were simultaneously studied in comparison with those of 10 drugs having potential to prolong the QT interval (positive drugs: bepridil, haloperidol, dl-sotalol, terfenadine, thioridazine, moxifloxacin, pimozide, sparfloxacin, diphenhydramine, imipramine and ketoconazole) and four drugs lacking such property (negative drugs: enalapril, phenytoin, propranolol or verapamil) with the halothane-anesthetized guinea pig model. A dose of each drug that caused 10 % prolongation of Fridericia-corrected QT interval (QTcF) was calculated, which was compared with respective known hERG K(+) IC50 value and currently obtained heart/plasma concentration ratio. Each positive drug prolonged the QTcF in a dose-related manner, whereas such effect was not observed by the negative drugs. Drugs with more potent hERG K(+) channel inhibition showed higher heart/plasma concentration ratio, resulting in more potent QTcF prolongation in vivo. The potency of dl-sotalol for QTcF prolongation was flat middle, although its hERG K(+) channel inhibitory property as well as heart/plasma concentration ratio was the smallest among the positive drugs, which may be partly explained by its lack of binding to plasma protein.

Early drug development: assessment of proarrhythmic risk and cardiovascular safety

INTRODUCTION

hERG assays and thorough ECG trials have been mandated since 2005 to evaluate the QT interval and potential proarrhythmic risk of new chemical entities. The high cost of these studies and the shortcomings inherent in these binary and limited approaches to drug evaluation have prompted regulators to search for more cost effective and mechanistic paradigms to assess drug liability as exemplified by the CiPA initiative and the exposure response ICH E14(R3) guidance document. Areas covered: This review profiles the changing regulatory landscape as it pertains to early drug development and outlines the analyses that can be performed to characterize preclinical and early clinical cardiovascular risk. Expert commentary: It is further acknowledged that the narrow focus on the QT interval needs to be expanded to include a more comprehensive evaluation of cardiovascular risk since unanticipated off target effects have led to the withdrawal of multiple drugs after they had been approved and marketed.

Top-down, Bottom-up and Middle-out Strategies for Drug Cardiac Safety Assessment via Modeling and Simulations

Cardiac safety is an issue causing early terminations at various stages of drug development. Efforts are put into the elimination of false negatives as well as false positives resulting from the current testing paradigm. In silico approaches offer mathematical system and data description from the ion current, through cardiomyocytes level, up to incorporation of inter-individual variability at the population level. The article aims to review three main modelling and simulation approaches, i.e. "top-down" which refers to models built on the observed data, "bottom-up", which stands for a mechanistic description of human physiology, and "middle-out" which combines both strategies. Modelling and simulation is a well-established tool in the assessment of drug proarrhythmic potency with an impact on research and development as well as on regulatory decisions, and it is certainly here to stay. What is more, the shift to systems biology and physiology-based models makes the cardiac effect more predictable.

Ascending Single-Dose, Double-Blind, Placebo-Controlled Safety Study of Noribogaine in Opioid-Dependent Patients

Ibogaine is a psychoactive substance that may reduce opioid withdrawal symptoms. This was the first clinical trial of noribogaine, ibogaine's active metabolite, in patients established on methadone opioid substitution therapy (OST). In this randomized, double-blind, placebo-controlled single ascending-dose study, we evaluated the safety, tolerability, and pharmacokinetics of noribogaine in 27 patients seeking to discontinue methadone OST who had been switched to morphine during the previous week. Noribogaine doses were 60, 120, or 180 mg (n = 6/dose level) or matching placebo (n = 3/dose level). Noribogaine was well tolerated. The most frequent treatment-emergent adverse events were noneuphoric changes in light perception ∼1 hour postdose, headache, and nausea. Noribogaine had dose-linear increases for AUC and C_max and was slowly eliminated (mean t_1/2 range, 24-30 hours). There was a concentration-dependent increase in QTcI (0.17 ms/ng/mL), with the largest observed mean effect of ∼16, 28, and 42 milliseconds in the 60-, 120-, and 180-mg groups, respectively. Noribogaine showed a nonstatistically significant trend toward decreased total score in opioid withdrawal ratings, most notably at the 120-mg dose; however, the study design may have confounded evaluations of time to resumption of OST. Future exposure-controlled multiple-dose noribogaine studies are planned that will address these safety and design issues.

Propofol-associated QTc prolongation

OBJECTIVES

Propofol is a preferred agent for sedation in patients in the intensive care unit (ICU) due, in part, to its established safety profile. Despite this, recent case reports have suggested a potential for prolongation of the corrected QT interval (QTc) in ICU patients receiving propofol, though limited empirical work has been conducted to evaluate this association. As such, the purpose of this study was to assess the relationship between propofol infusion and QTc prolongation in a historical cohort of ICU patients.

METHODS

A single-center, historical, observational, pre-post cohort analysis of medical records from admitted patients ⩾18 years old with cardiovascular disease was conducted, involving cases who received propofol infusion for ⩾3 hours with sequential electrocardiogram monitoring from 2006 to 2012. A multivariable, generalized linear model regression was employed to assess the primary outcome of on-propofol QTc interval (QTc2), controlling for various demographic and clinical factors.

RESULTS

A total of 96 patients met inclusion criteria, averaging 56.1 ± 14.1 years of age and 86.1 ± 25.0 kg, with 37.5% being female. A mean prolongation in QTc interval of 30.4 ± 55.5 ms (p < 0.001) was observed during the propofol infusion, with 43.8% of cases exhibiting an on-infusion QTc2 of ⩾ 500 ms. Regression analyses suggested that prolongation in on-propofol QTc was independently associated with baseline QTc interval and amiodarone use, while weight as inversely associated with QTc2 (p < 0.05).

CONCLUSION

This historical cohort analysis of adult ICU patients receiving propofol suggests that on-infusion QTc prolongation was associated with increasing baseline QTc interval and with amiodarone use. Further research is needed to evaluate the clinical significance and cause-and-effect relationship between potential QTc changes and propofol use in the ICU.

Randomized, Controlled, Thorough QT/QTc Study Shows Absence of QT Prolongation with Luseogliflozin in Healthy Japanese Subjects

Luseogliflozin is a selective sodium glucose co-transporter 2 (SGLT2) inhibitor. To evaluate the cardiac safety of luseogliflozin, a thorough QT/QTc study was conducted in healthy Japanese subjects. The effects of moxifloxacin on QT prolongation in Japanese subjects were also evaluated. In this double-blind, placebo- and open-label positive-controlled, 4-way crossover study, 28 male and 28 female subjects received a single dose of luseogliflozin 5 mg (therapeutic dose), luseogliflozin 20 mg (supratherapeutic dose), placebo, and moxifloxacin 400 mg. Serial triplicate digital 12-lead electrocardiograms (ECGs) were recorded before and after dosing, and results were analyzed using the Fridericia correction (QTcF) method. Serial blood sampling was performed for pharmacokinetic analyses of luseogliflozin and moxifloxacin to analyze the relationship between QTcF interval and plasma concentration. The upper limits of the two-sided 90% confidence intervals (CIs) for baseline and placebo-adjusted QTcF intervals (ΔΔQTcF) in the 5 mg and 20 mg luseogliflozin groups were less than 10 ms at all time points. No correlation between plasma luseogliflozin concentrations and ΔΔQTcF was observed. In the moxifloxacin group, the lower limits of the two-sided 90% CIs for ΔΔQTcF were greater than 5 ms at all time points. A positive relationship was observed between plasma moxifloxacin concentration and change in ΔΔQTcF. Luseogliflozin was well tolerated at both dose levels. The majority of adverse events were mild in severity, and no serious or life-threatening adverse events occurred. Neither therapeutic (5 mg) nor supratherapeutic (20 mg) doses of luseogliflozin affected QT prolongation in healthy Japanese subjects.

Health Canada Warning on Citalopram and Escitalopram--Its Effects on Prescribing in Consultation-Liaison Psychiatry

BACKGROUND

Reports have suggested that citalopram and escitalopram may prolong the QTc interval, leading Health Canada to issue a warning to limit their dosages in 2012. Little is known about the effects of this warning and similar ones (e.g., by the Food and Drug Administration) on antidepressant prescribing in inpatients with acute medical illness, who are theoretically at high risk of QTc prolongation. The main objective of our study is to examine the effect of the Health Canada warning on citalopram/escitalopram prescribing patterns in the consultation-liaison (C-L) psychiatry setting.

METHODS

We performed a retrospective cohort study including 275 randomly selected inpatients with medical illness assessed by the psychiatric C-L team of a large Canadian academic hospital between 2008 and 2014. We grouped patients based on whether they were assessed by the C-L team before or after the citalopram Health Canada warning. Our primary outcome was change in citalopram/escitalopram prescribing patterns.

RESULTS

We found that of patients seen before the Health Canada warning, a significantly higher number were prescribed citalopram/escitalopram (44.1% vs. 22.3%, χ(2) = 14.835, p < 0.001), even after controlling for confounders. However, the percentage of patients using a citalopram/escitalopram dose exceeding those recommended by the Health Canada warning was similar in both groups (8.9% vs. 12.1%, χ(2) = 0.233, p = 0.63).

CONCLUSIONS

Overall, C-L psychiatrists were less likely to prescribe citalopram/escitalopram following the Health Canada warning, which did not translate into safer dosing. Clinicians should not avoid prescribing citalopram/escitalopram appropriately in medically vulnerable inpatients when benefits outweigh disadvantages.

Single Doses up to 800 mg of E-52862 Do Not Prolong the QTc Interval--A Retrospective Validation by Pharmacokinetic-Pharmacodynamic Modelling of Electrocardiography Data Utilising the Effects of a Meal on QTc to Demonstrate ECG Assay Sensitivity

Background

E-52862 is a Sigma-1 receptor antagonist (S1RA) currently under investigation as a potential analgesic medicine. We successfully applied a concentration-effect model retrospectively to a four-way crossover Phase I single ascending dose study and utilized the QTc shortening effects of a meal to demonstrate assay sensitivity by establishing the time course effects from baseline in all four periods, independently from any potential drug effects.

Methods

Thirty two healthy male and female subjects were included in four treatment periods to receive single ascending doses of 500 mg, 600 mg or 800 mg of E-52862 or placebo. PK was linear over the dose range investigated and doses up to 600 mg were well tolerated. The baseline electrocardiography (ECG) measurements on Day-1 were time-matched with ECG and pharmacokinetic (PK) samples on Day 1 (dosing day).

Results

In this conventional mean change to time-matched placebo analysis, the largest time-matched difference to placebo QTcI was 1.44 ms (90% CI: -4.04, 6.93 ms) for 500 mg; -0.39 ms (90% CI: -3.91, 3.13 ms) for 600 mg and 1.32 ms (90% CI: -1.89, 4.53 ms) for 800 mg of E-52862, thereby showing the absence of any QTc prolonging effect at the doses tested. In addition concentration-effect models, one based on the placebo corrected change from baseline and one for the change of QTcI from average baseline with time as fixed effect were fitted to the data confirming the results of the time course analysis.

Conclusion

The sensitivity of this study to detect small changes in the QTc interval was confirmed by demonstrating a shortening of QTcF of -8.1 (90% CI: -10.4, -5.9) one hour and -7.2 (90% CI: -9.4, -5.0) three hours after a standardised meal.

Trial Registration

EU Clinical Trials Register EudraCT 2010 020343 13

Evaluation of drug-induced QT interval prolongation in animal and human studies: a literature review of concordance

Evaluating whether a new medication prolongs QT intervals is a critical safety activity that is conducted in a sensitive animal model during non-clinical drug development. The importance of QT liability detection has been reinforced by non-clinical [International Conference on Harmonization (ICH) S7B] and clinical (ICH E14) regulatory guidance from the International Conference on Harmonization. A key challenge for the cardiovascular safety community is to understand how the finding from a non-clinical in vivo QT assay in animals predicts the outcomes of a clinical QT evaluation in humans. The Health and Environmental Sciences Institute Pro-Arrhythmia Working Group performed a literature search (1960–2011) to identify both human and non-rodent animal studies that assessed QT signal concordance between species and identified drugs that prolonged or did not prolong the QT interval. The main finding was the excellent agreement between QT results in humans and non-rodent animals. Ninety-one percent (21 of 23) of drugs that prolonged the QT interval in humans also did so in animals, and 88% (15 of 17) of drugs that did not prolong the QT interval in humans had no effect on animals. This suggests that QT interval data derived from relevant non-rodent models has a 90% chance of predicting QT findings in humans. Disagreement can occur, but in the limited cases of QT discordance we identified, there appeared to be plausible explanations for the underlying disconnect between the human and non-rodent animal QT outcomes.

Considerations for assessing the potential effects of antidiabetes drugs on cardiac ventricular repolarization: A report from the Cardiac Safety Research Consortium

Thorough QT studies conducted according to the International Council on Harmonisation E14 guideline are required for new nonantiarrhythmic drugs to assess the potential to prolong ventricular repolarization. Special considerations may be needed for conducting such studies with antidiabetes drugs as changes in blood glucose and other physiologic parameters affected by antidiabetes drugs may prolong the QT interval and thus confound QT/corrected QT assessments. This review discusses potential mechanisms for QT/corrected QT interval prolongation with antidiabetes drugs and offers practical considerations for assessing antidiabetes drugs in thorough QT studies. This article represents collaborative discussions among key stakeholders from academia, industry, and regulatory agencies participating in the Cardiac Safety Research Consortium. It does not represent regulatory policy.

QT Prolongation and Oncology Drug Development

Many pharmaceutical agents interact with cardiac ion channels resulting in abnormal ventricular repolarization and prolongation of the QT interval. In rare circumstances, this has resulted in the development of the potentially life-threatening arrhythmia, torsades de pointes. It is recognized, however, that accurate measurement of the QT interval is challenging, and it is a poor predictor for the development of this arrhythmia. Nevertheless, QT interval monitoring is an essential part of pharmaceutical development, and significant increases in the QT interval may prevent a drug from gaining approval.

Evaluation of opicapone on cardiac repolarization in a thorough QT/QTc study

Opicapone, a novel third-generation catechol-O-methyltransferase inhibitor for use as adjunctive therapy in levodopa-treated Parkinson's disease patients, was investigated on cardiac repolarization in healthy adult volunteers. This was a single-center, randomized, double-blind, placebo-controlled, open-label active-controlled, 4-period crossover study conducted in 64 subjects. In each period, subjects received a single oral dose of 50 mg opicapone, 800 mg opicapone, placebo, or 400 mg moxifloxacin and 24-hour 12-lead Holter monitoring was performed on day -1 (baseline) and after each single dose. After a single oral administrations of 50 and 800 mg opicapone, opicapone was the major entity in the circulation, with a median tmax of 1.5-2.0 hours. Opicapone was rapidly eliminated, with an elimination half-life of 1-2 hours. There was no clinically relevant effect of 50 and 800 mg opicapone versus placebo on cardiac depolarization or repolarization. All upper bounds of the 1-sided 95% confidence interval (CI) were below 10 milliseconds, confirming that opicapone has no QT-prolonging effect. Moxifloxacin caused an increase in the QTcI, with a lower bound of the 2-sided 95% CI always higher than 5 milliseconds, around the tmax of peak concentration, demonstrating assay sensitivity. In conclusion, administration of opicapone at therapeutic (50 mg) and supratherapeutic (800 mg) doses did not induce a clinically significant prolongation of the QTc interval.

Why are we prolonging QT interval monitoring?

BACKGROUND

At present, monitoring of the QT interval (QTI) is not a standard practice in the medical intensive care unit setting, where many drugs that prolong the QTI are administered. This literature review looked at the current research for evidence-based standards to support QTI monitoring of patients with risk factors for QTI prolongation, which can result in life-threatening arrhythmias such as torsade de pointes.

OBJECTIVE/AIM

The objective of this article is to establish the existence of evidence-based standards for monitoring of the QTI and to raise awareness in the nursing profession of the need for such monitoring among patients who are at high risk for prolonged QTI.

METHOD

To determine whether published standards for QTI monitoring exist, a search was conducted of the bibliographic databases CINAHL, EBSCOhost, Medline, PubMed, Google Scholar, and the Cochrane Library for the years 2013 and 2014. Also, a survey was conducted to determine whether practice standards for QTI monitoring are being implemented at 4 major hospitals in the Memphis area, including a level 1 trauma center.

RESULTS

The database search established the existence of published guidelines that support the need for QTI monitoring. Results of the hospital survey indicated that direct care nurses were not aware of the need to identify high-risk patients, drugs with the potential to prolong QTI that were being administered to their patients, or evidence-based standards for QTI monitoring.

DISCUSSION

Review of the research literature underscored the need for QTI monitoring among high-risk patients, that is, those with genetic conditions that predispose them to QTI prolongation, those with existing cardiac conditions being treated with antiarrhythmic medications, or those who are prescribed any new medication classified as high risk on the basis of clinical research. This need is especially crucial in intensive care unit settings, where many antiarrhythmic medications are administered.

Orally administered moxifloxacin prolongs QTc in healthy Chinese volunteers: a randomized, single-blind, crossover study

AIM

To investigate the QT/QTc effects of orally administered moxifloxacin in healthy Chinese volunteers.

METHODS

This was a single-blinded, randomized, single-dose, placebo-controlled, two-period cross-over study. A total of 24 healthy Chinese volunteers were enrolled, randomly assigned to two groups: one group received moxifloxacin (400 mg, po) followed by placebo with a 7-d interval, another group received placebo followed by moxifloxacin with a 7-d interval. On the days of dosing, 12-lead 24 h Holter ECGs were recorded and evaluated by an ECG laboratory blind to the treatments. Blood samples were collected to determine plasma concentrations of moxifloxacin.

RESULTS

The orally administered moxifloxacin significantly prolonged the mean QTc at all time points except 0.5 h post-dose. The largest time-matched difference in the QTcI was 8.35 ms (90% CI: 5.43, 11.27) at 4 h post-dose. The peak effect on QTcF was 9.35 ms (90% CI: 6.36, 12.34) at 3 h post-dose. A pharmacokinetic-QTc model suggested a 2.084 ms increase in the QTc interval for every 1000 ng/mL increase in plasma concentration of moxifloxacin. In addition, the orally administered moxifloxacin was well tolerated by the subjects.

CONCLUSION

Orally administered moxifloxacin significantly prolongs QTc, which supports its use as a positive control in ICH-E14 TQT studies in Chinese volunteers.

A thorough QT/QTc study of the effect of fasiglifam, a GPR40 agonist, on cardiac repolarization in healthy adults

This double-blind, randomized, placebo- and active-controlled, parallel group trial evaluated the potential for multiple-dose fasiglifam to prolong the QT/QTc interval in healthy adults. A total of 280 men and women aged 18-50 years were randomized to receive 14 days of fasiglifam 50 mg (n = 69), fasiglifam 400 mg (n = 70), or placebo (n = 70), or 13 days of placebo followed by single-dose moxifloxacin 400 mg (positive control; n = 71). The primary endpoint was the least square mean difference between fasiglifam and placebo in time-matched change from baseline to last dosing day in QT interval corrected using the Fridericia method (QTcF, calculated as QT/RR(0) (.333) ). For both fasiglifam doses, differences from placebo in QTcF were between -4.9 and 3.0 milliseconds at all postdose time points; maximum upper bounds of the one-sided 95% confidence interval for the difference were 5.7 milliseconds for fasiglifam 50 mg and 2.3 milliseconds for fasiglifam 400 mg, meeting predefined criteria for absence of prolongation. Alternate correction methods (Bazett and Individual) showed similar results. Fasiglifam was well tolerated; no subject withdrew due to an adverse event after receiving fasiglifam. In summary, multiple-dose fasiglifam did not affect cardiac repolarization at therapeutic and supratherapeutic doses and was well tolerated in healthy subjects.

Cardiac effects of sertindole and quetiapine: analysis of ECGs from a randomized double-blind study in patients with schizophrenia

The QT interval is the most widely used surrogate marker for predicting TdP; however, several alternative surrogate markers, such as Tpeak-Tend (TpTe) and a quantitative T-wave morphology combination score (MCS) have emerged. This study investigated the cardiac effects of sertindole and quetiapine using the QTc interval and newer surrogate markers. Data were derived from a 12 week randomized double-blind study comparing flexible dosage of sertindole 12-20mg and quetiapine 400-600mg in patients with schizophrenia. ECGs were recorded digitally at baseline and after 3, 6 and 12 weeks. Between group effects were compared by using a mixed effect model, whereas assessment within group was compared by using a paired t-test. Treatment with sertindole was associated with QTcF and QTcB interval prolongation and an increase in MCS, T-wave asymmetry, T-wave flatness and TpTe. The mean increase in QTcF from baseline to last observation was 12.1ms for sertindole (p<0.001) and -0.5ms for quetiapine (p=0.8). Quetiapine caused no increase in MCS, T-wave asymmetry, T-wave flatness or TpTe compared to baseline. In the categorical analysis, there were 11 patients (9.6%) receiving quetiapine who experienced more than 20ms QTcF prolongation compared with 36 patients (33.3%) in the sertindole group. Sertindole (12-20mg) was associated with moderate QTc prolongation and worsening of T-wave morphology in a study population of patients with schizophrenia. Although, quetiapine (400-600mg) did not show worsening of repolarization measures some individual patients did experience significant worsening of repolarization. Clinical Trials NCT00654706.

Clinical ECG Assessment

With the adoption of the ICH E14 guidance, the thorough QT/QTc (TQT) study has become the focus of clinical assessment of an NCE's effects on ECG parameters. The TQT study is used as a guide to the liability of a drug to cause proarrhythmias on the basis of delayed cardiac repolarization. Around 300 TQT studies have been performed since 2005 and through interactions between sponsors and regulators, especially FDA's Interdisciplinary Review Team (IRT) for QT studies. These studies can today be performed more effectively and with great confidence in the generated data. This chapter will discuss technical features and the design and analysis of TQT studies, how assay sensitivity is demonstrated, and examples from recently conducted studies. ECG assessment for drugs that cannot be safely given to healthy volunteers is also addressed, and examples from studies in cancer patients and in healthy volunteers with tyrosine kinase inhibitors are discussed. The TQT study is resource intensive and designed to solely evaluate whether an NCE prolongs the QTc interval. If data with similar confidence can be generated from other studies that are routinely performed as part of the clinical development, this would represent a more optimal use of human resources. Methods and approaches to increase the confidence in ECG data derived from "early QT assessment" in single-ascending/multiple-ascending dose studies are therefore discussed, and a path toward replacing the TQT study using these approaches will be outlined.

A Historical View and Vision into the Future of the Field of Safety Pharmacology

Professor Gerhard Zbinden recognized in the 1970s that the standards of the day for testing new candidate drugs in preclinical toxicity studies failed to identify acute pharmacodynamic adverse events that had the potential to harm participants in clinical trials. From his vision emerged the field of safety pharmacology, formally defined in the International Conference on Harmonization (ICH) S7A guidelines as "those studies that investigate the potential undesirable pharmacodynamic effects of a substance on physiological functions in relation to exposure in the therapeutic range and above." Initially, evaluations of small-molecule pharmacodynamic safety utilized efficacy models and were an ancillary responsibility of discovery scientists. However, over time, the relationship of these studies to overall safety was reflected by the regulatory agencies who, in directing the practice of safety pharmacology through guidance documents, prompted transition of responsibility to drug safety departments (e.g., toxicology). Events that have further shaped the field over the past 15 years include the ICH S7B guidance, evolution of molecular technologies leading to identification of new therapeutic targets with uncertain toxicities, introduction of data collection using more sophisticated and refined technologies, and utilization of transgenic animal models probing critical scientific questions regarding novel targets of toxicity. The collapse of the worldwide economy in the latter half of the first decade of the twenty-first century, continuing high rates of compound attrition during clinical development and post-approval and sharply increasing costs of drug development have led to significant strategy changes, contraction of the size of pharmaceutical organizations, and refocusing of therapeutic areas of investigation. With these changes has come movement away from dedicated internal safety pharmacology capability to utilization of capabilities within external contract research organizations. This movement has created the opportunity for the safety pharmacology discipline to come "full circle" and return to the drug discovery arena (target identification through clinical candidate selection) to contribute to the mitigation of the high rate of candidate drug failure through better compound selection decision making. Finally, the changing focus of science and losses in didactic training of scientists in whole animal physiology and pharmacology have revealed a serious gap in the future availability of qualified individuals to apply the principles of safety pharmacology in support of drug discovery and development. This is a significant deficiency that at present is only partially met with academic and professional society programs advancing a minimal level of training. In summary, with the exception that the future availability of suitably trained scientists is a critical need for the field that remains to be effectively addressed, the prospects for the future of safety pharmacology are hopeful and promising, and challenging for those individuals who want to assume this responsibility. What began in the early part of the new millennium as a relatively simple model of testing to assure the safety of Phase I clinical subjects and patients from acute deleterious effects on life-supporting organ systems has grown with experience and time to a science that mobilizes the principles of cellular and molecular biology and attempts to predict acute adverse events and those associated with long-term treatment. These challenges call for scientists with a broad range of in-depth scientific knowledge and an ability to adapt to a dynamic and forever changing industry. Identifying individuals who will serve today and training those who will serve in the future will fall to all of us who are committed to this important field of science.

Detection of QTc effects in small studies--implications for replacing the thorough QT study

BACKGROUND

ECG assessment with exposure response analysis applied to data from First-in-Man studies has been proposed to replace the thorough QT study for the detection of small QT effects.

METHODS

Data from five thorough QT studies, three with moxifloxacin, one study with a drug with a large QTc effect (∼25 ms) and one with ketoconazole with a smaller QT effect (∼8 ms) were used. By subsampling, studies with 6-18 subjects on drug and six on placebo were simulated 1000 times per sample size to assess whether small QTc effects using ICH E14 criteria could be excluded and the impact of sample size on the estimate and variability of the slope of the concentration/QTc relation.

RESULTS

With a sample size of nine or more on drug and six on placebo, the fraction of "false negative studies" was at or below 5% with data from the studies with moxifloxacin and from the drug with a large QTc effect. With the same sample size and no underlying QTc effect (placebo), the fraction of studies in which an effect above 10 ms could be excluded was above 85%. A treatment effect in the linear concentration-effect model resulted in a lower proportion of "false negatives." Sample size had little influence on the average slope estimate of the concentration/QTc relationship.

CONCLUSIONS

For drugs with a QTc effect of around 12-14 ms, exposure response analysis applied to First-in-Man studies with careful ECG assessment can be used to replace the through QT study.

A repeat-dose thorough QT study of inhaled fluticasone furoate/vilanterol combination in healthy subjects

AIMS

This study was designed as a thorough QT (TQT) study to evaluate the effects of fluticasone furoate (FF)/vilanterol (VI) in healthy subjects. Supportive data from a TQT study conducted with FF are also presented.

METHODS

This was a randomized, placebo- and positive-controlled, double-dummy, double-blind, four-way crossover study, in which healthy subjects (n = 85) were randomized to 7 days of once-daily treatment of FF/VI (200/25 or 800/100 μg) or placebo or single-dose oral moxifloxacin (single-blind, 400 mg). In the supportive TQT study, subjects (n = 40) were randomized to single-dose inhaled FF (4000 μg), oral moxifloxacin (400 mg) or placebo.

RESULTS

There was a lack of effect of FF/VI (200/25 μg) on QTcF (Fridericia's correction); all time-matched mean differences from baseline relative to placebo (0-24 h) were <5 ms, with upper 90% confidence intervals (CI) of <10 ms. At 800/100 μg, FF/VI had no significant clinical effect on QTcF except at 30 min postdose when the 90% CI was >10 ms [mean (90% CI), 9.6 ms (7.2, 12.0)]. No effect on QTci (individually corrected) was observed at either strength of FF/VI, with mean time-matched treatment differences <5 ms at all time points [upper 90% CIs <10 ms (0-24 h)]. Assay sensitivity was confirmed; moxifloxacin prolonged QTcF and QTci, with time-matched mean differences from baseline relative to placebo of >10 ms (1-8 h postdose).

CONCLUSIONS

Repeat once-daily dosing of FF/VI (200/25 μg), which is the highest therapeutic strength used in phase III studies, is not associated with QTc prolongation in healthy subjects. Supratherapeutic strength FF/VI (800/100 μg) demonstrated a small transient effect on QTcF but not on QTci.

Drug-induced QT interval prolongation: mechanisms and clinical management

The prolonged QT interval is both widely seen and associated with the potentially deadly rhythm, Torsades de Pointes (TdP). While it can occur spontaneously in the congenital form, there is a wide array of drugs that have been implicated in the prolongation of the QT interval. Some of these drugs have either been restricted or withdrawn from the market due to the increased incidence of fatal polymorphic ventricular tachycardia. The list of drugs that cause QT prolongation continues to grow, and an updated list of specific drugs that prolong the QT interval can be found at www.qtdrugs.org. This review focuses on the mechanism of drug-induced QT prolongation, risk factors for TdP, culprit drugs, prevention and monitoring of prolonged drug-induced QT prolongation and treatment strategies.

Electrocardiographic safety of cangrelor, a new intravenous antiplatelet agent: a randomized, double-blind, placebo- and moxifloxacin-controlled thorough QT study

Cangrelor is an intravenous P2Y12 inhibitor under investigation as an antiplatelet drug in the setting of acute coronary syndromes. To determine the electrophysiologic safety of parenteral cangrelor, cardiac repolarization effects were measured in 67 healthy volunteers (aged 18-45 years) in a randomized crossover design, including 4 treatment sequences of therapeutic cangrelor, supratherapeutic cangrelor, placebo, and moxifloxacin (positive control). Triplicate electrocardiogram measurements and pharmacokinetic samples were collected at baseline and 9 time points postdose on day 1. For both cangrelor and moxifloxacin, time-matched, placebo-adjusted change in QT from baseline was evaluated using an individual (QTcI) heart rate correction. After cangrelor dosing, change in QTcI was <5 ms at all times points and all corresponding upper 2-sided 90% confidence intervals (CIs) were <10 ms. Although moxifloxacin failed to show a lower CI >5 ms, expected time trends and lower CI >4.0 ms demonstrate assay sensitivity. QTcI was not affected by plasma concentrations of cangrelor metabolites, and cangrelor had no other adverse effects on electrocardiographic parameters. Clinically, cangrelor exposure was well tolerated. Thus, this thorough QT study demonstrated that therapeutic and supratherapeutic cangrelor doses do not adversely affect cardiac repolarization in normal volunteers (clinicaltrials.gov; identifier NCT00699504).

Quetiapine, QTc interval prolongation, and torsade de pointes: a review of case reports

Recently, both the manufacturer of quetiapine and the US Food and Drug Administration warned healthcare providers and patients about quetiapine-induced QTc interval prolongation and torsade de pointes (TdP) when using this drug within the approved labeling.  We reviewed the case-report literature and found 12 case reports of QTc interval prolongation in the setting of quetiapine administration. There were no cases of quetiapine-induced TdP or sudden cardiac death (SCD) among patients using quetiapine appropriately and free of additional risk factors for QTc interval prolongation and TdP. Among the 12 case reports risk factors included female sex (nine cases), coadministration of a drug associated with QTc interval prolongation (eight cases), hypokalemia or hypomagnesemia (six cases) quetiapine overdose (five cases), cardiac problems (four cases), and coadministration of cytochrome P450 3A4 inhibitors (two cases). There were four cases of TdP. As drug-induced TdP is a rare event, prospective studies to evaluate the risk factors associated with QTc prolongation and TdP are difficult to design, would be very costly, and would require very large samples to capture TdP rather than its surrogate markers. Furthermore, conventional statistical methods may not apply to studies of TdP, which is rare and an 'outlier' manifestation of QTc prolongation. We urge drug manufacturers and regulatory agencies to periodically publish full case reports of psychotropic drug-induced QTc interval prolongation, TdP, and SCD so that clinicians and investigators may better understand the clinical implications of prescribing such drugs as quetiapine.

Albiglutide Does Not Prolong QTc Interval in Healthy Subjects: A Thorough ECG Study

INTRODUCTION

Albiglutide, a selective once-weekly glucagon-like peptide-1 receptor agonist, is being developed for the treatment of type 2 diabetes mellitus. Albiglutide's effect on cardiac repolarization (QTc interval) was assessed in a randomized, double-blind, placebo-controlled, parallel-group study in healthy subjects with a nested crossover comparison for moxifloxacin.

METHODS

Subjects were randomized to albiglutide (n = 85) or placebo (n = 89) and received injections of 30 mg albiglutide or placebo on Days 1 and 8 and 50 mg albiglutide or placebo on Days 15, 22, 29, and 36. In the placebo group, moxifloxacin was administered on Day -1 in half the subjects and on Day 40 in the other half. Blood samples for albiglutide plasma concentration were drawn on Days 4 and 39 and serial ECGs were extracted from continuous recordings on Days -2 (baseline), -1, 4, 39, and 40.

RESULTS

Demographics were generally similar between albiglutide and placebo subjects: mean age was 29 years and BMI 25 kg/m(2). Mean change-from-baseline QTcI (∆QTcI, which was corrected for individual heart rate) on Day 4 after a single dose of albiglutide 30 mg and on Day 39 after repeat dosing with albiglutide 50 mg once weekly was similar to the placebo response. The placebo-corrected ΔQTcI (ΔΔQTcI) on both albiglutide doses was small with the largest ΔΔQTcI of 1.1 ms (upper bound of 90% CI 3.8 ms) on Day 4 and -0.6 ms (upper bound of CI 1.8 ms) on Day 39. Moxifloxacin caused the largest mean effect on ΔΔQTcI of 10.9 ms and the lower bound of the CI was above 5 ms at all preselected timepoints, thereby demonstrating assay sensitivity. Albiglutide was well tolerated and there were no clinically relevant differences in safety data between albiglutide and placebo.

CONCLUSION

Albiglutide at doses up to 50 mg in healthy subjects did not prolong the QTc interval.

Macitentan, a dual endothelin receptor antagonist for the treatment of pulmonary arterial hypertension, does not affect cardiac repolarization in healthy subjects

Macitentan is an orally active dual endothelin receptor antagonist, which demonstrated a reduction of the risk of morbidity/mortality events in pulmonary arterial hypertension patients. This double-blind, randomized, placebo- and positive-controlled, four-way crossover thorough QTc study was designed to investigate the effects of therapeutic and supratherapeutic doses of macitentan on cardiac repolarization in healthy male and female subjects. Each subject received the following treatments: moxifloxacin 400 mg, macitentan 10 mg, macitentan 30 mg, and placebo. Each treatment period lasted 9 days and was followed by at least 10 days of washout. The primary endpoint of this study was the baseline-adjusted, placebo-corrected QT interval corrected using the Fridericia method (ΔΔQTcF). Pharmacokinetic (PK), safety, and tolerability assessments were performed during each treatment. A total of 64 subjects were randomized. The upper bound of the 2-sided 90% confidence interval for ΔΔQTcF following macitentan was <10 ms at all time points and no correlation was observed between ΔΔQTcF and PK parameters. Findings in the analysis of the morphological patterns of the ECGs were randomly distributed across all treatments and did not indicate an association with macitentan. Macitentan was well tolerated in this study. Headache and nasopharyngitis were the most frequently reported adverse events. No effects on clinical laboratory and vital signs parameters were observed. In summary, repeated doses of macitentan 10 mg and 30 mg did not indicate any pro-arrhythmic potential.

Assessment of testing methods for drug-induced repolarization delay and arrhythmias in an iPS cell-derived cardiomyocyte sheet: multi-site validation study

A prospective comparison study across 3 independent research laboratories of a pure IKr blocker E-4031 was conducted by using the same batch of human iPS cell-derived cardiomyocytes in order to verify the utility and reliability of our original standard protocol. Field potential waveforms were recorded with a multi-electrode array system to measure the inter-spike interval and field potential duration. The effects of E-4031 at concentrations of 1 to 100 nM were sequentially examined every 10 min. In each facility, E-4031 significantly prolonged the field potential duration corrected by Fridericia's formula and caused early afterdepolarizations occasionally resulting in triggered activities, whereas it tended to decrease the rate of spontaneous contraction. These results were qualitatively and quantitatively consistent with previous non-clinical in vitro and in vivo studies as well as clinical reports. There were inter-facility differences in some absolute values of the results, which were not observed when the values were normalized as percentage change. Information described in this paper may serve as a guide when predicting the drug-induced repolarization delay and arrhythmias with this new technology of stem cells.

Randomized, placebo-controlled study to assess the impact on QT/QTc interval of supratherapeutic doses of ceftazidime-avibactam or ceftaroline fosamil-avibactam

Potential effects of supratherapeutic doses of intravenous (IV) ceftazidime-avibactam and ceftaroline fosamil-avibactam on cardiac repolarization were assessed in a thorough QT/QTc study. This was a double-blind, randomized, placebo-controlled, four-period crossover Phase I study (NCT01290900) in healthy males (n = 51). Subjects received, in randomized order and separated by ≥3 days washout: single doses of IV ceftaroline fosamil 1,500 mg with avibactam 2,000 mg; IV ceftazidime 3,000 mg with avibactam 2,000 mg; oral moxifloxacin 400 mg (open-label positive control); and IV placebo (saline). Least square mean and two-sided 90% confidence intervals (CI) for change from baseline in Fridericia-corrected QT interval (ΔQTcF) for active treatments versus placebo were estimated at 10 time points over 24 hours. The upper bound of the two-sided 90% CI for placebo-corrected ΔQTcF did not exceed 10 milliseconds at any time point over 24 hours for ceftaroline fosamil-avibactam or ceftazidime-avibactam. The lower bound of the two-sided 90% CI for the difference between moxifloxacin and placebo in ΔQTcF over 1-4 hours was >5 milliseconds, confirming assay sensitivity. Pharmacokinetics results confirmed achievement of supratherapeutic plasma concentrations. No safety concerns were raised. In conclusion, supratherapeutic doses of ceftaroline fosamil-avibactam or ceftazidime-avibactam were not associated with QT/QTc prolongation in this study population.

Lomitapide at supratherapeutic plasma levels does not prolong the Qtc interval--results from a TQT study with moxifloxacin and ketoconazole

BACKGROUND

The aim of this study was to assess the effect of high plasma levels of lomitapide and its main metabolite on ECG parameters.

METHODS

In this randomized five-way cross-over thorough QT study, 56 healthy subjects were enrolled. Study treatments were administered orally for 3 days in five separate periods in which subjects were dosed with (1) a single dose of 75 mg lomitapide on Day 1 followed by a single dose of 200 mg on Day 3; (2) ketoconazole 200 mg BID; (3) ketoconazole with a single dose of 75 mg lomitapide on Day 3; (4) a single dose of 400 mg moxifloxacin on Day 3 and (5) placebo.

RESULTS

Single doses of 75 and 200 mg lomitapide alone or in combination with ketoconazole caused minor changes in the change-from-baseline QTcI (ΔQTcI), whereas moxifloxacin and ketoconazole caused an increase of ΔQTcI with a peak effect at 1 and 3 hours postdosing, respectively. The largest mean placebo-corrected ΔQTcI (ΔΔQTcI) for lomitapide did not exceed 3 ms (upper bound of 90% CI: 4.7 ms) at any time points postdosing. Ketoconazole caused mild QT prolongation with mean ΔΔQTcI of 5.9 and 6.5 ms at 2 and 3 hours postdosing, and exposure-response analysis demonstrated a significantly positive slope of 1.3 ms per μg/mL (90% CI: 1.0-1.7). Moxifloxacin met the criteria for assay sensitivity.

CONCLUSIONS

Lomitapide does not have an effect on cardiac repolarization. The study's ability to detect small QTc changes was demonstrated with both moxifloxacin and ketoconazole.

Early QT assessment--how can our confidence in the data be improved?

Exposure-response (ER) analysis has emerged as an important tool to interpret QT data from thorough QT (TQT) studies and allows the prediction of effects in the targeted patient population. Recently, ER analysis has also been applied to data from early clinical pharmacology studies, such as single and multiple ascending dose studies, in which high plasma concentrations are often achieved. In line with this, there is an on-going discussion between sponsors, academicians and regulators on whether 'early QT assessment' can provide sufficiently high confidence in assessment of QT prolongation to replace the TQT study. In this article, we discuss how QT assessment can be applied to early clinical studies ('early QT assessment') and what we believe is needed to achieve the same high confidence in the data as we currently obtain from data from the TQT study. The power to exclude a QTc effect exceeding 10 ms in small sample sizes using ER analysis will be discussed and compared with time-matched analysis, as described in the ICH E14 guidance. Two examples of early QT assessment are shared; one negative and one positive, and the challenge in terms of demonstrating assay sensitivity in the absence of a pharmacological positive control will be discussed. Finally, we describe a recent research proposal, which may generate data to support the replacement of the TQT study with data from QT assessment in early phase 1 studies.

Azithromycin, cardiovascular risks, QTc interval prolongation, torsade de pointes, and regulatory issues: A narrative review based on the study of case reports

Over the past year, three articles have appeared in the New England Journal of Medicine describing conflicting findings about azithromycin and cardiac safety, particular azithromycin-induced QTc interval prolongation and torsade de pointes. The FDA wants healthcare providers to consider azithromycin-induced fatal cardiac arrhythmias for patients already at risk for cardiac death and other potentially arrhythmogenic cardiovascular conditions. In a systematic review of case reports we sought to determine factors that link to azithromycin-induced/associated QTc interval prolongation and torsade de pointes. We found 12 cases: seven female and five male. Of the nine adults with reported azithromycin doses, concurrent QTc interval measurement, and without congenital long QT syndrome, we found no significant relationship between dose and QTc interval duration. Additional risk factors were female sex, older age, heart disease, QTc interval prolonging drugs and metabolic inhibitors, hypokalemia, and bradycardia. All 12 subjects had at least two additional risk factors. Elderly women with heart disease appear to be at particularly risk for drug-related QTc interval prolongation and torsade de pointes.

Exenatide at therapeutic and supratherapeutic concentrations does not prolong the QTc interval in healthy subjects

Aims

Exenatide has been demonstrated to improve glycaemic control in patients with type 2 diabetes, with no effect on heart rate corrected QT (QT_c) at therapeutic concentrations. This randomized, placebo- and positive-controlled, crossover, thorough QT study evaluated the effects of therapeutic and supratherapeutic exenatide concentrations on QT_c.

Methods

Intravenous infusion was employed to achieve steady-state supratherapeutic concentrations in healthy subjects within a reasonable duration (i.e. days). Subjects received exenatide, placebo and moxifloxacin, with ECGs recorded pre-therapy and during treatment. Intravenous exenatide was expected to increase heart rate to a greater extent than subcutaneous twice daily or once weekly formulations. To assure proper heart rate correction, a wide range of baseline heart rates was assessed and prospectively defined methodology was applied to determine the optimal QT correction.

Results

Targeted steady-state plasma exenatide concentrations were exceeded (geometric mean ± SEM 253 ± 8.5 pg ml⁻¹, 399 ± 11.9 pg ml⁻¹ and 627 ± 21.2 pg ml⁻¹). QT_cP, a population-based method, was identified as the most appropriate heart rate correction and was prespecified for primary analysis. The upper bound of the two-sided 90% confidence interval for placebo-corrected, baseline-adjusted QT_cP (ΔΔQT_cP) was <10 ms at all time points and exenatide concentrations. The mean of three measures assessed at the highest steady-state plasma exenatide concentration of ∼500 pg ml⁻¹ (ΔΔQT_cP^avg) was −1.13 [−2.11, −0.15). No correlation was observed between ΔΔQT_cP and exenatide concentration. Assay sensitivity was confirmed with moxifloxacin.

Conclusions

These results demonstrated that exenatide, at supratherapeutic concentrations, does not prolong QT_c and provide an example of methodology for QT assessment of drugs with an inherent heart rate effect.

Daily dosing of vismodegib to steady state does not prolong the QTc interval in healthy volunteers

INTRODUCTION

Vismodegib was assessed as being of low risk for QT interval prolongation based on prior nonclinical and clinical experience. A dedicated study was conducted to further assess the potential for vismodegib to prolong the QTc interval.

METHODS AND RESULTS

Given the nonlinear pharmacokinetics of vismodegib, a thorough QTc study as is typically designed was not possible, and an innovative design was employed. This dedicated QTc study was powered to exclude a 20-millisecond change from the baseline QTc interval. The subjects were administered daily oral 150 mg of vismodegib for 7 days, or a single dose of 400 mg of moxifloxacin, with corresponding matching placebos. The upper limits of the 90% confidence intervals for the difference in ΔQTcF between vismodegib and placebo at steady state were <20 milliseconds at all timepoints with a maximum of 10 milliseconds at 12 hours postdose. Exposure-response analysis yielded an estimated slope equal to 0.11 ms/μM, which was not statistically significant. After a single dose of moxifloxacin was administered, the lower limits of the 90% confidence interval of the difference in ΔQTcF between moxifloxacin and placebo were >5 milliseconds from 1-12 hours postdose, thereby establishing assay sensitivity.

CONCLUSIONS

There was no effect of vismodegib on the QTc interval when dosed daily at 150 mg to steady state.

Gene-specific effect of beta-adrenergic blockade on corrected QT interval in the long QT syndrome

BACKGROUND

In the long QT syndrome (LQTS) the effects of beta-blocker treatment on prevention of cardiac events differs according to the genotype. We aimed to assess the effect of beta-blocker treatment on QT/QTc duration in Type 1 LQTS (LQT1) and Type 2 LQTS (LQT2) patients.

METHODS

24-hour digital Holter ECG were recorded before and after beta-blocking therapy initiation in LQT1 (n = 30) and LQT2 patients (n = 16). QT duration was measured on consecutive 1-minute averaged QRS-T complexes leading to up to 1440 edited QT-RR pairs for each recording. We computed subject- and treatment-specific log/log QT/RR relationships which were used to correct the QT intervals. The QT duration was also evaluated at predefined heart rates and after correction using Bazett and Fridericia coefficients.

RESULTS

At baseline, individual QT/RR coefficients were higher in LQT2 than in LQT1 patients (0.53 ± 0.10 vs. 0.40 ± 0.11, P < 0.001) and QT1000 was longer in LQT2 than in LQT1 patients (521 ± 38 vs. 481 ± 39 ms, P < 0.01). Beta-blockers significantly prolonged the mean RR interval (from 827 ± 161 to 939 ± 197 ms, P < 0.0001). The individual QT/RR coefficients were not significantly modified by beta-blockers. Beta-blocker treatment was associated with a prolongation of the QT1000 interval (from 481 ± 39 to 498 ± 43 ms, P < 0.01) in LQT1 patients but with a shortening in LQT2 patients (from 521 ± 38 to 503 ± 32 ms, P < 0.01).

CONCLUSIONS

The effect of beta-adrenergic blockade on QTc duration is different in LQT1 and LQT2 patients. Our data suggest that, in LQT1 patients, the well-known positive effect of beta-blockade might be associated with a prolongation of QTc duration. The mechanisms of beta-blockade protection may be different in LQT1 and in LQT2 patients.

Evaluation of an in silico cardiac safety assay: using ion channel screening data to predict QT interval changes in the rabbit ventricular wedge

INTRODUCTION

Drugs that prolong the QT interval on the electrocardiogram present a major safety concern for pharmaceutical companies and regulatory agencies. Despite a range of assays performed to assess compound effects on the QT interval, QT prolongation remains a major cause of attrition during compound development. In silico assays could alleviate such problems. In this study we evaluated an in silico method of predicting the results of a rabbit left-ventricular wedge assay.

METHODS

Concentration-effect data were acquired from either: the high-throughput IonWorks/FLIPR; the medium-throughput PatchXpress ion channel assays; or QSAR, a statistical IC50 value prediction model, for hERG, fast sodium, L-type calcium and KCNQ1/minK channels. Drug block of channels was incorporated into a mathematical differential equation model of rabbit ventricular myocyte electrophysiology through modification of the maximal conductance of each channel by a factor dependent on the IC50 value, Hill coefficient and concentration of each compound tested. Simulations were performed and agreement with experimental results, based upon input data from the different assays, was evaluated.

RESULTS

The assay was found to be 78% accurate, 72% sensitive and 81% specific when predicting QT prolongation (>10%) using PatchXpress assay data (77 compounds). Similar levels of predictivity were demonstrated using IonWorks/FLIPR data (121 compounds) with 78% accuracy, 73% sensitivity and 80% specificity. QT shortening (<-10%) was predicted with 77% accuracy, 33% sensitivity and 90% specificity using PatchXpress data and 71% accuracy, 42% sensitivity and 81% specificity using IonWorks/FLIPR data. Strong quantitative agreement between simulation and experimental results was also evident.

DISCUSSION

The in silico action potential assay demonstrates good predictive ability, and is suitable for very high-throughput use in early drug development. Adoption of such an assay into cardiovascular safety assessment, integrating ion channel data from routine screens to infer results of animal-based tests, could provide a cost- and time-effective cardiac safety screen.

Ions, equations and electrons: the evolving role of computer simulations in cardiac electrophysiology safety evaluations

Reliable preclinical cardiac safety evaluations of drug candidates are essential for selecting the best therapeutic agents. Advanced automated patch clamp technologies now allow for characterizing drug effects on multiple cardiac currents, enabling subsequent simulations of integrated electrophysiological responses on cellular, tissue and organ levels. In this issue, Mirams et al. summarize the strengths and limitations of models and simulations predicting drug-induced electrophysiological responses, emphasizing delayed repolarization and Torsades de Pointes pro-arrhythmia. The utility of computational approaches is contingent upon realistic models of ventricular electrophysiology, robust characterization of drug-channel interactions and an understanding of channel-myocyte interactions and pro-arrhythmic mechanisms. Simulations evaluating effects on repolarization (hazard identification) should aid in selecting safer drug candidates early in drug discovery, while simulations evaluating risk of Torsades de Pointes (incorporating known risk factors) should quantify pro-arrhythmic risk and reduce the need for costly clinical QT studies later in development. The wider adoption of realistic models and simulation studies will depend on simulation performance compared with 'gold standard' clinical findings.