Drug-induced prolongation of the QT interval: regulatory dilemmas and implications for approval and labelling of a new chemical entity

A pharmacogenomic investigation of the cardiac safety profile of ondansetron in children and pregnant women

BACKGROUND

Ondansetron is a highly effective antiemetic for the treatment of nausea and vomiting. However, this medication has also been associated with QT prolongation. Pharmacogenomic information on therapeutic response to ondansetron exists, but no investigation has been performed on genetic factors that influence the cardiac safety of this medication.

METHODS

Three patient groups receiving ondansetron were recruited and followed prospectively (pediatric post-surgical patients n = 101; pediatric oncology patients n = 98; pregnant women n = 62). Electrocardiograms were conducted at baseline, and 5- and 30-min post-ondansetron administration, to determine the effect of ondansetron treatment on QT interval. Pharmacogenomic associations were assessed via analyses of comprehensive CYP2D6 genotyping and genome-wide association study data.

RESULTS

In the entire cohort, 62 patients (24.1%) met the criteria for prolonged QT, with 1.2% of the cohort exhibiting unsafe QT prolongation. The most significant shift from baseline occurred at five minutes post-ondansetron administration (P = 9.8 × 10^-4). CYP2D6 activity score was not associated with prolonged QT. Genome-wide analyses identified novel associations with a missense variant in TLR3 (rs3775291; P = 2.00 × 10^-7) and a variant linked to the expression of SLC36A1 (rs34124313; P = 1.97 × 10^-7).

CONCLUSIONS

This study has provided insight into the genomic basis of ondansetron-induced cardiac changes and has emphasized the importance of genes that have been implicated in serotonin-related traits. These biologically-relevant findings represent the first step towards understanding this adverse event with the overall goal to improve the safety of this commonly used antiemetic medication.

An Introduction to Computational Modeling of Cardiac Electrophysiology and Arrhythmogenicity

Mathematical modeling is a powerful tool to study the complex and orchestrated biological process of cardiac electrical activity. By integrating experimental data from key components of cardiac electrophysiology, systems biology simulations can complement empirical findings, provide quantitative insight into physiological and pathophysiological mechanisms of action, and guide new hypotheses to better understand this complex biological system to develop novel cardiotherapeutic approaches. In this chapter, we briefly introduce in silico methods to describe the dynamics of physiological and pathophysiological single-cell and tissue-level cardiac electrophysiology. Using a "bottom-up" approach, we first describe the basis of ion channel mathematical models. Next, we discuss how the net flux of ions through such channels leads to changes in transmembrane voltage during cardiomyocyte action potentials. By applying these fundamentals, we describe how action potentials propagate in models of cardiac tissue. In addition, we provide case studies simulating single-cell and tissue-level arrhythmogenesis, as well as promising approaches to circumvent or overcome such adverse events. Overall, basic concepts and tools are discussed in this chapter as an accessible introduction to nonmathematicians to foster an understanding of electrophysiological modeling studies and help facilitate communication with dry lab colleagues and collaborators.

Pharmacogenetics of trazodone in healthy volunteers: association with pharmacokinetics, pharmacodynamics and safety

Aim: The aim was to evaluate the effect of polymorphisms in metabolizing enzymes and transporters on the pharmacokinetics, pharmacodynamics and adverse effects of trazodone in healthy volunteers. Materials & methods: 36 healthy volunteers receiving a single 100-mg oral dose of trazodone were genotyped for 11 variants in CYP3A4, CYP3A5, CYP2D6 and ABCB1 by real-time PCR. Plasma concentrations were measured using liquid chromatography-tandem mass spectrometry method. Results & conclusion: Sex affected the pharmacokinetics of trazodone with higher clearance in women. Polymorphisms in ABCB1, but not in CYP3A or CYP2D6, influenced trazodone pharmacokinetics. Trazodone decreased blood pressure and prolonged the corrected QT interval interval. CYP2D6 and ABCB1 polymorphisms were associated with the incidence of dizziness and prolonged corrected QT interval, respectively. Subjects with adverse drug reactions had lower concentrations of trazodone suggesting its metabolite (m-chlorophenylpiperazine) could be responsible for these effects.

Coupling Data Mining and Laboratory Experiments to Discover Drug Interactions Causing QT Prolongation

BACKGROUND

QT interval-prolonging drug-drug interactions (QT-DDIs) may increase the risk of life-threatening arrhythmia. Despite guidelines for testing from regulatory agencies, these interactions are usually discovered after drugs are marketed and may go undiscovered for years.

OBJECTIVES

Using a combination of adverse event reports, electronic health records (EHR), and laboratory experiments, the goal of this study was to develop a data-driven pipeline for discovering QT-DDIs.

METHODS

1.8 million adverse event reports were mined for signals indicating a QT-DDI. Using 1.6 million electrocardiogram results from 380,000 patients in our institutional EHR, these putative interactions were either refuted or corroborated. In the laboratory, we used patch-clamp electrophysiology to measure the human ether-à-go-go-related gene (hERG) channel block (the primary mechanism by which drugs prolong the QT interval) to evaluate our top candidate.

RESULTS

Both direct and indirect signals in the adverse event reports provided evidence that the combination of ceftriaxone (a cephalosporin antibiotic) and lansoprazole (a proton-pump inhibitor) will prolong the QT interval. In the EHR, we found that patients taking both ceftriaxone and lansoprazole had significantly longer QTc intervals (up to 12 ms in white men) and were 1.4 times more likely to have a QTc interval above 500 ms. In the laboratory, we found that, in combination and at clinically relevant concentrations, these drugs blocked the hERG channel. As a negative control, we evaluated the combination of lansoprazole and cefuroxime (another cephalosporin), which lacked evidence of an interaction in the adverse event reports. We found no significant effect of this pair in either the EHR or in the electrophysiology experiments. Class effect analyses suggested this interaction was specific to lansoprazole combined with ceftriaxone but not with other cephalosporins.

CONCLUSIONS

Coupling data mining and laboratory experiments is an efficient method for identifying QT-DDIs. Combination therapy of ceftriaxone and lansoprazole is associated with increased risk of acquired long QT syndrome.

Evaluation of the Relationship Between Pharmacokinetics and the Safety of Aripiprazole and Its Cardiovascular Effects in Healthy Volunteers

AIMS

The aim of this study was the evaluation of the possible relationship between pharmacokinetics and the safety of aripiprazole as well as its influence on blood pressure (BP), heart rate (HR), and corrected QT (QTc) interval.

METHODS

The study population comprised 157 healthy volunteers from 6 bioequivalence clinical trials. Subjects were administered a single 10-mg oral dose of each formulation separated by a 28-day washout period. Plasma concentrations were measured using high-performance liquid chromatography coupled to mass spectrometry. Blood pressure was measured at the following times: predose and 0.5, 2, 4, 6, and 8 hours postdose. An electrocardiogram was recorded at predose, 4, and 8 hours postdose.

RESULTS

Area under the curve (AUC), maximum plasma concentration, half-life, and distribution volume corrected for weight were higher in women. Aripiprazole treatment produced a decrease of BP (9.3 mm Hg on systolic and 6.2 mm Hg on diastolic pressure) and an increase in HR (12.1 beats per minute) and QTc interval (9.1 milliseconds). There were sex differences in BP, HR, and QTc interval. Women and subjects with higher AUC and maximum plasma concentration values were more prone to experience adverse drug reactions and gastrointestinal adverse reactions. The AUC was related with systolic BP and diastolic BP decrease and HR increase but there was no relationship between aripiprazole concentrations and QTc increase.

CONCLUSIONS

Aripiprazole decreases BP and increases HR and QTc interval. Pharmacokinetics, pharmacodynamics, and safety of aripiprazole are affected by sex. There is a directly proportional relationship between pharmacokinetic parameters and adverse drug reactions and effect on BP and HR.

The role of concentration-effect relationships in the assessment of QTc interval prolongation

Population pharmacokinetic and pharmacokinetic-pharmacodynamic (PKPD) modelling has been widely used in clinical research. Yet, its application in the evaluation of cardiovascular safety remains limited, particularly in the evaluation of pro-arrhythmic effects. Here we discuss the advantages of disadvantages of population PKPD modelling and simulation, a paradigm built around the knowledge of the concentration-effect relationship as the basis for decision making in drug development and its utility as a guide to drug safety. A wide-ranging review of the literature was performed on the experimental protocols currently used to characterize the potential for QT interval prolongation, both pre-clinically and clinically. Focus was given to the role of modelling and simulation for design optimization and subsequent analysis and interpretation of the data, discriminating drug from system specific properties. Cardiovascular safety remains one of the major sources of attrition in drug development with stringent regulatory requirements. However, despite the myriad of tests, data are not integrated systematically to ensure accurate translation of the observed drug effects in clinically relevant conditions. The thorough QT study addresses a critical regulatory question but does not necessarily reflect knowledge of the underlying pharmacology and has limitations in its ability to address fundamental clinical questions. It is also prone to issues of multiplicity. Population approaches offer a paradigm for the evaluation of drug safety built around the knowledge of the concentration-effect relationship. It enables quantitative assessment of the probability of QTc interval prolongation in patients, providing better guidance to regulatory labelling and understanding of benefit/risk in specific populations.

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.

The anti-addiction drug ibogaine and the heart: a delicate relation

The plant indole alkaloid ibogaine has shown promising anti-addictive properties in animal studies. Ibogaine is also anti-addictive in humans as the drug alleviates drug craving and impedes relapse of drug use. Although not licensed as therapeutic drug and despite safety concerns, ibogaine is currently used as an anti-addiction medication in alternative medicine in dozens of clinics worldwide. In recent years, alarming reports of life-threatening complications and sudden death cases, temporally associated with the administration of ibogaine, have been accumulating. These adverse reactions were hypothesised to be associated with ibogaine’s propensity to induce cardiac arrhythmias. The aim of this review is to recapitulate the current knowledge about ibogaine’s effects on the heart and the cardiovascular system, and to assess the cardiac risks associated with the use of this drug in anti- addiction therapy. The actions of 18-methoxycoronaridine (18-MC), a less toxic ibogaine congener with anti-addictive properties, are also considered.

Randomized, blinded, placebo- and positive-controlled crossover study to determine the effect of multiple doses of apixaban on the QTc interval

Apixaban is an oral, direct factor Xa inhibitor indicated for the prevention and treatment of thromboembolic disease. This randomized, blinded, 4-way crossover study investigated the potential effect of apixaban on the QTc interval. Forty healthy subjects (39 completers) each received 3 days of the following treatments: blinded apixaban 10 mg once daily (QD), 50 mg QD (supratherapeutic), matched apixaban placebo QD, and a single dose of open-label moxifloxacin 400 mg on Day 3, preceded by 2 days of placebo QD. Triplicate electrocardiograms obtained over 24 hours on Days -1 (baseline) and 3 were read by a blinded third party. The mean placebo-adjusted, time-matched, Fridericia-corrected change from baseline QTc (ΔΔQTcF) for apixaban and moxifloxacin was estimated at each time point. The maximum ΔΔQTcF was 1.51 milliseconds (one-sided upper 95% confidence interval [CI] 3.71 milliseconds) after apixaban 50 mg QD, 1.36 milliseconds (one-sided upper 95%CI 3.54 milliseconds) after apixaban 10 mg QD, and 10.21 milliseconds (lower 95%CI 8.07 milliseconds) after moxifloxacin. Concentration-response analysis suggested no evidence of a positive relationship between apixaban concentration and ΔQTcF. Apixaban doses up to 50 mg QD for 3 days were well tolerated and did not prolong the QTc interval in healthy subjects.

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.

Evaluation of Assay Sensitivity and the Concentration-Effect Relationship of Moxifloxacin in a QT/QTc Study in Japan

To investigate the potential for a QT/QTc study in Japan, a randomized, single-blind, crossover study was conducted using moxifloxacin in 64 healthy Japanese male volunteers. A 12-lead Holter electrocardiogram was used to test a relatively small population at each of 4 incorporated clinical research units to confirm the assay sensitivity and efficiency. Moxifloxacin (400 mg) significantly prolonged QT intervals, as previously reported, with small variations in this study. In addition, the placebo-adjusted mean QTcF changes from predose baseline showed that the lower bounds of the 1-sided 95% confidence interval exceeded 5 milliseconds at all of the clinical research units. The data also indicated statistically significant concentration-QT relationships in 3 of the 4 research units by separate analysis. These findings and the small amount of variability in this study suggest the feasibility of conducting a high-quality QT/QTc study in Japan.

Efeitos cardiotóxicos resultantes da interação da risperidona com diuréticos tiazídicos

Antipsicóticos atípicos têm sua ação em doses que podem produzir efeitos colaterais importantes. A risperidona é o antipsicótico atípico de nova geração mais utilizado na atualidade e seu uso está associado a tratamento de esquizofrenia, transtornos psicóticos, episódios de mania e nos distúrbios de comportamento, entre outros. Os efeitos adversos mais importantes estão relacionados ao sistema nervoso central e autônomo, sistema endócrino e sistema cardiovascular. Neste último, pode haver efeitos inotrópicos negativos e alterações no eletrocardiograma, como prolongamento do intervalo QT, podendo causar taquicardia e arritmias. Relatamos um caso de um homem de 48 anos com história de delírio persecutório após ser ameaçado no trabalho, que estava sendo tratado com risperidona e paroxetina. Por não haver melhora, suas doses foram aumentadas e o paciente apresentou alargamento do intervalo QTc, com diminuição da amplitude da onda T e aumento da onda U, e hipocalemia. Além disso, o paciente era hipertenso e estava em uso de hidroclorotiazida. A risperidona tem o potencial de bloquear o componente rápido do canal cardíaco de potássio e isso prolonga o processo de repolarização dos ventrículos, podendo causar torsade de pointes, morte súbita e arritmias. Já a hidroclorotiazida causa hipocalemia, provocando alterações na contração e relaxamento do miocárdio. Houve interação medicamentosa grave entre duas drogas com potencial arritmogênico, o que levou às alterações no eletrocardiograma e produziu sintomas danosos ao paciente. A troca do antipsicótico atípico para um típico e da hidroclorotiazida por um diurético que não causa hipocalemia trouxe melhoras ao paciente.

Not-in-trial simulation I: Bridging cardiovascular risk from clinical trials to real-life conditions

AIMS

The assessment of heart rate-corrected QT (QTc) interval prolongation relies on the evidence of drug effects in healthy subjects. This study demonstrates the relevance of pharmacokinetic-pharmacodynamic (PKPD) relationships to characterize drug-induced QTc interval prolongation and explore the discrepancies between clinical trials and real-life conditions.

METHODS

d,l-Sotalol data from healthy subjects and from the Rotterdam Study cohort were used to assess treatment response in a phase I setting and in a real-life conditions, respectively. Using modelling and simulation, drug effects at therapeutic doses were predicted in both populations.

RESULTS

Inclusion criteria were shown to restrict the representativeness of the trial population in comparison to real-life conditions. A significant part of the typical patient population was excluded from trials due to weight and baseline QTc interval criteria. Relative risk was significantly different between sotalol users with and without heart failure, hypertension, diabetes and myocardial infarction (P < 0.01). Although drug effects do cause an increase in the relative risk of QTc interval prolongation, the presence of diabetes represented an increase from 4.0 [95% confidence interval (CI) 2.7-5.8] to 6.5 (95% CI 1.6-27.1), whilst for myocardial infarction it increased from 3.4 (95% CI 2.3-5.13) to 15.5 (95% CI 4.9-49.3).

CONCLUSIONS

Our findings show that drug effects on QTc interval do not explain the observed QTc values in the population. The prevalence of high QTc values in the real-life population can be assigned to co-morbidities and concomitant medications. These findings substantiate the need to account for these factors when evaluating the cardiovascular risk of medicinal products.

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).

Drug induced QT prolongation: the measurement and assessment of the QT interval in clinical practice

There has been an increasing focus on drug induced QT prolongation including research on drug development and QT prolongation, following the removal of drugs due to torsades de pointes (TdP). Although this has improved our understanding of drug-induced QT prolongation there has been much less research aimed at helping clinicians assess risk in individual patients with drug induced QT prolongation. This review will focus on assessment of drug-induced QT prolongation in clinical practice using a simple risk assessment approach. Accurate measurement of the QT interval is best done manually, and not using the measurement of standard ECG machines. Correction for heart rate (HR) using correction formulae such as Bazett's is often inaccurate. These formulae underestimate and overestimate the duration of cardiac repolarization at low and high heart rates, respectively. Numerous cut-offs have been suggested as an indicator of an abnormal QT, but are problematic in clinical practice. An alternative approach is the QT nomogram which is a plot of QT vs. HR. The nomogram has an 'at risk' line and QT-HR pairs above this line have been shown in a systematic study to be associated with TdP and the line is more sensitive and specific than Bazett's QTc of 440 ms or 500 ms. Plotting the QT-HR pair for patients on drugs suspected or known to cause QT prolongation allows assessment of the QT interval based on normal population QT variability. This risk assessment then allows the safer commencement of drugs therapeutically or management of drug induced effects in overdose.

Drug-induced QT interval prolongation: does ethnicity of the thorough QT study population matter?

Inter-ethnic differences in drug responses have been well documented. Drug-induced QT interval prolongation is a major safety concern and therefore, regulatory authorities recommend a clinical thorough QT study (TQT) to investigate new drugs for their QT-prolonging potential. A positive study, determined by breach of a preset regulatory threshold, significantly influences late phase clinical trials by requiring intense ECG monitoring. A few studies that are currently available, although not statistically conclusive at present, question the assumption that ethnicity of the study population may not influence the outcome of a TQT study. Collective consideration of available pharmacogenetic and clinical information suggests that there may be inter-ethnic differences in QT-prolonging effects of drugs and that Caucasians may be more sensitive than other populations. The information also suggest s that (a) these differences may depend on the QT-prolonging potency of the drug and (b) exposure-response (E-R) analysis may be more sensitive than simple changes in QT(c) interval in unmasking this difference. If the QT response in Caucasians is generally found to be more intense than in non-Caucasians, there may be significant regulatory implications for domestic acceptance of data from a TQT study conducted in foreign populations. However, each drug will warrant an individual consideration when extrapolating the results of a TQT study from one ethnic population to another and the ultimate clinical relevance of any difference. Further adequately designed and powered studies, investigating the pharmacologic properties and E-R relationships of additional drugs with different potencies, are needed in Caucasians, Oriental/Asian and African populations before firm conclusions can be drawn.

Frequency of electrocardiogram testing among HIV-infected patients at risk for medication-induced QTc prolongation

OBJECTIVES

HIV-infected patients are commonly prescribed several medications and are thus at risk for drug interactions that may result in QTc prolongation. We sought (1) to identify the frequency of electrocardiogram (ECG) monitoring (2), to determine the prevalence of drug interactions involving QTc-prolonging medications, and (3) to quantify the prevalence of QTc prolongation.

METHODS

A cross-sectional study was conducted among HIV-infected adults. Demographics, medications, drug interactions and comorbidities were abstracted from patients' medical records. Abnormal QTc interval was defined per the UK Committee for Proprietary Medicinal Products. Clinical characteristics were compared among ECG recipients and nonrecipients. Among ECG recipients, the prevalence and predictors of QTc prolongation were assessed.

RESULTS

Among the 454 patients included in the study, 80.8% were prescribed a medication associated with QTc prolongation and 39% had drug interactions expected to increase QTc prolongation risk. There were 138 patients (30.3%) who received ECG testing. Receipt of ECG monitoring was associated with increasing age, diabetes, increasing total number of medications and gastroesophageal reflux disease. Among ECG recipients, the prevalence of abnormal QTc interval was 27.5%. Chronic kidney disease [prevalence ratio (PR) 3.47; 95% confidence interval (CI) 1.37-8.83; P = 0.009], hepatitis C virus coinfection (PR 2.26; 95% CI 0.97-5.27; P = 0.06) and hypertension (PR 2.11; 95% CI 0.93-4.81; P = 0.07) were independently associated with an abnormal QTc interval.

CONCLUSIONS

A low frequency of ECG testing was observed, despite a high use of medications associated with QTc prolongation. The risk of abnormal QTc interval was highest among patients with chronic kidney disease, hypertension and hepatitis C virus coinfection.

Assessing the probability of drug-induced QTc-interval prolongation during clinical drug development

Early in the course of clinical development of new non-antiarrhythmic drugs, it is important to assess the propensity of these drugs to prolong the QT/QTc-interval. The current regulatory guidelines suggest using the largest time-matched mean difference between drug and placebo (baseline-adjusted) groups over the sampling interval, thereby neglecting any potential exposure-effect relationship and nonlinearity in the underlying physiological fluctuation in QT values. Thus far, most of the attempted models for characterizing drug-induced QTc-interval prolongation have disregarded the possibility of model parameterization in terms of drug-specific and system-specific properties. Using a database consisting of three compounds with known dromotropic activity, we built a bayesian hierarchical pharmacodynamic (PD) model to describe QT interval, encompassing an individual correction factor for heart rate, an oscillatory component describing the circadian variation, and a truncated maximum-effect model to account for drug effect. The explicit description of the exposure-effect relationship, incorporating various sources of variability, offers advantages over the standard regulatory approach.

Thorough QT study of the effects of vildagliptin, a dipeptidyl peptidase IV inhibitor, on cardiac repolarization and conduction in healthy volunteers

OBJECTIVE

This randomized, double-blind study evaluated the effects of vildagliptin, a dipeptidyl peptidase IV inhibitor for treating type 2 diabetes, on cardiac repolarization and conduction.

METHODS

Healthy volunteers (n = 101) were randomized (1:1:1:1 ratio) to vildagliptin 100 or 400 mg, moxifloxacin 400 mg (active control), or placebo once daily for 5 days. Electrocardiograms were recorded at baseline and day 5 for 24 hours post-dose. Placebo-adjusted mean change from baseline in QT interval, heart-rate-corrected QT intervals by Fridericia's (QTcF) or Bazett's (QTcB) formula, and PR and QRS intervals were compared at each time-point (time-matched analysis) and for values averaged across the dosing period (time-averaged analysis).

RESULTS

For time-matched analysis, mean changes in QTcF with vildagliptin were below predefined limits for QTc prolongation (mean increase <5 ms; upper 90% confidence interval [CI] < 10 ms), except for vildagliptin 100 mg at 1 and 8 hours post-dose (upper 90% CI > 10 ms). With moxifloxacin, significant QTcF prolongation occurred at most time-points, demonstrating assay sensitivity. No vildagliptin- or placebo-treated volunteer had QTcF > 450 ms. Incidences of QTcF increases ≥30 ms with vildagliptin (100 and 400 mg) and placebo were similar (4-8%) and were much lower than with moxifloxacin (39%). No QTcF increase ≥60 ms was observed with vildagliptin or placebo (versus one with moxifloxacin). Time-averaged, time-matched, and categorical analyses of QT/QTcF/QTcB showed similar results. Drug exposure analysis showed no correlation between vildagliptin plasma levels and QTc changes. Vildagliptin had no effect on PR or QRS intervals. Although this study, completed before publication of current ICH E14 guidelines, was underpowered for time-matched analysis, the results are consistent with lack of effect of vildagliptin on QTc.

CONCLUSION

Vildagliptin did not prolong QT interval or affect cardiac conduction at the highest daily therapeutic dose or a fourfold higher dose.

Effects on prolongation of Bazett's corrected QT interval of seven second-generation antipsychotics in the treatment of schizophrenia: a meta-analysis

The use of second-generation antipsychotics (SGAs) for the treatment of schizophrenia has surged worldwide. Amisulpride, aripiprazole, olanzapine, quetiapine, risperidone, sertindole and ziprasidone have now been commonly prescribed. Their effects on QT interval differ but evidence remains sparse and mostly inconclusive. Since prolongation of heart-rate corrected QT interval has been implicated as an useful surrogate marker to predict drug-related cardiac mortality and pro-arrhythmic potentials, it is timely and necessary to compare the effects of Bazett's corrected QT interval (QT(Bc)) prolongation for the commonly prescribed SGAs. A meta-analysis was conducted according to suggestions by the Quality of Reporting of Meta-analysis group with literature identified using various databases and augmented with hand-searching to assess the magnitude and risk on QT(Bc) prolongation by these seven SGAs for treatments in adult subjects with schizophrenia. Because of incomplete QT(Bc) data reporting, quetiapine could not be assessed by the meta-analytical approach in this study. Aripiprazole was the only SGA associated with both statistically significant lower risk and mean change in QT(Bc), with sertindole giving a statistically significant worsening effect on mean QT(Bc). Other analyses did not demonstrate any statistically significant pooled effects for the studied SGAs, neither on the magnitude over mean or mean change, nor the risk on QT(Bc) prolongation.

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

The ICH E14 guidance on how to clinically assess a new drug's liability to prolong the QT interval was adopted in May 2005. A centre-piece of the guidance was the establishment of one single trial, the 'thorough QT/QTc study', intended to confidently identify drugs that may cause QT prolongation. Initially perceived as a great challenge, this study has rapidly become a standard component of all clinical development programs for new molecular entities. The study is normally conducted in healthy volunteers, includes both a positive and a negative (placebo) control and is stringently powered to exclude an effect on the QTc interval exceeding 10 ms. The E14 guidance was intentionally not very prescriptive and allowed sponsors and service providers to explore new methodologies. This has allowed for a rapid development of new methods during the first years after the guidance's implementation, such as computer-assisted algorithms for QT measurements. Regulators have worked in close collaboration with pharmaceutical industry to set standards for the design and conduct of the 'thorough QT/QTc study', which therefore has evolved as a key component of cardiac safety assessment of new drugs. This paper summarizes the requirements on the 'thorough QT/QTc study' with emphasis on the standard that has evolved based on interactions between regulators and sponsors and the experience from a large number of completed studies.

Moving towards better predictors of drug-induced torsades de pointes

Drug-induced torsades de pointes (TdP) remains a significant public health concern that has challenged scientists who have the responsibility of advancing new medicines through development to the patient, while assuring public safety. As a result, from the point of discovering a new molecule to the time of its registration, significant efforts are made to recognize potential liabilities, including the potential for TdP. With this background, the ILSI (HESI) Proarrhythmia Models Project Committee recognized that there was little practical understanding of the relationship between drug effects on cardiac ventricular repolarization and the rare clinical event of TdP. A workshop was therefore convened at which four topics were considered including: Molecular and Cellular Biology Underlying TdP, Dynamics of Periodicity, Models of TdP Proarrhythmia and Key Considerations for Demonstrating Utility of Pre-Clinical Models. The series of publications in this special edition has established the background, areas of debate and those that deserve scientific pursuit. This is intented to encourage the research community to contribute to these important areas of investigation in advancing the science and our understanding of drug-induced proarrhythmia.

Randomized, double-blind, crossover study to investigate the effect of rivaroxaban on QT-interval prolongation

BACKGROUND

Rivaroxaban (BAY 59-7939) is a novel, oral, direct Factor Xa inhibitor in advanced clinical development for the prevention and treatment of thromboembolic disorders. Unwanted pro-arrhythmic effects are a common reason for drugs failing to gain regulatory approval; these properties can be detected by assessing the effect of the drug on the QT interval.

OBJECTIVE

This study was performed, in accordance with International Conference on Harmonisation (ICH) E14 guidance, to assess whether rivaroxaban prolongs the QT interval.

STUDY DESIGN

This was a prospective, randomized, double-blind, double-dummy, four-way crossover study.

SETTING

The study was conducted at a clinical pharmacology research unit.

SUBJECTS

Healthy male and female subjects (n = 54) aged > or =50 years were enrolled and remained in the study unit for 3 days for each treatment. Of these, 50 patients were eligible for the QT analysis.

INTERVENTION

Subjects received single oral doses of rivaroxaban 45 mg or 15 mg, moxifloxacin 400 mg (positive control), or placebo.

OUTCOME MEASURES

Multiple ECGs were taken at frequent intervals after drug administration, and the QT interval was measured manually under blinded conditions at a central laboratory. The Fridericia correction formula (QTcF) was used to correct the QT interval for heart rate. The primary outcome was the effect of rivaroxaban or moxifloxacin on the placebo-subtracted QTcF 3 hours after administration. The frequency of outlying QTcF values and the tolerability of the treatments were also assessed.

RESULTS

All treatments were well tolerated and had no effect on heart rate. Moxifloxacin established the required assay sensitivity; placebo-subtracted QTcF 3 hours after moxifloxacin administration was prolonged by 9.77 ms (95% CI 7.39, 12.15). Placebo-subtracted QTcF values 3 hours after rivaroxaban administration were -0.91 ms (95% CI -3.33, 1.52) and -1.83 ms (95% CI -4.19, 0.54) with rivaroxaban 45 mg and 15 mg, respectively. QTcF was not prolonged with rivaroxaban at any time, and the frequency of outlying results with rivaroxaban and placebo was similar.

CONCLUSION

This thorough QT study, which was performed in accordance with ICH E14 guidelines, shows that rivaroxaban does not prolong the QTc interval. Therefore, the potential of rivaroxaban for the prevention and treatment of thromboembolic disorders, including chronic cardiovascular disorders, can be investigated in appropriate clinical studies without the need for intensive monitoring of the QTc interval.

Current assessment of risk-benefit by regulators: is it time to introduce decision analyses?

Regulatory risk-benefit assessments may overweight small but serious risks relative to benefits. Using terfenadine and torsade de pointes as an exemplar, we illustrate how a different decision may result when outcomes are assessed using quality-adjusted life-years within a decision-analytical framework. The adoption of common measures of health outcome and the use of decision analyses, which will allow uncertainty to be characterized and evidence to be compiled from disparate sources, may inform complex risk-benefit decisions and should be used in conjunction with qualitative assessments.

The Food and Drug Administration Office of Women's Health: Impact of Science on Regulatory Policy

In 1994, the Food and Drug Administration Office of Women's Health (FDA-OWH) was created to provide leadership and policy direction for the Agency regarding issues of women's health. Within its first year, the FDA-OWH established a science program for women's health research, promoting the development of sound policy and regulation. In a little over a decade, the program has provided approximately 14 million dollars to fund more than 100 women's health research studies covering a broad range of health topics affecting women across their lifespan. Some studies, such as those elucidating drug effects on QT prolongation in women and drug-dietary supplement interaction, have had significant influence on regulatory decisions. Other studies have provided sound scientific data on sex and gender differences supporting FDA guidelines to protect women's health. This paper describes the science program at the FDA-OWH, providing examples of how funded research impacts regulatory policy.

Clinical evaluation of QT/QTc prolongation and proarrhythmic potential for nonantiarrhythmic drugs: the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use E14 guideline

Proarrhythmias due to drug-induced QT prolongation are the second most common cause for drug withdrawal and have caused increasing concern. Two new International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) guidelines were recently endorsed in which nonclinical (S7B) and clinical (E14) methodologies are discussed and guidance is given to the industry. This commentary describes the key components of the E14 document, the impact of nonclinical testing on the clinical program, the thorough QT study, and the impact of its result on late-stage development. The studies described in S7B and E14 will contribute to a better understanding of the link between nonclinical assays and QT prolongation in humans. Differences in interpretation among individual regulators in the major regions with respect to measures proposed in the E14 guideline might impact regional regulatory decisions. These differences include the value of nonclinical assays for the subsequent clinical testing and how predictive a negative thorough QT study result is for proarrhythmic risk in patients.

Man versus machine: is there an optimal method for QT measurements in thorough QT studies?

Electrocardiographic (ECG) recordings from 3 placebo-controlled thorough QT healthy volunteer studies were used to compare QT intervals obtained by manual measurement with those generated by ECG machines. The effect of the positive control was compared to placebo at each time point for data obtained from both sources. Both manual and automated techniques consistently demonstrated statistically significant prolongation of QTcF with the positive controls. The proportion of outlier values was small for both methods. The pairwise comparison between manual and automated uncorrected QT intervals demonstrated clear differences, with intervals derived from one machine on average 16 to 19 milliseconds shorter and from the other 7 milliseconds longer than the manually measured QT intervals, but these differences disappeared when analyzing QT change from baseline. Both manual and automated, commercially available QT algorithms demonstrated small statistically significant effects on the QTc interval induced by positive controls.

Tolérance cardiaque de la moxifloxacine: expérience clinique issue d'une large étude observationnelle française en pratique médicale usuelle (étude IMMEDIAT)

BACKGROUND

Moxifloxacin (Izilox) is prescribed for bacterial respiratory tract infections. ECG analysis done in clinical trials showed a mean QT prolongation at 6 ms that could lead to Torsades de Pointe. However, Izilox was well tolerated during clinical trials. To confirm the correct safety profile of Izilox in a large sample of patients, a French PMS study - MMEDIAT - was carried out in usual medical practice.

METHODS

This prospective observational uncontrolled and monitored study was conducted in 13,578 patients with respiratory tract infection and treated with moxifloxacin 400 mg daily (duration: 5 to 10 days in accordance to the Market Authorization). Any clinical event being potentially a surrogate of a ventricular rhythm disorder ("critical event") were collected and analyzed by a Scientific Committee in charge to determine the potential cardiac origin of the reported event and to establish a causal relationship with the treatment.

RESULTS

Among 13,578 patients, 1046 adverse events (678 patients [5%]) were reported, including 854 drug related events (564 patients [4.15%]). Of these 1046 adverse events, 95 (62 patients [0.46%]) were serious. A total of 189 critical adverse events (159 patients [1.2%]) were reviewed by the Scientific Committee. After analysis, 34 adverse events (28 patients [0.21%]) were assessed from potential cardiac origin. Of these 34 adverse events, 25 (19 patients [0.14%]) were assessed as drug-related: palpitations [13 patients], tachycardia [4 patients], malaise [4 patients], vertigo [3 patients] and pallor [1 patient]. All adverse events were transient and had favourable outcome.

CONCLUSION

This PMS study confirmed that Izilox is well-tolerated in usual medical practice, in adequation with the safety data obtained in clinical trials.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Drug-induced q-T prolongation

Drug therapy may induce Q-T prolongation by alteration of potassium ion currents in cardiac cells, resulting in abnormal repolarization. Q-T prolongation, whether congenital or acquired, has been associated with the development of the malignant dysrhythmia Torsade de Pointes (TdP), which may result in sudden death. Re-cent regulatory actions and drug withdrawals due to Q-T prolongation or TdP have focused attention on this issue. Although our understanding of the pathophysiology continues to evolve, both patient and medication factors contribute to the individual risk of drug-induced Q-T prolongation or TdP. The clinician should be aware of these issues when prescribing new drugs and should weigh the risks and benefits carefully when prescribing drugs known to prolong the Q-T interval.

Investigation of the effects of physiological and vasodilation-induced autonomic activation on the QTc Interval in healthy male subjects

AIMS

Drug-induced prolongation of the QTc interval is an important marker for potential proarrhythmic action. Prolongation of the QTc interval results from alteration of the ionic currents that regulate cardiac repolarisation. Such effects may result from direct drug action or alternatively they could also occur indirectly by drug-induced modulation of autonomic tone, which is known to regulate cardiac repolarization. This study examined the effects of physiological and drug-induced autonomic activation on heart rate, QT and QTc intervals.

METHODS

We studied 29 healthy male subjects aged 18-30 years. Electrocardiographs were recorded before and during autonomic activation induced by mental activation, standing, exercise and glyceryl trinitrate (GTN) (0.5 mg sublingual)-induced vasodilation in the presence and absence of beta-blockade (atenolol 100 mg daily for 4 days). QT intervals were measured manually by electronic callipers and corrected using the Fridericia formula.

RESULTS

Heart rates were significantly increased during mental arithmetic, standing, exercise and GTN and this effect was significantly attenuated by atenolol, except for mental activation. QTc intervals were significantly reduced on standing and exercise and this was significantly attenuated by atenolol during exercise. In contrast, GTN increased QTc intervals (Delta = 5.7 ms, confidence interval +/- 3.2 ms, P < 0.005) and this was not attenuated by atenolol.

CONCLUSIONS

Alteration in QTc intervals may result from physiological manoeuvres and vasodilation, interventions known to induce autonomic activation. We suggest that QTc prolongation due to GTN is indirectly mediated and unlikely to carry any proarrhythmic effect. Understanding whether drug-induced QTc prolongation is directly or indirectly mediated may be important to determine any potential proarrhythmic risk.

Development of a surgical approach for telemetering guinea pigs as a model for screening QT interval effects

INTRODUCTION

Identifying a compound's risk of potentially producing Torsade de Pointes (TdP)/QT interval prolongation has become a goal early within the drug development process. Our aim was to develop a surgical approach for instrumenting guinea pigs for collecting ECG data.

METHODS

Male Dunkin Hartley guinea pigs (386-661 g) were surgically implanted with telemetry transducers for the measurement of lead II ECG and arterial blood pressure. Using strict aseptic techniques and isofluorane anaesthesia (0.5-5.0%), one of the three implantation procedures was used. In Phase I the animals were either implanted intraperitoneally (abdominal aorta cannulated) or subcutaneously (carotid artery cannulated). In Phase II all animals were implanted subcutaneously and the subcutaneous pocket formed either with a single incision, as in Phase I, or a double incision.

RESULTS

Phase I-During intraperitoneal implantation, rupture of the aorta occurred in 50% of the animals. The remaining animals were terminated between 2 and 14 days postsurgery on human grounds. All of the animals implanted subcutaneously survived the surgical procedure and the following 28 days. Skin thinning over the implant occurred in 25% of the animals in weeks 5-6. Phase II-Following single incision subcutaneous implantation 72% of the animals were terminated within the 28-day postsurgery due to skin rupture over the implant body, with only 22% of the animals viable after 28 days. Following double incision subcutaneous implantation 86% of animals were viable after 28 days and thus the recommended method for implantation.

DISCUSSION

The improvements to the surgical approach have improved survival rates and increased the potential for robust, long term use of telemetered guinea pig colonies for screening for QT prolonging potential and additional cardiovascular assessment in vivo.

Preclinical strategies to assess QT liability and torsadogenic potential of new drugs: The role of experimental models

The recognition of QT prolongation and torsade de pointes (TdP) in humans has resulted in the re-labeling of some drugs and the removal of others from the market in the past decade. Recent regulatory guidelines have recommended a battery of preclinical tests to assess a new drug for the QT liability in humans. The assessment includes the effect of a drug on: 1) the ionic current in stable cell lines expressing hERG channel; 2) action potential duration (APD) measured in isolated ventricular tissues; 3) the QTc interval and TdP in animals in vivo; and 4) APD, the QT interval, transmural dispersion of repolarization (TDR) and TdP potential in the isolated arterially-perfused ventricular wedge preparation. Because a noncardiac drug with an incidence of TdP even less than 0.1% can be potentially removed from the market, the experimental models used for preclinical testing have to be high sensitive and specific to the signals related to TdP. Among available experimental models, the rabbit left ventricle wedge preparation exhibits a high sensitivity and a high specificity in the identification of compounds positive and negative for QT prolongation and TdP. This is attributed to the fact that the preparation demonstrates strong signals related to QT prolongation in response to even a weaker QT prolonging agent. Signals specifically pertinent to the development of TdP, ie, early afterdepolarization (EAD) and an increase in TDR can be detected as well. The preclinical data obtained from the wedge preparation correlate well with clinical outcomes.

Pharmacogenetic aspects of drug-induced torsade de pointes: potential tool for improving clinical drug development and prescribing

Drug-induced torsade de pointes (TdP) has proved to be a significant iatro-genic cause of morbidity and mortality and a major reason for the withdrawal of a number of drugs from the market in recent times. Enzymes that metabolise many of these drugs and the potassium channels that are responsible for cardiac repolarisation display genetic polymorphisms. Anecdotal reports have suggested that in many cases of drug-induced TdP, there may be a concealed genetic defect of either these enzymes or the potassium channels, giving rise to either high plasma drug concentrations or diminished cardiac repolarisation reserve, respectively. The presence of either of these genetic defects may predispose a patient to TdP, a potentially fatal adverse reaction, even at therapeutic dosages of QT-prolonging drugs and in the absence of other risk factors. Advances in pharmacogenetics of drug metabolising enzymes and pharmacological targets, together with the prospects of rapid and inexpensive genotyping procedures, promise to individualise and improve the benefit/risk ratio of therapy with drugs that have the potential to cause TdP. The qualitative and the quantitative contributions of these genetic defects in clinical cases of TdP are unclear because not all of the patients with TdP are routinely genotyped and some relevant genetic mutations still remain to be discovered. There are regulatory guidelines that recommend strategies aimed at uncovering the risk of TdP associated with new chemical entities during their development. There are also a number of guidelines that recommend integrating pharmacogenetics in this process. This paper proposes a strategy for integrating pharmacogenetics into drug development programmes to optimise association studies correlating genetic traits and endpoints of clinical interest, namely failure of efficacy or development of repolarisation abnormalities. Until pharmacogenetics is carefully integrated into all phases of development of QT-prolonging drugs and large-scale studies are undertaken during their post-marketing use to determine the genetic components involved in induction of TdP, routine genotyping of patients remains unrealistic. Even without this pharmacogenetic data, the clinical risk of TdP can already be greatly minimised. Clinically, a substantial proportion of cases of TdP are due to the use of either high or usual dosages of drugs with potential to cause TdP in the presence of factors that inhibit drug metabolism. Therefore, choosing the lowest effective dose and identifying patients with these non-genetic risk factors are important means of minimising the risk of TdP. In view of the common secondary pharmacology shared by these drugs, a standard set of contraindications and warnings have evolved over the last decade. These include factors responsible for pharmacokinetic or pharmacodynamic drug interactions. Among the latter, the more important ones are bradycardia, electrolyte imbalance, cardiac disease and co-administration of two or more QT-prolonging drugs. In principle, if large scale prospective studies can demonstrate a substantial genetic component, pharmacogenetically driven prescribing ought to reduce the risk further. However, any potential benefits of pharmacogenetics will be squandered without any reduction in the clinical risk of TdP if physicians do not follow prescribing and monitoring recommendations.

Evaluation of vardenafil and sildenafil on cardiac repolarization

This novel study evaluated the effects of vardenafil and sildenafil on QT and corrected QT (QTc) duration using a model that minimizes experimental error to obtain the most accurate assessment of observed QTc effects. A placebo-controlled and positive-controlled, period-balanced, double-blinded, 6-way crossover study evaluated therapeutic and supratherapeutic oral doses of vardenafil (10 and 80 mg, respectively) and sildenafil (50 and 400 mg, respectively), therapeutic doses of moxifloxacin (400 mg), and a placebo in 58 healthy men (mean age 53 years), with dosing every 3 days. Six replicate, 12-lead, digital electrocardiograms (ECGs) were recorded at 3 time points before and 5 time points after dosing to cover the time course of maximum exposure to study drugs and their metabolites. An independent laboratory blindly analyzed approximately 17,000 ECGs. For the placebo, mean change in QTcF (Fridericia) duration 1 hour after dose (approximate Tmax of vardenafil and sildenafil) was 0 ms (+/-0.7 SD). QT/QTc variability was small across regimens, indicating statistically powerful results. Moxifloxacin demonstrated an expected 8-ms mean change and was the only drug to prolong absolute QT. Placebo-corrected mean changes in QTcF duration (90% confidence interval) at 1 hour after dose were 8 ms (range 6 to 9) for vardenafil 10 mg and 6 ms (range 5 to 8) for sildenafil 50 mg. QTci (linear and nonlinear per patient) yielded similar trends: 4 ms (range 3 to 6) for vardenafil 10 mg and 4 ms (range 2 to 5) for sildenafil 50 mg. Dose response demonstrated very shallow QTc relations for study drugs. Therapeutic and supratherapeutic doses produced only small increases in the QTcF interval, which were considered to be clinically irrelevant. This well-controlled, statistically powerful study in middle-aged men demonstrated that vardenafil and sildenafil produced no increase of absolute QT and only similar, small increases of the QTc interval, with a shallow dose-response curve. The study design and conduct may serve as a guide for future QT assessment of new drugs.