Current concepts in the mechanisms and management of drug-induced QT prolongation and torsade de pointes

Incorporating receptor theory in mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) modeling

Pharmacokinetic-Pharmacodynamic (PK-PD) modeling helps to better understand drug efficacy and safety and has, therefore, become a powerful tool in the learning-confirming cycles of drug-development. In translational drug research, mechanism-based PK-PD modeling has been recognized as a tool for bringing forward early insights in drug efficacy and safety into the clinical development. These models differ from descriptive PK-PD models in that they quantitatively characterize specific processes in the causal chain between drug administration and effect. This includes target site distribution, binding and activation, pharmacodynamic interactions, transduction and homeostatic feedback mechanisms. Compared to descriptive models mechanism-based PK-PD models that utilize receptor theory concepts for characterization of target binding and target activation processes have improved properties for extrapolation and prediction. In this respect, receptor theory constitutes the basis for 1) prediction of in vivo drug concentration-effect relationships and 2) characterization of target association-dissociation kinetics as determinants of hysteresis in the time course of the drug effect. This approach intrinsically distinguishes drug- and system specific parameters explicitly, allowing accurate extrapolation from in vitro to in vivo and across species. This review provides an overview of recent developments in incorporating receptor theory in PK-PD modeling with a specific focus on the identifiability of these models.

Cardiovascular complications of cancer therapy: incidence, pathogenesis, diagnosis, and management

Cancer treatment today employs a combination of chemotherapy, radiotherapy, and surgery to prolong life and provide cure. However, many of these treatments can cause cardiovascular complications such as heart failure, myocardial ischemia/infarction, hypertension, thromboembolism, and arrhythmias. In this article we review the incidence of cardiotoxicity caused by commonly used chemotherapeutic agents as well as discuss the pathogenesis, diagnosis, management, and prevention of these cardiovascular side effects. Cardiotoxicity related to anticancer treatment is important to recognize as it may have a significant impact on the overall prognosis and survival of cancer patients, and it is likely to remain a significant challenge for both cardiologists and oncologists in the future due to an increasing aging population of patients with cancer and the introduction of many new cancer therapies.

A case of catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a familial cardiac arrhythmia that is related to RYR2 or CASQ2 gene mutation. It occurs in patients with structurally normal heart and causes exercise-emotion-triggered syncope and sudden cardiac death. We experienced a case of CPVT in an 11 year-old female patient who was admitted for sudden cardiovascular collapse. The initial electrocardiogram (ECG) on emergency department revealed ventricular fibrillation. After multiple defibrillations, sinus rhythm was restored. However, recurrent ventricular fibrillation occurred during insertion of nasogastric tube without sedation in coronary care unit. On ECG monitoring, bidirectional ventricular tachycardia occurred with sinus tachycardia and then degenerated into ventricular fibrillation. To our knowledge, there has been no previous case report of CPVT triggered by sinus tachycardia in Korea. Therefore, we report the case as well as a review of the literature.

Assessing proarrhythmic potential of drugs when optimal studies are infeasible

Assessing the potential for a new drug to cause life-threatening arrhythmias is now an integral component of premarketing safety assessment. International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use Guideline (ICH) E14 recommends the "Thorough QT Study" (TQT) to assess clinical QT risk. Such a study calls for careful evaluation of drug effects on the electrocardiographic QT interval at multiples of therapeutic exposure and with a positive control to confirm assay sensitivity. Yet for some drugs and diseases, elements of the TQT Study may be impractical or unethical. In these instances, alternative approaches to QT risk assessment must be considered. This article presents points to consider for evaluation of QT risk when alternative approaches are needed.

Comparison of QTinno, a fully automated electrocardiographic analysis program, to semiautomated electrocardiographic analysis methods in a drug safety study in healthy subjects

BACKGROUND

Improved automated methods for electrocardiographic (ECG) analysis are needed, particularly for drug development purposes.

OBJECTIVES

This study compared a novel fully automated method for ECG analysis (QTinno; NewCardio, Santa Clara, CA) to 2 semiautomated digital methods: global measurement from the earliest QRS onset to the latest T-wave offset on representative superimposed beats (global) and tangent measurement on 3 consecutive beats in one lead (tangent).

METHODS

All 3 methods were used to determine uncorrected and rate-corrected QT interval duration (QT and QTcF) and related metrics in 1422 digital 12-lead ECGs from a phase 1 drug study. Global and tangent annotations were manually adjusted by the same 3 cardiologists wherever necessary. No adjustments were made in QTinno determinations.

RESULTS

QTinno returned QTcF change from time-matched baseline (DeltaQTcF) that differed minimally from both global and tangent methods (mean pairwise difference: 0.1 millisecond between QTinno and global, 1.1 milliseconds between QTinno and tangent). The average absolute QT and QTcF intervals by QTinno were approximately 5 milliseconds longer than global and 25 milliseconds longer than by tangent. QTinno had lower intrinsic variability for DeltaQTcF than either global or tangent (between-subject SD: QTinno 4.0 milliseconds, global 5.6 milliseconds, tangent 6.4 milliseconds; within-subject SD: QTinno 4.8 milliseconds, global 7.4 milliseconds, tangent 10.6 milliseconds). All methods were robust in detecting the largest placebo-adjusted mean time-matched DeltaQTcF (15-25 milliseconds) induced by study drug.

CONCLUSIONS

The methods show good agreement for drug-induced QTc prolongation. Lower intrinsic variability of DeltaQTcF by QTinno could facilitate smaller sample sizes or increase study power in thorough QTc studies.

Risiken von Antipsychotika im Alter, speziell bei Demenzen 1Prof. Dr. Hans Gutzmann zum 60. Geburtstag gewidmet

Antipsychotika werden häufig zur Behandlung von herausforderndem Verhalten bei Demenz eingesetzt. Antipsychotika der zweiten Generation («atypische Neuroleptika») spielen dabei mittlerweile eine größere Rolle als die älteren Substanzen. Der nur mäßigen Wirksamkeit stehen schwerwiegende Risiken gegenüber: so ist unter allen Antipsychotika die Mortalität insgesamt erhöht, aber auch das Risiko für plötzlichen Herztod, Schlaganfallereignisse oder venöse Thrombosen. Die Unterschiede zwischen Antipsychotika der ersten und der zweiten Generation sind dabei gering: hochpotente Antipsychotika der ersten Generation führen häufiger zu extrapyramidalmotorischen Symptomen, unter Antipsychotika der zweiten Generation ist das allgemeine Mortalitätsrisiko wahrscheinlich etwas geringer, andererseits wahrscheinlich venöse Thrombosen und metabolische Nebenwirkungen häufiger. Für die übrigen Nebenwirkungen bestehen keine gesicherten Unterschiede. Angesichts der großen Heterogenität der Antipsychotika erscheint der Nutzen einer pauschalen Aufteilung in Antipsychotika der ersten und zweiten Generation fragwürdig. Für die Auswahl einer Substanz sind substanzspezifische Nebenwirkungen, Dosierung, Aufdosierungsgeschwindigkeit sowie Beachtung von Komorbidität, Kontraindikationen und Arzneimittelinteraktionen in Relation zum individuellen Patienten erheblich wichtiger als die Wahl nach bloßer pauschaler Zuordnung zu einer dieser beiden Gruppen. Am wichtigsten ist aber, dass Antipsychotika nur bei klarer Indikation zur Anwendung kommen!

Druggable targets for sudden cardiac death prevention: lessons from the past and strategies for the future

Sudden cardiac death (SCD) is most commonly caused by ventricular fibrillation (VF). The single largest cohort of victims is the population with little or no prior overt heart disease. Effective prevention will require long-term prophylaxis by drugs in large numbers of people identified by risk factors. This means that safe as well as effective drugs are required. Drugs with overt effects on cardiac electrophysiology have failed in the clinic owing to poor effectiveness and/or adverse effects. This article examines possible new drug targets. We have focused on acute myocardial ischaemia as it is the most strikingly proarrhythmic pathology, and the most common cause of coronary artery disease-related VF and SCD according to inferences from epidemiology, drug trials and decades of animal research. To set the scene we have briefly explored drugs that have failed in the clinic in order to identify possible targets that have been overlooked or underexploited. We conclude that the best strategy is identification of pathology-specific targets that render drugs active only where and when their action is required.

Prevalence of long QTc interval in methadone maintenance patients

BACKGROUND

There is a concern about cardiac rhythm disorders related to QTc interval prolongation induced by methadone. A cross-sectional study was designed to evaluate the prevalence of long QTc (LQTc) interval in patients in methadone maintenance treatment (MMT) and risk factors for LQTc.

METHODS

The study population included 109 subjects (74 males, median age 43 years). Socio-demographic and toxicological variables were recorded, as well as concomitant use of drugs related with QT prolongation, history of heart diseases, and corrected QT interval by heart rate (QTc) in the ECG. Plasma concentrations of (R)-methadone and (S)-methadone enantiomers were determined in 69 subjects.

RESULTS

Ten patients (9.2%) presented a QTc above 440 ms but a QTc above 500 ms was observed in only 2 (1.8%). Patients with QTc above 440 ms compared with the remaining subjects were older (median [25th-75th percentile range]: 49 [39-56] years vs. 37 [33-43]; Wilcoxon's W=217.5, p=0.002) and took a higher daily dose of methadone (median [25th-75th percentile range]: 120 [66-228] mg/day vs. 60 [40-110] mg/day; W=298.5, p=0.037). Methadone dose correlated with QTc interval (Pearson's r(2)=0.291, p=0.002). Patients with and without long QTc showed no differences in plasma concentrations of (R)-methadone and (S)-methadone enantiomers.

CONCLUSIONS

The prevalence of LQTc was 9.2%. An association between LQTc and methadone doses was observed but the relationship with plasma concentrations of methadone enantiomers is unclear.

Terlipressin-induced ventricular arrhythmia

During intravenous treatment with terlipressin for recurrent gastrointestinal (GI) bleeding, a 50-year-old male with no history of heart disease developed a newly prolonged QT interval and torsade de pointes. Risk factors present for acquired long QT syndrome were mineral dysbalance and a history of alcohol abuse with hepatic impairment. The patient was brought back to a normal sinus rhythm after a single 300-J counter-shock. Terlipressin was discontinued, and the patient's QTc interval subsequently returned to baseline. During 6 weeks of monitoring, arrhythmia did not recur.

Pharmacogenomics of anesthetic drugs in transgenic LQT1 and LQT2 rabbits reveal genotype-specific differential effects on cardiac repolarization

Anesthetic agents prolong cardiac repolarization by blocking ion currents. However, the clinical relevance of this blockade in subjects with reduced repolarization reserve is unknown. We have generated transgenic long QT syndromes type 1 (LQT1) and type 2 (LQT2) rabbits that lack slow delayed rectifier K+ currents (IKs) or rapidly activating K+ currents (IKr) and used them as a model system to detect the channel-blocking properties of anesthetic agents. Therefore, LQT1, LQT2, and littermate control (LMC) rabbits were administered isoflurane, thiopental, midazolam, propofol, or ketamine, and surface ECGs were analyzed. Genotype-specific heart rate correction formulas were used to determine the expected QT interval at a given heart rate. The QT index (QTi) was calculated as percentage of the observed QT/expected QT. Isoflurane, a drug that blocks IKs) prolonged the QTi only in LQT2 and LMC but not in LQT1 rabbits. Midazolam, which blocks inward rectifier K+ current (IK1), prolonged the QTi in both LQT1 and LQT2 but not in LMC. Thiopental, which blocks both IKs and IK1, increased the QTi in LQT2 and LMC more than in LQT1. By contrast, ketamine, which does not block IKr, IKs, or IK1, did not alter the QTi in any group. Finally, anesthesia with isoflurane or propofol resulted in lethal polymorphic ventricular tachycardia (pVT) in three out of nine LQT2 rabbits. Transgenic LQT1 and LQT2 rabbits could serve as an in vivo model in which to examine the pharmacogenomics of drug-induced QT prolongation of anesthetic agents and their proarrhythmic potential. Transgenic LQT2 rabbits developed pVT under isoflurane and propofol, underlining the proarrhythmic risk of IKs blockers in subjects with reduced IKr.

Short-coupled variant of torsade de pointes

A 36-year-old man with a history of primary sclerosing cholangitis and epilepsy was admitted to our hospital for cholangitis. During admission he was resuscitated because of ventricular fibrillation. ECGs showed multiple ventricular premature beats (VPBs) with a short coupling interval (240 ms), resulting in frequent torsade de pointes (TdP). In total, the patient had to be defibrillated 12 times. Short-coupled TdP is a rare variant of polymorphic ventricular tachycardia, with unknown aetiology. Verapamil seems to be the only drug able to suppress the arrhythmia. Verapamil, however, does not lower the risk of sudden death; therefore, an ICD implantation is advised. (Neth Heart J 2008;16:246-9.).

Etravirine has no effect on QT and corrected QT interval in HIV-negative volunteers

BACKGROUND

Etravirine (TMC125), a next-generation nonnucleoside reverse transcriptase inhibitor, has shown antiviral efficacy in 2 large Phase 3 trials. In vitro and in vivo studies have shown that etravirine is not associated with proarrhythmic potential. Electrocardiograms (ECGs) from healthy and HIV 1-infected volunteers showed no clinically relevant changes.

OBJECTIVE

To evaluate the effect of 2 etravirine dosing regimens on QT/corrected QT interval (QTc) in HIV-negative volunteers and assess pharmacokinetic and additional safety parameters.

METHODS

A double-blind, double-dummy, randomized, placebo- and active-controlled, 4-period crossover trial was conducted in 41 HIV-negative volunteers. Participants received 4 regimens: etravirine 200 mg twice daily, etravirine 400 mg once daily, moxifloxacin 400 mg once daily (positive control), and placebo in separate 8-day sessions, with each followed by a washout period of 14 or more days. On days -1, 1, and 8 of each session, ECGs were recorded at 11 time points over 12 hours. Pharmacokinetic profiles of etravirine regimens were evaluated and safety was assessed.

RESULTS

Thirty-seven subjects completed the study. For etravirine, the upper limit of the 90% CIs of mean time-matched differences in QTc determined using Fridericia's formula (QTcF) was below 10 msec at all time points, the threshold for prolonged QT as defined by regulatory guidelines. The maximum mean (90% CI) difference of time-matched changes in QTcF versus placebo on day 1 was +0.1 msec (-2.6 to 2.9), -0.2 msec (-2.6 to 2.1), and +10.1 msec (7.3 to 12.8) for etravirine 200 mg twice daily, etravirine 400 mg once daily, and moxifloxacin, respectively. On day 8, these values were +0.6 msec (-2.1 to 3.3), -1.0 msec (-4.4 to 2.5), and +10.3 msec (6.8 to 13.9), respectively. Etravirine produced no clinically significant changes in other ECG parameters. No significant differences between males and females were observed. Both etravirine regimens had similar pharmacokinetic exposure and safety profiles.

CONCLUSIONS

Etravirine does not prolong the QTc interval. No clinically relevant ECG changes were observed in HIV-negative volunteers. Short-term dosing of etravirine in HIV-negative volunteers was generally safe and well tolerated.

Importance of vagally mediated bradycardia for the induction of torsade de pointes in an in vivo model

BACKGROUND AND PURPOSE

Bradycardia is a risk factor for the development of torsade de pointes (TdP). The aim of this work was to compare the importance of changes in heart rate and arterial blood pressure in the development of drug-induced TdP and to investigate the role of vagal influences.

EXPERIMENTAL APPROACH

Experiments were performed in open-chest, pentobarbital-anaesthetized, male rabbits which were given clofilium (20, 60 and 200 nmol kg(-1) min(-1)) with rising doses of either phenylephrine (75, 150, 225 and 300 nmol kg(-1) min(-1)), angiotensin II (0.25, 0.5, 0.75 and 1 nmol kg(-1) min(-1)) or saline. A fourth group received phenylephrine and cloflium after bilateral vagotomy. ECGs, haemodynamics and epicardial monophasic action potentials were recorded.

KEY RESULTS

TdP occurred in 57% of rabbits given phenylephrine and clofilium. Replacement of phenylephrine with saline or angiotensin II reduced the incidence of TdP to 0 and 17%, respectively. Vagotomy prevented TdP in rabbits given phenylephrine and clofilium. Increases in blood pressure induced by phenylephrine and angiotensin II were similar. Bradycardia only occurred with phenylephrine and was reduced but not abolished by vagotomy. Neither short-term variability of repolarization nor action potential triangulation could predict TdP.

CONCLUSIONS AND IMPLICATIONS

These results indicate that reflex activation of vagal nerve activity is essential for the induction of drug-induced TdP in alpha1-adrenoceptor-stimulated anaesthetized rabbits. This implies that alterations in vagal activity may also precipitate episodes of drug-induced TdP in man and that this should be considered in selecting models used in drug development.

Recording hERG potassium currents and assessing the effects of compounds using the whole-cell patch-clamp technique

The complex gating of the hERG channel makes it ideally suited to its principal role in controlling phase 3 repolarization of the cardiac ventricular action potential. Any abnormal delay in repolarization can lead to the re-activation of Ca(2)+ channels, giving rise to early after-depolarizations, and coupled with increased cardiac dispersion, typically associated with these delays, provides respectively both the trigger and substrate for the potentially life threatening arrhythmia Torsardes de Pointes (TdP). Owing to the fundamental role of hERG in controlling the duration of the cardiac action potential, it is not surprising that any drugs that potently and selectively block this channel are liable to have these effects. Consequently, much effort has been expended in developing standard voltage protocols to reliably assess the effects of compounds on hERG currents in vitro. This chapter describes how to record hERG currents in a recombinant cell line using the whole-cell patch-clamp technique. It also provides typical voltage protocols used for assessing the basic electrophysiological properties of these currents and for assessing the effects of compounds on hERG tail currents.

Cardiac side effects of psychiatric drugs

This review describes the common effects of psychotropic drugs on the cardiovascular system and offers guidance for practical management. Selected reports from the literature describing common side effects associated with psychotropic drugs are reviewed, and suggestions for further reading are given throughout the text. Orthostatic hypotension is the most common adverse autonomic side effect of antipsychotic drugs. Among the atypical antipsychotics the risk of orthostatic hypotension is highest with clozapine and among the conventional drugs the risk is highest with low potency agents. Rarely, orthostatic hypotension may result in neurocardiogenic syncope. QTc prolongation can occur with all antipsychotics but an increased risk is seen with pimozide, thioridazine, sertindole and zotepine. QTc prolongation is a marker of arrhythmic risk. Torsade de pointe, a specific arrhythmia, may lead to syncope, dizziness or ventricular fibrillation and sudden death. Heart muscle disease presents most commonly in the elderly as chronic heart failure, but myocarditis and cardiomyopathy, although relatively rare, are devastating, but potentially reversible complications of psychotropic drug therapy have been particularly linked to clozapine treatment. Patients with severe mental illness (SMI) are a 'high risk' population with regard to cardiovascular morbidity and mortality. It is probable that many patients accumulate an excess of 'traditional' risk factors for the development of cardiovascular disease, but other mechanisms including psychotropic drugs may also be influential in increasing risk in this vulnerable group. These risks need to be seen in the context of the undoubted therapeutic efficacy of the psychotropic armamentarium and the relief that these drugs bring to those suffering from mental disorder.

Long QT syndrome: Genetic implications and drug influence

<zakljucak> Produzeni QT interval predstavlja problem u klinickoj praksi kome se posvecuje sve veca paznja i koji je oblast intenzivnog istrazivanja. Genetske studije kod pojedinaca koji imaju klinicki izrazene simptome produzenog QT intervala i/ili pozitivnu porodicnu anamnezu za iznenadnu srcanu smrt, mogu za pocetak da budu ogranicene na KCNQ1, HERG i SCN5A gene sa verovatnocom otkrivanja mutacije od 65%. Predstojece studije tek treba da objasne znacaj polimorfizma odredjenih gena za pojavu produzenja QT intervala.

Recent Publications on Medications and Pharmacy

Hospital Pharmacy presents this feature to keep pharmacists abreast of new publications in the medical/pharmacy literature. Articles of interest will be abstracted monthly regarding a broad scope of topics.