Safety of non-antiarrhythmic drugs that prolong the QT interval or induce torsade de pointes: an overview

Antimicrobials and the risk of torsades de pointes: the contribution from data mining of the US FDA Adverse Event Reporting System

BACKGROUND

Drug-induced torsades de pointes (TdP) is a complex regulatory and clinical problem due to the rarity of this sometimes fatal adverse event. In this context, the US FDA Adverse Event Reporting System (AERS) is an important source of information, which can be applied to the analysis of TdP liability of marketed drugs.

OBJECTIVE

To critically evaluate the risk of antimicrobial-induced TdP by detecting alert signals in the AERS, on the basis of both quantitative and qualitative analyses.

METHODS

Reports of TdP from January 2004 through December 2008 were retrieved from the public version of the AERS. The absolute number of cases and reporting odds ratio as a measure of disproportionality were evaluated for each antimicrobial drug (quantitative approach). A list of drugs with suspected TdP liability (provided by the Arizona Centre of Education and Research on Therapeutics [CERT]) was used as a reference to define signals. In a further analysis, to refine signal detection, we identified TdP cases without co-medications listed by Arizona CERT (qualitative approach).

RESULTS

Over the 5-year period, 374 reports of TdP were retrieved: 28 antibacterials, 8 antifungals, 1 antileprosy and 26 antivirals were involved. Antimicrobials more frequently reported were levofloxacin (55) and moxifloxacin (37) among the antibacterials, fluconazole (47) and voriconazole (17) among the antifungals, and lamivudine (8) and nelfinavir (6) among the antivirals. A significant disproportionality was observed for 17 compounds, including several macrolides, fluoroquinolones, linezolid, triazole antifungals, caspofungin, indinavir and nelfinavir. With the qualitative approach, we identified the following additional drugs or fixed dose combinations, characterized by at least two TdP cases without co-medications listed by Arizona CERT: ceftriaxone, piperacillin/tazobactam, cotrimoxazole, metronidazole, ribavirin, lamivudine and lopinavir/ritonavir.

DISCUSSION

Disproportionality for macrolides, fluoroquinolones and most of the azole antifungals should be viewed as 'expected' according to Arizona CERT list. By contrast, signals were generated by linezolid, caspofungin, posaconazole, indinavir and nelfinavir. Drugs detected only by the qualitative approach should be further investigated by increasing the sensitivity of the method, e.g. by searching also for the TdP surrogate marker, prolongation of the QT interval.

CONCLUSIONS

The freely available version of the FDA AERS database represents an important source to detect signals of TdP. In particular, our analysis generated five signals among antimicrobials for which further investigations and active surveillance are warranted. These signals should be considered in evaluating the benefit-risk profile of these drugs.

Interferences of the autonomic nervous system with drug induced QT prolongation: a point to consider in non-clinical safety studies

INTRODUCTION

QT interval assessment by telemetry has become one of the most useful models in testing strategies adopted for detection of drug induced QT prolongation in non-clinical safety pharmacology studies. This study reports experimental data showing that the autonomic nervous system might influence drug induced QT prolongation.

METHODS

Animals were instrumented with telemetric transmitters and epicardial ECG leads. Effects on QT interval of reference drugs such as thioridazine and terfenadine were analysed with different approaches, the Holzgrefe's probabilistic method, the QT shift method and an individual analysis of beat-to-beat QT/RR pair distribution visualised as points-cloud.

RESULTS

Two cases of unexpected absence of QT interval prolongation are reported with thioridazine and terfenadine in conscious beagle dogs under conditions of concomitant tachycardia. The pro-arrhythmic properties of these two molecules were unmasked by co-treatment with sympatholytic agents, atenolol and clonidine respectively suggesting that sympathetic activation and/or parasympathetic withdrawal might impair a drug induced QT prolongation.

DISCUSSION

The apparent absence of changes in the QT interval due to novel drug candidates should be interpreted cautiously under conditions of concomitant tachycardia or elevated heart rate levels in non-clinical safety studies.

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

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

Drug-induced QT interval shortening: potential harbinger of proarrhythmia and regulatory perspectives

ATP-dependent potassium channel openers such as pinacidil and levcromakalim have long been known to shorten action potential duration and to be profibrillatory in non-clinical models, raising concerns on the clinical safety of drugs that shorten QT interval. Routine non-clinical evaluation of new drugs for their potential to affect cardiac repolarization has revealed that drugs may also shorten QT interval. The description of congenital short QT syndrome in 2000, together with the associated arrhythmias, suggests that drug-induced short QT interval may be proarrhythmic, and an uncanny parallel is evolving between our appreciation of the short and the long QT intervals. Epidemiological studies report an over-representation of short QT interval values in patients with idiopathic ventricular fibrillation. Therefore, as new compounds that shorten QT interval are progressed further into clinical development, questions will inevitably arise on their safety. Arising from the current risk-averse clinical and regulatory environment and concerns on proarrhythmic safety of drugs, together with our lack of a better understanding of the clinical significance of short QT interval, new drugs that substantially shorten QT interval will likely receive an unfavourable regulatory review unless these drugs fulfil an unmet clinical need. This review provides estimates of parameters of QT shortening that may be of potential clinical significance. Rufinamide, a recently approved anticonvulsant, illustrates the current regulatory approach to drugs that shorten QT interval. However, to further substantiate or confirm the safety of these drugs, their approval may well be conditional upon large-scale post-marketing studies with a focus on cardiac safety.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

CONCLUSION

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

Fatal cardiotoxicity related to halofantrine: a review based on a worldwide safety data base

Background

Halofantrine (HF) was considered an effective and safe treatment for multi-drug resistant falciparum malaria until 1993, when the first case of drug-associated death was reported. Since then, numerous studies have confirmed cardiac arrythmias, possibly fatal, in both adults and children. The aim of the study was to review fatal HF related cardiotoxicity.

Methods

In addition, to a systematic review of the literature, the authors have had access to the global safety database on possible HF related cardiotoxicity provided by GlaxoSmithKline.

Results

Thirty-five cases of fatal cardiotoxicity related to HF, including five children, were identified. Females (70%) and patients from developing countries (71%) were over-represented in this series. Seventy-four percent of the fatal events occurred within 24 hours of initial exposure to HF. Twenty six patients (74%) had at least one predisposing factor for severe cardiotoxicity, e.g., underlying cardiac disease, higher than recommended doses, or presence of a concomitant QT-lengthening drug. All (100%) of the paediatric cases had either a contraindication to HF or an improper dose was given. In six cases there was no malaria.

Conclusion

A distinction should be made between common but asymptomatic QT-interval prolongation and the much less common ventricular arrhythmias, such as torsades de pointes, which can be fatal and seem to occur in a very limited number of patients. The majority of reported cardiac events occurred either in patients with predisposing factors or with an improper dose.

Therefore, in the rare situations in which HF is the only therapeutic option, it can still be given after carefully checking for contraindications, such as underlying cardiac disease, bradycardia, metabolic disorders, personal or family history of long QT-interval or concomitant use of another QT-prolonging drug (e.g., mefloquine), especially in females.

Block effect of capsaicin on hERG potassium currents is enhanced by S6 mutation at Y652

The objectives of this study were to investigate the inhibitory action of capsaicin on wild-type (WT) and mutation human ether-a-go-go-related gene (hERG) potassium channel currents (I(hERG)), and to determine whether mutations in the S6 region are significant for the inhibition of I(hERG) by capsaicin. The hERG channel (WT, Y652A and F656A) was expressed in Xenopus oocytes and studied using standard two-microelectrode voltage-clamp techniques. The results show that capsaicin blocks WT hERG in a concentration-dependent manner, with an IC(50) of 17.45microM and a negative shift in the steady-state inactivation curve. Characteristics of blockade were consistent with capsaicin causing components of block in both the closed and open channel states. However, mutating the Y652 residue to Ala enhances the blockade effect of capsaicin with an IC(50) of 4.11microM, whereas mutation of F656A does not significantly alter drug potency. Simultaneously, for Y652A, the steady-state activation parameter is shifted to a more positive value by 5mV and the inactivation parameter is shifted to a more negative value by -29mV in the presence of 25microM capsaicin. In conclusion, capsaicin blocks hERG channels by binding to both the closed and open channel states.Y652 was important as a molecular determinant of blockade. Mutation Y652A enhances the drug block, which may cause some patients to be particularly sensitive to capsaicin clinically.

Hypokalemia is associated with lengthening of QT interval in psychiatric patients on admission

Several studies have revealed a relatively high frequency of hypokalemia in the general psychiatric population. This may be explained by adrenergic stimulation observed in the acute phase of psychiatric disorders. Little is known about the effects of hypokalemia on cardiac repolarisation in these circumstances. The current study was designed to determine if the hypokalemia observed among patients with acute psychiatric disorders can cause significant QT interval prolongation, and thus increase the risk of ventricular arrhythmia. Electrocardiograms were obtained in 282 non-selected patients admitted to a psychiatric unit. Heart-rate adjusted QT intervals (QTc) were compared to serum potassium levels and to other risk factors for QT prolongation (bradycardia, age, gender, and administration of antipsychotics). Hypokalemia, diagnosed in more than 11% of the patients, was associated with a significantly longer QTc interval (means 423.5+/-40 ms vs 408.5+/-31 ms), as was female sex. Multiple linear regression analysis on the studied risk factors revealed that only hypokalemia and female sex were independently associated with lengthening of the QT interval. According to our results, hypokalemia seems to be one of the most important risk factors for QT prolongation. We therefore strongly recommend that psychiatric patients should be screened for hypokalemia on admission.

Integrated risk assessment and predictive value to humans of non-clinical repolarization assays

The potential for drugs to be associated with the life-threatening arrhythmia, Torsades de Pointes (TdeP), continues to be a topic of regulatory, academic and industrial concern. Despite being an imperfect biomarker, prolongation of the QT interval of the surface ECG is used to assess the risk of a drug being associated with TdeP such that a thorough examination of drug effects on the QT interval is required for all new chemical entities. Numerous studies have investigated the relationship between non-clinical findings and the risk of TdeP and QT prolongation in the general population. There are many literature references supporting the strong correlation between the clinical safety margin over human ether-a-go-go (hERG) inhibitory potency and the risk of drug-induced arrhythmia and sudden death. A quantitative analysis of the relationship between non-clinical studies and the outcome of a human Thorough QT study has also been reported. In the current manuscript, based on the outcome of the non-clinical assays the sensitivity and specificity of each assay and an integrated risk assessment for predicting the outcome of the human Thorough QT study has been conducted. The data suggest that for QT prolongation mediated through inhibition of the hERG current the non-clinical assays are highly predictive of drug effects on the QT interval. Based on the literature review and specific quantitative analysis reported above it is concluded that non-clinical assays predict the risk of compounds to prolong the QT interval and cause TdeP in humans if the mechanism is through inhibition of the hERG current.

Increased prevalence of prolonged QT interval in males with primary or secondary hypogonadism: a pilot study

Symptoms and signs of male hypogonadism span all organ systems, including the cardiovascular apparatus. The electrocardiographic QT interval reflects cardiac ventricular repolarization and, if prolonged, increases the risk of malignant arrhythmias. QT interval duration is similar in boys and girls during childhood, but shortens in males after puberty and experimental studies suggest that testosterone is a major contributor to shortening of QT interval in men. The aim of the present pilot study was to assess the duration of ventricular repolarization in adult males with primary or secondary hypogonadism. Standard ECG recordings were performed in 26 men (mean age 39.2 +/- 2.17 years) with pituitary or testicular hypogonadism and repeated in 15 patients during testosterone replacement. Twenty-six age-matched control men were also analysed. Measured QT intervals were corrected for heart rate according to Bazzett's formula (QTc = QT/radical RR interval). The prevalence of prolonged QTc was considerably higher in hypogonadal patients (four of 26 men) than in control men (none, p < 0.05) and in the general, healthy population (<2.5%). QTc interval normalized on hormone replacement therapy in the four patients presenting prolonged QTc in the hypogonadal state. Heart rate and left ventricular mass did not differ among the two groups and no known QT-prolonging factor was apparent in patients with abnormal QTc interval. In conclusion, a high number prolonged QT interval measurements was observed in hypogonadal men who may therefore be at increased risk for cardiac arrhythmias. This observation reveals an additional feature of male hypogonadism, which may benefit from testosterone replacement therapy.

A new homogeneous high-throughput screening assay for profiling compound activity on the human ether-a-go-go-related gene channel

Long QT syndrome, either inherited or acquired from drug treatments, can result in ventricular arrhythmia (torsade de pointes) and sudden death. Human ether-a-go-go-related gene (hERG) channel inhibition by drugs is now recognized as a common reason for the acquired form of long QT syndrome. It has been reported that more than 100 known drugs inhibit the activity of the hERG channel. Since 1997, several drugs have been withdrawn from the market due to the long QT syndrome caused by hERG inhibition. Food and Drug Administration regulations now require safety data on hERG channels for investigative new drug (IND) applications. The assessment of compound activity on the hERG channel has now become an important part of the safety evaluation in the process of drug discovery. During the past decade, several in vitro assay methods have been developed and significant resources have been used to characterize hERG channel activities. However, evaluation of compound activities on hERG have not been performed for large compound collections due to technical difficulty, lack of throughput, and/or lack of biological relevance to function. Here we report a modified form of the FluxOR thallium flux assay, capable of measuring hERG activity in a homogeneous 1536-well plate format. To validate the assay, we screened a 7-point dilution series of the LOPAC 1280 library collection and reported rank order potencies of ten common hERG inhibitors. A correlation was also observed for the hERG channel activities of 10 known hERG inhibitors determined in this thallium flux assay and in the patch clamp experiment. Our findings indicate that this thallium flux assay can be used as an alternative method to profile large-volume compound libraries for compound activity on the hERG channel.

Management of the critically poisoned patient

BACKGROUND

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

METHODS

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

DISCUSSION

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

Effect of macrolide and fluoroquinolone antibacterials on the risk of ventricular arrhythmia and cardiac arrest: an observational study in Italy using case-control, case-crossover and case-time-control designs

OBJECTIVE

To compare the effect of macrolide and fluoroquinolone antibacterials on the onset of ventricular arrhythmia and cardiac arrest using three different observational designs.

METHODS

A population-based case-control study was performed by linking automated databases from the Varese Province of Italy. Cases were all subjects who experienced ventricular arrhythmia or cardiac arrest from July 1998 to December 2003. For each case, up to ten controls were randomly selected after matching for sex, age, practitioner and date of arrhythmia onset. The use of macrolides and fluoroquinolones during two time windows denoted as recent and referent intervals was ascertained. Odds ratios were estimated using case-control, case-crossover and case-time-control approaches.

RESULTS

1275 cases and 9189 controls met the inclusion criteria. Adjusted odds ratios (and corresponding 95% CIs) associated with recent exposure to macrolides were 2.13 (1.34, 3.39), 1.70 (0.88, 3.26) and 1.62 (0.78, 3.34) by using case-control, case-crossover and case-time-control designs, respectively. The corresponding estimates for fluoroquinolones were 3.58 (2.51, 5.12), 1.98 (1.19, 3.29) and 1.59 (0.88, 2.87), respectively.

CONCLUSIONS

Three observational study designs each using entirely different sets of controls consistently showed that recent use of macrolide and fluoroquinolone antibacterials may be associated with increased risk of ventricular arrhythmia and cardiac arrest.

Calcium channel blockers, NOS1AP, and heart-rate-corrected QT prolongation

OBJECTIVES

To study whether NOS1AP single nucleotide polymorphisms (SNPs), rs10494366 T>G and rs10918594 C>G, modify the heart-rate-corrected QT (QTc) prolonging effect of calcium channel blockers.

BACKGROUND

Common variation in the NOS1AP gene has been associated with QT interval variation in several large population samples. NOS1 is presumed to influence intracellular calcium.

METHODS

The prospective population-based Rotterdam Study includes 16 603 ECGs from 7565 participants (>or=55 years), after exclusion of patients with left ventricular hypertrophy, left and right bundle branch block, as well as carriers of pacemakers. The endpoint was the length of the QTc interval in calcium channel blocker users and non-users with the minor alleles compared with the major alleles (wild type). We used a repeated-measurement analysis, adjusted for all known confounders.

RESULTS

Use of verapamil was associated with a significant QTc interval prolongation [6.0 ms 95% confidence interval (CI) 1.7; 10.2] compared with non-users. Furthermore, users of verapamil with the rs10494366 GG genotype showed significantly more QTc prolongation than users with the TT genotype [25.4 ms (95% CI: 5.9-44.9)] (P value for multiplicative interaction 0.0038). Users of isradipine with the GG genotype showed more QTc prolongation than users with the TT genotype [19.8 ms (95% CI: 1.9-37.7)]; however, SNP rs10494366 did not modify the effect on QTc interval on a multiplicative scale (P=0.3563). SNP rs10918594 showed similar results.

CONCLUSION

In conclusion, we showed that the minor alleles of both NOS1AP SNPs significantly potentiate the QTc prolonging effect of verapamil.

Common candidate gene variants are associated with QT interval duration in the general population

OBJECTIVES

QT interval prolongation is associated with increased risk of sudden cardiac death at the population level. As 30-40% of the QT-interval variability is heritable, we tested the association of common LQTS and NOS1AP gene variants with QT interval in a Finnish population-based sample.

METHODS

We genotyped 12 common LQTS and NOS1AP genetic variants in Health 2000, an epidemiological sample of 5043 Finnish individuals, using Sequenom MALDI-TOF mass spectrometry. ECG parameters were measured from digital 12-lead ECGs and QT intervals were adjusted for age, gender and heart rate with a nomogram (Nc) method derived from the present study population.

RESULTS

The KCNE1 D85N minor allele (frequency 1.4%) was associated with a 10.5 ms (SE 1.6) or 0.57 SD prolongation of the adjusted QT(Nc) interval (P=3.6 x 10(-11)) in gender-pooled analysis. In agreement with previous studies, we replicated the association with QT(Nc) interval with minor alleles of KCNH2 intronic SNP rs3807375 [1.6 ms (SE 0.4) or 0.08 SD, P=4.7 x 10(-5)], KCNH2 K897T [-2.6 ms (SE 0.5) or -0.14 SD, P=2.1 x 10(-7)] and NOSA1P variants including rs2880058 [4.0 ms (SE 0.4) or 0.22 SD, P=3.2 x 10(-24)] under additive models.

CONCLUSIONS

We demonstrate that each additional copy of the KCNE1 D85N minor allele is associated with a considerable 10.5 ms prolongation of the age-, gender- and heart rate-adjusted QT interval and could thus modulate repolarization-related arrhythmia susceptibility at the population level. In addition, we robustly confirm the previous findings that three independent KCNH2 and NOSA1P variants are associated with adjusted QT interval.

Psychotropic drugs associated with corrected QT interval prolongation

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

A common NOS1AP genetic polymorphism is associated with increased cardiovascular mortality in users of dihydropyridine calcium channel blockers

AIM

Recently, a polymorphism in the NOS1AP gene (rs10494366), a regulator of neuronal nitric oxide synthase (nNOS), was associated with QTc prolongation. Both nNOS and calcium channel blockers (CCBs) regulate intracellular calcium levels and have an important role in cardiovascular homeostasis. The aim was to investigate whether this polymorphism is associated with cardiovascular mortality in users of CCBs.

METHODS

The data from the Rotterdam study, a population-based closed cohort study of Caucasian individuals of > or =55 years of age, were used. We identified 1113 participants in the Rotterdam Study who were prescribed CCBs for the first time between 1991 and 2005. All-cause and cardiovascular mortality was assessed in participants who were prescribed CCBs with different NOS1AP rs10494366 genotypes using Cox proportional hazard models.

RESULTS

In participants starting on dihydropyridine CCBs (amlodipine, nifedipine and others) all-cause mortality (n = 79) risks were higher in participants with the TG [hazard ratio (HR) 2.57, 95% confidence interval (CI) 1.24, 5.34] or the GG genotype (HR 3.18, 95% CI 1.18, 8.58) than in participants with the referent TT genotype. Cardiovascular mortality (n = 54) risks were 3.51 (95% CI 1.41, 8.78) for the TG genotype and 6.00 (95% CI 1.80, 20.0) for the GG genotype. No differences in all-cause mortality or cardiovascular mortality were seen in participants starting with the nondihydropyridine CCBs verapamil or diltiazem.

CONCLUSION

The minor G allele of rs10494366 in the NOS1AP gene is associated with increased all-cause and cardiovascular mortality in Caucasian users of dihydropyridine CCBs. The mechanism underlying the observed association is unknown.

Identification of a common variant at the NOS1AP locus strongly associated to QT-interval duration

QT-interval prolongation is an electrophysiologic phenomenon associated with sudden cardiac death. The QT-interval in the general population is approximately 35% heritable. In genome-wide association studies, a common variant (rs10494366T > G) within the nitric oxide synthase 1 adaptor protein (NOS1AP) gene was identified and consistently associated with QT-interval duration. Yet, the causal variant remains unclear. Therefore, we performed fine mapping of the association of the NOS1AP locus with QT-interval within the Rotterdam Study, a population-based, prospective cohort study of individuals of > or =55 years of age. First, we tested the association of single-nucleotide polymorphisms (SNPs) in or within +/-100 kb of the NOS1AP gene with QT-interval duration, using sex-specific unstandardized residuals after regression on age and RR-interval, in 385 individuals using the combined set of SNPs present in the Affymetrix 500k and Illumina 550k chip arrays. Subsequently, we examined correspondence of the association signals in 4606 individuals using the Illumina 550k array. A C-to-T SNP at chromosome 1 position 160300514 (rs12143842, T-allele frequency = 24%) was associated with a QT-interval duration increase of 4.4 ms per additional T-allele (P = 4.4 x 10(-28)). For comparison, the most strongly associated variant to date, rs10494366T > G, was associated with a 3.5 ms increase (P = 1.6 x 10(-23)) per additional G-allele. None of the inferred haplotypes showed a stronger effect than the individual rs12143842C > T SNP. In conclusion, we found rs12143842 6 kb upstream distance of NOS1AP to be more strongly associated to QT-interval duration than rs10494366T > G. Functional analysis of this marker is warranted.

Critical care toxicology

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

Electropharmacological properties of telmisartan in blocking hKv1.5 and HERG potassium channels expressed on Xenopus laevis oocytes

AIM

The objectives of this study were to investigate the inhibitory action of telmisartan, a selective angiotensin II type 1 receptor antagonist, on hKv1.5 and human ether-a-go-go-related gene (HERG) channels expressed on Xenopus laevis oocytes.

METHODS

hKv1.5 and HERG channels were expressed on Xenopus laevis oocytes and studied using the 2-microelectrode voltage clamp technique.

RESULTS

In hKv1.5 channels, telmisartan produced a voltage- and concentration-dependent inhibition; the efficacies of blockade were different at peak and 1.5 s end-pulse currents, which were 7.75%+/-2.39% (half-maximal inhibition concentration [IC50]=2.25+/-0.97 micromol/L) and 52.64%+/-3.77% (IC50=0.82+/-0.39 micromol/L) at 1 micromol/L telmisartan, respectively. Meanwhile, telmisartan accelerated the inactivation of the channels. However, telmisartan exhibited a low affinity for HERG channels (IC50=24.35+/-5.06 micromol/L); the blockade was voltage- and concentration-dependent. Telmisartan preferentially blocked open-state HERG channels. The slow time constants of deactivation were accelerated (n=6, P<0.05), which was inconsistent with the "foot-in-the-door"effect.

CONCLUSION

Telmisartan blocks hKv1.5 potassium channels involving open and inactivated states at plasma concentration levels of therapeutic doses; whereas the blockade of HERG channels occurs only at supra plasma concentration levels of therapeutic doses and preferentially in open and closed-state channels.

A composite model for HERG blockade

hERG blockade is one of the major toxicological problems in lead structure optimization. Reliable ligand-based in silico models for predicting hERG blockade therefore have considerable potential for saving time and money, as patch-clamp measurements are very expensive and no crystal structures of the hERG-encoded channel are available. Herein we present a predictive QSAR model for hERG blockade that differentiates between specific and nonspecific binding. Specific binders are identified by preliminary pharmacophore scanning. In addition to descriptor-based models for the compounds selected as hitting one of two different pharmacophores, we also use a model for nonspecific binding that reproduces blocking properties of molecules that do not fit either of the two pharmacophores. PLS and SVR models based on interpretable quantum mechanically derived descriptors on a literature dataset of 113 molecules reach overall R(2) values between 0.60 and 0.70 for independent validation sets and R(2) values between 0.39 and 0.76 after partitioning according to the pharmacophore search for the test sets. Our findings suggest that hERG blockade may occur through different types of binding, so that several different models may be necessary to assess hERG toxicity.

Drug-induced torsades de pointes: a review of the Swedish pharmacovigilance database

AIM

To describe spontaneously reported cases of torsades de pointes (TdP) in Sweden and to investigate if this adverse drug reaction (ADR) was labelled in the summary of product characteristics (SPC) for the drugs implicated.

METHODS

Reported cases of TdP 1991-2006 were identified and evaluated with regard to drug use and other possible risk factor.

RESULTS

Among a total of 61 788 ADRs, 88 cases of TdP were identified. In these cases, 27 different suspected drugs were implicated. Cardiac drugs were involved in most reports (74%; 65/88), with sotalol being the most frequently suspected drug (57%, 58/88). In addition to drug treatment two or more established risk factors were present in 85% of the cases (75/88). Heart disease (90%; 79/88) was the most common risk factor followed by age over 65 years (72%; 63/88) and female gender (70%; 62/88). TdP or QT prolongation were labelled in the SPC for 33% (9/27) of the drugs implicated in the 88 cases. However, supporting evidence for an association was found elsewhere in 56% (15/27) for the different drugs implicated in the reports. Although citalopram was the third most common suspected drug in the reports (10%; 9/88), TdP was not listed in the SPC.

CONCLUSION

TdP is a rarely reported ADR. Several risk factors are often present. In two thirds of the drugs implicated in the reports neither TdP nor QT prolongation was labelled in the SPC. Further investigations are needed regarding the association between citalopram and TdP.

Impact of study design on proarrhythmia prediction in the SCREENIT rabbit isolated heart model

INTRODUCTION

Prediction of the propensity of a compound to induce Torsades de Pointes continues to be a formidable challenge to the pharmaceutical industry. Development of an in vitro model for assessment of proarrhythmic potential offers the advantage of higher throughput and reduced compound quantity requirements when compared to in vivo studies. A rabbit isolated heart model (SCREENIT) has been reported to identify compounds with proarrhythmic potential based on the observance of compound-induced triangulation and instability of the monophasic action potential (MAP), ectopic beats, and reverse-use dependence of prolongation of the MAP duration. Previous reports have indicated that this model qualitatively identifies proarrhythmic compounds and suggest the use of this model to assign safety margins for human clinical use. The intent of this series of studies was to evaluate the impact of study design on the proarrhythmic concentration predicted by this model.

METHODS

Nine compounds of varying proarrhythmic potential and a negative control were tested in a blinded fashion using a series of different experimental protocols: Compounds were tested at multiple concentration ranges and extended perfusion times were also evaluated.

RESULTS

In general when the dataset is viewed as a whole, the model did identify proarrhythmic compounds, however the concentration at which action potential prolongation, triangulation, instability, reverse-use dependence and ectopic beats occurred often varied based on the concentration range selected. Further analysis using extended compound perfusion times demonstrated that variability may be due in part to lack of adequate equilibration of compound with the cardiac tissue.

DISCUSSION

We report that the model correctly identified proarrhythmic agents in a qualitative manner, but that study design impacts the proarrhythmic concentration derived from the model.

[Cardiological monitoring of antipsychotic-treated patients: evaluation and evolution of a hospital protocol]

INTRODUCTION

Following the Agence Française de Sécurité Sanitaire des Produits de Santé (Afssaps) (French Health Authority) recommendations in 2001, which impose the rigorous follow-up (electrocardiogram [ECG] and ionogram) of patients treated with antipsychotics (AP), a monitoring protocol was elaborated and set up in the Caen psychiatric hospital in April 2002. Protocol evaluation compared with fixed aims was performed after two years' follow-up.

AIM OF THE STUDY

This protocol had to answer a triple aim: better identification of patients at risk, ensure in-treatment monitoring, be simple and adapted to daily practice.

INCLUSION CRITERIA

A systematic admission check-up (S0) which includes cardiological and biological controls and after one and six months' treatment control (S1 and S6) were recommended. The major risk factors (RF) researched were long QT interval, bradycardia and hypokaliemia.

RESULTS

The initial monitoring was conducted in 601 patients (that only corresponded to 17% of hospital admission active files during the considered period). Means delays before obtaining an ECG were three times those obtained existing biological check-ups (11 days versus three days after date of admission). Systematic and integrated characterisation controls on admission were not respected. We noted that two-third of patients admitted during this period were hospitalized for only five days, although the mean time to obtain an ECG is of 11 days. This delay (approximately one week) between ECG and biological check-up is not compatible with a complete patient RF evaluation. Respectively, 83 and 68 patients were controlled under treatment at S1 and S6. Only half of the patients were controlled at the one-month (S1) and 16% at the six-months' theoretical dates (S6). These delays are inappropriate, notably with regard to the mean time of hospitalisation (15-17 days). The incidence of major RF was higher in treated (71%) than in non-treated patients. Major RF presence at S0 was not systematically associated with an AP treatment contraindication. The excessive delay before the first ECG could partially explain why this initial check-up was not able to detect a pretreatment contraindication. On the other hand, AP treated patients who presented at least one major RF at S0 were more frequently monitored at S1 than patients who did not (26% versus 13%, p=0.05). Among the 168 patients treated with AP or other drugs prolonging the QT interval at risk, 33 had at least one follow-up. This risk population was not better controlled than the initial cohort.

DISCUSSION

Protocol evaluation is essential to improve its interest and feasibility. If systematic characterisation is simple, its application in practice is very difficult. The second version of the protocol presented here proposes to substitute the systematic ECG characterisation with the classification on admission of patients in "risk groups" that will condition the subsequent monitoring. Risk groups are identified into two RF types: those which are not related to AP treatment and those which are therapeutic attitude is adapted according to initial QTcorrigé (QTc), its progression between S0 and S (seven days) and kaliemia.