Cardiac Arrest Associated with Combination Cisapride and Itraconazole Therapy

Loss of Consciousness in the Young Child

In the very young child (less than eight years of age), transient loss of consciousness represents a diagnostic and management dilemma for clinicians. While most commonly benign, syncope may be due to cardiac dysfunction which can be life-threatening. It can be secondary to an underlying ion channelopathy, cardiac inflammation, cardiac ischemia, congenital heart disease, cardiomyopathy, or pulmonary hypertension. Patients with genetic disorders require careful evaluation for a cardiac cause of syncope. Among the noncardiac causes, vasovagal syncope is the most common etiology. Breath-holding spells are commonly seen in this age group. Other causes of transient loss of consciousness include seizures, neurovascular pathology, head trauma, psychogenic pseudosyncope, and factitious disorder imposed on another and other forms of child abuse. A detailed social, present, past medical, and family medical history is important when evaluating loss of consciousness in the very young. Concerning characteristics of syncope include lack of prodromal symptoms, no preceding postural changes or occurring in a supine position, after exertion or a loud noise. A family history of sudden unexplained death, ion channelopathy, cardiomyopathy, or congenital deafness merits further evaluation. Due to inherent challenges in diagnosis at this age, often there is a lower threshold for referral to a specialist.

Cardiovascular safety of prokinetic agents: A focus on drug-induced arrhythmias

BACKGROUND

Gastrointestinal sensorimotor dysfunction underlies a wide range of esophageal, gastric, and intestinal motility and functional disorders that collectively constitute nearly half of all referrals to gastroenterologists. As a result, substantial effort has been dedicated toward the development of prokinetic agents intended to augment or restore normal gastrointestinal motility. However, the use of several clinically efficacious gastroprokinetic agents, such as cisapride, domperidone, erythromycin, and tegaserod, is associated with unfavorable cardiovascular safety profiles, leading to restrictions in their use.

PURPOSE

The purpose of this review is to detail the cellular and molecular mechanisms that lead commonly to drug-induced cardiac arrhythmias, specifically drug-induced long QT syndrome, torsades de pointes, and ventricular fibrillation, to examine the cardiovascular safety profiles of several classes of prokinetic agents currently in clinical use, and to explore potential strategies by which the risk of drug-induced cardiac arrhythmia associated with prokinetic agents and other QT interval prolonging medications can be mitigated successfully.

Dealing with global safety issues : was the response to QT-liability of non-cardiac drugs well coordinated?

Drug-induced torsade de pointes (TdP) is a potentially fatal iatrogenic entity. Its reporting rate in association with non-cardiac drugs increased exponentially from the early 1990s and was associated with an increasing number of new non-cardiac drugs whose proarrhythmic liability was not appreciated pre-marketing. This epidemic provoked a comprehensive global response from drug regulators, drug developers and academia, which resulted in stabilization of the reporting rate of TdP. This commentary reviews the chronology and nature of, and the reasons for, this response, examines its adequacy, and proposes future strategies for dealing with such iatrogenic epidemics more effectively. It is concluded that the response was piecemeal and lacked direction. No one entity was responsible, with the result that important contributions from regulators, industry and academia lacked coordination. While the process of dealing with QT crisis seemed to have worked reasonably well in this instance, it does not seem wise to expect the next crisis in drug development to be managed as well. Future crises will need better management and the challenge is to implement a system set up to respond globally and efficiently to a perceived drug-related hazard. In this regard, we discuss the roles of new tools the legislation has provided to the regulators and the value of an integrated expert assessment of all pre-approval data that may signal a potential safety issue in the postmarketing period. We also discuss the roles of other bodies such as the WHO Collaborating Centre for International Drug Monitoring, CIOMS and the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH).

Updates on cytochrome p450-mediated cardiovascular drug interactions

Cytochrome P (CYP) 450 is a superfamily of hemoproteins that play an important role in the metabolism of steroid hormones, fatty acids, and many medications. Many agents used for management of cardiovascular diseases are substrates, inhibitors, or inducers of CYP450 enzymes. When two agents that are substrates, inhibitors, or inducers of CYP450 are administered together, drug interactions with significant clinical consequences may occur. This review discusses CYP450-mediated cardiovascular drug interactions as well as noncardiovascular drug interactions that produced significant cardiovascular side effects. The principles in predicting drug interactions are also discussed.

Updates on cytochrome P450-mediated cardiovascular drug interactions

Cytochrome P (CYP) 450 is a superfamily of hemoproteins that play an important role in the metabolism of steroid hormones, fatty acids, and many medications. Many agents used for management of cardiovascular diseases are substrates, inhibitors, or inducers of CYP450 enzymes.When two agents that are substrates, inhibitors, or inducers of CYP450 are administered together, drug interactions with significant clinical consequences may occur. This review discusses CYP450-mediated cardiovascular drug interactions as well as noncardiovascular drug interactions that produced significant cardiovascular side effects. The principles in predicting drug interactions are also discussed.

The cardiovascular safety profile of renzapride, a novel treatment for irritable bowel syndrome

The cardiac safety of renzapride, a novel benzamide currently under clinical development for the treatment of irritable bowel syndrome, was investigated in a four-way randomized crossover electrocardiographic clinical study in healthy human subjects and also in an in vitro cardiac conductivity study in sheep isolated Purkinje fibres. The primary endpoint in the clinical study was prolongation of the individually corrected QT interval (QTci). No clinically or statistically significant prolongation of QTci after 4 or 20 mg renzapride compared with placebo was observed. The relative effects of renzapride and cisapride in the in vitro study showed that the cardiac action potential duration was unaltered by 0.2 and 2 microM renzapride, shortened by 20 microM renzapride, and prolonged by 1 microM cisapride. Cisparide was also a 1000-fold more potent inhibitor of human ether-a-go-go related gene (hERG) channels in HEK293 cells than renzapride. These studies indicate that therapeutic doses of renzapride are unlikely to prolong cardiac action potentials and, therefore, are also unlikely to cause cardiac arrhythmias in clinical use.

Application of the Bradford Hill Criteria to Assess the Causality of Cisapride-Induced Arrhythmia

INTRODUCTION

The Bradford Hill criteria are a widely used, useful tool for the assessment of biomedical causation. We have examined their application to pharmacovigilance using the example of cisapride-induced QTc interval prolongation/arrhythmia.

METHODS

A literature search was conducted using MEDLINE, EMBASE, Reactions Weekly and regulatory websites to identify evidence for the association between cisapride and QTc interval prolongation/arrhythmia that had been published in the English language. Two hundred and five publications were identified as being potentially suitable for the study. After excluding irrelevant articles, studies on high-risk populations and review articles, 70 publications were assessed using the Bradford Hill criteria. These included 24 case reports, case series or spontaneous report summaries; eight epidemiological studies; 22 clinical studies; and 16 experimental (in vivo and in vitro) publications.

RESULTS

The most compelling evidence for an association between cisapride use and QTc interval prolongation/arrhythmia came from case/spontaneous reports and biological plausibility. Considering the rare incidence of serious cardiac events, these criteria formed the basis for the strength of the association. The number of reports from different populations showed consistency. Specificity was supported by clinical and cardiographic characterisation of the events. There were temporal relationships between the events and the initiation of cisapride treatment, increases in the dosage and the receipt of interacting medications. The relationships between the adverse events and the latter two factors exhibited biological gradients. Experimental evidence could be found from biological models, as well as reports of positive dechallenge and/or rechallenge found in individual patients. Cisapride was found to bind the human ether-a-go-go-related gene (HERG) potassium channel, which provides a plausible mechanism for QTc interval prolongation/arrhythmia. Other QTc interval-prolonging/arrhythmic drugs that also bind to HERG provided an analogy for cisapride causing QTc interval prolongation/arrhythmia via this mechanism. The evidence provided by clinical studies was inconsistent, and epidemiological studies failed to demonstrate an association. Nevertheless, this did not prevent the assessment of causation.

DISCUSSION

This study showed how different types of evidence found in pharmacovigilance can be evaluated using the Bradford Hill criteria. Further work is required to examine how the criteria can be applied to different types of adverse events and how they may be applied to pharmacovigilance.

Torsade de pointes induced by systemic antifungal agents: lessons from a retrospective analysis of published case reports

Torsade de pointes (TdP) is a potentially fatal arrhythmia that might be associated with systemic antifungal agent (SAFAs) administration. The objective of this study was to investigate all published reports on TdP induced by SAFAs in order to characterise this association. Each original report was analysed for the presence of risk factors for TdP: female gender, structural heart disease, electrolyte imbalance, concomitant use of a QT interval prolonging agent which SAFA inhibits its liver metabolism, liver cirrhosis, renal failure and more. Naranjo probability scale for adverse drug reactions was applied for every full report. Twenty-one reports on 28 patients were analysed. All patients survived. Most patients (25/28; 89.2%) used one or more agents that might have prolonged the QT interval and their liver metabolism might have been inhibited by SAFA. Female gender was the second most common risk factor for TdP (20/28; 71.4%). All patients, including female patients, had one or more risk factors for TdP prior to SAFA administration. According to Narajno probability scale, there was no definite association between TdP and SAFA in any report. SAFA alone might seldom trigger TdP. We wish to raise the level of awareness of risk factors for TdP prior to SAFA administration and for concomitant use of other dysrhythmogenic agents in particular.

QT prolongation with antimicrobial agents: understanding the significance

Cardiac toxicity has been relatively uncommon within the antimicrobial class of drugs, but well described for antiarrhythmic agents and certain antihistamines. Macrolides, pentamidine and certain antimalarials were traditionally known to cause QT-interval prolongation, and now azole antifungals, fluoroquinolones and ketolides can be added to the list. Over time, advances in preclinical testing methods for QT-interval prolongation and a better understanding of its sequelae, most notably torsades de pointes (TdP), have occurred. This, combined with the fact that five drugs have been removed from the market over the last several years, in part because of QT-interval prolongation-related toxicity, has elevated the urgency surrounding early detection and characterisation methods for evaluating non-antiarrhythmic drug classes. With technological advances and accumulating literature regarding QT prolongation, it is currently difficult or overwhelming for the practising clinician to interpret these data for purposes of formulary review or for individual patient treatment decisions. Certain patients are susceptible to the effects of QT-prolonging drugs. For example, co-variates such as gender, age, electrolyte derangements, structural heart disease, end organ impairment and, perhaps most important, genetic predisposition, underlie most if not all cases of TdP. Between and within classes of drugs there are important differences that contribute to delayed repolarisation (e.g. intrinsic potency to inhibit certain cardiac ion currents or channels, and pharmacokinetics). To this end, a risk stratification scheme may be useful to rank and compare the potential for cardiotoxicity of each drug. It appears that in most published cases of antimicrobial-associated TdP, multiple risk factors are present. Macrolides in general are associated with a greater potential than other antimicrobials for causing TdP from both a pharmacodynamic and pharmacokinetic perspective. The azole antifungal agents also can be viewed as drugs that must be weighed carefully before use since they also have both pharmacodynamic and pharmacokinetic characteristics that may trigger TdP. The fluoroquinolones appear less likely to be associated with TdP from a pharmacokinetic perspective since they do not rely on cytochrome P450 (CYP) metabolism nor do they inhibit CYP enzyme isoforms, with the exception of grepafloxacin and ciprofloxacin. Nonetheless, patient selection must be carefully made for all of these drugs. For clinicians, certain responsibilities are assumed when prescribing antimicrobial therapy: (i) appropriate use to minimise resistance; and (ii) appropriate patient and drug selection to minimise adverse event potential. Incorporating information learned regarding QT interval-related adverse effects into the drug selection process may serve to minimise collateral iatrogenic toxicity.

Drugs and cardiotoxicity in HIV and AIDS

The advent of potent antiretroviral drugs in recent years has had an impressive impact on mortality and disease progression in HIV-infected patients, so that issues related to long-term effects of drugs are of growing importance. Hyperlipidemia, hyperglycemia, and lipodystrophy are increasingly described adverse effects of highly active antiretroviral therapy (HAART), in particular when protease inhibitors are used. Hyperlipidemia is strikingly associated with the use of most available protease inhibitors, with an estimated prevalence of up to 50%. Because of the short observation period and the small number of cardiovascular events, epidemiological evidence for an increased risk of coronary heart disease in HIV-infected patients treated with HAART is not adequate at present; however, it is likely that shortly more data will accumulate to quantify this risk. Before starting HAART and during treatment it is reasonable to evaluate all patients for traditional coronary risk factors, including lipid profile. Among the drugs that are currently used in HIV+ patients, antibacterials, antifungals, psychotropic drugs and anti-histamines have been associated with QT prolongation or torsade de pointe, a life-threatening ventricular arrhythmia. Among the risk factors that may precipitate an asymptomatic electrocardiographic abnormality into a dangerous arrhythmia is the concomitant use of drugs that share the CYP3A metabolic pathway. Since most protease inhibitors are potent inhibitors of CYP3A, clinicians should be aware of this potentially dangerous effect of HAART. Anthracyclines are potent cytotoxic antibiotics that have been widely used for the treatment of HIV-related neoplasms. Their cardiotoxicity is well known, ranging from benign and reversible arrhythmias to progressive severe cardiomyopathy. The increased survival and quality of life of HIV+ patients emphasize the importance of a high awareness of adverse drug-related cardiac effects.

Evaluation and treatment of syncope in infants

Syncope in the infant and newborn occurs as a loss of consciousness due to a variety of etiologies. Because syncope at this age may be a harbinger of sudden infant death, the symptom provokes anxiety and challenges clinicians to identify those babies with an increased risk for life threatening events. Recently introduced diagnostic tests and advances in molecular biology offer promising potential, but the population at risk remains unknown. Controversy surrounds: many potential risk factors; the value of home monitoring; and appropriate preventive and therapeutic strategies. This article reviews the differential diagnosis of syncope in children less than 18 months of age, with particular attention to those diagnoses and problems specific to the evaluation and treatment in this age group. Recommendations are presented for an efficient evaluation, which must include a careful history, complete physical examination and thorough investigation of the family history and home environment. In addition, specific diagnostic tests and a practical approach to treatment are suggested.

Postmarketing reports of QT prolongation and ventricular arrhythmia in association with cisapride and Food and Drug Administration regulatory actions

OBJECTIVE

To describe the postmarketing safety data used in the risk assessment of cisapride and to summarize the regulatory actions of the Food and Drug Administration (FDA).

METHODS

The FDA analyzed reports of patients who developed QT prolongation, torsades de pointes, and ventricular arrhythmia in association with the use of cisapride to assess probable etiology and risk factors.

RESULTS

While cisapride was being marketed from 1993-1999, the FDA received reports of the following patients: 117 who developed QT prolongation; 107, torsades de pointes; 16, polymorphic ventricular tachycardia; 18, ventricular fibrillation; 27, ventricular tachycardia; 25, cardiac arrest; 16, serious (unspecified) arrhythmia; and 15, sudden death; for a total of 341 individual patients affected, following use of cisapride. Eighty (23%) of the 341 patients died. Deaths were directly or indirectly associated with an arrhythmic event. Factors that suggested an association with cisapride included a temporal relationship between use of cisapride and arrhythmia, the absence of identified risk factors and other explanations for arrhythmia in some patients, and cases of positive dechallenge and rechallenge. In most individuals, the arrhythmia occurred in the presence of risk factors (other drugs and/or medical conditions).

CONCLUSIONS

Postmarketing reports and pharmacokinetic and electrophysiological data provided evidence that cisapride is associated with the occurrence of QT prolongation and torsades de pointes. The risk of fatal arrhythmia with cisapride was believed to outweigh the benefit for the approved indication, treatment of nocturnal heartburn due to gastroesophageal reflux disease, leading to the drug's discontinuation in the United States.

Risk assessment for antimicrobial agent-induced QTc interval prolongation and torsades de pointes

Over the past several years a multitude of new pharmaceutical agents have been released to the market. Several of them were withdrawn altogether or their use severely restricted to certain indications due to unexpected adverse events, including fatalities. Progress in developing new compounds clearly has surpassed our technology, in some cases, to measure and predict certain toxicities. Prolongation of the QT interval, which may lead to potentially life-threatening ventricular arrhythmias such as torsades de pointes, is one example. Regulatory agencies such as the Food and Drug Administration are increasing standards by which drugs are evaluated for cardiac toxicity related to QT interval prolongation. It is imperative that clinicians be knowledgeable of the risk factors for QT prolongation and avoid the use of culpable agents in patients at risk for QT prolongation.

Inhibition of the human ether-a-go-go-related gene (HERG) potassium channel by cisapride: affinity for open and inactivated states

1 Cisapride is a prokinetic agent which has been associated with QT prolongation, torsades de pointes and cardiac arrest. The cellular mechanism for these observations is high affinity blockade of IKr (encoded by HERG). 2 In a chronic transfection model using CHO-K1 cells, cisapride inhibited HERG tail currents after a step to +25 mV with similar potency at room and physiological temperatures (IC50 16. 4 nM at 20-22 degrees C and 23.6 nM at 37 degrees C). 3 Channel inhibition exhibited time-, voltage- and frequency-dependence. In an envelope of tails test, channel blockade increased from 27+/-8% after a 120 ms depolarizing step to 50+/-4% after a 1.0 s step. These findings suggested affinity for open and/or inactivated channel states. 4 Inactivation was significantly accelerated by cisapride in a concentration-dependent manner and there was a small (-7 mV) shift in the voltage dependence of steady state inactivation. 5 Channel blockade by cisapride was modulated by [K+]o, with a 26% reduction in the potency of channel blockade when [K+]o was increased from 1 to 10 mM. 6 In conclusion, HERG channel inhibition by cisapride exhibits features consistent with open and inactivated state binding and is sensitive to external potassium concentration. These features may have significant clinical implications with regard to the mechanism and treatment of cisapride-induced proarrhythmia.

Cardiac complications in the intensive care unit

Advances in the care of critically ill patients has been startling, especially in patients with acute coronary syndromes. With new therapies and procedures, however, have come new complications. On balance, our patients are better off, but the stakes are now higher and the complications more serious. The need for constant vigilance has never been greater.