Torsades de pointes ventricular tachycardia induced by mosapride and flecainide in the presence of hypokalemia

Prokinetics-safety and efficacy: The European Society of Neurogastroenterology and Motility/The American Neurogastroenterology and Motility Society expert review

BACKGROUND

Prokinetics are a class of pharmacological drugs designed to improve gastrointestinal (GI) motility, either regionally or across the whole gut. Each drug has its merits and drawbacks, and based on current evidence as high-quality studies are limited, we have no clear recommendation on one class or other. However, there remains a large unmet need for both regionally selective and/or globally acting prokinetic drugs that work primarily intraluminally and are safe and without systemic side effects.

PURPOSE

Here, we describe the strengths and weaknesses of six classes of prokinetic drugs, including their pharmacokinetic properties, efficacy, safety and tolerability and potential indications.

Flecainide Toxicity Secondary to Accidental Overdose: A Pediatric Case Report of Two Brothers

Flecainide is a class 1C antiarrhythmic with a narrow therapeutic window and thereby a high-risk medication for causing acute toxicity. Dysrhythmias secondary to flecainide ingestion are often refractory to antiarrhythmics and cardioversion, and patients commonly require extracorporeal support. We review the successful resuscitation of two brothers aged 2 and 4 who presented two years apart with unstable wide-complex tachyarrhythmia suspicious for severe flecainide toxicity. Each patient received sodium bicarbonate and 20% intravenous lipid emulsion with a full recovery. While extracorporeal support is often required following flecainide ingestion, we present two cases where it was avoided due to aggressive multimodal management with sodium bicarbonate, electrolyte repletion, and 20% intravenous lipid emulsion. In addition, avoidance of agitation-induced tachycardia may be beneficial.

Fast and furious: flecainide toxicity presenting as monomorphic ventricular tachycardia

A 63-year-old woman on flecainide, furosemide, and triamterene-hydrochlorothiazide presented with weakness and diarrhoea. She had profound hyponatraemia, hypokalaemia and a pre-renal acute kidney injury (AKI). Her ECG showed a regular wide complex tachycardia concerning for monomorphic ventricular tachycardia. She was haemodynamically stable and treated with aggressive electrolyte repletion and amiodarone. Flecainide toxicity can present as a variety of arrhythmias and early recognition is crucial. This case focuses on flecainide toxicity from multiple concomitant insults: diuretic use, diarrhoea, hypokalaemia, hyponatraemia and pre-renal AKI. We emphasise the importance of close outpatient monitoring of electrolytes in a patient on diuretics and flecainide to prevent life-threatening arrhythmias. We discourage use of multiple diuretics in patients taking flecainide.

Usefulness of cardiotoxicity assessment using calcium transient in human induced pluripotent stem cell-derived cardiomyocytes

Monitoring dramatic changes in intracellular calcium ion levels during cardiac contraction and relaxation, known as calcium transient, in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) would be an attractive strategy for assessing compounds on cardiac contractility. In addition, as arrhythmogenic compounds are known to induce characteristic waveform changes in hiPSC-CMs, it is expected that calcium transient would allow evaluation of not only compound-induced effects on cardiac contractility, but also compound arrhythmogenic potential. Using a combination of calcium transient in hiPSC-CMs and a fast kinetic fluorescence imaging detection system, we examined in this study changes in calcium transient waveforms induced by a series of 17 compounds that include positive/negative inotropic agents as well as cardiac ion channel activators/inhibitors. We found that all positive inotropic compounds induced an increase in peak frequency and/or peak amplitude. The effects of a negative inotropic compound could clearly be detected in the presence of a β-adrenergic receptor agonist. Furthermore, most arrhythmogenic compounds raised the ratio of peak decay time to peak rise time (D/R ratio) in calcium transient waveforms. Compound concentrations at which these parameters exceeded cutoff values correlated well with systemic exposure levels at which arrhythmias were reported to be evoked. In conclusion, we believe that peak analysis of calcium transient and determination of D/R ratio are reliable methods for assessing compounds' cardiac contractility and arrhythmogenic potential, respectively. Using these approaches would allow selection of compounds with low cardiotoxic potential at the early stage of drug discovery.

Role of abnormal repolarization in the mechanism of cardiac arrhythmia

In cardiac patients, life-threatening tachyarrhythmia is often precipitated by abnormal changes in ventricular repolarization and refractoriness. Repolarization abnormalities typically evolve as a consequence of impaired function of outward K⁺ currents in cardiac myocytes, which may be caused by genetic defects or result from various acquired pathophysiological conditions, including electrical remodelling in cardiac disease, ion channel modulation by clinically used pharmacological agents, and systemic electrolyte disorders seen in heart failure, such as hypokalaemia. Cardiac electrical instability attributed to abnormal repolarization relies on the complex interplay between a provocative arrhythmic trigger and vulnerable arrhythmic substrate, with a central role played by the excessive prolongation of ventricular action potential duration, impaired intracellular Ca²⁺ handling, and slowed impulse conduction. This review outlines the electrical activity of ventricular myocytes in normal conditions and cardiac disease, describes classical electrophysiological mechanisms of cardiac arrhythmia, and provides an update on repolarization-related surrogates currently used to assess arrhythmic propensity, including spatial dispersion of repolarization, activation-repolarization coupling, electrical restitution, TRIaD (triangulation, reverse use dependence, instability, and dispersion), and the electromechanical window. This is followed by a discussion of the mechanisms that account for the dependence of arrhythmic vulnerability on the location of the ventricular pacing site. Finally, the review clarifies the electrophysiological basis for cardiac arrhythmia produced by hypokalaemia, and gives insight into the clinical importance and pathophysiology of drug-induced arrhythmia, with particular focus on class Ia (quinidine, procainamide) and Ic (flecainide) Na⁺ channel blockers, and class III antiarrhythmic agents that block the delayed rectifier K⁺ channel (dofetilide).

Itopride in the treatment of functional dyspepsia in Chinese patients: a prospective, multicentre, post-marketing observational study

BACKGROUND

Prokinetic agents are commonly used in the symptomatic treatment of functional dyspepsia (FD). Safety or efficacy issues associated with the use of available prokinetics, such as metoclopramide, domperidone, cisapride and mosapride, mean there is a need for an effective and well tolerated prokinetic agent. Itopride is a novel prokinetic agent with a dual mode of action, good safety profile and documented efficacy in placebo-controlled trials.

OBJECTIVE

The objective of this study was to assess the effectiveness and safety of itopride in the management of FD.

METHODS

This was a prospective, multicentre, post-marketing observational study carried out in private outpatient clinics throughout China. The study included patients with symptomatic FD aged ≥18 years. Patients were prescribed itopride 50 mg three times daily before meals for 4 weeks, after which there was a 2-week follow-up period during which they did not take itopride. Effectiveness and tolerability data obtained from patients who completed 4 weeks of therapy were analysed. The treatment response rate after 4 weeks was measured by patient global assessment; scores at the end of treatment were compared with baseline scores. Response rate based on symptom scoring was also measured after 4 weeks, with an effective treatment being defined as a symptom improvement of ≥50%.

RESULTS

In total, 587 patients with FD were enrolled. The mean ± SD difference in the total symptom score before and after the 4-week treatment period was -5.62 ± 3.27, corresponding to a 69.23 ± 26.53% reduction from baseline (p < 0.001). The treatment response rates in patients who fulfilled Rome I, II and III criteria for FD were 33.68%, 34.71% and 35.50%, respectively, after 1 week of treatment; 52.82%, 54.61% and 56.51%, respectively, after 2 weeks; 66.67%, 67.23% and 68.64%, respectively, after 3 weeks; and 72.82%, 73.54% and 75.15%, respectively, after 4 weeks. Response rates were significantly different at 1 week versus 4 weeks of treatment. Nine patients (1.54%) had adverse events: four were probably related to the study drug, three were possibly related and two were not related. Of the nine patients with adverse events, two discontinued the study drug, two suspended (i.e. temporarily discontinued the drug until the adverse event subsided) the study drug, and five continued the study drug. Seven of the nine patients with adverse events had adverse reactions (defined as adverse events considered causally related to the study drug): two improved, three recovered and two showed no change. No adverse reactions were serious enough to warrant discontinuation of therapy.

CONCLUSION

Itopride was an effective and well tolerated drug in the management of FD in this patient population.

Systematic review: cardiovascular safety profile of 5-HT(4) agonists developed for gastrointestinal disorders

BACKGROUND

The nonselective 5-HT(4) receptor agonists, cisapride and tegaserod have been associated with cardiovascular adverse events (AEs).

AIM

To perform a systematic review of the safety profile, particularly cardiovascular, of 5-HT(4) agonists developed for gastrointestinal disorders, and a nonsystematic summary of their pharmacology and clinical efficacy.

METHODS

Articles reporting data on cisapride, clebopride, prucalopride, mosapride, renzapride, tegaserod, TD-5108 (velusetrag) and ATI-7505 (naronapride) were identified through a systematic search of the Cochrane Library, Medline, Embase and Toxfile. Abstracts from UEGW 2006-2008 and DDW 2008-2010 were searched for these drug names, and pharmaceutical companies approached to provide unpublished data.

RESULTS

Retrieved articles on pharmacokinetics, human pharmacodynamics and clinical data with these 5-HT(4) agonists, are reviewed and summarised nonsystematically. Articles relating to cardiac safety and tolerability of these agents, including any relevant case reports, are reported systematically. Two nonselective 5-HT(4) agonists had reports of cardiovascular AEs: cisapride (QT prolongation) and tegaserod (ischaemia). Interactions with, respectively, the hERG cardiac potassium channel and 5-HT(1) receptor subtypes have been suggested to account for these effects. No cardiovascular safety concerns were reported for the newer, selective 5-HT(4) agonists prucalopride, velusetrag, naronapride, or for nonselective 5-HT(4) agonists with no hERG or 5-HT(1) affinity (renzapride, clebopride, mosapride).

CONCLUSIONS

5-HT(4) agonists for GI disorders differ in chemical structure and selectivity for 5-HT(4) receptors. Selectivity for 5-HT(4) over non-5-HT(4) receptors may influence the agent's safety and overall risk-benefit profile. Based on available evidence, highly selective 5-HT(4) agonists may offer improved safety to treat patients with impaired GI motility.

Investigational agents for the irritable bowel syndrome

IMPORTANCE OF THE FIELD

Irritable bowel syndrome (IBS) is a common disorder with significant health and economic consequences. The etiology of IBS is complex and appears to be multifactorial. Traditional IBS therapies have been directed primarily at the relief of individual symptoms but have been largely disappointing. This has triggered the search for newer treatment strategies with improved patient outcomes.

AREAS COVERED IN THIS REVIEW

Enhanced knowledge about the putative pathophysiology of IBS has allowed the identification of new mechanistic targets for treatment. Our aim is to review emerging and promising drugs in the treatment of IBS based on disease pathophysiology. Data were extracted using Medline and PubMed search engines until January 2010. Abstracts were identified through 'Web of Science' and abstract supplements of major gastrointestinal scientific meetings. Drugs were classified according to mechanism of action and those with efficacy in trials involving human subjects examined.

WHAT THE READER WILL GAIN

Additional insight into the pathophysiology as well as current and prospective treatments of IBS.

TAKE HOME MESSAGE

A multitude of putative drug targets have been identified and some novel treatments have progressed through to human clinical trials, but very few will be approved for the market in the near future. Moreover, and in keeping with the complex and multifactorial nature of this syndrome, it is unlikely that there will be one dominant and universally effective form of therapy for all IBS patients.

Flecainide cardiotoxicity precipitated by electrolyte imbalance. Caution with thiazide diuretics

A man presented with recurrent syncope, weakness and fatigue. His ECG showed marked QRS widening and he had gross hyponatraemia and hypokalaemia. His medications included bendroflumethiazide (long term) and flecainide (started 2 months previously). This presentation was consistent with flacainide cardiotoxicity exacerbated by electrolyte disturbance. The syncopal episodes probably represented life-threatening arrhythmias. The ECG and symptoms resolved completely once the electrolytes were corrected. Increased cardiotoxicity with hypokalaemia is documented, but not widely recognised. Hyponatraemia-induced flecainide cardiotoxicity has not been documented. The clinical effects of flecainide are due to use-dependent block of sodium channels. There are reports that support the use of hypertonic sodium salts to reverse flecainide toxicity via antagonism at the receptor. By this rationale, hyponatraemia would lead to Flecainide toxicity. Flecainide has been shown to reduce salt absorption in animal bowel. It is possible that in combination with bendroflumethiazide it acted synergistically to produce profound electrolyte disturbance. Flecainide cardiotoxicity has a significant mortality and can present non-specifically. Thus, early recognition is essential. This case demonstrates the importance of strict electrolyte control in patients who are on flecainide. We would discourage concomitant use of flecainide and bendroflumethiazide.

Torsade-de-pointes in a patient under flecainide treatment, an unusual case of proarrhythmicity

Flecainide is an antiarrhythmic considered safe in patients who have no structural cardiopathy, and frequently used in the prevention of atrial fibrillation. However, in patients with a history of infarction and/or severe conduction disorders, its proarrhythmicity may be lethal. Torsade-de-pointes type tachycardia is not included as one of these proarrhythmic effects, since the drug's scant action on ventricular repolarization makes this adverse effect very unlikely. We present the case of a patient who, shortly after beginning treatment with flecainide, was admitted because of syncope related to bradyarrhythmias, long QT, and torsade-de-pointes. There have been very few published cases in which one finds such an association between flecainide and this infrequent arrhythmia.

QT PRODACT: A Multi-site Study of In Vitro Action Potential Assays on 21 Compounds in Isolated Guinea-Pig Papillary Muscles

To construct a non-clinical database for drug-induced QT interval prolongation, the electrophysiological effects of 11 positive and 10 negative compounds on action potentials (AP) in guinea-pig papillary muscles were investigated in a multi-site study according to a standard protocol. Compounds with a selective inhibitory effect on the rapidly activated delayed rectifier potassium current (IKr) prolonged action potential duration at 90% repolarization (APD90) in a concentration-dependent manner, those showing Ca2+ current (ICa) inhibition shortened APD30, and those showing Na+ current (INa) inhibition decreased action potential amplitude (APA) and Vmax. Some of the mixed ion-channel blockers showed a bell-shaped concentration-response curve for APD90, probably due to their blockade of INa and/or ICa, sometimes leading to a false-negative result in the assay. In contrast, all positive compounds except for terfenadine and all negative compounds with IKr-blocking activity prolonged APD30-90 regardless of their INa- and/or ICa-blocking activities, suggesting that APD30-90 is a useful parameter for evaluating the IKr-blocking activity of test compounds. Furthermore, the assay is highly informative regarding the modulation of cardiac ion channels by test compounds. Therefore, when APD90 and APD30-90 are both measured, the action potential assay can be considered a useful method for assessing the risk of QT interval prolongation in humans in non-clinical safety pharmacology studies.

Flecainide induced ventricular tachycardia (torsades de pointes)

This case report describes a 68-year-old woman presenting with flecainide induced syncope due to torsades de pointes (TP) ventricular tachycardia. Before TP onset, the QTc interval reached 680 ms without changes in QRS duration. None of the usual triggers were found. Prolongation of QT under flecaïnide is exceptional and the occurrence of TP without concurrent triggers has not been reported in the literature.

Structural and functional basis for the long QT syndrome: relevance to veterinary patients

Long QT syndrome (LQTS) is a condition characterized by prolongation of ventricular repolarization and is manifested clinically by lengthening of the QT interval on the surface ECG. Whereas inherited forms of LQTS associated with mutations in the genes that encode ion channel proteins are identified only in humans, the acquired form of LQTS occurs in humans and companion animal species. Often, acquired LQTS is associated with drug-induced block of the cardiac K+ current designated I(Kr). However, not all drugs that induce potentially fatal ventricular arrhythmias antagonize I(Kr), and not all drugs that block I(Kr), are associated with ventricular arrhythmias. In clinical practice, the extent of QT interval prolongation and risk of ventricular arrhythmia associated with antagonism of I(Kr) are modulated by pharmacokinetic and pharmacodynamic variables. Veterinarians can influence some of the potential risk factors (eg, drug dosage, route of drug administration, presence or absence of concurrent drug therapy, and patient electrolyte status) but not all (eg, patient gender/genetic background). Veterinarians need to be aware of the potential for acquired LQTS during therapy with drugs identified as blockers of HERG channels and I(Kr).