Utilization of the chronic atrioventricular block cynomolgus monkey as an in vivo model to evaluate drug interaction-associated torsade de pointes.

It has been difficult to experimentally reproduce synergistic effects of ketoconazole on terfenadine-induced torsade de pointes. We assessed proarrhythmic effects of terfenadine (30 mg/kg, p.o.) with/without ketoconazole (100 mg/kg, p.o.) pretreatment using the chronic atrioventricular block cynomolgus monkeys with repeated-measured design (n = 4). Terfenadine with ketoconazole pretreatment repeatedly induced non-sustained torsade de pointes in each animal, although terfenadine alone did not induce it at all. Thus, the chronic atrioventricular block cynomolgus monkeys can be used for studying drug interaction-associated torsade de pointes, providing a non-clinical strategy to circumvent untoward drug interactions in patients specially under polypharmacy.

Enzalutamide inhibits testosterone-induced growth of human prostate cancer xenografts in zebrafish and can induce bradycardia.

The zebrafish has become a popular human tumour xenograft model, particularly for solid tumours including prostate cancer (PCa). To date PCa xenotransplantation studies in zebrafish have not been performed in the presence of testosterone, even when employing androgen-dependent cell models, such as the LNCaP cell line. Thus, with the goal of more faithfully modelling the hormonal milieu in which PCa develops in humans, we sought to determine the effects of exogenous testosterone on the growth of LNCaP, or androgen-independent C4-2 cells xenografted into zebrafish embryos. Testosterone significantly increased engrafted LNCaP proliferation compared to control xenografts, which could be inhibited by co-administration of the anti-androgen receptor drug, enzalutamide. By contrast, C4-2 cell growth was not affected by either testosterone or enzalutamide. Enzalutamide also induced bradycardia and death in zebrafish embryos in a dose-dependent manner and strongly synergized with the potassium-channel blocking agent, terfenadine, known to induce long QT syndrome and cardiac arrhythmia. Together, these data not only indicate that testosterone administration should be considered in all PCa xenograft studies in zebrafish but also highlights the unique opportunity of this preclinical platform to simultaneously evaluate efficacy and toxicity of novel therapies and/or protective agents towards developing safer and more effective PCa treatments.

Sensitivity and Reliability of Halothane-anaesthetized Microminipigs to Assess Risk of Drug-induced Long QT Syndrome.

Using moxifloxacin and terfenadine, which are known to induce benign and malignant QT interval prolongation, respectively, we analysed whether halothane-anaesthetized microminipigs are an appropriate model for assessing the risk of drug-induced long QT syndrome. Moxifloxacin (0.03, 0.3 and 3 mg/kg) and terfenadine (0.03, 0.3 and 3 mg/kg) were intravenously infused over 10 min. with a pause of 20 min. to the halothane-anaesthetized microminipigs (n = 4 for each drug). Moxifloxacin decreased the heart rate, whereas it increased the blood pressure in a dose-related manner. It also prolonged the PR interval and QT/QTc in a dose-related manner without altering the QRS width. Terfenadine decreased the heart rate and blood pressure, whereas it prolonged the PR interval, QRS width and QT/QTc in a dose-related manner. Terfenadine significantly prolonged the beat-to-beat variability of QT interval reflecting its pro-arrhythmic potential, which was not observed with moxifloxacin. The peak plasma concentrations of moxifloxacin and terfenadine after doses of 3 mg/kg were 4.81 and 10.15 µg/mL, respectively, which were both 1.5 times less in microminipigs than those previously reported in dogs. These results indicate that halothane-anaesthetized microminipigs would be useful for detecting drug-induced cardiovascular responses as well as differentiating benign from malignant QT interval prolongation like dogs, although there may be some differences in pharmacokinetic profile between these animals.

Does terfenadine-induced ventricular tachycardia/fibrillation directly relate to its QT prolongation and Torsades de Pointes?

BACKGROUND AND PURPOSE: Terfenadine has been reported to cause cardiac death. Hence, we investigated its pro-arrhythmic potential in various in vitro models. EXPERIMENTAL APPROACH: Pro-arrhythmic effects of terfenadine were investigated in rabbit isolated hearts and left ventricular wedge preparations. Also, using whole-cell patch-clamp recording, we examined its effect on the human ether-à-go-go-related gene (hERG) current in HEK293 cells transfected with hERG and on the I(Na) current in rabbit ventricular cells and human atrial myocytes. KEY RESULTS: Terfenadine concentration- and use-dependently inhibited I(Na) in rabbit myocytes and in human atrial myocytes and also inhibited the hERG. In both the rabbit left ventricular wedge and heart preparations, terfenadine at 1 µM only slightly prolonged the QT- and JT-intervals but at 10 µM, it caused a marked widening of the QRS complex, cardiac wavelength shortening, incidences of in-excitability and non-TdP-like ventricular tachycardia/fibrillation (VT/VF) without prolongation of the QT/JT-interval. At 10 µM terfenadine elicited a lower incidence of early afterdepolarizations versus non- Torsades de Pointes (TdP)-like VT/VF (100% incidence), and did not induce TdPs. Although the concentration of terfenadine in the tissue-bath was low, it accumulated within the heart tissue. CONCLUSION AND IMPLICATIONS: Our data suggest that: (i) the induction of non-TdP-like VT/VF, which is caused by slowing of conduction via blockade of I(Na) (like Class Ic flecainide), may constitute a more important risk for terfenadine-induced cardiac death; (ii) although terfenadine is a potent hERG blocker, the risk for non-TdP-like VT/VF exceeds the risk for TdPs; and (iii) cardiac wavelength (λ) could serve as a biomarker to predict terfenadine-induced VT/VF.

Block of the hERG channel by bupivacaine: Electrophysiological and modeling insights towards stereochemical optimization.

The hERG voltage-gated potassium channel mediates the cardiac I(Kr) current, which is crucial for the duration of the cardiac action potential. Undesired block of the channel by certain drugs may prolong the QT interval and increase the risk of malignant ventricular arrhythmias. Although the molecular determinants of hERG block have been intensively studied, not much is known about its stereoselectivity. Levo-(S)-bupivacaine was the first drug reported to have a higher affinity to block hERG than its enantiomer. This study strives to understand the principles underlying the stereoselectivity of bupivacaine block with the help of mutagenesis analyses and molecular modeling simulations. Electrophysiological measurements of mutated hERG channels allowed for the identification of residues involved in bupivacaine binding and stereoselectivity. Docking and molecular mechanics simulations for both enantiomers of bupivacaine and terfenadine (a non-stereoselective blocker) were performed inside an open-state model of the hERG channel. The predicted binding modes enabled a clear depiction of ligand-protein interactions. Estimated binding affinities for both enantiomers were consistent with electrophysiological measurements. A similar computational procedure was applied to bupivacaine enantiomers towards two mutated hERG channels (Tyr652Ala and Phe656Ala). This study confirmed, at the molecular level, that bupivacaine stereoselectively binds the hERG channel. These results help to lay the foundation for structural guidelines to optimize the cardiotoxic profile of drug candidates in silico.

Effects of fexofenadine on inflammatory mediators in nasal lavage fluid in intermittent allergic rhinitis.

OBJECTIVE: Allergic rhinitis, a disease that impairs quality of life, is characterized by inflammation due to an allergic reaction. Fexofenadine is a second-generation histamine receptor blocker well known for its potent interaction with this inflammatory process. The main aim of this study was to further clarify the anti-inflammatory effects exerted by fexofenadine in patients with intermittent allergic rhinitis. METHODS: Twenty patients with intermittent allergic rhinitis due to birch and mugwort pollen were enrolled. Fexofenadine was administered once a day at a dose of 120 mg. Clinical improvement was assessed by a symptom score, and nasal airway flows were measured by anterior rhinomanometry at baseline and after 2 weeks of treatment with fexofenadine. Nasal smears were tested for eosinophils and nasal lavage fluid were examined for histamine, cysteinyl leukotrienes, soluble intercellular adhesion molecule-1, eosinophil cationic protein, and albumin by enzyme-linked immunosorbent assay. All the tests were performed during the pollen season. RESULTS: Fexofenadine induced a significant improvement in nasal and ocular symptoms (P < .001), nasal edema and secretion (P < .001), and nasal airway flow (P < .001). The clinical improvement was related to a significant reduction in all inflammatory mediators (P < .01 in all cases). CONCLUSION: This study demonstrates that fexofenadine is able to mediate significant changes in different nasal lavage markers from patients with intermittent allergic rhinitis. The changes observed in the markers analyzed in both nasal secretions and serum are attributable to the anti-inflammatory effects of fexofenadine in vivo.

Hydroxypropyl beta-cyclodextrins: a misleading vehicle for the in vitro hERG current assay.

Delayed cardiac repolarization and fatal proarrhythmia have been linked to block of the repolarizing current, Ikr or hERG (human ether-a-go-go related gene) current. Thus, determining the potency of hERG block is critical in evaluating cardiac safety during preclinical development. Hydroxypropyl beta-cyclodextrins (HbetaC) are cyclic oligosaccharides used to enhance drug solubility. To evaluate the utility of HbetaC to enhance drug solubility in hERG screening assays, we studied the effect of HbetaC on hERG current and the sensitivity of the hERG assay to 3 structurally different hERG blocking drugs using whole-cell voltage clamp technique and HEK-293 cells expressing the hERG channel. HbetaC inhibited hERG activation and tail current and accelerated current deactivation in a concentration-dependent manner. HbetaC (6%) reduced the apparent potency of block by terfenadine (IC50 12000 nM vs 45 nM), cisapride (IC50 281 nM vs 28 nM), and E-4031 (163 nM vs 26 nM). Reduced potency of block was consistent with loss of activity as a result of complexation with HbetaC by terfenadine and cisapride (demonstrated in solubility studies) and interactions with HbetaC by E-4031 (demonstrated in absorbance studies). These results demonstrate that HbetaC is an unsuitable agent for enhancing compound solubility in the in vitro hERG current assay and may mask drug effects, allowing potentially dangerous drugs to advance into clinical development.

[Extension of QT interval as a consequence of risk factor accumulation--case study]. / Prodlouzení QT intervalu jako dusledek kumulace rizikových faktoru: kazuistika.

BACKGROUND: Many non-cardiovascular drugs have a potential for QT interval prolongation. This phenomenon can be related to occurence of ventricular tachycardia torsades de pointes, syncopi and even sudden death. DESCRIPTION OF THE CASE: A female patient treated with antracycline cytostatics developed a depression of left ventricle ejection fraction. At the same time she was administered 2 common drugs with proarrhythmic potential--terfenadine and itraconazole. In this patient hypokalemia also occured. Combination of the above mentioned risk factors led to QT interval prolongation and frequent ventricular tachycardias torsades de pointes degenerating in ventricular fibrillations with need of repeated defibrillations. Both drugs were withdrawn and dysiontaemia corrected. Then arrhythmias disappeared and QT interval completely normalized. In this patient the congenital long QT syndrome was not proved. DISCUSSION AND CONCLUSIONS: In proarrhythmic effect of non-cardiovascular drugs the following factors play role: predisposition of a particular individual, "repolarization reserve", interindividual differences in drug metabolism. The risk factors are age, sex, dysiontaemia, heart disease and drug interactions. By different choice of medication and attention to risk factors teh life threat to the described patient could have been avoided.

Drug-induced proarrhythmia and use of QTc-prolonging agents: clues for clinicians.

Use of drugs with the potential for prolongation of the QTc interval and proarrhythmia is a growing challenge facing clinicians. Many pharmaceutical agents have been denied approval for human use, approved with restrictions and warnings regarding proarrhythmia, or withdrawn from the market based upon arrhythmic risk. Despite known risk factors for QTc prolongation and drug-induced arrhythmia, precise prediction of the risk of torsades de pointes (TdP) in an individual patient remains difficult. The mechanism of drug-induced TdP typically involves use of an agent that blocks the I(Kr) cardiac potassium current, often in combination with risk-amplifying factors such as high drug levels, reduced drug metabolism, polypharmacy, and patient-specific factors such as gender, age, and genetic polymorphism. For the clinician, an integrated approach involving appreciation of the risk factors for proarrhythmia combined with computer-based risk assessment is the best method for reducing the risk of drug-induced proarrhythmia in clinical practice.

Drugs, hERG and sudden death.

Early recognition of potential QT/TdP liability is now an essential component of the drug discovery/drug development program. The hERG assay is an indispensable step and a high-quality assay must accompany any investigational new drug (IND) application. While it is the gold standard at present, the hERG assay is too labor-intensive and too low throughput to be used as a screen early in the discovery/development process. A variety of indirect high throughput screens have been used.

[Effects of clinically available drugs on the repolarization process of the heart assessed by the in vivo canine models].

The proarrhythmic effects of class III antiarrhythmic agents and non-cardiovascular drugs, which have been shown to prolong QT interval, were assessed using two types of in vivo canine models. First, electrophysiological effects of dofetilide, nifekalant, amiodarone, cisapride, astemizole, sulpiride, haloperidol, and sparfloxacin were assessed using halothane-anesthetized dogs. Each drug prolonged the monophasic action potential (MAP) duration and effective refractory period (ERP) at clinically recommended daily doses. The extent of increase was greater in the refractoriness than in the repolarization only for amiodarone, indicating abbreviation of the terminal repolarization period. The reverse was true for the other drugs. Next, torsadogenic action of sematilide, nifekalant, amiodarone, cisapride, terfenadine, sulpiride, and sparfloxacin was assessed using chronic complete atrioventricular block dogs with Holter ECG monitoring in the conscious state. Oral administration of 1-10 times higher doses than the clinically relevant doses of the drugs induced polymorphic ventricular tachycardia torsades de pointes (TdP), except for amiodarone. These results indicate that the prolongation and backward shift of the terminal repolarization period may be closely related to the drug-induced TdP and suggest that these in vivo models can be used to screen proarrhythmic potential of new drugs.

The antihistamine fexofenadine does not affect I(Kr) currents in a case report of drug-induced cardiac arrhythmia.

1. The human HERG gene encodes the cardiac repolarizing K(+) current I(Kr) and is genetically inactivated in inherited long QT syndrome 2 (LQTS2). The antihistamine terfenadine blocks HERG channels, and can cause QT prolongation and torsades de pointes, whereas its carboxylate fexofenadine lacks HERG blocking activity. 2. In the present study the ability of fexofenadine to block the K897T HERG channel variant was investigated. The underlying single nucleotide polymorphism (SNP) A2960C was identified in a patient reported to develop fexofenadine-associated LQTS. 3. K897T HERG channels produced wild-type-like currents in Xenopus oocytes. Even at a concentration of 100 micro M, fexofenadine did not inhibit wild-type or K897T HERG channels. Coexpression of wild-type and K897T HERG with the ss-subunit MiRP1, slightly changed current kinetics but did not change sensitivity to terfenadine and fexofenadine. 4. Western blot analysis and immunostaining of transiently transfected COS-7 cells demonstrated that overall expression level, glycosylation pattern and subcellular localization of K897T HERG is indistinguishable from wild-type HERG protein, and not altered in the presence of 1 micro M fexofenadine. 5. We provide the first functional characterization of the K897T HERG variant. We demonstrated that K897T HERG is similar to wild-type HERG, and is insensitive to fexofenadine. Although the polymorphism changes PKA and PKC phosphorylation sites, regulation of K897T HERG by these kinases is not altered. 6. Our results strongly indicate that QT lengthening and cardiac arrhythmia in the reported case of drug-induced LQT are not due to the K897T exchange or to an inhibitory effect of fexofenadine on cardiac I(Kr) currents. British Journal of

Suppression of the early and late cutaneous allergic responses using fexofenadine and montelukast.

BACKGROUND: The relative contribution of histamine and the cysteinyl leukotrienes to the early and late cutaneous allergic responses (ECAR and LCAR) can be studied using antagonists of these mediators. OBJECTIVE: To determine the relative suppression of the ECARs and LCARs using standard doses of an H1-receptor antagonist, a cysteinyl leukotriene1-receptor antagonist, and the two antagonists administered concurrently. METHODS: We carried out a prospective, randomized, double-blind, placebo-controlled, four-way crossover study in 12 highly allergic participants. Intradermal tests with standardized allergen, and with histamine phosphate, LTD4, and saline controls were performed on 5 different test days as follows: pretreatment baseline and at steady state immediately after the seventh and last dose of a 1-week course of treatment with once-daily fexofenadine, 120 mg; montelukast, 10 mg; fexofenadine and montelukast administered concurrently; or placebo. On each test day, the skin test results were read at intervals from 0.25 to 24 hours after the intradermal injections were performed. RESULTS: After allergen injection, compared with baseline, all treatment regimens significantly decreased the ECAR and LCAR. After allergen injection, compared with placebo, fexofenadine significantly decreased the ECAR and the LCAR from 0.25 to 2 hours and at 8 hours. Montelukast did not significantly decrease the ECAR or LCAR. Fexofenadine and montelukast administered concurrently were not more effective than fexofenadine alone at any time. In the control skin tests, compared with placebo, fexofenadine, but not montelukast, significantly decreased the histamine-induced response, and montelukast, but not fexofenadine, significantly decreased the LTD4-induced response. CONCLUSIONS: Fexofenadine and montelukast administered concurrently were not significantly more effective than fexofenadine alone in decreasing the ECAR and LCAR. Montelukast does not need to be discontinued before allergen skin testing. Further studies of the effect of concurrent treatment with higher doses of a histamine antagonist and a leukotriene modifier on the allergic response in the skin are needed.

Comparative efficacy of terfenadine, loratadine, and astemizole in perennial allergic rhinitis.

Nonsedating H1 antihistamines such as terfenadine, loratadine, and astemizole are widely prescribed for the treatment of allergic rhinitis. The comparative efficacy of these agents has not been thoroughly studied. We studied 14 subjects in an open-label four-way crossover trial. Patients were recruited from an outpatient allergy clinic. Inclusion criteria were documented rhinitis symptoms for at least 2 years before the study and skin-test positivity in response to perennial allergens. Each subject underwent sequential 2-week trials of each of four H1 antihistamines: terfenadine, loratadine, astemizole, and chlorpheniramine. No placebo was included. Outcome measures were subjective rhinitis symptom scores, overall efficacy scores, and concomitant pseudoephedrine use. In addition, nasal-examination scores were obtained by way of physician assessment at the end of each 2-week trial, and side effects were tabulated. Nasal-examination scores for each of the four H1 antihistamines were significantly better than the baseline scores (p < 0.05). No statistically significant differences in rhinitis symptom scores, overall efficacy scores, or concomitant pseudoephedrine use were noted. We detected no clinically significant differences in efficacy among terfenadine, loratadine, astemizole, and chlorpheniramine in the treatment of perennial allergic rhinitis.

Anti-histamínicos "näo clássicos" e cardiotoxidade / Non-classical antihistamines and cardiotoxicity

O desenvolvimento dos anti-histamínicos "nao-clásicos" tem sido considerado um significante avanço no tratamento dos pacientes alérgicos. Além de proporcionarem reduçao dos sintomas, sao medicamentos de uso oral que nao causam sedaçao ou prejuízo à atividade psicomotora do paciente. Entretanto, alguns relatos de casos com efeitos cardíacos adversos atribuídos à terfenadina e ao astemizol, administrados em altas doses e/ou associados ao cetoconazol ou a antibióticos macrolídeos, têm causado muita discussao. Neste trabalho revemos tais eventos, bem como suas possíveis explicaçoes.

Estado actual de antihistamínicos / Current state of antihistamine drugs

El aumento de la prevalencia mundial de las patologías respiratorias alérgicas conlleva un aumento simultáneo en la prescripción de antihistamínicos orales. Los efectos adversos que dichos medicamentos provocan en el sistema nervioso central son muy frecuentes(1), por lo que se presenta una revisión actualizada de los antihistamínicos sistémicos bajo el clásico adagio de la Medicina: "Primum non nocere" ("antes que nada no dañar"). En esta revisión se describe las generalidades de la acción de la histamina en el organismo. Los efectos terapéuticos y secundarios de los antihistamínicos de primera y segunda generación y finalmente se presenta una descripción acabada del nuevo antialérgico epinastina

HERG, a primary human ventricular target of the nonsedating antihistamine terfenadine.

BACKGROUND: Administration of the antihistamine terfenadine (Seldane) to patients may result in acquired long QT syndrome and ventricular arrhythmias. One human cardiac target is Kv1.5, which expresses the ultrarapid outward K+ current (Ikur) in atrium but may play only a minor role in ventricle. Another possible target is HERG, the human ether-a-go-go-related gene that expresses a delayed rectifier current (IKr) in human ventricle and produces hereditary long QT syndrome when defective. METHODS AND RESULTS: We therefore heterologously expressed Kv1.5 and HERG in Xenopus oocytes to compare the sensitivity of each to terfenadine. We found that HERG was 10 times more sensitive than Kv1.5 to terfenadine block. The apparent Kd values for HERG and Kv1.5 currents were 350 nmol/L and 2.7 mumol/L, respectively. These Kd values compare well with values reported for terfenadine block of IKr and IKur currents in human atrial myocytes. The Kd value for HERG block is relevant to the toxicity of the antihistamine, since the clinical terfenadine concentrations in human plasma may reach the 100 nmol/L range. CONCLUSIONS: Terfenadine carboxylate, the major metabolite of terfenadine, does not block either HERG or Kv1.5, which agrees with the hypothesis that the buildup of parent terfenadine is the likely explanation for its cardiotoxicity. We propose that the blocking of HERG by terfenadine explains the acquired long QT syndrome. HERG is likely to be the primary target for the known cardiotoxic effects of other, related antihistamines.

An assessment of cognitive function and mood in chronic fatigue syndrome.

Data were gathered regarding the associates of chronic fatigue syndrome (CFS) with: (1) speed of cognitive processing, (2) motor speed, (3) ability to sustain attention, and (4) mood. Patients were given a brief neuropsychological test battery before and after double-blind treatment with terfenadine or placebo and completed a daily mood rating scale (Positive and Negative Affect Schedule) during the study. CFS patients exhibited slower cognitive processing and motor speed and lower positive affect, as compared to data reported from previous studies of healthy subjects and other patient groups; however, CFS patients did not exhibit deficits in sustained attention in comparison to other groups. The CFS patients' ability to attend to verbal versus figural stimuli and mood ratings were different from those reported in studies of patients with depression. Because of methodological limitations, these findings are preliminary, but they encourage further assessment of cognitive dysfunction and mood in CFS.