Electrophysiological effects of cetirizine, astemizole and D-sotalol in a canine model of long QT syndrome

The role and choice criteria of antihistamines in allergy management - expert opinion

Allergic diseases are the most common chronic conditions lasting throughout the patient’s life. They not only cause significant deterioration in the quality of life of patients but also lead to significant absenteeism and reduced productivity, resulting in very high costs for society. Effective and safe treatment of allergic diseases is therefore one of the main challenges for public health and should be carried out by all the specialists in family medicine, internists and paediatricians in collaboration with allergists, otorhinolaryngologists and dermatologists. Antihistamines are most commonly used in the treatment of allergies. Several dozen drugs are available on the pharmaceutical market, and their generic forms are advertised widely as very effective drugs for the treatment of allergic diseases. What is the truth? What are the data from clinical trials and observational studies? Are all drugs equally effective and safe for the patient? According to a panel of experts representing various fields of medicine, inappropriate treatment of allergies can be very risky for patients, and seemingly equally acting medications may differ greatly. Therefore, a panel of experts gathered the latest data from the entire scientific literature and analysed the latest standards and recommendations prepared by scientific societies. This paper provides a summary of these studies and highlights the importance for the patient of the proper choice of drug to treat his allergies.

Torsades de pointes liability inter-model comparisons: the experience of the QT PRODACT initiative

Safety pharmacologists from the Japanese pharmaceutical industries and contract laboratories made a database to evaluate drug effects on the QT interval in 2005. This QT PRODACT project was a prospective study of 12 QT-prolonging (positive) drugs and 10 non-prolonging (negative) drugs to evaluate the specificity and sensitivity of several in vivo and in vitro animal models: in vitro guinea pig papillary muscle action potential recordings and in vivo ECG recordings in unanesthetized or anesthetized beagle dogs, cynomolgus monkeys and miniature pigs. In guinea pig papillary muscle action potential recordings, positive drugs showed lengthening of the action potential duration (APD). By using a new measure to detect triangulation of the action potential configuration, an IKr blocking activity of drugs with Ca channel blocking action was detected. All in vivo studies showed a QT-prolonging effect of greater than 10% for the positive drugs. These in vivo models were useful to distinguish positive from negative drugs. The QT PRODACT project showed reliability and sensitivity of the experiments to detect positive drugs. The proarrhythmic effects of these positive drugs could not be detected even though, in some animal models (e.g., unanesthetized monkey), torsades de pointes (TdP)-type arrhythmias were shown by terfenadine. We compared in vivo arrhythmia models for proarrhythmia. The halothane-anesthetized open chest coronary occlusion-reperfusion canine model, the halothane-adrenaline arrhythmia model and the chronic AV block dog models seemed to be useful to detect the arrhythmogenic potential of QT-prolonging drugs.

The Effect of Antihistamine Cetirizine on Ventricular Repolarization in Congenital Long QT Syndrome

INTRODUCTION

Many drugs are known to block cardiac potassium channels, thus prolonging QT interval and predisposing to malignant arrhythmias. Patients with congenital long QT syndrome are particularly vulnerable, but usually electrophysiological effects of drugs have not been assessed in these patients at risk.

METHODS

Fifteen asymptomatic patients with type 1 (LQT1), 15 patients with type 2 (LQT2) long QT syndrome, and 15 healthy volunteers took a placebo and cetirizine 10 mg. In addition, healthy volunteers took cetirizine 50 mg. The study was single-blinded and randomized. Exercise tests were performed during stable plasma concentrations. The electrocardiogram was recorded with a body surface potential mapping system (BSPM). Data were analyzed with an automated analyze program. QT intervals to the T wave apex and T wave end and their difference (Tp-e) were determined at rest and at specified heart rates during and after exercise.

RESULTS

Cetirizine did not lengthen the QT intervals at rest or during exercise and recovery in any group. It shortened Tp-e at rest in LQT1 and LQT2 patients and during exercise test in LQT1 patients, thus slightly decreasing electrocardiographic transmural dispersion of repolarization.

CONCLUSIONS

Cetirizine does not adversely modify ventricular repolarization in types 1 and 2 long QT syndrome, suggesting that it might be used safely in these long QT syndrome patients.

Cetirizine: a review of its use in allergic disorders

Cetirizine is a selective, second-generation histamine H1 receptor antagonist, with a rapid onset, a long duration of activity and low potential for interaction with drugs metabolised by the hepatic cytochrome P450 system. Cetirizine was generally more effective than other H1 receptor antagonists at inhibiting histamine-induced wheal and flare responses. Cetirizine is an effective and well tolerated agent for the treatment of symptoms of seasonal allergic rhinitis (SAR), perennial allergic rhinitis (PAR) and chronic idiopathic urticaria (CIU) in adult, adolescent and paediatric patients. In adults with these allergic disorders, cetirizine was as effective as conventional dosages of ebastine (SAR, PAR, CIU), fexofenadine (SAR), loratadine (SAR, CIU) or mizolastine (SAR). This agent was significantly more effective, and with a more rapid onset of action, than loratadine in 2-day studies in environmental exposure units (SAR). In paediatric patients, cetirizine was as at least as effective as chlorphenamine (chlorpheniramine) [SAR], loratadine (SAR, PAR) and oxatomide (CIU) in the short term, and more effective than oxatomide and ketotifen (PAR) in the long term. Cetirizine was effective in reducing symptoms of allergic asthma in adults and reduced the relative risk of developing asthma in infants with atopic dermatitis sensitised to grass pollen or house dust mite allergens. It had a corticosteroid-sparing effect in infants with severe atopic dermatitis and was effective in ameliorating reactions to mosquito bites in adults. Cetirizine was well tolerated in adults, adolescents and paediatric patients with allergic disorders. In adult, adolescent and paediatric patients aged 2-11 years, the incidence of somnolence with cetirizine was dose related and was generally similar to that with other second-generation H1 receptor antagonists. Although, its sedative effect was greater than that of fexofenadine in some clinical trials and that of loratadine or fexofenadine in a postmarketing surveillance study. In infants aged 6-24 months, the tolerability profile of cetirizine was similar to that of placebo. Cetirizine did not have any adverse effects on cognitive function in adults, or cognitive function, behaviour or achievement of psychomotor milestones in paediatric patients. Cetirizine was not associated with cardiotoxicity.

CONCLUSION

Cetirizine is well established in the treatment of symptoms of SAR, PAR or CIU. It demonstrated a corticosteroid-sparing effect and reduced the relative risk of developing asthma in sensitised infants with atopic dermatitis. Cetirizine was effective in the treatment of allergic cough and mosquito bites; however, its precise role in these indications has yet to be clearly established. On the basis of its favourable efficacy and tolerability profile and rapid onset of action, cetirizine provides an important option for the treatment of a wide range of allergic disorders.

Sex differences in ventricular repolarization: from cardiac electrophysiology to Torsades de Pointes

A number of non-cardiovascular drugs have been withdrawn from clinical use due to unacceptable adverse cardiac side-effects involving drug-induced Torsades de Pointes (TdP)--a rare, life-threatening polymorphic ventricular tachycardia associated with prolongation of the action potential duration of ventricular myocytes and, hence, prolongation of the QT interval, of the electrocardiogram (ECG), which measures the total time for activation of the ventricles and their recovery to the resting state. Research has suggested that women are more prone to develop TdP than men during administration of medicines that share the potential to prolong the QT interval, with 65-75% of drug-induced TdP occurring in women. Clinical and experimental studies show that female sex demonstrate differences in the electrocardiographic pattern of ventricular repolarization in human and other animal species and is associated with a longer rate-corrected QT (QTc) interval at baseline than males. Reports of a similar propensity towards drug-induced TdP in both premenopausal and postmenopausal women support factors in addition to those of female sex hormones eliciting sex-based differences in ventricular repolarization. However, conflicting evidence suggests sex hormones may have a role in increasing the susceptibility of women or ultimately reducing the susceptibility of men to TdP. Cyclical variations in hormone levels during the menstrual cycle have been associated with an increased and reduced risk of TdP. In contradiction to this finding, the male sex hormone is thought to be beneficial. Modulation of the ventricular repolarization by testosterone may explain why the QTc interval shortens at puberty, and might account for the tendency towards an age-dependent reduction in the incidence of drug-induced TdP in men. Mechanisms underlying these differences are not fully understood but a case for the involvement of gonadal steroids is obviously strong. Therefore, further non-clinical/clinical investigations ought to be a necessary step to elucidate any sex differences in cardiac repolarization characteristics, QT interval prolongation and susceptibility to cardiac arrhythmias. This may have implications for the development of the safest medicinal products and for the clinical management of cardiac arrhythmias.

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).

Rate-correction technique for QT interval in long-term telemetry ECG recording in beagle dogs

The establishment of a new rate-correction method for the QT interval is presented for long-term telemetry ECG recording in free-moving beagle dogs. First, in order to define the QT-RR relation to derive the correction formula, the diurnal variations of the QT and RR intervals and the influencing factors were analyzed, and the QT-RR regression coefficient beta was estimated under various conditions: steady and non-steady states of animal, light and dark periods, and over 24 h. In the results, the diurnal rhythm of the QT interval was synchronized with the RR interval reflecting the physical and emotional states of the animal. The coefficient beta had considerable variation during the day: beta; 0.276 +/- 0.052 (maximum to minimum: 0.495 to 0.153). Thus, it was considered that the ideal rate-correction technique for telemetry ECG requires the selection of a flexible coefficient beta adjusted to the condition of the measurement. Therefore, rate-correction utilizing analysis of covariance estimating the coefficient beta for each dog, was compared with previously proposed formulas which fix the rate-correction coefficient, based on the capacity to dissociate the effects of heart rate on the QT interval. This was then tested by the levels of discrimination apparent in the QT prolongation caused by a class III antiarrhythmic drug, which ranked the formulas on the levels of correction achieved as follows: covariance adjustment > Matsunaga > Van de Water > Bazett. Thus, the rate-correction method utilizing analysis of covariance is proven adequate for data from telemetry ECG recordings.

Drug-induced ventricular tachyarrhythmia in isolated rabbit hearts with atrioventricular block

The aims of this study were to develop a suitable model to study proarrhythmic potential using isolated rabbit hearts with atrioventricular block and to examine the proarrhythmic potential of several drugs using this model. With a normal K/Mg solution (K+=5.7 mM and Mg2+=1 mM), d,l-sotalol (10 and 30 microM), a class III antiarrhythmic drug, prolonged ventricular repolarization, such as QT intervals and monophasic action potential duration, and induced early after-depolarization and polymorphic ventricular tachyarrhythmia. Cisapride (0.1 and 0.3 microM), a 5-HT4 receptor agonist, also prolonged the ventricular repolarization, and induced early after-depolarization. With a low K/Mg solution (K+=1.5 mM and Mg2+=0.35 mM), d,l-sotalol at 30 microM and cisapride at 0.3 microM more potently prolonged the ventricular repolarization than with a normal K/Mg solution. Furthermore, the incidence of polymorphic ventricular tachyarrhythmia caused by cisapride at 0.3 microM with a low K/Mg solution was higher than that with a normal K/Mg solution. Mosapride citrate, another 5-HT4 receptor agonist, at 10 microM prolonged the ventricular repolarization and induced early after-depolarization with a low K/Mg solution, whereas the drug at 1 and 3 microM did not affect any of the parameters examined. Des-4-fluorobenzyl-mosapride, a metabolite of mosapride citrate, at 10 microM slightly prolonged the ventricular repolarization without inducing early after-depolarization or ventricular tachyarrhythmia. These results suggest that mosapride citrate and des-4-fluorobenzyl-mosapride have much less proarrhythmic potential than cisapride and that isolated rabbit heart with atrioventricular block, perfused with a low K/Mg solution, is a suitable model for predicting the proarrhythmic potential of drugs.

Electrophysiologic parameters and predisposing factors in the generation of drug-induced Torsade de Pointes arrhythmias

When a new (cardiovascular) drug shows signs of QT interval prolongation on the ECG (delay in repolarization time), the regulatory agencies demand screening of its possible proarrhythmic potential before approving it for clinical practice. In this review, identified predisposing factors have been related to specific electrophysiological parameters, allowing quantification of their contribution to Torsade de Pointes arrhythmias. In addition, arrhythmogenic mechanisms involved in the initiation and perpetuation of drug-induced Torsade de Pointes are discussed.

The ACVD task force on canine atopic dermatitis (XXI): antihistamine pharmacotherapy

Antihistamines frequently are recommended by veterinary dermatologists for symptomatic treatment of pruritus associated with canine atopic dermatitis (AD), perhaps because of their moderate success in some human patients with AD. A critical review of the literature describing antihistamine use in canine AD reveals that the majority of published, peer-reviewed studies are open, uncontrolled or partially-controlled trials. Such studies vary widely in reported efficacy, from perhaps 0 to 75% of patients, even using the same drug. The few blinded placebo-controlled trials available have failed to confirm efficacy of these drugs to relieve the pruritus of canine AD. Some studies indicate that synergistic effects could occur with concurrent use of essential fatty acid supplements. Consequently, at the time of this writing, there is insufficient evidence to conclude for or against the efficacy of antihistamines for treatment of canine AD. Additional blinded, randomized and controlled trials with larger numbers of patients are necessary to establish which of the antihistamine drugs currently available, if any, are truly efficacious for canine AD. Nevertheless, present clinician consensus suggests that several different antihistamine drugs should be evaluated in sequence, for 7-14 days each, in canine patients with AD.