Blockade of cardiac potassium and other channels by antihistamines

Five years of the CiPA project (2013-2018): what did we learn?

Cases of drug-induced QT prolongation and sudden cardiac deaths resulted in market withdrawal of many drugs and world-wide regulatory changes through accepting the ICH guidelines E14 and S7B. However, because the guidelines were not comprehensive enough to cover the electrophysiological changes by drug-induced cardiac ion channel blocking, CiPA was initiated by experts in governments and academia in the USA, Europe, and Japan in 2013. Five years have passed since the launch of the CiPA initiative that aimed to improve the current ICH guidelines. This report reviews the current achievements of the CiPA initiative and explores unresolved issues.

Management of anaphylaxis and allergies in patients with long QT syndrome: A review of the current evidence

OBJECTIVE

To develop a treatment algorithm for patients with long QT syndrome (LQTS) in case they need antiallergic medications for allergic reactions, including asthma and anaphylaxis.

DATA SOURCES

A literature review was performed to assess safety and to develop antiallergic treatment strategies for patients with LQTS.

STUDY SELECTIONS

LQTS is a heterogeneous group of myocardial repolarization disorders characterized by prolongation of the QT interval that potentially results in life-threatening torsades de pointes tachycardia. Data on pharmacologic treatment in case of anaphylaxis in LQTS are sparse. For this narrative review, all currently available articles on the use of antiallergic drugs for allergic reactions, anaphylaxis, and asthma in patients with LQTS were used.

RESULTS

Local allergic symptoms can be safely treated primarily with fexofenadine, levocetirizine, desloratadine, or cetirizine and, if needed, a short course of corticosteroids. In case of systemic symptoms, epinephrine should be administered. It may be less effective in patients with LQTS treated with β-blockers, necessitating the use of glucagon as add-on treatment. In case of lower airway obstruction, ipratropium bromide should be used, but if not effective, inhaled β₂-adrenergic agents may be used. Continuous cardiac monitoring is indicated with the use of epinephrine and inhaled β₂-adrenergic agents. The use of the latter also warrants intense monitoring of serum potassium levels. Clemastine and dimetindene should be avoided in patients with LQTS.

CONCLUSION

Patients with LQTS have a higher risk of life-threatening complications during the treatment of their allergic reactions because of the underlying disease and concomitant treatment with β-blockers. Treatment algorithms will certainly decrease these complications.

Drug-induced Inhibition and Trafficking Disruption of ion Channels: Pathogenesis of QT Abnormalities and Drug-induced Fatal Arrhythmias

Risk of severe and fatal ventricular arrhythmias, presenting as Torsade de Pointes (TdP), is increased in congenital and acquired forms of long QT syndromes (LQTS). Drug-induced inhibition of K+ currents, IKs, IKr, IK1, and/or Ito, delay repolarization, prolong QT, and increase the risk of TdP. Drug-induced interference with IKr is the most common cause of acquired LQTS/TdP. Multiple drugs bind to KNCH2-hERG-K+ channels affecting IKr, including antiarrythmics, antibiotics, antivirals, azole-antifungals, antimalarials, anticancer, antiemetics, prokinetics, antipsychotics, and antidepressants. Azithromycin has been recently added to this list. In addition to direct channel inhibition, some drugs interfere with the traffic of channels from the endoplasmic reticulum to the cell membrane, decreasing mature channel membrane density; e.g., pentamidine, geldalamicin, arsenic trioxide, digoxin, and probucol. Other drugs, such as ketoconazole, fluoxetine, norfluoxetine, citalopram, escitalopram, donepezil, tamoxifen, endoxifen, atazanavir, and roxitromycin, induce both direct channel inhibition and impaired channel trafficking. Although many drugs prolong the QT interval, TdP is a rare event. The following conditions increase the risk of drug-induced TdP: a) Disease states/electrolyte levels (heart failure, structural cardiac disease, bradycardia, hypokalemia); b) Pharmacogenomic variables (presence of congenital LQTS, subclinical ion-channel mutations, history of or having a relative with history of drug-induced long QT/TdP); c) Pharmacodynamic and kinetic factors (high doses, women, elderly, metabolism inhibitors, combining two or more QT prolonging drugs, drugs that prolong the QT and increase QT dispersion, and drugs with multiple actions on ion channels). Because most of these conditions are preventable, careful evaluation of risk factors and increased knowledge of drug use associated with repolarization abnormalities are strongly recommended.

Altered cytosolic Ca2+ dynamics in cultured Guinea pig cardiomyocytes as an in vitro model to identify potential cardiotoxicants

Altered intracellular calcium (Ca(i)(2+)) handling by cardiomyocytes has been implicated in drug-induced cardiomyopathy and arrhythmogenesis. To explore whether such alterations predict cardiotoxicity, Ca(i)(2+) imaging was conducted in cultured, spontaneously contracting Guinea pig cardiomyocytes to characterize the effects of 13 cardiotoxicants and 2 safe drugs. All cardiotoxicants perturbed Ca(i)(2+) at therapeutically relevant concentrations. The cytotoxic chemotherapeutics doxorubicin and epirubicin, known to cause cardiomyopathy, preferentially reduced Ca(i)(2+) transient amplitude and sarcoplasmic reticulum (SR) Ca(2+) content, whereas Torsade de Pointes (TdP) inducers and potent hERG channel blockers (amiodarone, cisapride, dofetilide, E-4031 and terfenadine) predominately suppressed diastolic Ca(i)(2+) and contraction rate, and prolonged Ca(i)(2+) transient duration. The molecularly targeted cancer therapeutics, sunitinib and imatinib, exhibited profound effects on Ca(i)(2+), combining effects of cytotoxic chemotherapeutics, TdP inducers and potent hERG channel blockers. TdP inducers lacking direct hERG inhibition, ouabain and pentamidine, significantly elevated Ca(i)(2+) transient amplitude and SR Ca(2+) content while aconitine primarily accelerated automaticity and elevated diastolic Ca(i)(2+) similar to ouabain. Finally, amoxicillin and aspirin did not exert any significant effects on Ca(i)(2+) at concentrations up to 100 microM. These results suggest that detecting altered Ca(i)(2+) handling in cultured cardiomyocytes may be used as an in vitro model for early cardiac drug safety assessment.

Iatrogenic QT Abnormalities and Fatal Arrhythmias: Mechanisms and Clinical Significance

Severe and occasionally fatal arrhythmias, commonly presenting as Torsade de Pointes [TdP] have been reported with Class III-antiarrhythmics, but also with non-antiarrhythmic drugs. Most cases result from an action on K(+) channels encoded by the HERG gene responsible for the IKr repolarizing current, leading to a long QT and repolarization abnormalities. The hydrophobic central cavity of the HERG-K+ channels, allows a large number of structurally unrelated drugs to bind and cause direct channel inhibition. Some examples are dofetilide, quinidine, sotalol, erythromycin, grepafloxacin, cisapride, dolasetron, thioridazine, haloperidol, droperidol and pimozide. Other drugs achieve channel inhibition indirectly by impairing channel traffic from the endoplasmic reticulum to the cell membrane, decreasing channel membrane density (pentamidine, geldalamicin, arsenic trioxide, digoxin, and probucol). Whereas, ketoconazole, fluoxetine and norfluoxetine induce both direct channel inhibition and impaired channel trafficking. Congenital long QT syndrome, subclinical ion-channel mutations, subjects and relatives of subjects with previous history of drug-induced long QT or TdP, dual drug effects on cardiac repolarization [long QT plus increased QT dispersion], increased transmural dispersion of repolarization and T wave abnormalities, use of high doses, metabolism inhibitors and/or combinations of QT prolonging drugs, hypokalemia, structural cardiac disease, sympathomimetics, bradycardia, women and older age, have been shown to increase the risk for developing drug-induced TdP. Because most of these reactions are preventable, careful evaluation of risk factors and increased knowledge of drugs use associated with repolarization abnormalities is strongly recommended. Future genetic testing and development of practical and simple provocation tests are in route to prevent iatrogenic TdP.

The pharmacophore hypotheses of IKr potassium channel blockers: novel class III antiarrhythmic agents

Predictive pharmacophore models were developed for a large series of I(Kr) potassium channel blockers as class III antiarrhythmic agents using HypoGen in Catalyst software. The pharmacophore hypotheses were generated using a training set consisting of 34 compounds carefully selected from documents. Their biological data, expressed as IC(50), spanned from 1.5 nM to 2.8 mM with 7 orders difference. The most predictive hypothesis (Hypo1), consisting of four features (one positive ionizable feature, two aromatic rings and one hydrophobic group), had a best correlation coefficient of 0.825, a lowest rms deviation of 1.612, and a highest cost difference (null cost-total cost) of 77.552, which represents a true correlation and a good predictivity. The hypothesis Hypo1 was then validated by a test set consisting of 21 compounds and by a cross-validation of 95% confidence level with randomizing the data using CatScramble program. Accordingly, our model has strong predictivity to identify structural diverse I(Kr) potassium channel blockers with desired biological activity by virtual screening

QT Prolongation and Fatal Arrhythmias: A Review of Clinical Implications and Effects of Drugs

A long QT interval due to prolonged repolarization may be associated with a polymorphic ventricular tachycardia known as torsades de pointes. During marked prolongation of the action potential (long QT) early after depolarizations may occur, which when propagated may trigger an arrhythmia. The duration of QTc interval is the major determinant of the risk of drug-induced torsades. Congenital long QT syndrome, female gender, hypokalemia and use of sympathomimetics increase the risk of torsades, and potentiate the QT prolonging effects of drugs. Antiarrhythmics that block the potassium channel prolong the QT and increase the risk for torsades (amiodarone, sotalol, quinidine, procainamide, ibutilide, disopyramide). Additionally, some macrolide and fluoroquinolone antibiotics, antipsychotic and antidepressant drugs, serotonin agonists of the triptan class, cisapride, dolasetron and others have been reported to be associated with QT prolongation or cases of torsades. Drug-induced effects on the QT interval with the associated possibility of inducing fatal arrhythmias have become a new challenge for the practitioner, the drug development process and the regulatory agencies.

Cardiotoxic interaction of metabolites from a prodrug segment cilexetil (cyclohexyloxy-carbonyloxy-ethyl) with digoxin in the canine failing heart

Potential risks of cyclohexanol (CH) and cyclohexanediol (CHD) isomers, which are the metabolites derived from cilexetil ester side-chain of several prodrugs such as antibiotics (e.g. cefotiam hexetil) and an antihypertensive agent (candesartan cilexetil), were examined in beagles that were made congestive heart failure (CHF) by rapid ventricular pacing. The following three experiments tested the cardiac effects of i.v. doses of: (1) the metabolites alone, (2) the metabolites under the digoxin-induced bradycardia, and (3) the metabolites given concomitantly with digoxin (0.02 mg kg(-1)). Experiment 1: t-1,2- or 1,4-CHD alone (0.1-12 mg kg(-1)) exerted transient yet reproducible supraventricular or ventricular arrhythmia dose-dependently, whereas CH and 1,3-CHD at 12 mg kg(-1) showed no cardiac effect at all. Experiment 2: t-1,2-CHD (0.1-4 mg kg(-1)), but not CH or 1,3-CHD, induced the additive arrhythmia dose-dependently; t-1,2-CHD (12 mg kg(-1)) caused frequent premature supraventricular contractions and/or irreversible paroxysmal supraventricular tachycardia. Experiment 3: t-1,2-CHD, not CH or 1,3-CHD, caused fatal arrhythmia: one dog showed torsade de pointes followed by ventricular fibrillation, while another showed 3rd degree atrioventricular block and eventually cardiac arrest. In both Experiments 2 and 3, saline vehicle added onto digoxin never caused the irreversible, fatal arrhythmia. In a separate study using healthy dogs without CHF, none of these metabolites did produce cardiac effect. Given the potential risk of generating cardiotoxic metabolites from cilexetil-bearing prodrugs, the use of such prodrugs should be avoided from the patients with CHF, particularly from those who are receiving cardiac glycosides.

The relationship of clinical QT prolongation to outcome in the conscious dog using a beat-to-beat QT-RR interval assessment

QT interval prolongation of the electrocardiogram has been associated with the occurrence of life-threatening fatal ventricular arrhythmias. To understand the relationship between preclinical cardiac conduction assessment to clinical outcome, comparisons of free (unbound)-plasma drug concentrations and their associated effects in the conscious mongrel dog were made to the free plasma concentrations in humans reported to produce QT prolongation. E-4031 (an experimental class III antiarrhythmic), cisapride, terfenadine, terodiline, and verapamil all affect cardiac repolarization and can produce QT prolongation in humans. In the conscious dog, the QT interval was assessed on a beat-to-beat basis in relation to each preceding RR interval at concentrations approximating the same unbound human concentrations. E-4031, cisapride and terodiline statistically increased the QT(RR1000) interval [the QT interval at a 60 beats/min (bpm) heart rate] 23, 8, and 9 ms, respectively, at concentrations 0.3 to 15.8 times their relevant clinical level. Increases were not observed for terfenadine or verapamil (p > 0.05 at all doses). Inspection of individual dog QT versus RR interval relationships showed clear QT interval responses specific to each treatment but not readily apparent when data are averaged at a heart rate of 60 bpm. For specific rectifier K(+) current (IKr) blockers, robust effects on mean QT prolongation can be detected. However, for drugs that affect repolarization through multiple channels, the effect on the mean QT interval may be more difficult to detect. Inspection of the beat-to-beat QT-RR interval relationship in an individual animal can increase the sensitivity for more accurate clinical prediction.

Review of the pharmacokinetics, pharmacogenetics, and drug interaction potential of antidepressants: focus on venlafaxine

Improving outcomes for patients with depression involves selecting the best possible drug therapy. Considerations relevant to drug product selection include: 1) pharmacokinetic issues such as half-life and time to steady-state, and protein binding; 2) pharmacodynamic drug-drug interactions; and 3) drug metabolism-related drug interactions. A comparison of selected antidepressants with an emphasis on venlafaxine's similarities and differences is presented. Based on these parameters, selecting an antidepressant medication, such as venlafaxine, that has a low potential for drug interactions at the Cytochrome P450 (CYP) enzyme system, and is easy to monitor and dose, facilitate successful treatment of patients. Venlafaxine has been evaluated in clinical studies that demonstrate low to negligible drug interaction potential at CYP2D6, CYP1A2, CYP2C19, and CYP3A4. Its short half-life and time to steady-state, when coupled with the extended release characteristics of the preferred dosage formulation allow for once daily dosing and rapid attainment of therapeutic effects. The CYP3A4 system is involved in both first-pass metabolism and systemic clearance of medications. Drug interactions at this isoenzyme have proven to be of high clinical relevance ranging from cardiovascular toxicity and death with commonly used drugs such as cisapride, to subtherapeutic levels of cyclosporine or protease inhibitors leading to transplant rejection or HIV relapse. Reasons for the under detection and reporting of drug interaction mediated adverse events include healthcare system structure, the poor return to follow up of non-adherent patients, the need for greater education and training of clinicians to recognize drug-related adverse events, and the reluctance of patients to spontaneously communicate about the unpleasant effects of their medication.

Histamine H1 and H2 receptor antagonists accelerate skin barrier repair and prevent epidermal hyperplasia induced by barrier disruption in a dry environment

Keratinocytes have histamine H1 and H2 receptors, but their functions are poorly understood. To clarify the role of histamine receptors in the epidermis, we examined the effects of histamine receptor antagonists and agonists applied epicutaneously on the recovery of skin barrier function disrupted by tape stripping in hairless mice. Histamine H2 receptor antagonists famotidine and cimetidine accelerated the recovery of skin barrier function, but histamine and histamine H2 receptor agonist dimaprit delayed the barrier repair. Application of compound 48/80, a histamine releaser, also delayed the recovery. Imidazole, an analog of histamine, had no effect. The histamine H1 receptor antagonists diphenhydramine and tripelennamine accelerated the recovery. Histamine H3 receptor agonist Nalpha-methylhistamine and antagonist thioperamide had no effect. In addition, topical application of famotidine or diphenhydramine prevented epidermal hyperplasia in mice with skin barrier disrupted by acetone treatment in a dry environment (humidity < 10%) for 4 d. In conclusion, both the histamine H1 and H2 receptors in the epidermis are involved in skin barrier function and the cutaneous condition of epidermal hyperplasia.

Effects of rupatadine, a new dual antagonist of histamine and platelet-activating factor receptors, on human cardiac kv1.5 channels

1. The effects of rupatadine, a new dual antagonist of both histamine H1 and platelet-activating factor receptors, were studied on human cloned hKv1.5 channels expressed in Ltk- cells using the whole-cell patch-clamp technique. 2. Rupatadine produced a use- and concentration-dependent block of hKv1.5 channels (KD=2.4+/-0.7 micronM) and slowed the deactivation of the tail currents, thus inducing the 'crossover' phenomenon. 3. Rupatadine-induced block was voltage-dependent increasing in the voltage range for channel opening suggesting an open channel interaction. At potentials positive to +10 mV the blockade decreased with a shallow voltage-dependence. Moreover, rupatadine also modified the voltage-dependence of hKv1.5 channel activation, which exhibited two components, the midpoint of the steeper component averaging -25. 2+/-2.7 mV. 4. When the intracellular K+ concentration ([K+]i) was lowered to 25% the voltage-dependent unblock observed at positive potentials was suppressed and the activation curve in the presence of rupatadine did not exhibit two components even when the midpoint of the activation curve was shifted to more negative potentials (-30. 3+/-1.3 mV). 5. On channels mutated on the residue R485 (R485Y) which is located on the external entryway of the pore the rupatadine-induced block did not decrease at potentials positive to +10 mV. In contrast, on V512M channels rupatadine reproduced all the features of the blockade observed on wild type channels. 6. All these results suggest that rupatadine blocks hKv1.5 channels binding to an external and to an internal binding site but only at concentrations much higher than therapeutic plasma levels in man. Efflux of K+ promotes the unbinding from the external site. Furthermore, rupatadine binds to an internal site and dramatically modifies the voltage-dependence of channel opening.