Effects of quinidine versus procainamide on the QT interval

Drug-induced QT prolongation: Concordance of preclinical anesthetized canine model in relation to published clinical observations for ten CiPA drugs

INTRODUCTION

The Comprehensive In Vitro Proarrhythmia Assay (CiPA) initiative differentiates torsadogenic risk of 28 drugs affecting ventricular repolarization based on multiple in vitro human derived ionic currents. However, a standardized prospective assessment of the electrophysiologic effects of these drugs in an integrated in vivo preclinical cardiovascular model is lacking. This study questioned whether QTc interval prolongation in a preclinical in vivo model could detect clinically reported QTc prolongation and assign torsadogenic risk for ten CiPA drugs.

METHODS

An acute intravenous administered ascending dose anesthetized dog cardiovascular model was used to assess QTc prolongation along with other electrocardiographic (PR, QRS intervals) and hemodynamic (heart rate, blood pressures, left ventricular contractility) parameters at plasma concentrations spanning and exceeding clinical exposures. hERG current block potency was characterized using IC₅₀ values from automated patch clamp.

RESULTS

All eight drugs eliciting clinical QTc prolongation also delayed repolarization in anesthetized dogs at plasma concentrations within four-fold clinical exposures. In vitro QTc safety margins (defined based on clinical C_max values/plasma concentrations eliciting statistically significant QTc prolongation in dogs) were lower for high vs intermediate torsadogenic risk drugs. In comparison, hERG IC₁₀ values represented as total drug concentrations were better predictors of preclinical QTc prolongation than hERG IC₅₀ values.

CONCLUSION

There was good concordance for QTc prolongation in the anesthetized dog model and clinical torsadogenic risk assignment. QTc assessment in the anesthetized dog remains a valuable part of a more comprehensive preclinical integrated risk assessment for delayed repolarization and torsadogenic risk as part of a global cardiovascular evaluation.

Cardiovascular pharmacology of K2P17.1 (TASK-4, TALK-2) two-pore-domain K+ channels

K_2P17.1 (TASK-4, TALK-2) potassium channels are expressed in the heart and represent potential targets for pharmacological management of atrial and ventricular arrhythmias. Reduced K_2P17.1 expression was found in atria and ventricles of heart failure (HF) patients. Modulation of K_2P17.1 currents by antiarrhythmic compounds has not been comprehensively studied to date. The objective of this study was to investigate acute effects of clinically relevant antiarrhythmic drugs on human K_2P17.1 channels to provide a more complete picture of K_2P17.1 electropharmacology. Whole-cell patch clamp and two-electrode voltage clamp electrophysiology was employed to study human K_2P17.1 channel pharmacology. K_2P17.1 channels expressed in Xenopus laevis oocytes were screened for sensitivity to antiarrhythmic drugs, revealing significant activation by propafenone (+ 296%; 100 μM), quinidine (+ 58%; 100 μM), mexiletine (+ 21%; 100 μM), propranolol (+ 139%; 100 μM), and metoprolol (+ 17%; 100 μM) within 60 min. In addition, the currents were inhibited by amiodarone (- 13%; 100 μM), sotalol (- 10%; 100 μM), verapamil (- 21%; 100 μM), and ranolazine (- 8%; 100 μM). K_2P17.1 channels were not significantly affected by ajmaline and carvedilol. Concentration-dependent K_2P17.1 activation by propafenone was characterized in more detail. The onset of activation was fast, and current-voltage relationships were not modulated by propafenone. K_2P17.1 activation was confirmed in mammalian Chinese hamster ovary cells, revealing 7.8-fold current increase by 100 μM propafenone. Human K_2P17.1 channels were sensitive to multiple antiarrhythmic drugs. Differential pharmacological regulation of repolarizing K_2P17.1 background K⁺ channels may be employed for personalized antiarrhythmic therapy.

Validation of a population-based method to assess drug-induced alterations in the QT interval: a self-controlled crossover study

PURPOSE

The purpose of this study was to ascertain, in the context of an integrated health care delivery system, the association between a comprehensive list of drugs known to have potential QT liability and QT prolongation or shortening.

METHODS

By using a self-controlled crossover study with 59 467 subjects, we ascertained intra-individual change in log-linear regression-corrected QT (QTcreg ) during the period between 1995 and mid-2008 for 90 drugs while adjusting for age, gender, race/ethnicity, comorbid conditions, number of electrocardiograms (ECGs), and time between pre-ECG and post-ECG. The proportion of users of each drug-developing incident long QT was also estimated.

RESULTS

Two drugs (nicardipine and levalbuterol) had no statistically significant intra-individual QTcreg shortening effects, 10 drugs had no statistically significant prolonging effect, and 78 (87%) of the drugs had statistically significant intra-individual mean QTcreg lengthening effects, ranging from 7.6 ms for aripiprazole to 25.2 ms for amiodarone. Three drugs were associated with mean QTcreg prolongation of 20 ms or greater: amiodarone (antiarrhythmic), terfenadine (antihistaminic), and quinidine (antiarrhythmic); whereas 11 drugs were associated with mean QTcreg prolongation of 15 ms or greater but less than 20 ms: trimipramine (tricyclic antidepressant), clomipramine (tricyclic antidepressant), disopyramide (antiarrhythmic), chlorpromazine (antipsychotic), sotalol (beta blocker), itraconazole (antifungal), phenylpropanolamine (decongestant/anorectic), fenfluramine (appetite suppressant), midodrine (antihypotensive), digoxin (cardiac glycoside/antiarrhythmic), and procainamide (antiarrhythmic).

CONCLUSIONS

QT prolonging effects were common and varied in strength. Our results lend support to past Food and Drug Administration regulatory actions and support the role for ongoing surveillance of drug-induced QT prolongation.

Heart rate-Qt interval relationship during postural change and exercise. A possible connection to cardiac contractility

The QT interval of the electrocardiogram, although often coordinated in an inverse relationship to heart rate, appears from the existing evidence to be regulated by mechanisms separate from those that govern heart rate. The purpose of this inquiry was to explore further the relationship of the two and to test other factors that may contribute to the regulation of QT. Heart rate and QT duration were measured in healthy human subjects during postural change and exercise. The data showed that, while coordinated in an inverse relationship under some circumstances, under others heart rate and QT were discordant, leading to the inference that there is no fixed linkage between the two. Previous work by the authors and other published studies have suggested that ventricular contractility may have more predictable association with QT shortening than do increases in heart rate. Observations of force of ventricular contraction (HI and IJ velocity) as reflected in ballisto-cardiographic tracings were made using each of 12 human subjects as the authors' own control. The data revealed a highly significant correlation between the velocity measures and QT duration (p less than 0.01) but not heart rate. These findings led to the conclusion that there is clearly not a fixed relationship between heart rate and QT interval and to the hypothesis that QT may more closely reflect the degree of cardiac contractility.

Pirmenol: an antiarrhythmic drug with unique electrocardiographic features--a double-blind placebo-controlled comparison with quinidine

Previous reports have stated that pirmenol is a Class IA antiarrhythmic drug that prolongs the QT interval, but did not use computerized electrocardiography. We randomized 18 patients with frequent ventricular ectopic depolarizations to pirmenol (8 patients) or quinidine (10 patients). Pirmenol was effective and tolerated for suppression of arrhythmia in all 7 patients treated (1 patient withdrew for personal reasons) but quinidine was effective and tolerated for 4 weeks in only 5 of 10 patients (p less than 0.05). Using computerized 12-lead electrocardiography, the mean change in PR interval from placebo to treatment was 5 +/- 18 ms for quinidine and 5 +/- 11 ms for pirmenol (p = NS). The mean change in QRS interval was 5 +/- 14 ms for quinidine and 10 +/- 5 ms for pirmenol (p = NS). The mean change in QT interval was 46 +/- 30 ms for quinidine and 8 +/- 9 ms for pirmenol (p less than 0.01) and the mean change in JT interval was 41 +/- 36 ms for quinidine and -2 +/- 10 ms for pirmenol (p less than 0.01). After the double-blind phase, 4 quinidine patients had computerized electrocardiographic intervals measured on pirmenol; the above findings were confirmed. These electrocardiographic features of pirmenol clearly distinguish it from quinidine, the prototype Class IA drug. However, pirmenol has minimal effect on the PR and QRS intervals, and thus does not appear to be a Class IC drug either. Although its electrocardiographic features are closest to Class IB, its electrophysiology in isolated cells and its antiarrhythmic and side effect profile are atypical for a IB agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Poisoning due to class IA antiarrhythmic drugs. Quinidine, procainamide and disopyramide

Quinidine, procainamide and disopyramide are antiarrhythmic drugs in the class 1A category. These drugs have a low toxic to therapeutic ratio, and their use is associated with a number of serious adverse effects during long term therapy and life-threatening sequelae following acute overdose. Class 1A agents inhibit the fast inward sodium current and decrease the maximum rate of rise and amplitude of the cardiac action potential. Prolonged Q-T interval and, to a lesser extent, QRS duration may be observed at therapeutic concentrations of quinidine. With increasing plasma concentrations, progressive depression of automaticity and conduction velocity occur. 'Quinidine syncope' (a transient loss of consciousness due to paroxysmal ventricular tachycardia, frequently of the torsade de pointes type) occurs with therapeutic dosing, often in the first few days of therapy. Extracardiac adverse effects of quinidine include potentially intolerable gastrointestinal effects and hypersensitivity reactions such as fever, rash, blood dyscrasias and hepatitis. Procainamide produces electrophysiological changes that are similar to those of quinidine, although Q-T interval prolongation with the former is less pronounced at therapeutic concentrations. Hypersensitivity reactions including fever, rash and (more seriously) agranulocytosis are associated with procainamide, and a frequent adverse effect requiring cessation of therapy is the development of systemic lupus erythematosus. Of the 3 drugs, disopyramide has the most pronounced negative inotropic effects, which are especially significant in patients with pre-existing left ventricular dysfunction. As with quinidine, unexpected 'disopyramide syncope' at therapeutic concentrations has been described. Anticholinergic side effects are common with this drug and may require cessation of therapy. Disopyramide therapy may unpredictably induce severe hypoglycaemia. Severe intoxication with the class 1A agents may result from acute accidental or intentional overdose, or from accumulation of the drugs during long term therapy. Acute overdose can result in severe disturbances of cardiac conduction and hypotension, frequently accompanied by central nervous system toxicity. Decreased renal function can cause significant accumulation of procainamide and its active metabolite acecainide (N-acetyl-procainamide), resulting in severe intoxication. Mild to moderate renal dysfunction is less likely to lead to quinidine or disopyramide intoxication, unless renal failure is severe or concurrent hepatic dysfunction is present. Management of acute intoxication with class 1A drugs includes gut decontamination with provision of respiratory support and treatment of seizures as needed. Hypertonic sodium bicarbonate, by antagonising the inhibitory effect of quinidine on sodium conductance, may reverse many or all manifestations of cardiovascular toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

QT interval and repolarization time in patients with intraventricular conduction delay

A prolonged QT interval is an important prognostic indicator for cardiac arrhythmias and sudden death. The conventional QT interval measurement, however, includes in its measure the cardiac depolarization (QRS) as well as the cardiac repolarization (JT) intervals. To evaluate the relative contribution of the depolarization and the repolarization time prolongation to the prolonged QT interval in patients with intraventricular conduction delay (IVCD), the QRS, QT, and JT intervals were measured in 72 subjects with various types of IVCD. The observed intervals in IVCD subjects were compared to similar intervals in 33 healthy individuals in whom there was no evidence for intraventricular conduction abnormalities. The QTc (QT interval corrected for heart rate) in subjects with IVCD were 445 +/- 6.8 msec (mean +/- SEM) in those with LAD, 470 +/- 9.1 msec with RBBB, and 489 +/- 6.9 msec with LBBB. All of these intervals were significantly prolonged compared to 430 +/- 4.3 msec in the control group. The prolongation of QTc interval in each category of IVCD subjects was entirely secondary to a prolonged depolarization time, as the repolarization intervals were not significantly different from those observed in the control group (F = 0.5, p = NS). These observations may provide an explanation for the differential prognosis for subjects with prolonged QT interval with prolonged repolarization time as compared to those with prolonged QT interval with prolonged depolarization time.

The pharmacokinetics and pharmacodynamics of quinidine and 3-hydroxyquinidine

1. The pharmacokinetics and pharmacodynamics of quinidine and 3-hydroxyquinidine based upon measurements of total and unbound serum concentrations were determined after a single dose (400 mg) and at steady state (200 mg every 6 h). 2. The oral clearance (7.6 +/- 1.9 vs 4.8 +/- 2.0 ml min-1 kg-1; P less than 0.05) and renal clearance (1.2 +/- 0.3 vs 0.63 +/- 0.25 ml min-1 kg-1; P less than 0.005) or quinidine were lower during steady state than after the single dose. 3. The area under the serum concentration vs time curve (AUC) of 3-hydroxyquinidine was greater at steady state than after the single dose (2.0 +/- 0.7 vs 3.0 +/- 0.6 mg l-1 h; P less than 0.05) and its renal clearance was less (3.0 +/- 1.1 vs 1.54 +/- 0.38 ml min-1 kg-1; P less than 0.05). 4. The slope of the relationship between quinidine concentration and change in QTc interval was greater at steady state (40.1 +/- 21.7 vs 72.2 +/- 41.7 ms/(mg l-1); P less than 0.05).