Clinical efficacy and electrophysiology of oral propafenone for ventricular tachycardia

Cardiac sodium channel antagonism - Translation of preclinical in vitro assays to clinical QRS prolongation

INTRODUCTION

Cardiac sodium channel antagonists have historically been used to treat cardiac arrhythmias by preventing the reentry of the electrical impulse that could occur following myocardial damage. However, clinical studies have highlighted a significant increase in mortality associated with such treatment. Cardiac sodium channel antagonist activity is now seen as an off-target pharmacology that should be mitigated during the drug development process. The aim of this study was to examine the correlation between in vitro/ex vivo assays that are routinely used to measure Nav1.5 activity and determine the translatability of the individual assays to QRS prolongation in the clinic.

METHODS

A set of clinical compounds with known Nav1.5 activity was profiled in several in vitro/ex vivo assays (binding, membrane potential, patch clamp and the Langendorff isolated heart). Clinical data comprising compound exposure levels and changes in QRS interval were obtained from the literature. Sensitivity/specificity analysis was performed with respect to the clinical outcome.

RESULTS

The in vitro assays showed utility in predicting QRS prolongation in the clinic. Optimal thresholds were defined for each assay (binding: IC₂₀; membrane potential: IC₁₀; patch clamp: IC₂₀) and sensitivity (69-88%) and specificity (53-84%) values were shown to be similar between assay formats.

DISCUSSION

The data provide clear statistical insight into the translatability of Nav1.5 antagonism data generated in vitro to potential clinical outcomes. These results improve our ability to understand the liability posed by such activity in novel development compounds at an early stage.

Methodologies to characterize the QT/corrected QT interval in the presence of drug-induced heart rate changes or other autonomic effects

This White Paper, written collaboratively by members of the Cardiac Safety Research Consortium from academia, industry, and regulatory agencies, discusses different methods to characterize the QT effects for drugs that have a substantial direct or indirect effect on heart rate. Descriptions and applications are provided for individualized QT-R-R correction, Holter bin, dynamic QT beat-to-beat, pharmacokinetic-pharmacodynamic modeling, and QT assessment at constant heart rate. Most of these techniques are optimally performed using continuous electrocardiogram data obtained in clinical studies designed to characterize a drug's effect on the QT interval. An important study design element is the collection of drug-free data over a range of heart rates seen on treatment. The range of heart rates is increased at baseline by using ambulatory electrocardiogram recordings in addition to those collected under semisupine, resting conditions. Discussions in this study summarize areas of emerging consensus and other areas in which consensus remains elusive and provide suggestions for additional research to further increase our knowledge and understanding of this topic.

Comparative Evaluation of HERG Currents and QT Intervals following Challenge with Suspected Torsadogenic and Nontorsadogenic Drugs

The purpose of the present study was to comparatively evaluate human HERG currents and QT intervals following challenge with suspected torsadogenic and nontorsadogenic drugs. Various concentrations of 14 different drugs were initially evaluated in terms of their relative potency to block I(HERG) in stably transfected human embryonic kidney cells. Four general categories of drugs were identified: high-potency blockers (IC50 < 0.1 microM) included lidoflazine, terfenadine, and haloperidol; moderate-potency blockers (0.1 microM < IC50 < 1 microM) included sertindole, thioridazine, and prenylamine; low-potency blockers (IC50 > 1 microM) included propafenone, loratadine, pyrilamine, lovastatin, and chlorpheniramine; and ineffective blockers (IC50 > 300 microM) included cimetidine, pentamidine, and arsenic trioxide. All measurements were performed using similar conditions and tested acute drug effects only (<30 min of drug exposure per measurement). Since two of the drugs that were ineffective I(HERG) blockers, arsenic trioxide and pentamidine, have been associated with cardiac repolarization delays (QT interval lengthening) and torsades de pointes ventricular arrhythmias in patients, we chose to evaluate them further using the isolated perfused rabbit heart model. Neither arsenic trioxide nor pentamidine had any significant effect on QT intervals in this model, even at relatively high (micromolar) concentrations. Similar results were obtained for loratadine in this model. When the hearts were challenged with a known torsadogenic drug such as cisapride, significant QT lengthening was rapidly induced. These results demonstrate that arsenic trioxide and pentamidine are essentially devoid of direct acute effects on cardiac repolarization or inhibition of I(HERG).

Placebo-controlled evaluations of propafenone for atrial tachyarrhythmias

This review summarizes the results of placebo-controlled trials of propafenone, a class IC antiarrhythmic drug, in patients with supraventricular tachycardia, atrial fibrillation (AF), and atrial flutter. Success rates for cardioversion from AF or flutter to sinus rhythm of 9-93% have been obtained with intravenous propafenone. The duration of arrhythmia is an important factor in the degree of success. The use of a single oral dose has also been reported to be effective in a number of studies. Several placebo-controlled studies have confirmed the effectiveness of propafenone in the long-term suppression of both suproventricular tachycardia and AF and flutter. These reported trials have shown consistent benefit with propafenone compared with placebo in preventing arrhythmia recurrence. The adverse side effect profile for propafenone has also been reviewed with particular reference to the potential for proarrhythmia. The rate of side effects is dose-dependent and tends to be higher in patients with underlying structural heart disease. Overall propafenone has been shown to be an effective antiarrhythmic drug with an acceptable side effect profile for the acute and long-term treatment of supraventricular arrhythmias.

Therapeutic drug monitoring: antiarrhythmic drugs

Antiarrhythmic agents are traditionally classified according to Vaughan Williams into four classes of action. Class I antiarrhythmic agents include most of the drugs traditionally thought of as antiarrhythmics, and have as a common action, blockade of the fast-inward sodium channel on myocardium. These agents have a very significant toxicity, and while they are being used less, therapeutic drug monitoring (TDM) does significantly increase the safety with which they can be administered. Class II agents are antisympathetic drugs, particularly the beta-adrenoceptor blockers. These are generally safe agents which do not normally require TDM. Class III antiarrhythmic agents include sotalol and amiodarone. TDM can be useful in the case of amiodarone to monitor compliance and toxicity but is generally of little value for sotalol. Class IV antiarrhythmic drugs are the calcium channel blockers verapamil and diltiazem. These are normally monitored by haemodynamic effects, rather than using TDM. Other agents which do not fall neatly into the Vaughan Williams classification include digoxin and perhexiline. TDM is very useful for monitoring the administration (and particularly the safety) of both of these agents.

Cardiac electrophysiological effects of propafenone and its 5-hydroxylated metabolite in the conscious dog

We studied the cardiac electrophysiological effects of propafenone and its 5-hydroxylated metabolite in conscious dogs. Sinus rate, corrected sinus recovery time and Wenckebach point were measured in 6 intact dogs. Atrial rate, ventricular rate and atrial effective refractory period were measured in 6 atrioventricular-blocked dogs. In both groups, we also determined blood pressure and plasma drug concentrations. Each dog received, with at least an 8-day interval, propafenone (hydrochloride) and 5-hydroxypropafenone (hydrochloride) in 4 successive intravenous injections, 30 min apart, at 0.5, 0.5, 1 and 2 mg kg(-1). Propafenone increased sinus rate and atrial rate more markedly than 5-hydroxypropafenone, and also transiently ventricular rate, whereas 5-hydroxypropafenone decreased it weakly. Propafenone shortened corrected sinus recovery time and increased Wenckebach point at the highest dose only, whereas 5-hydroxypropafenone did not modify corrected sinus recovery time and increased Wenckebach point less markedly than propafenone. Both drugs produced an identical atrial effective refractory period lengthening. Propafenone either increased mean blood pressure (in intact dogs) or decreased it (in atrioventricular-blocked dogs) at the highest dose only, whereas 5-hydroxypropafenone did not produce any effect on this parameter. Overall, these results show that propafenone and 5-hydroxypropafenone exhibit cardiac electrophysiological effects, reflecting (a) direct vagolytic action for both drugs associated with cardiodepressant effects for 5-hydroxypropafenone, and (b) marked atrial antiarrhythmic properties for 5-hydroxypropafenone probably involved in the therapeutic effect of propafenone.

Safety and tolerability of long-term propafenone therapy for supraventricular tachyarrhythmias. The Propafenone Multicenter Study Group

An important issue regarding the long-term use of antiarrhythmic drugs concerns the safety of these agents, particularly with regard to cardiac toxicity. Propafenone is an effective drug for preventing supraventricular tachyarrhythmia, but the incidence of side effects during longterm therapy in patients with such arrhythmias has not been adequately reported. A total of 480 patients received oral propafenone as therapy for symptomatic atrial fibrillation, atrial flutter, or supraventricular tachycardia. During the follow-up (mean 14.4 months), 290 patients (60%) discontinued propafenone therapy, but in only 70 patients (15%) was the reason for discontinuation an adverse drug reaction. Overall, 284 patients (59%) experienced at least 1 adverse reaction, and the incidence was related to dose and age >65 years. The overall incidence of side effects was not related to structural heart disease; however, cardiovascular toxicity including arrhythmia aggravation, congestive heart failure, and serious conduction disturbances occurred more often in those with heart disease (20% vs 13%). Sixteen patients died during drug therapy, but in only 1 case was the drug considered contributory. For patients with a supraventricular arrhythmia, propafenone was well tolerated and was infrequently discontinued because of side effects. The incidence of serious cardiac toxicity when propafenone was used to treat supraventricular arrhythmia was low, and these side effects were more frequent in patients with structural heart disease.

Effects of oral propafenone on defibrillation and pacing thresholds in patients receiving implantable cardioverter-defibrillators. Propafenone Defibrillation Threshold Investigators

OBJECTIVES

The effects of propafenone, a predominantly class IC antiarrhythmic drug, on defibrillation and pacing thresholds were evaluated in patients undergoing cardioverter-defibrillator implantation.

BACKGROUND

Previous studies have shown that the class IC agents encainide and flecainide may increase the energy requirements for pacing and defibrillation. Animal studies with propafenone have shown inconsistent results regarding its effect on defibrillation energy requirements. This report investigated the effects of propafenone on defibrillation and pacing thresholds in humans.

METHODS

After cardioverter-defibrillator implantation, 47 patients were enrolled in a double-blind, three-way parallel, randomized trial of 450 mg/day (Group 1) or 675 mg/day (Group 2) of oral propafenone or placebo (Group 3) for 3 to 7 days. Predischarge defibrillation and pacing thresholds after treatment were compared with baseline thresholds obtained at implantation.

RESULTS

There was no statistically significant difference between implantation and predischarge defibrillation thresholds in the three groups (Group 1: [mean +/- SE] 11.0 +/- 1.3 vs. 12.1 +/- 1.5 J; Group 2: 11.5 +/- 1.1 vs. 13.6 +/- 1.3 J; Group 3: 12.5 +/- 1.2 vs. 13.3 +/- 1.6 J), and no significant difference between treatment groups was found with a 0.86 power to detect a 5-J difference between groups. Paired pulse width pacing thresholds at 2.8 V were compared in 14 patients. A small increase of 0.02 ms was noted at predischarge testing in patients treated with propafenone and placebo.

CONCLUSIONS

Short-term oral propafenone (450 and 675 mg/day) does not significantly affect defibrillation or pacing thresholds. Concomitant use of propafenone in patients with implantable cardioverter-defibrillators with recurrent ventricular or atrial tachyarrhythmias should not interfere with proper device function.

Propafenone versus disopyramide for maintenance of sinus rhythm after electrical cardioversion of chronic atrial fibrillation: a randomized, double-blind study. PRODIS Study Group

Safety and efficacy of propafenone and disopyramide for long-term maintenance of sinus rhythm after electrical cardioversion was studied in 56 patients with chronic atrial fibrillation (median arrhythmia duration, 5 months). After cardioversion, patients were randomly assigned to receive double-blind propafenone 300 mg tid (25 patients) or disopyramide 250 mg tid (31 patients). Downward dose adjustment was allowed in case of intolerable side effects. The endpoints were arrhythmia recurrence; and side effects not amenable to dose reduction. For patients randomized to propafenone (mean dose, 878 +/- 65 mg/day), 66% [95% confidence interval [(CI) 46-85%] and 55% (95% CI, 34-76%) remained in sinus rhythm at 3 and 6 months, respectively (Kaplan-Meier method). Similar figures were found with disopyramide (mean dose, 704 +/- 81 mg/day): 71% (95% CI, 54-87%) and 67% (95% CI, 50-84%) at 3 and 6 months, respectively (p = NS). In the patients with a relapse of atrial fibrillation, the ventricular rate while still using the prophylactic agents did not increase significantly compared with precardioversion. However, one patient on disopyramide had an excessively high relapse heart rate (170 vs. 100 beats/min). Side effects were more frequent on disopyramide. Side effects necessitating drug discontinuation occurred in 12 patients: 4 patients (16%) on propafenone and 8 (26%) on disopyramide. Severe adverse effects occurred in two patients, who developed heart failure while on disopyramide. There were no proarrhythmic events or deaths. Thus, propafenone and disopyramide are equally effective for maintaining sinus rhythm after cardioversion of atrial fibrillation. Propafenone is, however, better tolerated than disopyramide, which may cause heart failure.

Electrophysiological effects of Org 7797 in the closed-chest anaesthetized dog

1. The intravenous electrophysiological effects of a new antifibrillatory agent, Org 7797, were studied in closed chest anaesthetized dogs. Effects of fast sodium and slow calcium-mediated action potentials were also examined in guinea-pig isolated papillary muscle. 2. The major effects of a known antifibrillatory dose of Org 7797 (0.5 mg kg-1) were a protracted slowing of AV nodal conduction (for at least 20 min) and prolongation of the AV nodal functional refractory period. Conduction in the atria and His-Purkinje system (reflected by the St-A and HV intervals) were not significantly modified whilst ventricular conduction (reflected by the QRS interval) and the ventricular functional refractory period were only transiently prolonged. No other electrophysiological changes were seen. 3. A higher dose of Org 7797 (1.5 mg kg-1) slowed conduction at all levels of the myocardium (as evidenced by increases in the St-A, AH, HV and QRS intervals), slightly shortened cardiac repolarization (as assessed from JTc) and decreased Wenckebach rate. Atrial refractory periods were increased whereas effects on ventricular refractory periods were modest. 4. Neither heart rate nor sinus node recovery time were modified by either dose of Org 7797. 5. Org 7797, at a concentration (20 microM) which reduced Vmax of fast sodium-mediated action potentials in isolated papillary muscle by 83%, did not modify Vmax of slow calcium-mediated action potentials. It prolonged duration of the latter but did not modify that of the former. However, the plateau phase of both the 'fast' and especially the 'slow' action potentials was prolonged. 6. It is concluded that the main electrophysiological effects of a known antifibrillatory dose of Org 7797 in dogs with normal cardiac function are seen at the level of the AV node, actions which are unlikely to be explained by calcium channel block. Higher doses display a class Ic profile. This preferential action on the AV node may contribute to the control of ventricular rate during atrial fibrillation in the absence of infra-nodal conduction disturbances.7. These results contrast with those previously obtained in infarcted dogs and might further suggest that myocardial infarction enhances the Class I action of Org 7797.

Efficacy of class 1C antiarrhythmic agents in patients with inducible ventricular tachycardia refractory to therapy with class 1A antiarrhythmic drugs

The efficacy of class 1C antiarrhythmic agents was determined in 36 patients with inducible sustained monomorphic ventricular tachycardia during baseline electrophysiology study (EPS), who continued to have inducible monomorphic ventricular tachycardia during EPS on class 1A antiarrhythmic therapy. Of 12 patients who partially responded to class 1A drugs, 11 (91.7%) continued to have a partial response during EPS on class 1C therapy, whereas one patient did not respond. Of 24 nonresponders to class 1A therapy, 2 (8.3%) responded during EPS on class 1C therapy, 7 (29.2%) partially responded, and 15 (62.5%) did not respond. In the 24 nonresponders to class 1A therapy, 9 of 17 patients (53%) with left ventricular ejection fraction (EF) > or = 30% responded or partially responded to class 1C therapy, compared with none of 7 patients with EF < 30% (P < .05). The EPS on class 1C agents in patients who fail to respond to class 1A therapy may be warranted only in those with EF > or = 30%.

Comparison of the electrophysiological effects of Org 7797, disopyramide, mexiletine and propafenone in anaesthetized dogs with myocardial infarcts

1. The electrophysiological effects of intravenously administered Org 7797 were compared with those of disopyramide (class Ia), mexiletine (Ib) and propafenone (Ic) in anaesthetized dogs with 5-6 day-old left ventricular myocardial infarcts. 2. Org 7797 (0.5 mg kg-1) slowed conduction at all levels of the myocardium as shown by increases in St-A, AH, HV and QRS intervals, very modestly prolonged atrial and ventricular refractory periods and slightly shortened ventricular repolarization. Sinus node recovery time was increased whilst the RR interval was unchanged. A higher dose (2 mg kg-1) prolonged RR and rendered 5 out of 8 dogs unable to follow an atrial pacing stimulus of mean cycle length 322 ms. 3. Electrophysiological changes induced by propafenone (2 mg kg-1) were qualitatively similar to those of Org 7797 (0.5 mg kg-1). 4. Electrophysiological changes induced by mexiletine (2 mg kg-1) were small or insignificant. The most noticeable effect was a modest increase in the St-A interval and a slight shortening of ventricular repolarization. A higher dose (8 mg kg-1) additionally slowed conduction in the His-Purkinje system and in the ventricular myocardium. 5. Disopyramide (2 and 5 mg kg-1) prolonged all cardiac intervals including JTc, QTc and QT during pacing and prolonged cardiac refractory periods. 6. It was concluded that the electrophysiological profile of Org 7797 is more like that of the Ic agent propafenone than that of the class Ia and Ib drugs, disopyramide and mexiletine.

The value of class IC antiarrhythmic drugs for acute conversion of paroxysmal atrial fibrillation or flutter to sinus rhythm

In a single-blind randomized study, the efficacy and safety of intravenous propafenone (2 mg/kg body weight per 10 min) versus flecainide (2 mg/kg per 10 min) were assessed in 50 patients with atrial fibrillation or flutter. Treatment was considered successful if sinus rhythm occurred within 1 h. Conversion to sinus was achieved in 11 (55%) of 20 patients with atrial fibrillation treated with propafenone and in 18 (90%) of 20 with atrial fibrillation treated with flecainide (p less than 0.02). If atrial fibrillation was present less than or equal to 24 h, conversion to sinus rhythm was achieved in 8 (57%) of 14 patients in the propafenone group and 13 (93%) of 14 in the flecainide group (p less than 0.05). Atrial flutter was converted in two (40%) of five patients treated with propafenone and in one (20%) of five with flecainide (p = NS). Mean time to conversion was 16 +/- 10 min in the propafenone group versus 18 +/- 13 min in the flecainide group (p = NS). QRS lengthening (83 +/- 15 to 99 +/- 20 ms) was observed only in the patients treated with flecainide (p less than 0.001). Patients successfully treated with propafenone showed significantly higher plasma levels than those whose arrhythmia did not convert to sinus rhythm. Transient adverse effects were more frequent in the flecainide group (40%) than in the propafenone group (8%) (p less than 0.01). In conclusion, at a dose of 2 mg/kg in 10 min, flecainide is more effective than propafenone for conversion of paroxysmal atrial fibrillation to sinus rhythm. However, considering the propafenone plasma levels and very few adverse effects, the dose or infusion rate, or both, used in the propafenone group may not have been sufficient to achieve an optimal effect. Neither drug seems very effective in patients with atrial flutter.

Nonlinear kinetics of propafenone metabolites in healthy man

The pharmacokinetics of oral and i.v. propafenone and its major metabolites have been investigated in 8 healthy subjects. The total body clearance of propafenone was 963 ml/min, the terminal half-life 198 min and its absolute bioavailability was 15.5%. The two active metabolites (5-hydroxypropafenone and N-depropylpropafenone) showed non-linear kinetics in that both the dose-corrected area under the serum concentration-time curve and the amount excreted in the urine were larger after oral dosing. This resulted in considerably higher serum concentrations of the metabolites despite comparable serum concentrations of the parent compound. Thus, the concentration-effect relationship in the same patient may differ after oral and intravenous doses if concentrations of the active metabolite(s) are not taken into consideration. Although the mechanism of the nonlinearity is not clear, the data indicate that it may be due to saturable biliary excretion of the metabolites.

Conduction velocity depression and drug-induced ventricular tachyarrhythmias. Effects of lidocaine in the intact canine heart

Depression of myocardial conduction velocity can be an important mechanism of action of antiarrhythmic drugs but it can also facilitate arrhythmogenesis. We used lidocaine in an anesthetized canine preparation to address the hypothesis that drug-induced rate-dependent conduction velocity depression causes ventricular tachyarrhythmias. A closely spaced square array of 64 electrodes was used to determine conduction velocity longitudinal and transverse to epicardial ventricular fiber direction. Lidocaine caused rate-dependent decreases in conduction velocity that were proportionately greater in the longitudinal direction at the shortest pacing cycle lengths. Conduction velocity depression developed rapidly in the presence of lidocaine with a new steady state present by the second beat of the rapid train. Recovery from rate-dependent depression of conduction velocity was exponential with a time constant of 122 +/- 20 msec (mean +/- SD) in the longitudinal direction and 114 +/- 30 msec in the transverse direction; this difference was not significant. The relation between conduction velocity depression and ventricular arrhythmias was assessed by pacing for 3 minutes at cycle lengths of 1,000, 500, 300, and 250 msec, and for 1 minute at a cycle length of 200 msec. Arrhythmias did not occur in the baseline period in the dogs that received lidocaine, nor in 12 control dogs that were subjected to the same stimulation protocol except that saline was administered in place of lidocaine. Sustained polymorphic ventricular tachycardia (VT) occurred in six of 16 dogs given lidocaine. VT occurred in the presence of relatively high plasma lidocaine concentrations (8.4 +/- 2.3 micrograms/ml) and only at pacing cycle lengths of 300 msec or shorter. The dogs that developed VT demonstrated greater rate-dependent depression of conduction velocity than the other dogs, and activation patterns obtained just before the onset of VT showed marked conduction disturbances. Furthermore, QRS prolongation, loss of one-to-one capture, and increasingly distorted activation patterns preceded the onset of VT during fixed-rate pacing, suggesting progressive sodium channel block. In summary, rate-dependent conduction velocity depression and nonuniform activation were associated with VT in this model and can be responsible for some arrhythmias induced by antiarrhythmic drugs.

Recent antiarrhythmic drugs

Clinical failure of antiarrhythmic drugs often occurs in practice. Therefore, there is a need for new, effective and long-acting drugs with a wide therapeutic range and a low level of toxicity. Most new class I compounds block the fast sodium ion inward current of myocardial cells. According to their effects on the recovery kinetics of the sodium ion channel, these drugs are classified into 3 groups: IA (intermediate--cibenzoline, pirmenol, hydroxy-3-S-dihydroquinidine, quinacainol); IB (fast--tocainide, moricizine); IC (slow--flecainide, encainide, propafenone, lorcainide, indecainide, recainam and penticainide). Class IC drugs greatly depress intracardiac conduction and are the most potent antiarrhythmic compounds able to suppress ventricular premature beats. However, it is doubtful that long-term suppression of ventricular arrhythmias will improve survival of the patients. Some new drugs have been developed belonging to other classes: class II, esmolol, a new ultrashort-acting beta blocker; class III, N-acetyl-procainamide and sotalol, which prolong duration of the action potential and increase ventricular refractoriness; class IV, the mixed sodium ion-calcium ion-potassium ion antagonist, bepridil. The pharmacologic properties and the clinical effects of these new antiarrhythmic drugs are reviewed. However, future therapeutic trends will depend on the results of large multicenter clinical secondary prevention trials such as the Cardiac Arrhythmia Suppression Trial. New antiarrhythmic drugs with original electrophysiologic profiles and minimal adverse effects must prove their ability not only to suppress arrhythmias but also to reduce sudden cardiac death rate.

Propafenone--a new agent for the treatment of ventricular arrhythmias

Over the last several years a number of new and potent antiarrhythmic agents have been developed. One of these promising new drugs, propafenone hydrochloride (Rhythmol), will soon be available for use in this country. Although similar in some aspects to flecainide and encainide, the drug possesses some unique characteristics. The purpose of this review is to summarize the pharmacologic and physiologic effects of propafenone and to outline its clinical use.

Hemodialysis removal of propafenone

Propafenone kinetics were studied after intravenous and oral dosing in a patient with end-stage renal disease. Hemodialysis was performed within 10 hours of dosing in order to assess its effects. After intravenous administration of 70 mg propafenone, total-body clearance was 10.5 ml/min/kg before and 10.4 ml/min/kg during hemodialysis. After a single oral dose of 300 mg, clearance was 19.4 ml/min/kg before and 18.9 ml/min/kg during hemodialysis. Bioavailability was 48%.

Effects of propafenone on electrical and mechanical activities of single ventricular myocytes isolated from guinea-pig hearts

1. The effects of propafenone on the transmembrane action potential and sarcomere shortening during twitch contraction were investigated in single ventricular myocytes isolated from guinea-pig hearts. 2. Propafenone at low concentrations (3-5 x 10(-7) M) slightly lengthened action potential duration (APD), but shortened it at higher concentrations. The shortening of APD was accompanied by an attenuation of sarcomere shortening during twitch contraction. 3. Propafenone (greater than 10(-6) M) caused a concentration-dependent decrease in the maximum upstroke velocity (Vmax) of the action potential. In the presence of propafenone (3 x 10(-6) M), trains of stimuli led to an exponential decline in Vmax. A time constant for the recovery of Vmax from the use-dependent block was 4.8 s. 4. In myocytes treated with propafenone (3 x 10(-6) M), the Vmax of test action potentials preceded by the conditioning clamp pulses to 0 mV was progressively decreased by increasing the duration of single clamp pulse or by increasing the number of multiple brief clamp pulses. 5. These findings suggest that propafenone has use-dependent inhibitory action on the sodium channel by binding to the channel during both activated and inactivated states, and that the unbinding rate is comparable to that of Class-I antiarrhythmic drugs with intermediate kinetics. Propafenone may also have an inhibitory action on calcium and potassium channels.

Interaction between propranolol and propafenone in healthy volunteers

The effects of propafenone on the pharmacokinetics and pharmacodynamics of propranolol were evaluated in 12 healthy male subjects. Both propafenone and propranolol were each administered alone for one week followed by concomitant administration for an additional week. Blood samples, obtained at steady-state, were analyzed for propafenone and its two metabolites as well as for propranolol and 4-hydroxypropranolol. Left ventricular function, exercise performance and electrocardiographic intervals were assessed. Coadministration of propranolol did not produce any significant change in propafenone kinetics including peak plasma concentration (Cmax), time to peak plasma concentration (Tmax), elimination rate constant (t1/2), mean steady-state plasma concentration (Css), or area under the concentration vs time curves. However, concomitant propafenone administration significantly increased Cmax (83%), Tmax (55%), t1/2 (30%), and Css (213%) which were accompanied by significant decreases in plasma levels of 4-hydroxy-propranolol. Propafenone and propranolol significantly reduced supine systolic and diastolic blood pressure by 2.5 to 15.4%. The combination did not reduce diastolic blood pressure further (64.0 +/- 2.8 to 59.7 +/- 1.7 mmHg) nor did it produce a supplemental reduction in heart rate (12% reduction with propranolol, 10% reduction with concomitant administration). Propranolol, but not propafenone, significantly decreased end-diastolic volume index (13%), stroke volume index (15%), and velocity of circumferential fiber shortening (19%). The combination did not cause any further changes in echocardiographic measurements. Electrocardiographic intervals were not altered by either drug use alone or in combination.(ABSTRACT TRUNCATED AT 250 WORDS)

Usefulness of propafenone for recurrent paroxysmal atrial fibrillation

To evaluate the efficacy of propafenone for suppression of recurrent paroxysmal symptomatic atrial fibrillation (AF), patients with frequent episodes of AF entered an open-label, dose-ranging study to determine the maximal tolerated dose of propafenone and were subsequently randomized to alternate between propafenone and placebo every month for 4 months. Patients recorded each episode of AF in a diary and recorded a simultaneous electrocardiographic rhythm strip by means of a transtelephonic recorder and transmitter to validate the presence of AF. Eighteen patients were eligible for study. During dose ranging, 4 patients withdrew due to inadequate drug efficacy or poor compliance, 2 withdrew due to intolerable side effects and 1 died. The mean dose of propafenone at the end of dose ranging was 644 +/- 189 mg/day. During the crossover study, the percentage of days with an attack of AF was significantly reduced by propafenone compared with placebo (27 +/- 34 vs 51 +/- 34%, p less than 0.01). The rate of early crossover or withdrawal from the crossover study was 13.6% with propafenone and 45% with placebo (p = 0.056). Five patients went on to receive long-term propafenone and 4 continued treatment with suppression of AF for 12 to 21 months. During the crossover study there were 29 reported minor side effects with propafenone and 11 with placebo.

Propafenone: a novel type Ic antiarrhythmic agent

Propafenone is an investigational type Ic anti-arrhythmic agent that markedly slows conduction velocity in all cardiac tissues. Propafenone also possesses weak beta- and calcium-channel blocking properties. The bioavailability of propafenone is dose-dependent. Hepatic metabolism of this agent is polymorphic and appears to correlate with the ability of the liver to oxidize debrisoquin sulfate. Propafenone is effective in suppressing spontaneous ventricular ectopy; however, the drug may be less effective in patients with sustained ventricular tachycardia or ventricular fibrillation when evaluated using programmed stimulation. Propafenone is also useful in the treatment of supraventricular tachycardias including atrioventricular (AV) nodal reentrant tachycardia, AV reentrant tachycardia associated with the Wolff-Parkinson-White syndrome, and atrial fibrillation. Adverse reactions seen with propafenone affect the gastrointestinal, central nervous, and cardiovascular systems. Comparative studies with currently available type Ic agents are needed to better define propafenone's place in therapy.

Propafenone disposition in renal insufficiency and renal failure

The pharmacokinetics of a single intravenous dose of propafenone were studied in subjects with normal renal function (n = 5), renal insufficiency (n = 5), and renal failure (n = 3). No difference in central volume of distribution, total ischemic clearance or terminal half-life existed. None of the pharmacokinetic parameters examined correlated to creatinine clearance. Within the confines of the small number of patients studied, there does not appear to be any effect of renal insufficiency or failure on single-dose propafenone disposition.

Effects of propafenone on ventricular arrhythmias: double-blind, parallel, randomized, placebo-controlled dose-ranging study

Propafenone is a new class Ic antiarrhythmic compound with a broad pharmacologic profile. In this study, its dose-response relationship was examined in a double-blind, randomized, placebo-controlled five treatment parallel design protocol. Patients enrolled had heart disease with Lown grade 2 premature ventricular contractions (PVCs) (greater than or equal to 30/hr) documented on 24-hour Holter recordings. Propafenone was compared in four doses (337.5, 450, 675, and 900 mg/day) to placebo. The double-blind phase lasted 2 weeks. Two hundred twenty-six patients were enrolled, of whom 171 were men and 55 were women; their mean age was 59.8 years and 85% were Caucasian and 4% were black. The arrhythmias were symptomatic in 173. Twenty (8.8%) withdrew from the study before completion: 15 had adverse reactions, two had intercurrent illnesses, and three withdrew for administrative reasons. In one patient, the density of arrhythmia appeared to increase with propafenone. Side effects were of central nervous system or gastrointestinal origin; less than 5% of patients developed first-degree atrioventricular block or intraventricular conduction defect. There were no deaths in the study. The occurrence of side effects was not related to dose. Propafenone had no effect on heart rate. It increased the PR interval at all doses (9% to 22% compared to placebo at baseline; p less than 0.01) at 450 to 900 mg/day after 2 weeks of therapy. The drug increased the QRS duration at all doses, highly significantly at 675 mg/day (8.5 msec; p less than 0.01) and at 900 mg/day (15.7 msec; p less than 0.01) after 2 weeks of therapy. Only at the highest dose was the QTc slightly but significantly (14.3 msec; p less than 0.01) increased. Propafenone exerted a dose-dependent effect on PVCs recorded on serial 24-hour Holter recordings: compared to placebo, at 2 weeks 337.5 mg/day reduced PVCs by 70.8% (p less than 0.05), 450 mg/day reduced PVCs by 82.0% (p less than 0.01), 675 mg/day reduced PVCs by 90.2% (p less than 0.01) and 900 mg/day reduced PVCs by 95.3% (p less than 0.01). The effects of the two highest doses of propafenone were significantly greater than those of 337.5 mg/day. In 68% of the patients receiving 900 mg/day, 80% or greater reduction in total PVCs was found. In addition, there was a greater than 90% decrease in ventricular couplets, and 96% decrease in ventricular tachycardia (VT) beats. Propafenone eliminated PVCs in 8% of all patients, ventricular couplets in 58%, and VT beats in 91%.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacokinetic and pharmacodynamic interactions of propafenone and cimetidine

The pharmacokinetics and pharmacodynamics of the extensively metabolized antiarrhythmic agent propafenone were assessed alone and during concomitant administration of cimetidine. Twelve healthy subjects were given successively the following treatments: propafenone 225 mg q8h plus cimetidine placebo; cimetidine 400 mg q8h plus propafenone placebo; and propafenone 225 mg plus cimetidine 400 mg q8h. After a minimum of 5 days on each regimen, plasma drug concentrations and electrocardiogram conduction intervals were measured during a drug washout period. The maximum concentration of propafenone in plasma was 993 +/- 532 ng/mL when propafenone was given alone compared with 1230 +/- 591 ng/mL when propafenone was given with cimetidine (P = .0622). Differences in tmax, t1/2, and Cp ss did not approach statistical significance when propafenone alone was compared with propafenone plus cimetidine. When compared with cimetidine, propafenone significantly increased the PR interval from 161 +/- 5 msec to 192 +/- 6 msec (P less than .01) and the QRS duration from 89 +/- 3 msec to 98 +/- 4 msec (P less than .01). Combination therapy caused a modest additional increase in QRS duration to 103 +/- 3 msec (P less than .01). In conclusion, cimetidine caused small changes in propafenone pharmacokinetics and pharmacodynamics; but these changes are unlikely to be clinically important.

New antiarrhythmic drugs

While controversy still exists as to the precise indications for the treatment of all forms of ventricular arrhythmia, advances in the number and, more importantly, type of antiarrhythmic drugs can provide the clinician with a rational basis for selecting antiarrhythmic drug therapy. A host of new agents with different pharmacokinetic and electrophysiological actions are now available, and can be compared or contrasted to conventional antiarrhythmic agents such as quinidine, procainamide, disopyramide, lignocaine (lidocaine) and bretylium. This review summarises the electrophysiological, haemodynamic, pharmacokinetic, and efficacy and safety data of mexiletine, tocainide, flecainide, encainide, propafenone, amiodarone, sotalol, pirmenol, cibenzoline (cifenline) and ethmozine (moracizine, moricizine), and aims to provide a basis on which clinicians can compare and contrast these agents and form an algorithm for selection of antiarrhythmic drug therapy in the treatment of patients with ventricular arrhythmias.

Sustained therapeutic efficacy and safety of oral propafenone for treatment of chronic ventricular arrhythmias: a 2-year experience

Thirty-two men with chronic ventricular arrhythmias responded to propafenone, a new potent antiarrhythmic agent, in short-term trials with 85% or greater reduction of total ventricular premature complexes (VPCs) per hour, 95% or greater reduction of ventricular couplets (VCs) per hour, and 100% abolition of ventricular tachycardia (VT) beats per 24 hours. These patients were continued on long-term propafenone therapy to assess sustained therapeutic efficacy and safety. Thirty patients completed 1 year and 26 patients completed 2 years of testing with this agent; one patient died of sudden death and another died of a noncardiac cause. Although there were significantly fewer patient responders at 1 and 2 years, the majority of patients (greater than 79%) continued to respond optimally to propafenone. Side effects were minor and included bitter taste, dizziness, congestive heart failure, fatigue, and significant prolongation of the PR and QRS intervals. Propafenone has sustained antiarrhythmic efficacy after 2 years without serious toxicity.

Pharmacokinetics and pharmacodynamics of propafenone during acute and chronic administration

The pharmacokinetics of propafenone and 5-OH-propafenone and their relationship with the antiarrhythmic action and side effects have been studied in 10 patients with stable, frequent, premature ventricular beats (224-928 premature ventricular complexes/h). Observations were made after a single dose of propafenone 300 mg p.o., and after 1 and 3 months (only 5 out of 10 patients) of therapy with 300 mg t.d.s. After 1 month of treatment the plasma elimination half-life of propafenone (6.7 h) was almost twice as long as after a single dose (3.5 h), and the area under the plasma propafenone concentration-time curve (7620 ng.ml-1.h) was significantly larger than after single dose (3522 ng.ml-1.h); this was also true for the metabolite. The ratio of the AUCs of 5-OH-propafenone and propafenone decreased from the single dose (0.63) to 1 month (0.32). These variables remained stable up to 3 months. Eight patients had greater than or equal to 75% reduction of premature ventricular complexes after 3 days of therapy, and in 7 they were completely suppressed; the response was maintained over 1 to 3 months. Side effects were minor and in no case had the drug to be withdrawn or the dose reduced. Thus, the kinetics of propafenone were time-dependent. Its active metabolite did not accumulate greatly during chronic treatment. The lasting antiarrhythmic effect observed in some patients suggests a b.d.s. regimen instead of t.d.s. dosing in selected patients.

Propafenone. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in the treatment of arrhythmias

Propafenone is a Class I antiarrhythmic agent with weak beta-adrenoceptor antagonist activity which can be given both intravenously and orally. Dosage must be individualised because of dose-dependent pharmacokinetics, a wide range of clinically effective plasma concentrations (64 to 3271 micrograms/L) after comparable doses, the presence of an active metabolite (5-hydroxy-propafenone) and genetically determined metabolic oxidation. In non-comparative studies propafenone 450 and 900 mg/day orally significantly suppressed premature ventricular complexes and couplets in 96% and 75% of patients, respectively, and abolished ventricular tachycardia in 75% of patients. Efficacy was confirmed in placebo-controlled studies in which propafenone 300 to 900mg daily suppressed premature ventricular complexes (greater than 80%) in 77% of patients; 87% of patients had significant reductions in couplets and abolition of ventricular tachycardia. In patients with ventricular arrhythmias refractory to other antiarrhythmic agents, propafenone 450 to 1200 mg/day suppressed arrhythmias in 63% of patients (in long term therapy 66%). Electrically induced arrhythmias were prevented by intravenously administered propafenone in 12 to 23% of patients. However, long term oral therapy was effective in 77% of patients selected using programmed electrical stimulation. Propafenone was also effective in suppressing atrial and AV nodal/junctional re-entrant tachycardias and Wolff-Parkinson-White tachycardias involving accessory pathways. A limited number of comparisons with other antiarrhythmic drugs indicate that the antiarrhythmic efficacy of propafenone is superior or similar to that of quinidine, disopyramide and tocainide, and comparable to that of lignocaine (lidocaine), flecainide and metoprolol against ventricular arrhythmias and a smaller number of atrial arrhythmias. Cardiovascular side effects indicate a proarrhythmic effect similar to that with other Class I drugs, occasional precipitation of congestive heart failure and conduction abnormalities; the latter two occur more often in patients with underlying ventricular dysfunction. Non-cardiovascular side effects (neurological, gastrointestinal) are well tolerated and generally resolve with continued therapy or dosage reduction. Thus, propafenone is an effective antiarrhythmic agent, and is a useful addition to currently available drugs, although further studies will be required to determine clearly its place in therapy compared with more established antiarrhythmic drugs.

Randomized placebo-controlled trial of propafenone for treatment of atrial tachyarrhythmias after cardiac surgery

Fourteen patients with atrial fibrillation or flutter and a ventricular rate of greater than or equal to 120 beats/min occurring after cardiac surgery entered a double-blind placebo-controlled conditional crossover trial of intravenous propafenone. Patients randomly received either propafenone (2 mg/kg body weight) or placebo during a 10 minute intravenous infusion. If 20 minutes after the initiation of this infusion there was no conversion to sinus rhythm, the patient received a second intravenous infusion over 10 minutes (either propafenone or placebo, whichever was not given first). The electrocardiogram was recorded continuously throughout the study. Fourteen patients received propafenone and 10 received placebo. No patient's rhythm converted to sinus rhythm after placebo. In six patients (43%) (p less than 0.001), the arrhythmia converted to sinus rhythm between 5 and 10 minutes after the end of the propafenone infusion. After propafenone, the ventricular response to atrial fibrillation or flutter decreased significantly from 141.6 +/- 15.2 to 116.0 +/- 15.5 beats/min. Ventricular rate did not change after placebo. The mean propafenone plasma concentration was 3.46 +/- 2.17 mg/liter. The only side effect of propafenone noted was a decrease in systolic blood pressure of 9 +/- 9 mm Hg. Propafenone was useful for management of atrial fibrillation after cardiac surgery both for control of rapid ventricular response and for conversion to sinus rhythm.

Propafenone versus disopyramide: a double-blind randomized crossover trial in patients presenting chronic ventricular arrhythmias

In vitro and in vivo electrophysiological studies have shown that propafenone could be classified as a class I antiarrhythmic agent. The aim of this study was to investigate the short-term antiarrhythmic efficacy and safety of propafenone in 10 patients compared to disopyramide in a double-blind randomized protocol. Included patients suffered from ventricular arrhythmias with at least 60 ventricular premature beats (VPB) per hour refractory to at least two other antiarrhythmic agents. At the end of the control period and of the two treatment periods during which patients received either propafenone (300 mg three times a day) or disopyramide (200 mg three times a day), clinical examination, Holter recordings, electrocardiogram, and clinical laboratory tests were performed. The PR interval and the QRS interval were significantly increased with propafenone, but not with disopyramide. The cQT interval was not significantly changed by either propafenone or disopyramide. Heart rate was decreased with propafenone (p less than 0.05) with no change in the diurnal/nocturnal circadian ratio variation. Heart rate was significantly decreased with disopyramide only during the day. Five of nine patients in the propafenone group and two of nine patients in the disopyramide group showed a reduction in ventricular premature beats greater than 80%. Total resolution of severe arrhythmias (repetitive events) was seen in 5 of 8 patients with propafenone; 2 of 8 with disopyramide. Adverse events, when they occurred, were mild (visual disturbances, epigastric discomfort, changes in taste perception, transient atrioventricular block with propafenone, and photophobia with disopyramide), and did not require reduction or discontinuation of study drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmogenesis--a European perspective

Arrhythmogenesis as an effect of antiarrhythmic therapy is a relatively recent concern. Satisfactory definitions are lacking, but 2 categories, clinical and technical, can be recognized. Although arrhythmogenesis is an international problem and multifactorial, its expression depends on variables that differ according to geographic location. In Europe, use of antiarrhythmic therapy is more conservative than it is in the U.S. In the U.S., many antiarrhythmic drugs commonly used in Europe are either recently released, are on limited release or are available only in investigational protocols. Mexiletine, class IC agents and sotalol are agents in routine use in Europe. All have arrhythmogenic potential, although this appears lowest with mexiletine.