[The effect of sodium salicylate and phenobarbital on the anti-arrhythmia properties of novocainamide and acetylnovocainamide]

CaCl2 and aconitic models of arrhythmias were reproduced in experiments with rats. Sodium salicylate was found to decrease the preventive effect of ecetylnovocainamidum and increased the effect of novocainamidum on ECG changes. Sodium salicylate diminished the preventive effect of acetyl-novocainamidum by elevating myocardial Na+ concentrations, favoured the decrease in myocardial K+ levels, eliminated the preventive effects of novocainamide and acetylnovocainamide by altering myocardial energy metabolism in CaCl2-induced arrhythmia and improved the preventive effect of acetyl-novocainamide on these parameters in aconitic arrhythmia.

Acecainide (N-acetylprocainamide). A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in cardiac arrhythmias

Acecainide (N-acetylprocainamide), the N-acetylated metabolite of procainamide, is a Class III antiarrhythmic agent. It can be given either intravenously or orally, and is eliminated primarily by renal excretion. In a small number of noncomparative and placebo-controlled short term therapeutic trials acecainide markedly reduced premature ventricular beats and prevented induction of ventricular tachycardia in more than 70% of patients following intravenous administration and in about 50% after oral administration. Acecainide was effective in about one-quarter of patients refractory to other antiarrhythmic drugs. Interpretation of its effectiveness following long term oral therapy is complicated by the limited number of patients, and patients discontinuing due to adverse effects or lack of efficacy. However, about 40% of the small number treated for extended periods were controlled for periods of 6 months to 3 to 4 years. Comparative studies with other antiarrhythmic drugs have not been undertaken apart from a small study in atrial flutter where acecainide was better than quinidine plus digoxin. Thus, although further clinical experience is required before the relative place of acecainide in therapy can be determined, the drug nevertheless appears to offer advantages over procainamide, particularly with respect to the reduced formation of antinuclear antibodies.

Pharmacokinetic and pharmacodynamic interaction of N-acetyl procainamide and procainamide in humans

Procainamide is a sodium channel blocker which prolongs QRS and QTc intervals, yet its major active metabolite, N-acetylprocainamide (NAPA), generally prolongs only QTc and has very different electrophysiologic and antiarrhythmic actions. In greater than 50% of patients receiving chronic treatment with procainamide, plasma concentrations of NAPA exceed those of procainamide. In this study, we examined the hypothesis that NAPA might alter the disposition kinetics or pharmacologic actions of procainamide. Ten patients with frequent ventricular extrasystoles received intravenous (i.v.) infusions of procainamide alone (study day 1), procainamide and NAPA (study day 2), and NAPA alone (study day 3) at least 48 h apart. On study days 1 and 2, procainamide was administered at a constant rate for 4 h. On study days 2 and 3, NAPA was administered as a loading and maintenance infusion designed to reach a target pseudo-equilibrium plasma concentration of 8 micrograms/ml. NAPA increased procainamide elimination half-life (t1/2) from 275 +/- 42 min (mean +/- SD) on day 1 to 340 +/- 74 min on day 2 (p less than 0.01). A significant correlations was noted between the change in procainamide total clearance on day 2 relative to day 1 and the initial procainamide total clearance on day 1 (r = -0.77, p = 0.009). Findings were similar when procainamide fractional urinary excretion was considered (r = -0.89, p = 0.007). NAPA did not alter procainamide-induced QRS prolongation, but potentiated procainamide-induced QTc prolongation. The antiarrhythmic response to procainamide was not significantly altered by NAPA in seven of nine patients. One patient had greater arrhythmia suppression when NAPA and procainamide were combined than when either was administered alone. In one patient, NAPA apparently antagonized procainamide-induced arrhythmia suppression, but this effect was not reproducible. We conclude that accumulation of NAPA during procainamide therapy can alter both procainamide elimination as well as its electrophysiologic actions.

Evaluation of antiarrhythmic drugs on defibrillation energy requirements in dogs. Sodium channel block and action potential prolongation

Antiarrhythmic drugs have been reported to produce variable effects on defibrillation energy requirements. However, the relation between the in vitro electrophysiologic effects of these agents and the changes in defibrillation energy requirements have not been systematically examined. Therefore, we evaluated the effects of the sodium channel blocking drugs lidocaine and procainamide, the action potential prolonging drugs N-acetyl procainamide and clofilium, and the potassium current blocker cesium in acute canine models with the same internal spring and epicardial patch electrodes used in humans for ventricular defibrillation testing. Ten series of experiments were performed in 78 dogs. Nonlinear regression was used to derive curves of energy dose versus percent successful defibrillation attempts and the 50% and 90% effective energy dose for each experimental condition. Saline control experiments indicated that the preparation was stable throughout the 6-hour duration of the experiments. Lidocaine doubled the defibrillation energy requirement (p less than 0.001) at a mean plasma concentration of 8.2 micrograms/ml. The effect of lidocaine on defibrillation energy was reversible, present at therapeutic plasma concentrations, linearly related to plasma concentration (r = 0.69, p less than 0.002), and present even after only 5-second episodes of ventricular fibrillation. In contrast, procainamide had no effect on defibrillation energy at mean plasma concentrations of 8.5 and 13 micrograms/ml, even after prolonged (30-second) episodes of ventricular fibrillation, whereas N-acetyl procainamide, clofilium, and cesium all decreased the energy requirement for defibrillation by 13-27%. Moreover, with the addition of N-acetyl procainamide, there was a trend toward diminishing the increase in defibrillation energy requirement caused by lidocaine. All agents prolonged the mean ventricular fibrillation cycle length. Lidocaine shortened the QT interval, whereas all other agents increased the QT (p less than 0.05). The major electrophysiologic effect of lidocaine is of sodium channel blockade, whereas, N-acetyl procainamide, clofilium, and cesium predominantly increase the action potential duration, and procainamide exerts both effects. Thus, these data indicate that sodium channel block and action potential prolongation exert significant and antagonistic modulating effects on defibrillation energy requirements.

Oral N-acetylprocainamide compared to quinidine plus digoxin in the chronic suppression of atrial flutter in humans

Antiarrhythmic therapy for the suppression of atrial flutter has conventionally entailed the use of a class Ia agent such as quinidine or procainamide. However, atrial flutter often recurs despite the use of these conventional antiarrhythmic regimens. Experimental and clinical evidence suggests that the pharmacologic suppression of atrial flutter may depend on the prolongation of the atrial action potential duration and consequently the voltage-dependent refractoriness. Therefore, the efficacy and tolerance of the class III antiarrhythmic agent N-acetylprocainamide was compared to that of the conventional regimen of the class Ia agent quinidine combined with digoxin (to control ventricular response) in patients with a history of symptomatic sustained atrial flutter. The study was randomized but nonblinded, with a crossover to the alternate regimen if the first failed. Eighteen patients entered the study and were followed for up to 18 months. Of the 12 receiving N-acetylprocainamide (eight randomized and four crossovers), one (8%) failed therapy due to side effects, but none had atrial flutter. Of the 11 receiving quinidine and digoxin (10 randomized and one crossover), three (28%) had a recurrence of atrial flutter, two of whom also had intolerable side effects, and two more (18%) had side effects alone requiring withdrawal of therapy (total 46% failed). The probability of therapeutic success over time was greater (p less than 0.04) for N-acetylprocainamide than for quinidine and digoxin. The data suggest that N-acetylprocainamide may be more effective and better tolerated than the conventional regimen of quinidine plus digoxin. Therefore, large-scale blinded studies of the efficacy of N-acetylprocainamide in the suppression of atrial flutter may be warranted.

Effects of N-acetylprocainamide and recainam in the pharmacologic conversion and suppression of experimental canine atrial flutter: significance of changes in refractoriness and conduction

The electrophysiologic determinants of the pharmacologic conversion and the prevention of atrial flutter are poorly defined. This study investigated the effects of pharmacologically induced changes in atrial conduction velocity and refractoriness, in the conversion and suppression of atrial flutter induced in the open-chest anesthetized dog by intercaval crush and rapid atrial pacing. The effects of an intravenous infusion of the new class III antiarrhythmic drug N-acetylprocainamide (30 mg/kg over 15 min) and the class Ic antiarrhythmic drug recainam (10 mg/kg over 20 min followed by 10 mg/kg/h) were evaluated. N-acetylprocainamide restored sinus rhythm in 10 of 15 (66%) dogs, while recainam converted only 2 of 10 (20%). N-acetylprocainamide prevented reinduction in 3 (20%), while recainam was effective in none. In the atria, N-acetylprocainamide induced significant increases in effective refractory period (+27%, p less than 0.01), functional refractory period (+22%, p less than 0.01), and in atrial flutter cycle length (+13%, p less than 0.01). Recainam increased effective refractory period (+28%, p less than 0.01), functional refractory period (+20%, p less than 0.01), conduction time at atrial paced cycle length of 150 msec (+70%, p less than 0.01) and atrial flutter cycle length (+56%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of procainamide and N-acetylprocainamide on atrial flutter: studies in vivo and in vitro

We studied the effects of procainamide and N-acetylprocainamide (NAPA) in a conscious dog preparation of atrial flutter resulting from circus movement around the tricuspid orifice. We also recorded transmembrane potentials of atrial tissues from the circus path in vitro. In 12 instrumented dogs, average flutter cycle length was 157 msec, the duration of the excitable gap was 73 msec, and conduction velocity was 0.75 m/sec. At 4 and 8 mg/kg, procainamide moderately prolonged cycle length, but did not terminate the flutter. At a cycle length of 300 msec procainamide increased effective refractory period (ERP) by 12% and 20% and conduction time by 8% and 19%. At 16 and 32 mg/kg procainamide prolonged cycle length, ERP, and conduction time by 60% to 80% and stopped the flutter in all trials. NAPA, at 16, 32, and 64 mg/kg, increased flutter cycle length by 16%, 16%, and 31%, ERP by 14%, 28%, and 41%, and conduction time by less than 15%. NAPA terminated the flutter in two of six dogs given 32 mg/kg, and three of five dogs given 64 mg/kg. The excitable gap was lengthened by both procainamide and NAPA. Transmembrane potentials showed that at a cycle length from 1000 to 300 msec procainamide (10 mg/liter) increased action potential duration and decreased the first time derivative of phase O of the action potential (Vmax), whereas NAPA (20 mg/liter) increased action potential duration without changing Vmax. These findings show the difficulty of relating drug effects on transmembrane potentials to efficacy in vivo since the former do not necessarily indicate which changes in cellular electrical activity are responsible for efficacy against a particular arrhythmogenic mechanism.

Effect kinetics of N-acetylprocainamide-induced QT interval prolongation

We attempted to correlate clinical response with the effects of N-acetylprocainamide (NAPA) on the QT interval in five patients with stable chronic ventricular arrhythmias. A 15 mg/kg dose of NAPA was administered and a pharmacokinetic-pharmacodynamic model was used to relate plasma NAPA concentrations to changes in corrected QT interval (QTc). NAPA volume of distribution, elimination clearance, and elimination half-life averaged 1.37 +/- 0.19 L/kg, 174 +/- 63 ml/min, and 8.2 +/- 1.4 hours, respectively (mean +/- SD), and NAPA renal clearance averaged 1.9 +/- 0.6 times creatinine clearance. QTc prolongation was characterized by a linear-effect model in the first four patients and averaged 2.4 msec for every microgram per milliliter NAPA in a hypothetic biophase. QTc prolongation in patient 5 was exaggerated and was analyzed with an Emax model. Nonetheless, NAPA did not control this patient's arrhythmia. Conversely, patient 1 subsequently developed torsade de pointes even though QTc prolongation in this patient was comparable to that in patients 2 through 4, who responded satisfactorily to NAPA. We conclude that QT interval changes during initial NAPA administration do not reliably predict subsequent clinical response.

Effects of N-acetylprocainamide on experimental atrial flutter and atrial electrophysiologic properties in conscious dogs with sterile pericarditis: comparison with the effects of quinidine

N-acetylprocainamide (NAPA) is said to have class III antiarrhythmic drug properties. The effects of NAPA (25 mg/kg intravenously) on sustained, stable, reentrant atrial flutter induced in 12 conscious dogs using a sterile pericarditis model were studied and compared with the effects of quinidine (5 mg/kg intravenously) given on a different day in 10 of the same 12 dogs. The effects of these drugs on atrial excitability, the atrial effective refractory period and intraatrial conduction time measured during rapid atrial pacing performed during sinus rhythm were also compared. The mean NAPA and quinidine serum levels were 17.7 and 7.1 micrograms/ml, respectively. Both NAPA and quinidine immediately prolonged the atrial flutter cycle length in all dogs, from 118 +/- 15 to 141 +/- 18 ms and from 119 +/- 17 to 153 +/- 21 ms, respectively (both p less than 0.001), and then terminated atrial flutter in 11 of the 12 NAPA studies and in 6 of the 10 quinidine studies. Neither drug affected atrial excitability. Both NAPA and quinidine increased the atrial effective refractory period significantly, from 138 +/- 17 to 168 +/- 20 ms (p less than 0.001) and from 136 +/- 14 to 148 +/- 16 ms (p less than 0.01), respectively. NAPA did not change intraatrial conduction time measured during atrial pacing at 150 beats/min, but during atrial pacing at 300 beats/min, it prolonged it from 51 +/- 9 to 54 +/- 10 ms (p less than 0.05), and at 400 beats/min, from 52 +/- 10 to 64 +/- 13 ms (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of N-acetylprocainamide

Shortly after Dreyfus and his colleagues demonstrated that procainamide was metabolized by acetylation to N-acetylprocainamide (NAPA), Drayer, Reidenberg and Sevy reported that NAPA had antiarrhythmic activity in an animal model. We confirmed these findings and found that plasma levels of NAPA were high enough to warrant consideration in managing patients requiring procainamide therapy. However, the actual impetus for developing NAPA as an antiarrhythmic drug in its own right was provided by the initial studies of NAPA pharmacokinetics in normal subjects. In these studies, we showed that NAPA has an elimination-phase half-life that is more than twice as long as procainamide and suggested that patient compliance and arrhythmia suppression might be improved if NAPA were used to circumvent the inconvenience of the frequent dosing schedule that has been recommended for procainamide. From the standpoint of managing individual patients with NAPA, the pharmacokinetics of this drug continue to provide the scientific basis for designing dose regimens that will have maximal antiarrhythmic efficacy and minimal toxicity. This review summarizes the salient features of NAPA pharmacokinetics and outlines an approach for individualizing therapy with this drug.

N-acetylprocainamide's antiarrhythmic action in patients with ventricular tachycardia

Antiarrhythmic properties of N-acetylprocainamide, an active metabolite of procainamide, were studied in 15 patients who presented with a cardiac arrest or documented sustained ventricular tachycardia. Programmed electrical stimulation studies were performed. All patients tested had inducible ventricular tachycardia by programmed electrical stimulation techniques while off all antiarrhythmic therapy. Patients were then tested on procainamide 1000 mg administered intravenously, and ventricular tachycardia could be provoked in 8 of 10 patients. Twenty-four to 36 hours later, N-acetylprocainamide was administered, intravenously, and programmed stimulation was performed after 20 minutes. N-acetylprocainamide did not significantly change heart rate, mean arterial blood pressure, electrocardiographic intervals, A-H or H-V conduction times. N-acetylprocainamide prevented ventricular tachycardia induction in 6 of 15 patients. The mean serum N-acetylprocainamide levels in the group protected was 15.7 +/- 4 micrograms/ml and 16.2 +/- 4 micrograms/ml in the group not protected. These 6 patients were discharged on N-acetylprocainamide 1.5 grams orally every 8 hours. Three patients have been maintained on chronic N-acetylprocainamide every 8 hours. Three patients have been maintained on chronic N-acetylprocainamide therapy (6 +/- 2 months), two patients had breakthrough ventricular tachycardia on follow-up Holter monitoring and alternative therapy was given. N-acetylprocainamide has antiarrhythmic efficacy in preventing induction of ventricular tachycardia by programmed electrical stimulation in a high risk group of patients. On chronic oral therapy, N-acetylprocainamide appears to be well tolerated with antiarrhythmic efficacy that may be enhanced with further upward dose titration.

Arrhythmia control by selective lengthening of cardiac repolarization: role of N-acetylprocainamide, active metabolite of procainamide

In recent years, data has become available to support the concept that a selective lengthening of the cardiac action potential (a Class III antiarrhythmic action) by whatever mechanism with an attendant increase in the effective refractory period constitutes a distinct antiarrhythmic mechanism. Such an action is exemplified clinically by hypocalemia and hypothyroidism and pharmacologically by amiodarone, sotalol and bretylium, all of which have other associated features. The N-acetylation of procainamide leads to the pharmacologically active compound, N-acetylprocainamide (NAPA). The loss of propensity to block depolarization with the preservation of the effect on repolarization in the case of NAPA makes the compound a class III antiarrhythmic agent. The process of N-acetylation has also led to longer elimination half-life and predominantly renal excretion with linear kinetics but with the preservation of the antiarrhythmic properties of the parent compound. The electrophysiologic data are consistent with the results of studies which have demonstrated that NAPA has the potential to suppress premature ventricular contractions and prevent spontaneously occurring as well inducible ventricular tachycardia in patients with heart disease. The effects on atria indicate that the drug has the potential to electively reverse atrial flutter and fibrillation to normal rhythm and maintain stability of sinus rhythm. The overall experimental and clinical data warrant further evaluation of NAPA as an antiarrhythmic agent.

QT prolongation and arrhythmia suppression

It seems possible to draw some overall conclusions from the data on antiarrhythmic drug-induced QT prolongation and its role in drug effects. At one end of the spectrum are patients with highly exaggerated QT responses during therapy, most often in the setting of hypokalemia and long cycle lengths (post-ectopic pauses, bradycardia). These patients may be at high risk for development of arrhythmias during therapy. It should also be remembered that the presence of hypokalemia may render antiarrhythmic agents less effective in general. On the other hand, modest QT prolongation in the course of therapy with an antiarrhythmic drug may well be a marker of reduction of dispersion of action potential durations or refractory periods and hence represent an antiarrhythmic effect. The clinical actions of these drugs in patients with arrhythmias strongly suggest that this is the case. New agents with the ability to reduce dispersion of repolarization or of refractoriness without inducing arrhythmias may well become the agents of choice for the treatment of serious cardiac rhythm disturbances.

New drugs in the management of ventricular arrhythmias

New antiarrhythmic drugs are chiefly assigned to Class 1C and 1B: "procainamide analogues" (acecainide, lorcainide, flecainide, encainide) and propafenone for the former, and mexiletine, tocainide and aprindine for the latter. Pharmacokinetics vary widely among the different antiarrhythmic agents. These and other problems which regulate therapeutic interventions, such as patient compliance, drug interactions, efficacy/toxicity ratio, drug combinations, and drug monitoring with plasma concentrations of antiarrhythmic agents are briefly considered.

Torsade de pointes induced by N-acetylprocainamide

N-Acetylprocainamide (NAPA), a class III antiarrhythmic drug, caused torsade de pointes in a 72 year old woman who had this arrhythmia on two previous occasions while being treated with quinidine and disopyramide. Initial evaluation with an intravenous infusion of NAPA indicated a favorable antiarrhythmic response. The QTC interval was prolonged, but the 2.4 ms/microgram per ml incremental QTC interval lengthening caused by NAPA was not greater than usual. During subsequent oral therapy with NAPA, torsade de pointes developed at plasma levels of this drug that appeared to be well tolerated during the initial evaluation.

Efficacy and safety of N-acetylprocainamide in long-term treatment of ventricular arrhythmias

Four patients with chronic ventricular arrhythmias, shown to respond over the short term to N-acetylprocainamide (NAPA), were treated for between 3 and 4 yr with NAPA, and 24-hr ambulatory ECGs were obtained monthly to monitor their responses. When the patients were ambulatory and receiving NAPA, the mean frequency of premature ventricular complexes averaged 70% (range 60% to 82%) below that recorded at 6-mo intervals when the patients were hospitalized and receiving placebo. Analysis of variance showed that NAPA exerted an antiarrhythmic effect in these patients and that tolerance to this effect did not develop with long-term therapy. Plasma NAPA concentrations required to achieve this level of response averaged 21 micrograms/ml (12 to 35 micrograms/ml) and were roughly twice as high as those which appeared to be maximally effective when the patients were hospitalized for their initial evaluation. NAPA therapy was associated with positive antibody titers in only one patient and seems less prone to cause drug-induced lupus erythematosus than procainamide, but NAPA shares the gastrointestinal and other side effects of procainamide.

Electrophysiologic properties and antiarrhythmic mechanisms of intravenous N-acetylprocainamide in patients with ventricular dysrhythmias

To define electrophysiologic properties and antiarrhythmic mechanisms of N-acetylprocainamide (NAPA), we studied 16 patients with symptomatic ventricular dysrhythmias. Electrophysiologic studies were performed before and after intravenous infusion of NAPA at 20 mg/kg over 20 minutes, achieving plasma concentrations of 24 +/- 3.2 to 35.5 +/- 4.5 micrograms/ml. NAPA did not significantly change sinus cycle length or atrioventricular (AV) conduction times (PA, AH, HV, and QRS), but it lengthened the QTc interval (p less than 0.001) during sinus rhythm. Programmed atrial stimulation revealed that NAPA had no discernible effects on AV nodal conduction; however, it exerted depressive effects on the His-Purkinje system in 9 of 16 patients. In 7 of 16 patients who manifested frequent ventricular premature beats (VPBs), NAPA abolished VPBs in only three of them; NAPA induced progressive prolongation of the premature coupling interval before complete abolition of VPBs. In 8 of 16 patients who had inducible repetitive ventricular response (RVR) because of reentry within the His-Purkinje system, NAPA narrowed or abolished the RVR zone in 3 patients and slowed the RVR rate with widening of the RVR zone in the remaining 5 patients. In 2 of 16 patients with slow ventricular tachycardia (VT), NAPA had no antiarrhythmic effects. By contrast, in the other 2 of 16 patients in whom sustained VT could be reproducibly elicited with programmed ventricular stimulation, NAPA slowed the rate of VT and suppressed VT inducibility. We conclude that electrophysiologic properties of NAPA are slightly different from those of procainamide and that NAPA is not uniformly effective for suppressing ventricular dysrhythmias, but its antiarrhythmic mechanisms are similar to those of procainamide.

N-Acetylprocainamide kinetics and clinical response during repeated dosing

Kinetics of and clinical responses to N-acetylprocainamide (NAPA) were evaluated in 10 patients with chronic ventricular arrhythmias who had not responded to usual doses of currently available antiarrhythmic drugs. Kinetic data analysis was by measured NAPA concentrations (n = 149) collected during repeated dosing. Response was evaluated with serial 24-hr ambulatory ECGs. An a priori kinetic model based on earlier studies predicted NAPA concentrations well (r = 0.94, SEE = 3.6 mg/l). The capability for defining patient-specific estimates for drug disposition with six or seven serum concentrations measured at the outset of therapy was subsequently confirmed with larger data sets from the same patients. Mean values for elimination rate (0.082 hr -1 +/- 0.017) and volume of distribution (1.25 l/kg +/- 0.28) were of the same order as in earlier single-dose studies. A substantial degree of interpatient and intrapatient variability in the absorption rate for NAPA was observed. NAPA was not found to be clinically effective in any of the 10 patients, although two patients demonstrated a greater than 70% reduction in frequency of premature ventricular contractions. There were adverse effects in all patients, which frequently required dose reduction or cessation of therapy. In this group of patients with resistant arrhythmias, NAPA was no more effective than baseline therapy, and adverse effects often limited complete evaluation. The kinetic analysis demonstrated the feasibility of a strategy for developing patient-specific kinetic models that may have applications to other antiarrhythmic drugs.

The electropharmacology of acute drug testing using pacemakers

Acute drug testing in patients is useful to select prophylactic treatment for life-threatening or intractable tachycardias. This is generally done by induction of tachycardias with pacing. Acute studies that depend on temporary insertion of pacing electrodes do not determine efficacy in the same sense as longer term clinical drug trials because of the biased population referred for testing with pacemakers. However, the pharmacologic activity of compounds can be tested in terms of electrical functions such as conductivity and refractoriness not merely of the heart in general, but also of the arrhythmogenic focus. Such data can be directly applied to patients with similar arrhythmias, obviating the confusion often caused by interspecies and disease differences.

Selection of an antiarrhythmic drug for a sudden-death-prevention trial

Several therapeutic approaches have sought to prevent the occurrence of sudden cardiac death. Many sudden deaths are presumed to be due to an arrhythmia, but the drugs best known for antiarrhythmic activity, the local anesthetic agents, have not been suitable prophylactic agents because of their toxicities and other undesirable pharmacologic characteristics. Several new drugs in this class have been synthesized and are currently being tested for antiarrhythmic activity in clinical trials. One of them may prove to be worthy of a large-scale clinical trial to determine whether chronic arrhythmia suppression reduces the risk of sudden death. The characteristics of the "ideal" antiarrhythmic agent are discussed, and a brief summary of the drugs currently being tested in the United States is presented. The discussion of each drug emphasizes the characteristics that might make it suitable--or unsuitable--for use in a sudden-death trial. Many agents being tested are clearly not satisfactory for such a trial. However, they may be prototypes for an ideal drug or combination of drugs that might yet be developed.

Long-term antiarrhythmic therapy with acetylprocainamide

Nineteen patients whose arrhythmias were initially suppressed with acetylprocainamide underwent long-term treatment with this drug. Eleven patients were still taking the drug at the end of 12 months. Drug withdrawal with substitution of a placebo caused an increase in ventricular premature beats. Thus, suppression of ventricular premature beats persisted for 1 year. The eight withdrawals from the study were due to death during the year (n = 6) or recurrence of arrhythmias. The deaths occurred in patients who were in New York Heart Association functional class II (one patient), III (three patients) and IV (two patients). Ventricular performance, assessed from systolic time intervals, improved with drug therapy and declined during drug withdrawal. Symptomatic effects were common, with seven patients requiring a reduction in dosage or discontinuation of therapy. Three patients treated for 3 years continued to show drug suppression of ventricular premature beats compared with the level during placebo substitution. Small amounts of procainamide were present in all patients because of in vivo deacetylation of acetylprocainamide. Many patients with good initial responses to this drug had recurrent arrhythmias during long-term therapy. For this reason, the usefulness of acetylprocainamide as an antiarrhythmic drug appears to be limited.

Acetylprocainamide therapy in patients with previous procainamide-induced lupus syndrome

Acetylprocainamide was used to treat 11 patients with previous procainamide-induced lupus syndrome for their cardiac arrhythmias. Three patients from whom procainamide had been withdrawn and whose lupus was in remission did not have a recurrence during a course of acetylprocainamide therapy of a longer average duration than their prior procainamide therapy. Lupus symptoms subsided during treatment in two patients who had symptoms when acetylprocainamide was started. Drug fever developed in one patient, and another had a mild recurrence of lupus symptoms during high-dose acetylprocainamide therapy that regressed with dosage reduction. All patients had small amounts of circulating procainamide from in-vivo deacetylation of acetylprocainamide. These observations strongly support the hypothesis that the aromatic amino group on procainamide is important for induction of the lupus syndrome and that acetylating this amino group blocks the lupus-inducing effect.

Clinical pharmacology and antiarrhythmic efficacy of N-acetylprocainamide

Eleven patients with chronic ventricular arrhythmias took part in a study of N-acetylprocainamide (NAPA), the major metabolite of procainamide, in order to characterize further NAPA's clinical pharmacology and antiarrhythmic action. The frequency of ventricular arrhythmia on 24 hour ambulatory electrocardiographic recordings was comparable on recordings obtained in a prestudy screening, during treatment with placebo before administration of NAPA and after treatment with NAPA. The initial dosage of NAPA was 500 mg every 8 hours, which was increased by 500 mg increments every few days until 90 percent suppression of arrhythmia or intolerable adverse effects occurred. Only two patients achieved 90 percent suppression of ventricular ectopic complexes. The mean plasma concentration associated with 90 percent suppression of arrhythmia in these two patients ws 12.6 and 32.3 mg/ml, respectively. One of these two patients was unable to continue long-term therapy with NAPA because of a rash. Other adverse effects included gastrointestinal symptoms in seven patients with visual symptoms in four patients at plasma concentratons as low as 6.9 mg/ml. NAPA obeyed linear pharmacokinetics over the range of dosages studied (500 to 2,500 mg every 8 hours) and had a half-life of 10.7 +/- 1.98 hours (mean +/- standard deviation). There was no change in the P-R or QRS intervals and there was a dose-dependent prolongation of the Q-Tc interval. It is concluded that in this patient group, NAPA suppressed chronic ventricular ectopic complexes without adverse effects in only a minority of patients.

Antiarrhythmic efficacy, pharmacokinetics and safety of N-acetylprocainamide in human subjects: comparison with procainamide

The antiarrhythmic efficacy and pharmacokinetics of N-acetylprocainamide (NAPA), the major metabolite of procainamide, were investigated in 23 patients with chronic, high frequency ventricular ectopic depolarizations. An extensive trial design incorporated the approaches of (1) generation of dose-response relations, (2) randomized crossover, and (3) prolonged electrocardiographic monitoring. Seven patients with reproducible suppression of arrhythmias (70 percent or greater reduction in frequency) were thus identified. The mean plasma concentration of acecainide associated with efficacy was 14.3 micrograms/ml (range 9.4 to 19.5) and with side effects (primarily gastrointestinal) was 22.5 micrograms/ml (10.6 to 37.9). The antiarrhythmic response to procainamide did not predict response to acecainide; this finding implies that estimates of the antiarrhythmic contribution of acecainide concentrations achieved during long-term procainamide therapy are unlikely to be meaningful in a given person. The mean half-life of elimination after a single 500 mg dose of acecainide was 7.5 hours; this had prolonged significantly (p < 0.05) to 10.3 hours after higher dosages. No variable examined (including acetylator phenotype) was found to be a predictor of responsiveness to acecainide. Outpatient therapy (2 to 20 months) was not associated with the development of antinculear antibodies or the lupus syndrome; one patient's procainamide-induced arthritis resolved during therapy. Acecainide, unlike procainamide, is an agent whose pharmacokinetics allow long-term therapy on a practical schedule. It is effective in a subset of patients with ventricular arrhythmias yet appears much less likely to induce the lupus syndrome seen with the parent compound.

The clinical pharmacology and antiarrhythmic efficacy of acetylprocainamide in patients with arrhythmias

The actions of acetylprocainamide, the major metabolite of procainamide in man, were studied in a placebo-controlled oral-dose-ranging trial in 16 persons with arrhythmias. The occurrences of arrhythmias decreased in 15 patients receiving acetylprocainamide and increased subsequently in 10 of 13 patients given placebo. The frequency of arrhythmias was reduced by more than 75 percent in nine patients. Antiarrhythmic effects were dependent on dose and serum drug concentrations, with levels of 10 to 24 microgram/ml observed in patients with a reduction of more than 70 percent in premature ventricular complexes. The ratio of preejection period to left ventricular ejection time decreased during therapy. Side effects of light-headedness, insomnia, nausea and diarrhea occurred in six patients at serum levels ranging from 11 to 22 microgram/ml. The serum half-life of acetylprocainamide lengthened from 7 to 21 hours as the creatinine clearance decreased from 105 to 35 ml/min. Acetylprocainamide has antiarrhythmic efficacy, but causes side effects in human beings. This compound appears to contribute to the effects of procainamide therapy and may be useful as an antiarrhythmic drug.

Theoretical basis for interest in acetylprocainamide and clinical experiences with this new antiarrhythmic agent

In conclusion, it was the differential responses of slow and rapid acetylators to procainamide therapy that gave the initial clues that acetylprocainamide might be a safer drug than procainamide. So far, the experience with acetylprocainamide has been encouraging.