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Acecainide pharmacokinetics in normal subjects of known acetylator phenotype.

The purpose of this study was to determine the pharmacokinetics of acecainide (formerly N-acetylprocainamide) in six normal subjects of known acetylator phenotype. Three subjects were fast acetylators and three slow acetylators by sulfapyridine phenotyping criteria. Each subject received a 20-min, 3 mg kg-1 intravenous acecainide infusion. Concentrations of acecainide, procainamide, and their deethylated metabolites were measured in serum and urine samples using HPLC. Acecainide renal clearance, nonrenal clearance, steady-state volume of distribution, and other pharmacokinetic parameters were estimated using standard approaches. Acecainide renal clearance and steady-state volume of distribution were (mean +/- SD) 13.6 +/- 1.581 h-1 and 135 +/- 20.31, respectively, and were not significantly different in fast and slow acetylators. Acecainide nonrenal clearance in the six subjects was 3.0 +/- 1.01 h-1; however, nonrenal clearance in slow acetylators was 1.8 times that in fast acetylators (3.9 vs 2.21 h-1, p = 0.012) with clear separation of the subjects into two groups when the data were grouped by acetylator phenotype. The nonrenal clearance of acecainide was inversely correlated with percentage sulfapyridine acetylation. Computer simulations were conducted to explore possible explanations for the observed difference in nonrenal clearance.

Acecainide

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.

Acecainide

Analysis of procainamide hydrochloride and acecainide hydrochloride in rat feed.

An extraction and GLC assay procedure was developed for quantitation of procainamide hydrochloride and acecainide hydrochloride in rat feed. 4-Amino-N-[2-(dipropylamino)ethyl]benzamide hydrochloride was synthesized and utilized as an internal standard. The assay has good precision and accuracy and was used to establish the stability of acecainide hydrochloride and procainamide hydrochloride in rat feed.

Acecainide

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.

Acecainide

[New anti-arrhythmia drug. III. Comparative studies of the effects of N-propionylprocainamide, procainamide and N-acetylprocainamide on hemodynamics and cardiac blood flow].

Procainamide (PA) often applied in cases of ventricular arrhythmias causes numerous cardiac and extracardiac undesirable symptoms. Its active metabolite, N-acetylprocainamide (NAPA; Acecainide) is known to affect less noxiously the ventriculo-atrial conduction and the intraventricular++ conduction, and it does not impair contractility of the heart muscle. Many drugs with proven antiarrhythmic activity cannot be used in clinical practice because of disadvantageous effects on the function of the left ventricle and on the coronary blood flow, particularly in patients with the recent myocardial infraction. It seems that another acyl derivative of procainamide with potential antiarrhythmic activity, N-propionylprocainamide (NPPA) may be less harmful than PA, and NAPA. Effects of milimolarly equivalent doses of NPPA, NAPA and PA on the cardiac output and the stroke volume index, as well as on the coronary blood flow were investigated in rabbits by the radioisotope method. The obtained results were subjected to statistical analysis. NPPA was found to display no depressive action on the function of the left ventricle. Moreover, it was found to improve the coronary blood flow in rabbits.

Acecainide

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.

Acecainide

Heterocyclic analogues of benzamide antiarrhythmic agents.

A series of heterocyclic N-[(diethylamino)alkyl]arenamides related to acecainide was prepared and examined for antiarrhythmic activity. The compounds were synthesized from the corresponding known heterocyclic carboxylic acids or esters by using standard amide formation methods. The effects of the compounds on the electrophysiological properties of canine Purkinje fibers and ventricular muscle strips were determined. Most of the compounds showed effects consistent with weak class I activity. Two compounds, N-[2-(diethylamino)ethyl]-3,4,5-trimethyl-1H-pyrrole-2-carboxamide and N-[2-(diethylamino)ethyl]-1H-indole-2-carboxamide, displayed prolongation of the action potential duration and functional refractory period indicative of modest class III electrophysiological activity. Representative compounds were examined by using molecular modeling techniques. Compounds of differing activity classes displayed qualitatively different electrostatic potential maps.

Action Potentials

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)

Animals

The implications of procainamide metabolism to its induction of lupus.

The principal metabolic pathway of procainamide leads to formation of the less toxic N-acetyl-procainamide and the rapid acetylator phenotype is associated with a lower incidence of procainamide-induced lupus. Another metabolic pathway forms a reactive metabolite which causes revertants in the Ames test and covalently binds to microsomal protein. A study of the metabolism of procainamide revealed three metabolites that have not been previously described. A comparison of the metabolites of N-acetylprocainamide with those of procainamide suggests possibilities for the identity of the reactive metabolite. The hypotheses to be discussed explore the relationships between the formation of a reactive metabolite and the induction of lupus.

Acecainide

N-acetylprocainamide is a less potent inducer of T cell autoreactivity than procainamide.

We have reported that an inhibitor of DNA methylation, 5-azacytidine, makes cloned, antigen-specific CD4+ T cells autoreactive, and that procainamide and hydralazine mimic this effect. Those results suggested that procainamide and hydralazine may induce autoimmunity by inhibiting DNA methylation and causing T cell autoreactivity. We report now that N-acetylprocainamide, a procainamide derivative that does not induce lupus, is also a DNA methylation inhibitor, but it is 100 times less potent than procainamide in inducing T cell autoreactivity.

Acecainide

Lupus-inducing drugs alter the structure of supercoiled circular DNA domains.

We analyzed the effects of procainamide (PROC), hydralazine (HYD), N-acetylprocainamide (NAPA), and L-canavanine (CAN) on circular supercoiled plasmids as models for chromosomal loop domains. The supercoil-dependent B-Z equilibrium in recombinant plasmids was used as an indicator of structural changes induced in circular DNA. Two-dimensional gel electrophoresis showed that PROC and HYD strongly inhibited supercoil-induced Z-DNA formation, whereas NAPA caused less pronounced changes in the B-Z equilibrium, and CAN had no effect. Gel retardation assays showed that the binding of a Z-DNA-specific autoimmune antibody to a Z-DNA-containing plasmid was strongly perturbed by HYD, but not influenced by CAN. Both PROC and NAPA showed moderate inhibition of antibody binding. Our results demonstrate the different potentials of these 4 drugs to interact with DNA and to alter the tertiary topology of DNA domains. It is conceivable that the in vivo capacity of PROC and HYD to induce antinuclear antibodies may be related to their ability to influence structural features in chromosomal DNA domains or nucleosomes, thus liberating antigenic structural epitopes in DNA and/or DNA-associated proteins.

Acecainide

Concentration-dependent clearance of procainamide in normal subjects.

Four normal volunteers each received two intravenous doses of PA. The mean low dose was 3.30 mg kg-1 (infused over 20 minutes) while the mean high dose was 12.5 mg kg-1 (infused over 60 minutes). Blood samples were collected for 12 hours and urine was collected for 48 hours after each dose. PA concentrations were determined by both HPLC and fluorescent immunoassay methods. The reported concentrations and pharmacokinetic parameters are from the HPLC data unless otherwise indicated. The mean peak serum PA concentrations resulting from the low and high doses were 3.18 and 9.07 micrograms ml-1, respectively. Total PA clearance averaged 763 ml min-1 and 577 ml min-1 while renal clearance averaged 360 ml min-1 and 318 ml min-1 after the low and high doses, respectively. Concentration-dependent decreases in nonrenal PA clearance ranged from 31 to 43 percent (p less than 0.05) in the four subjects. Total clearance decreases ranged from 4.7 to 36 per cent (p less than 0.05). Differences between doses in renal clearance, elimination rate constant, and volume of distribution were not statistically significant. This study demonstrates that the nonrenal and total clearances of PA are concentration-dependent in normal subjects at therapeutic plasma PA concentrations and suggests that the total clearance changes are of sufficient magnitude to be clinically important.

Acecainide

Liquid chromatographic analysis of mexiletine in serum, with alternate application to tocainide, procainamide, and N-acetylprocainamide.

A simple and precise high performance liquid chromatographic method for the determination of mexiletine in human serum or plasma is described. Following addition of N-propionylprocainamide as internal standard the specimens are extracted, under basic conditions, into methylene chloride. After removal of the aqueous layer the drug is back-extracted into dilute acid, which is then injected directly for analysis. The extraction efficiency is 79% for both mexiletine and internal standard, and the assay is linear to 4 mg/L (twice upper therapeutic concentration). Inter-run coefficients of variation are 3.0% or less. The relative retention time of mexiletine to internal standard averages 1.3. An adaptation of this method is described for an alternate application to the analysis of tocainide, procainamide and N-acetylprocainamide.

Acecainide

N-Acetylprocainamide pharmacokinetics in functionally anephric patients before and after perturbation by hemodialysis.

NAPA pharmacokinetics were studied in 6 functionally anephric patients. Distribution and nonrenal elimination of this drug were found to be the same as in individuals with normal renal function but renal clearance was reduced, resulting in a mean elimination t 1/2 of 41.9 hr (6.2 hr in normal subjects). Renal clearance of NAPA correlated well with ClCr. Dialysis removed NAPA from both red blood cells and plasma and increased ClT approximately fourfold. Dialysis itself resulted in a 77% reduction in ClS that limited the total amount of NAPA removed by this procedure. This reduction in ClS was sustained for at least 3 hr after dialysis and attenuated rebound in plasma NAPA concentrations.

Acecainide

Chronopharmacokinetic studies of pranoprofen and procainamide.

There is increasing evidence demonstrating that plasma drug concentrations are affected by their time of administration. In the current study, the chronopharmacokinetic profiles of an antipyretic agent, pranoprofen, and an antiarrhythmic agent, procainamide, were examined. In the first study, 75 mg of pranoprofen was given orally in seven healthy subjects at 10:00 (morning trial) or 22:00 (evening trial). In the second study, 500 mg of procainamide was given orally in eight subjects with premature ventricular contractions at 10:00 or 22:00. Blood samples for plasma drug concentrations were taken for a 10-hour (pranoprofen study) or a 24-hour (procainamide study) post-drug period. In the first (pranoprofen) study, the mean time to maximum concentration was significantly shorter, and the mean maximum plasma concentration as well as absorption rate constant had a tendency to be greater after the morning than after the evening trial. The mean area under the plasma concentration-time curve, elimination half-life or oral clearance of the morning and evening dosages did not differ. In the second (procainamide) study, no significant difference was observed in any pharmacokinetic parameter concerning procainamide or its active metabolite, N-acetyl-procainamide (NAPA) between the morning and evening trials. These data indicate that plasma levels of pranoprofen are affected by its administration time while plasma concentrations of procainamide and NAPA do not vary with the time of dosage.

Acecainide

N-acetylprocainamide kinetics during intravenous infusions and subsequent oral doses in patients with coronary artery disease and ventricular arrhythmias.

The kinetics of N-acetylprocainamide (NAPA) were studied in 5 patients (all men, mean age = 62) with coronary artery disease and ventricular arrhythmias during loading infusions of 0.22-0.45 mg/kg/min, prolonged (19-48 hrs) intravenous infusions 2.5-5.2 mg/min, and in 4 of the patients, during subsequent oral doses 1.5-3 g every 8 hrs. Serum, concentrations of NAPA were determined by high-performance liquid chromatography. The individual concentration-time profiles could, with one exception, be described by a two-compartment, open, kinetic model with apparent first-order elimination. The kinetic variables were: initial distribution volume (Vc) 0.20 +/- 0.11 l/kg (mean +/- SD); steady-state distribution volume (Vss) 1.58 +/- 0.55 l/kg; distributional clearance (Cle) 133 +/- 23 ml/(kg X hr); absorption rate constant (Ka) 0.354 +/- 0.173 hr-1; and fraction of dose reaching systemic circulation (F) 1.00 +/- 0.14. The data for one patient who had received increasing oral dosages of 1.5, 2, 2.5 and 3 g every 8 hours resulted in systematic underprediction of observed concentrations at the two highest oral dosing rates. This suggests the possibility of some degree of nonlinearity or time-dependent change in the kinetic behavior of NAPA. Only low concentrations of procainamide, less than 1 mg/L, were found at the end of the infusions.

Acecainide