Plasma levels of procaine amide after administration of conventional and sustained-release tablets

Acetylation of procaine amide in man studied with a new gas chromatographic method

1 A specific gas-chromatographic method was developed for determination of N-acetylprocaine amide in plasma and urine, using 4-amino-N-(2-piperidinoethyl)benzamide as an internal standard. The investigation was performed in 50 cardiac patients who had reached steady-state plasma concentrations of procaine amide. 2 The plasma concentrations of the acetylated metabolite varied between 1.0 and 15.0 μg/ml and were thus of the same order of magnitude as those of the parent drug. Especially high plasma levels of the metabolite were seen in patients with poor kidney function. 3 The urinary excretion of the metabolite varied markedly between individuals and ranged between 6 and 52% of the administered daily dose. There was a clear tendency towards higher rates of acetylation of procaine amide in patients with short plasma half-lives of isoniazid, i.e. the phenotype rapid acetylators. Because of coexisting therapy with other drugs and impaired renal function in some patients studies are required in healthy human volunteers to ascertain whether the acetylation of procaine amide and isoniazid are mediated by the same enzyme system.

Acetylator phenotype and the clinical pharmacology of slow-release procainamide

Slow-release procainamide given 8-hourly is shown to produce plasma levels generally accepted as giving effective prophylaxis against ventricular dysrhythmias occurring after recent myocardial infarction. Patients can be classified into 'slow' and 'fast' acetylators of procainamide. Knowledge of acetylator status is helpful in determining the dose of procainamide necessary to attain effective steady-state plasma levels while avoiding toxic ones. Acetylator status cannot be assessed accurately using sulphadimidine when the patients are also taking procainamide.

Procainamide: clinical pharmacology and efficacy against ventricular arrhythmias

Procainamide (PA) has been a mainstay of treatment against acute and chronic supraventricular and ventricular arrhythmias for more than 30 years. PA's clinical pharmacology has been studied extensively and its bioavailability (75-95%); volume of distribution (1.5-2.5 liters per kg), plasma protein-binding (15-25%), half-time for elimination (3-7 hours), and metabolism are known. PA's efficacy against acute ventricular arrhythmias and chronic stable VPDs is associated with plasma drug concentrations of 4 to 10 micrograms per ml; but much higher plasma concentrations may be required against sustained ventricular arrhythmias. From 30 to 60% of a PA dose is excreted as the metabolite, N-acetylprocainamide (NAPA), and PA's metabolism is determined genetically (fast or slow acetylation phenotype). Studies in patients with VPDs indicate that NAPA is also antiarrhythmic, although the contribution of NAPA to the antiarrhythmic effect after PA is not known. Studies in patients with the systemic lupus-like syndrome from PA show that NAPA is not associated with this. Investigations comparing efficacy and adverse effects of PA with those of new antiarrhythmic agents available for clinical trials are indicated in the future.

Thin-layer chromatographic determination of procainamide and N-acetylprocainamide in human serum and urine at single-dose levels

Thin-layer chromatographic methods were applied for bioavailability studies of procainamide in serum and urine. Detection of the parent compound and the major metabolite was performed in the ultraviolet range at 275 nm. Using 100-microliter samples, detection limits were 60 ng of procainamide-HCl per ml serum and 7 micrograms/ml urine, and 60 ng of N-acetylprocainamide-HCl per ml serum and 5 micrograms/ml urine. Advantages over previous methods are discussed. From serum and urine data of five volunteers, the bioavailability of procainamide from a 250-mg dragee preparation compared with an intravenous dose was verified. Pharmacokinetic data were computed using one-compartment open models. Results corresponded well with values previously published.

Serum drug concentrations in patients with ischemic heart disease after administration of a sustained release procainamide preparation

Despite widespread marketing of a sustained release preparation of procainamide hydrochloride (PROCAN-SR, Parke-Davis), published literature demonstrating its efficacy in maintaining uniform serum drug levels over a 6-hour dosing interval is derived from only normal healthy volunteers. Thirty-three patients with ischemic heart disease, ages 30-88 years, were administered 1-4g/24 hours (mean dose 34 mg/kg/day) of PROCAN-SR in 4 equally divided doses on a Q6H schedule. After achievement of steady-state equilibrium drug concentration, procainamide and N-acetylprocainamide levels were determined by high-performance liquid chromatography on sera obtained from blood samples drawn 2, 3.5 and 5 hours after an oral dose. Mean maximal procainamide and N-acetylprocainamide serum concentrations were 4.6 +/- 1.8 microgram/ml and 4.2 +/- 2.1 micrograms/ml respectively. Mean minimal concentrations were 3.5 +/- 1.7 microgram/ml and 3.6 +/- 2.0 micrograms/ml respectively. The mean change in drug concentration was small (1.1 microgram/ml procainamide and 0.6 microgram/ml N-acetylprocainamide) with procainamide and N-acetylprocainamide concentrations varying only by 27 and 15 percent respectively. These data demonstrate in a population of patients with ischemic heart disease, that Q6H dosing with a sustained release procainamide hydrochloride preparation (PROCAN-SR, Parke-Davis) is associated with only a small acceptable variation between maximal and minimal serum procainamide and N-acetylprocainamide concentrations. This preparation should, therefore, offer greater patient convenience and compliance without sacrificing antiarrhythmic efficacy.

Efficacy, plasma concentrations and adverse effects of a new sustained release procainamide preparation

To assess the efficacy, plasma drug concentrations and adverse effects of a new sustained release preparation of procainamide, 33 patients with heart disease were studied in an acute dose-ranging protocol and a chronic treatment protocol. Patients initially received a daily dose of 3 g of sustained release procainamide; this dose was increased by 1.5 g daily until ventricular premature depolarizations were suppressed by 75 percent or more, adverse drug effects occurred or a total daily dose of 7.5 g of sustained-release procainamide was reached. Twenty-five patients (76 percent) had at least a 75 percent reduction (range 75 to 100percent [mean +/- standard deviation 91 +/- 8.2]) in ventricular permature depolarization frequency at a dosage of 4.8 +/- 1.46 g/day (range 3.0 to 7.5). Despite the 8 hour dosing interval, the variation between maximal and minimal plasma procainamide and N-acetylprocainamide concentrations under steady state conditions was very small. Mean maximal procainamide and N-acetylprocainamide plasma concentrations were 10.4 +/- 6.02 and 12.0 +/- 7.40 micrograms/ml, respectively. The respective mean minimal concentrations were 6.8 +/- 4.50 and 8.7 +/- 5.99 micrograms/ml. In nine patients (27 percent) treatment with sustained release procainamide resulted in conversion of the antinuclear antibody test from negative to positive. Adverse drug effects occurred in 17 (52 percent) of the subjects. In general, adverse effects were minor and abated within 24 hours after administration of the drug was stopped. One patient had the procainamide-induced systemic lupus erythematosus-like syndrome.

A pharmacokinetic comparison of two sustained-release oral procainamide preparations

1 The pharmacokinetics of two different sustained-release oral procainamide preparations were studied in ten hospital patients with normal blood ureas and no clinical evidence of heart failure. Each patient received either one or other preparation at 12 hourly intervals for four doses. Frequent blood sampling enabled close monitoring of blood levels. 2 Results showed that both preparations were essentially similar in their pharmacokinetics. Both effectively double the half-life of conventional oral procainamide to 6.5 h and are suitable as prophylactic preparations. One patient developed toxic levels, thought to be related to her metabolic status of being a very slow acetylator. To avoid toxicity pre-therapy assessment of a patient's cardiac and renal function and acetylator status is advised.

Significance of the acetylation phenotype and the therapeutic effect of procainamide

In order to estimate the relative anti-arrhythmic effect of procainamide and N-acetyl-procainamide, 18 randomly selected, patients with arrhythmia were divided into two groups; the first was treated with Pronestyl in the first half of the investigation period, followed by Duretter in the second half, and the second group began with Duretter and terminated with Pronestyl. The concentrations of procainamide and N-acetylprocainamide were measured twice a day during the steady state part of each treatment period. The acetylation phenotype of the patients was determined with sulfadimidine, and compared with the relative serum concentrations of procainamide and N-acetylprocainamide. N-acetylprocainamide was found to antagonize the action of procainamide.

Serum levels and electrophysiological effects of N-acetlyprocainamide as compared with procainamide in the dog heart in situ

The electrophysiological effects of procainamide and its major metabolite N-acetylprocainamide were tested and compared on the heart of the anaesthetized dog by means of His bundle electrography and programmed electrical stimulation. Both drugs exerted a negative chromotropic effect. They also increased intra-atrial and intraventricular conduction times; procainamide was, however, the more potent of the two drugs. In contrast to procainamide, N-caetylprocainamide did not increase His-Purkinje and atrioventricular nodal conduction times, and at the lowest dose employed, atrioventricular nodal conduction times were decreased during atrial pacing. Both drugs increased the functional and effective refractory period of the right atrium and ventricle. N-acetylprocainamide increased the functional refractory period of the atrioventricular node, but to a lesser extent than procainamide.

Maintenance therapy with a new retard tablet preparation of procainamide

The procainamide plasma concentration was followed during maintenance therapy with a new procainamide retard tablet preparation in 23 hospitalized patients suffering from acute or chronic coronary heart disease with complicating ventricular arrhythmias. After initial individually adjusted treatment with Pronestyl every third hour, either orally or intramuscularly, for at least eight dose intervals, the retard tablets were given at 6 hour intervals for 2 to 12 days, or more. In 19 patients with no major fluctuations in their circulatory or renal state, adequate and relatively stable plasma procainamide concentration was obtained upon a constant dose of the retard preparation. On an average, the difference from minimum to maximum concentration was 55 per cent within the 6 hour dose intervals. In four patients with unstable circulation and/or renal function, procainamide therapy had to be disrupted in two because of severe side effects and toxic concentrations, and the dose was adjusted in the remaining two. It is concluded that the formulation of procainamide tablet preparations has simplified procainamide therapy within and outside hospital and improved our possibilities to perform short-and long-term studies on the risk/ benefit ratio of procainamide treatment in patients with severe ventricular arrhythmias.

Procainamide absorption studies to test the feasibility of using a sustained-release preparation

Using in vitro techniques it was confirmed that whilst the release of procainamide from the conventional formulation (Pronestyl) was rapid, that from the sustained-release preparation (Cardiorytmin Retard) occurred over a prolonged period. 2 The peak plasma procainamide concentrations after single doses of Cardiorytmin Retard were relatively lower and occurred later than those after single doses of Pronestyl. Furthermore, after reaching a peak, the fall in plasma procainamide concentration was less rapid after the sustained-release preparation. Early urinary recovery of procainamide in patients and in healthy volunteers was greater after Pronestyl than after Cardiorytmin Retard, though overall recovery in urine was similar. These findings indicate that the absorption of the sustained-release preparation is slower, though the overall bioavailabilities of the two preparations are almost the same. 3 These results confirm the feasibility of using a sustained-release procainamide preparation, such as Cardiorytmin Retard, since it would be possible to administer the same amount of drug in fewer daily doses without plasma concentrations becoming ineffective towards the end of each dosing interval.

GLC determination of procainamide in biological fluids

A GLC method for the determination of procainamide in biological fluids is presented. By using a dipropyl analog of procainamide as an internal standard, both compounds can be chromatographed directly, yielding linear calibration curves and a sensitivity that allows quantitative determination of concentrations as low as 0.1 mug/ml. The extraction procedure was carefully modified to avoid hydrolysis of N-acetylprocainamide, a major metabolite of procainamide. The usefulness of the procedure is demonstrated by following the disappearance of procainamide from the plasma and urine of human subjects treated with the drug.

Effects of N-acetylprocainamide as compared with procainamide in isolated rat atria

The actions of procainamide and its major metabolite N-acetylprocainamide were tested and compared on isolated rat atria. While procainamide exerted a negative chronotropic and iontropic effect, N-acetylprocainamide had the opposite effect. It is suggested that a N-acetylprocainamide-induced increase in myocardial work can counteract the negative inotropic action of procainamide and thus to some extent explain the variable results with the latter compound on myocardial performance reported from in vivo experiments. Procainamide increased the refractory period and reduced the excitability of isolated rat atria. N-acetylprocainamide, on the other hand, caused negligible effects on these parameters.

Procainamide and phenytoin. Comparative study of their antiarrhythmic effects at apparent therapeutic plasma levels

The antiarrhythmic effects of procainamide and phenytoin were studied in 81 patients admitted to the coronary care unit at the University Hospital in Linköping because of a suspected or proven diagnosis of acute myocardial infarction, and who developed ventricular arrhyhmias, requiring treatment, during the first 8 hours in hospital. Patients were randomly allocated to a procainamide of phenytoin group. The drugs were given as intravenous and oral loading doses followed by oral maintenance therapy. Plasma levels of the two druge were frequently determined and the electrocardiogram was continuously recorded during the 24-hour trial and analysed minute by minute. A significantly higher frequency of therapeutic failure was found in the phenytoin group (23 of 35 patients)compared to the procainamide group(13 of 39 aptients) during the first 2 hours after initiation of therapy. Four patients in the phenytoin group and 2 in the procainamide group developed symptoms probably caused by the trial drugs, necessitating discontinuation of therapy. The mean plasma levels were usually within the apparent therapeutic range (for phenytoin 40-72 mumol/l (10-18 mug/ml), and for procainamide 17-34 mumol/l (4-8 mug/ml). Seventeen patients (68%) in the phenytoin group and 10 patients (48%) in the procainamide group had plasma concentrations within this range when the therapeutic failure was observed. Nine patients died in hospital but only one of them during the trial. The results of this investigation clearly demonstrate the overall superiority of procainamide over phenytoin as an antiarrhythmic drug in short-term therapy after acute myocardial infarction.

Comparison of procainamide and mexiletine in prevention of ventricular arrhythmias after acute myocardial infarction

The incidence of ventricular arrhythmias after myocardial infarction has been compared in a controlled study of procainamide, mexiletine, and placebo. Sixty male patients who has sustained a myocardial infarction and had received lignocaine for ventricular tachycardia or ventricular ectopic beats which were R-on-T, multiform, or close-coupled took part. The efficacy of the drugs was evaluated by continuous 24-hour recordings of the electrocardiogram on the 4th and 10th days after admission to the study. Procainamide was given as 500 mg. 4-hourly and mexiletine as 250 mg. 8-hourly with corresponding placebo regimens for 12 days. 77% of patients receiving placebo showed serious ventricular rhythm disorders compared with 33% receiving antiarrhythmic therapy (p smaller than 0.05). Although only 35% of patients receiving procainamide achieved accepted therapeutic plasma concentrations compared with 95% of those receiving mexiletine, both drugs were equally effective antiarrhythmically. The only major adverse effect of therapy noted was development of a positive antinuclear factor in a procainamide-treated patient. These results demonstrate the efficacy of oral antiarrhythmic agents in the management of ventricular arrhythmias after acute myocardial infarction. Mexiletine has the advantage of less frequent administration and lower toxicity.

Elimination rate of N-acetylprocainamide after a single intravenous dose of procainamide hydrochloride in man

Equations were derived which made it possible to determine the elimination rate of N-acetylprocainamide from urinary data after intravenous administration of procainamide hydrochloride. A single dose of 500 mg of the drug was infused intravenously in four healthy subjects. On the basis of theose equations, the formation rate of the metabolite could be calculated presuming that all rate processes were occurring by first-order processes. However, close examination of the excretion rate data appears to support the contention that the formation or excretion of N-acetylprocainamide may be occurring by a saturable process

Acetylation of procaine amide in man. A preliminary communication

The metabolism of procaine amide was studied in 41 cardiac patients who had achieved steady state plasma concentrations of the drug. Acetylated procaine amide accounted for 31 +/- 12% (range 16-63%) of the overall urinary recovery of the drug and is therefore a main metabolite in man. Plasma levels of the metabolite were usually lower but sometimes exceeded those of the parent compound with variations between 1 and 15 mug/ml. The metabolite had a weaker effect than procaine amide on the maximal electrical driving velocity of isolated atrial strips from guinea pig.