Pharmacokinetics of procainamide intravenously and orally as conventional and slow-release tablets

Physiologically-Based Pharmacokinetic Modeling for Drug-Drug Interactions of Procainamide and N-Acetylprocainamide with Cimetidine, an Inhibitor of rOCT2 and rMATE1, in Rats

Previous observations demonstrated that cimetidine decreased the clearance of procainamide (PA) and/or N-acetylprocainamide (NAPA; the primary metabolite of PA) resulting in the increased systemic exposure and the decrease of urinary excretion. Despite an abundance of in vitro and in vivo data regarding pharmacokinetic interactions between PA/NAPA and cimetidine, however, a mechanistic approach to elucidate these interactions has not been reported yet. The primary objective of this study was to construct a physiological model that describes pharmacokinetic interactions between PA/NAPA and cimetidine, an inhibitor of rat organic cation transporter 2 (rOCT2) and rat multidrug and toxin extrusion proteins (rMATE1), by performing extensive in vivo and in vitro pharmacokinetic studies for PA and NAPA performed in the absence or presence of cimetidine in rats. When a single intravenous injection of PA HCl (10 mg/kg) was administered to rats, co-administration of cimetidine (100 mg/kg) significantly increased systemic exposure and decreased the systemic (CL) and renal (CL_R) clearance of PA, and reduced its tissue distribution. Similarly, cimetidine significantly decreased the CL_R of NAPA formed by the metabolism of PA and increased the AUC of NAPA. Considering that these drugs could share similar renal secretory pathways (e.g., via rOCT2 and rMATE1), a physiologically-based pharmacokinetic (PBPK) model incorporating semi-mechanistic kidney compartments was devised to predict drug-drug interactions (DDIs). Using our proposed PBPK model, DDIs between PA/NAPA and cimetidine were successfully predicted for the plasma concentrations and urinary excretion profiles of PA and NAPA observed in rats. Moreover, sensitivity analyses of the pharmacokinetics of PA and NAPA showed the inhibitory effects of cimetidine via rMATE1 were probably important for the renal elimination of PA and NAPA in rats. The proposed PBPK model may be useful for understanding the mechanisms of interactions between PA/NAPA and cimetidine in vivo.

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.

Therapeutic Levels of Intravenous Procainamide in Neonates: A Retrospective Assessment

STUDY OBJECTIVES

To evaluate dosing and pharmacokinetic parameters of intravenous continuous-infusion procainamide in neonates, and to identify dosage regimens and factors leading to therapeutic procainamide levels and minimal adverse events.

DESIGN

Retrospective, observational study.

SETTING

Pediatric hospital.

PATIENTS

. Twenty-one patients (seven preterm, 14 full term) younger than 30 days who received continuous-infusion procainamide therapy for more than 15 hours or had two consecutive therapeutic procainamide levels obtained while receiving therapy between June 1, 2002, and December 31, 2005.

MEASUREMENTS AND MAIN RESULTS

Data on demographics, dosing, drug levels, and adverse effects were collected. Doses that achieved therapeutic levels were documented, and procainamide clearance was calculated and evaluated with regard to renal function and gestational age in patients who were at steady state. Mean clearance and mean N-acetylprocainamide (NAPA):procainamide ratios were compared between preterm and term neonates. No patients experienced hemodynamic instability or other adverse effects due to procainamide. Procainamide was given as a mean +/- SD 9.6 +/- 1.5-mg/kg bolus in 20 of 21 patients before continuous infusion. The mean +/- SD dose at which two therapeutic levels were achieved was 37.56 +/- 13.52 microg/kg/minute. Procainamide clearance was 6.36 +/- 8.85 ml/kg/minute and correlated with creatinine clearance (r=0.78, p<0.00001) and age at day of sampling (r=0.49, p<0.00001). The NAPA:procainamide ratio at steady state was 0.84 +/- 0.53; two patients were determined to be fast acetylators (ratio > 1). Preterm infants had lower mean clearance rates (p<0.001) but higher NAPA:procainamide ratios (p<0.01) than those of term infants. Five patients experienced seven supratherapeutic levels while receiving therapy; four of these patients were preterm, and all had creatinine clearances less than 30 ml/minute/1.73 m(2). Three patients had four pairs of levels obtained after discontinuation of procainamide, and elimination rate constant and half-life were calculated.

CONCLUSION

Procainamide can be safely used in neonates, with no short-term adverse effects. The dosage regimen for intravenous procainamide required to achieve therapeutic levels in neonates is similar to that of older infants and children. Doses may need to be reduced in premature infants and in those with renal dysfunction.

Prediction of volume of distribution values in humans for neutral and basic drugs using physicochemical measurements and plasma protein binding data

We present a method for the prediction of volume of distribution in humans, for neutral and basic compounds. It is based on two experimentally determined physicochemical parameters, ElogD(7.4) and f(i(7.4)), the latter being the fraction of compound ionized at pH 7.4 and on the fraction of free drug in plasma (f(u)). The fraction unbound in tissues (f(ut)), determined via a regression analysis from 64 compounds using the parameters described, is then used to predict VD(ss) via the Oie-Tozer equation. Accuracy of this method was determined using a test set of 14 compounds, and it was demonstrated that human VD(ss) values could be predicted, on average, within or very close to 2-fold of the actual value. The present method is as accurate as reported methods based on animal pharmacokinetic data, using a similar set of compounds, and ranges between 1.62 and 2.20 as mean-fold error. This method has the advantage of being amenable to automation, and therefore fast throughput, it is compound and resources sparing, and it offers a rationale for the reduction of the use of animals in pharmacokinetic studies. A discussion of the potential errors that may be encountered, including errors in the determination of f(u), is offered, and the caveats about the use of computed vs experimentally determined logD and pK(a) values are addressed.

A nomogram to predict the best biological half-life values for candidates for oral prolonged-release formulations

It is sometimes possible to maintain plasma concentrations between desired maximum and minimum limits by repetitively administering a drug in an oral prolonged-release formulation when this goal cannot be achieved with a rapid-release formulation. However, this approach does not work with all drugs. The biological half-life value of the drug can be one cause for failure of this approach. Although it is recognized that a half-life may be too long or too short, neither the criteria for determining these values nor the consequences of failing to meet them have been established. The best half-life values for prolonged-release candidates were found by simulating once-a-day and twice-a-day administration of formulations and examining the capacity of these formulations to maintain steady-state plasma concentrations between various selected limits. These observations were used to establish criteria to judge the acceptability of half-lives. Half-life values were considered too long if drugs were self-sustaining and simulations of their rapid-release formulations were also successful. Half-life values were considered too short if minor variability in prolonged-release rates resulted in plasma concentrations above and/or below the selected limits. The actual half-life values that were considered too long or too short depended on the dosing interval and the selected maximum and minimum plasma concentrations. A nomogram was constructed to assess the acceptability of the biological half-life of a candidate for once-a-day or twice-a-day prolonged-release formulations. The nomogram employs the user-selected limits for the desired plasma concentrations to predict whether the half-life of a candidate is (1) too long, (2) too short, or (3) acceptable (i.e., between 1 and 2).

Pharmacokinetic considerations in the adolescent: non-cytochrome P450 metabolic pathways

The non-oxidative metabolic reactions of methylation, acetylation, sulfation, glucuronidation, conjugation with amino acids (primarily with glycine), glutathione conjugation and esterase hydrolysis function to detoxify and enhance the elimination of drugs and pro-drugs, many of them as phase II reactions subsequent to oxidation. While the influence of maturation has been recognized in the development of hepatic oxidative capacity and specific pathways studied, considerably less attention has focused on the maturational effect in non-oxidative metabolism despite its role in drug deactivation, detoxification, and elimination. Consequently phase II metabolic capacities during adolescence remain primarily speculative. Conflicting data about one of these pathways, glucuronidation, suggest unexplored puberty- or gender-related phenomena influencing function in this system.

Practical optimisation of antiarrhythmic drug therapy using pharmacokinetic principles

The optimisation of antiarrhythmic drug therapy is dependent on the definitions and methods of short term efficacy testing and the characteristics of those drugs used for rhythm disturbances. The choice of an initial antiarrhythmic drug dosage is highly empirical, and will remain so until the measurement of free concentrations, enantiomeric fractions and genetic phenotyping becomes routine. However, the clinician can devise an efficient initial dosage for efficacy testing procedures based on pharmacokinetic principles and disposition variables in the literature. In this regard, a nomogram for commonly used agents and dosages was constructed and is offered as a guide to accomplish this goal. Verification of the accuracy and usefulness of this nomogram in a prospective manner in patients with symptomatic tachyarrhythmias is still required. On a long term basis, dosage regimens can be modified by the use of pharmacokinetic principles and patient-specific target concentrations, in accordance with the methods used to monitor arrhythmia recurrence and drug-related side effects.

Species differences in the pharmacokinetics of recainam, a new anti-arrhythmic drug

The pharmacokinetics of recainam, an anti-arrhythmic drug, were compared in mice, rats, rabbits, dogs, rhesus monkeys, and man. Bioavailability was virtually complete in monkeys and dogs, 67 per cent in man and 51 per cent in rats. Non-linear kinetics between the oral and i.v. dose in rabbits precluded estimation of bioavailability. Linear plasma dose proportionality occurred in dogs between 6 and 60 mg kg-1 oral doses and rhesus monkeys between 1 and 15 mg kg-1 i.v. doses. A greater than proportional increase in the plasma AUC of recainam occurred between oral doses ranging from 54-208 mg kg-1 in mice, 25-110 mg kg-1 in rats, and 50-100 mg kg-1 in rabbits. In human subjects, the AUC/unit dose was linear between 400 and 800 mg. The terminal elimination t1/2 of recainam ranged from 1-5h in laboratory animals and man. The plasma Cmax and AUC of recainam were virtually identical after single or multiple (21 day) oral doses in dogs. After an i.v. dose, plasma clearance of recainam (l kg-1 .h) was 4.9-5.2 in rats and rabbits and 0.4-1.9 in dogs, rhesus monkeys, and man. The steady state volume of distribution was 2-5 times larger than the total body water of laboratory animals and man. Recainam was very poorly bound (10-45 per cent) to the serum proteins of rodents, rabbits, dogs, rhesus monkeys and man. In rhesus monkeys and man, recainam accounted for 10 per cent and 70 per cent, respectively, of the plasma radioactivity at 6 h post-dose. The pharmacokinetic profile of recainam in dogs most closely resembled that of man.

Procainamide pharmacokinetics in patients with acute myocardial infarction or congestive heart failure

Abnormal procainamide pharmacokinetics (prolonged half-life and decreased volume of distribution) and pharmacodynamics (decreased threshold for the suppression of premature ventricular complexes) have been suggested in patients with acute myocardial infarction or congestive heart failure, or both. To better define procainamide kinetics, 37 patients in the acute care setting received intravenous procainamide (25 mg/min, median dose 750 mg) with peak and hourly blood samples taken over 6 hours. Compared with the 10 control patients, the 12 patients with acute myocardial infarction and the 15 patients with congestive heart failure had normal procainamide pharmacokinetics with respect to half-life (2.3 +/- 1.0, 2.5 +/- 0.9 and 2.6 +/- 0.8 hours, respectively), volume of distribution (1.9 +/- 0.7, 1.8 +/- 0.4 and 1.8 +/- 0.5 liters/kg, respectively), clearance (11.3 +/- 7.5, 9.3 +/- 3.6 and 9.1 +/- 3.5 ml/min per kg, respectively) and unbound drug fraction (66 +/- 9, 66 +/- 9 and 69 +/- 4%, respectively). Low thresholds for greater than 85% premature ventricular complex suppression were confirmed in these patients (median 4.7 micrograms/ml in patients with acute myocardial infarction and 3.3 micrograms/ml in patients with congestive heart failure). Thus, differences in the response of premature ventricular complexes to procainamide reflect electropharmacologic differences dependent on clinical setting rather than pharmacokinetic abnormalities. Furthermore, the reduction of procainamide dosing in patients with acute myocardial infarction or congestive heart failure, based solely on prior kinetic data, may result in inappropriate antiarrhythmic therapy.

Pharmacokinetics of cibenzoline in patients with renal impairment

Pharmacokinetic values of cibenzoline, a new, investigational, antiarrhythmic drug, were determined in 13 patients with varying degree of renal impairment, creatinine clearance range between 5 and 53 mL/min. Cibenzoline plasma levels were measured after direct intravenous injection of one single 1 mg/kg dose. The apparent volume of distribution of the drug (276 1) was similar to that reported in healthy subjects. Total body clearance decreased with creatinine clearance, and there was a close correlation between cibenzoline renal clearance and creatinine clearance (r = 0.956; P less than 0.001). Plasma elimination half-life was prolonged, with values ranging from 7:4 to 23.6 hours. This study showed that cibenzoline total body clearance correlated with the degree of renal impairment, and it is suggested that in patients with chronic renal failure dosage should be adjusted according to creatinine clearance values.

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.

Correlations between in vitro dissolution rate and bioavailability of alaproclate tablets

In two different absorption studies, quantitative correlations between the in vitro dissolution rate and the bioavailability have been shown after single administration of various tablet compositions of alaproclate hydrochloride to healthy subjects. Both statistical moment analysis and the use of empirical single value parameters were tested. For conventional tablets a linear relationship was obtained between mean dissolution time in vitro and in vivo. A similar relationship was obtained between the mean dissolution time in vitro and the mean residence time for controlled release tablets of the matrix type. It was also possible to establish an in vitro--in vivo correlation for these latter tablets by using the single point estimate of maximum plasma concentration as in vivo parameter. When comparing the mean dissolution time in vitro to the total area under the plasma drug concentration-time curve attained after different types of tablets, it is obvious that the extent of bioavailability of alaproclate will not fall below 80% of the value found for an aqueous solution until the mean dissolution time in vitro exceeds approximately 3 hr. Statistical moment analysis seems to have a broader applicability than the use of empirical point estimates, and it seems to be useful both for conventionally dissolving tablets and controlled release tablets.

Methods in testing interrelationships between excretion of drugs via urine and bile

The liver and kidney are largely responsible for inactivating and eliminating drugs and other chemicals. As the excretory capabilities of the two organs overlap, a damage of one system might be compensated by the other. Because of the specificity of both renal and hepatic elimination mechanisms such an alternative excretion route is not possible generally. Several interferences are possible to characterize the relation between hepatic and renal excretion of drugs and xenobiotics. Firstly, the simultaneous assay of excreted drug amounts in urine and bile can give some information concerning the main transport routes of this drug. Thereafter the total interruption of liver or kidney function elucidates the general possibility of alternative excretion routes. But it is important for clinical practice to distinguish between different localizations of organ damages. Today some experimental possibilities exist to exclude partial functions of both kidney and liver separately. Thus it can be clarified why a compound might be excreted via liver or kidney. Moreover it can be characterized whether or not a compensation for the loss of one main excretion organ is possible or not. Such investigations are of some practical importance. Dosing guidelines for drug therapy must be completed for cases of renal or hepatic failure. Moreover the developmental pattern of both elimination routes has consequences for drug use in paediatrics as well as geriatrics. Beside this point of view such investigations are necessary for the prediction of changes in the toxicity of drugs after renal or hepatic insufficiency.

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.

Pharmacokinetics in man of a new antiarrhythmic drug, cibenzoline

The kinetics of cibenzoline (UP 339.01), a new antiarrhythmic drug, was studied after i.v. and oral administration to 5 healthy subjects. Cibenzoline levels in plasma and urine cibenzoline were measured by a GLC method. After i.v. administration, the total clearance was 826 ml . min-1. The fraction of cibenzoline excreted unchanged in the urine was 0.602 and it was correlated with the creatinine clearance. After i.v. and oral administration, the renal clearances were 499 ml . min-1 and 439 ml . min-1, and the half-lives were 4 h 01 min and 3 h 24 min, respectively. The differences were not significant. Availability by the oral route was 0.92, the maximum plasma concentration being observed at 1 h 36 min. The results were compared with those for other antiarrhythmic drugs.

Significance of acetylator phenotype in pharmacokinetics and adverse effects of procainamide

The pharmacokinetics and development of antinuclear antibodies (ANAs) during procainamide (PA) therapy were studied in 35 patients with ventricular arrhythmias. Sixteen of the subjects were rapid and 19 were slow acetylators. Twenty-six of them (13 rapid and 13 slow acetylators) received PA therapy (2.4g sustained-release PA X HCl daily in three doses) for at least 16 weeks. On maintenance therapy, rapid acetylators had insignificantly lower serum PA concentrations and slightly higher N-acetylprocainamide (NAPA) concentrations than slow acetylators. The unchanged PA fraction (PA/PA + NAPA) in the rapid acetylators was somewhat lower than in the slow acetylators. Rapid acetylators excreted more NAPA in urine than did slow acetylators (p less than 0.05), whereas the difference in PA excretion was not significant. More than 80% of the given drug was excreted as PA and NAPA. Spontaneous or exercise-induced arrhythmias were recorded in 6 rapid and 8 slow acetylators. ANAs (titre at least 20) appeared in 6 rapid and 8 slow acetylators. The mean time until ANA development in rapid acetylators was only marginally longer than in slow acetylators. The results suggest that acetylation phenotyping is not of great significance in predicting the development of ANAs during PA therapy.

Ethanol-induced increase in procainamide acetylation in man

1 The effect of ethanol on procainamide pharmacokinetics was studied in humans by two different experimental designs. In one, ethanol was given 1.5 h after taking the drug followed by hourly drinks, while in the other ethanol was given 2 h before and subsequently after taking the drug. 2 In both studies, ethanol caused a significant reduction of T1/2 and a significant increase in total clearance of procainamide, while the apparent volume of distribution of procainamide, as well as the renal clearance of both procainamide and N-acetylprocainamide were unaffected by ethanol treatment. 3 Ethanol treatment increased the percentage of N-acetylprocainamide measured in blood and urine and the ratio of AUCNAPA/AUCPA significantly. 4 The T1/2 and total clearance of procainamide was significantly different in slow and rapid acetylators.

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.

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.

Compartment- and model-independent linear plateau principle of drugs during a constant-rate absorption or intravenous infusion

A simple general equation is derived to show the linear plateau principle under various conditions during or after a constant or changing rate of absorption or intravenous infusion. The time required to cause a certain fraction (ft) of the total shift or change between the two steady-state plasma concentrations is equal to the time required for the cumulative (from time zero) plasma area, AUC 0 leads to t, to reach the same fracton of AUC 0 leads to infinity assumed to be obtained after an instantaneous intravenous dosing. The role of the terminal biological half-life and the importance of the early distribution phase and its exponential half-life or lives in the plateau principle are discussed. Clinical implications and applications to multiple dosage regimens are also discussed.

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.

The pharmacokinetics of slow-release procainamide

Procainamide was given to 20 patients with normal renal function as an i.v. bolus of 500 mg followed by 1.0 or 1.5 g eight-hourly by mouth in the form of a slow release preparation (Durules). 97.6 +/- 27.1 (SD)% of the oral procainamide was absorbed, the absorption half life being 1.54 h. The elimination half life following the oral formulation was 6.0 +/- 0.8 h, compared to a mean of 3.4 +/- 0.4 h following i.v. administration. Elimination half life following i.v. administration was slightly related to acetylator status, being 2.75 +/- 0.9 h in fast acetylators, and 4.4 +/- 2.4 h in slow acetylators. This dependence on acetylator status was not seen in half life following oral administration. Total body clearance, steady state plasma procainamide and N-acetylprocainamide were not significantly dependent on acetylator status, although a few patients who are slow acetylators had unexpectedly low clearance and high steady state procainamide concentrations when given the higher dose.

Simultaneous determination of procainamide and N-acetylprocainamide in plasma by high-performance liquid chromatography

A sensitive, specific, high-performance liquid chromatographic procedure is described for the simultaneous determination of procainamide and its metabolite, N-acetylprocainamide, in plasma. Basic plasma (2.0 ml), containing pheniramine maleate as an internal standard, is partitioned with methylene dichloride. The organic extract is concentrated to between 0.3 and 0.5 ml, and 100-microliter aliquots are chromatographed on a microparticulate silica gel column using 0.1% acetic acid-20% 0.1 M ammonium acetate in acetonitrile as the mobile phase. With a fixed-wavelength (254-nm) UV detector, both compounds can be quantitated in the 0.1-8.0-microgram/ml of plasma range.

Effect of acetylator phenotype on the rate at which procainamide induces antinuclear antibodies and the lupus syndrome

To investigate the relation between acetvlator phenotype and the development of procainamide-induced lupus, we determined the rate of development of antinuclear antibodies in 20 patients of known acetylator phenotype receiving chronic procainamide therapy. The duration of therapy required to induce antibodies in 50 per cent of slow (11) and rapid (nine) acetylators was 2.9 and 7.3 months respectively. The median total dose that produced ant;bodies was 1.5 g per kilogram and 6.1 g per kilogram respectively. After one year antibodies had developed in 18 patients. Retrospective studies of patients in whom procainamide lupus had developed revealed that the duration of therapy required for induction in 14 slow and seven rapid acetylators was 12 +/- 5 and 48 +/- 22 months respectively (P less than 0.002). We conclude that acetylator phenotype influences the rate at which procainamide induces antinuclear antibodies and probably the lupus syndrome. Antibody production is probably related to the parent compound or a non-acetylated metabolite.

Kinetics of procainamide and N-acetylprocainamide in renal failure

Four normal subjects and four functionally anephric patients were given 6.5 mg/kg of body wt of procainamide hydrochloride i.v., and plasma concentrations of procainamide (PA) and its major active metabolite N-acetylprocainamide (NAPA) were measured. Two individuals in each group were fast isonicotinic acid hydrazide (INH) and PA acetylators. The pharmacokinetics of PA and NAPA were analyzed with a computer program (SAAM 23). Volume of distribution (Vdss) and renal clearance of PA were similar in normal subjects regardless of acetylator phenotype. Nonrenal clearance was faster (383 vs. 244 ml/min), and PA elimination half-life (t 1/2) was shorter (2.6 vs. 3.5 hr) in fast acetylators. In the functionally anephric patients, Vdss was similar to that of normal subjects. Nonrenal clearence was faster (117.5 vs. 93.5 ml/min) and PA t 1/2 shorter (10.8 vs. 17.0 hr) in fast than in slow acetylators. In these patients, acetylation accounted for 56% of PA elimination, and NAPA concentrations reached 0.8 microgram/ml or more. The t 1/2 of NAPA in renal failure was 41.5 hr, in accord with predictions from studies in normal subjects, assuming no impairment in nonrenal NAPA elimination. PA metabolism, however, is severely impaired by renal failure, so PA t 1/2 was prolonged to an unpredictably greater extent than would be expected from studies in normal subjects.

Absorption kinetics of procainamide in humans

Plasma procainamide concentrations following the administration of 500 mg of procainamide hydrochloride via intravenous infusion, conventional capsules, and sustained-release tablets were compared in 11 healthy male volunteers. Two-compartment open modeling of the plasma levels from the intravenous infusion experiments yielded mean Kel, k12, and k21 values of 0.0162, 0.0542, and 0.0233 min-1, respectively. The bioavailability of the oral preparations (versus intravenous) averaged 83% for the capsule and 79% for the sustained-release tablet. Calculations using a previously reported method suggested that absorption was a first-order process with mean ka's of 0.0336 and 0.0039 min-1 for the capsule and sustained-release tablet, respectively. The sustained-release formulation exhibited delayed release and adequate bioavailability.

Procaineamide blood levels after administration of a sustained-release preparation

Procaineamide is now available as a sustained-release preparation. This preparation was administered in an eight-hourly regime to 26 patients, and therapeutic blood levels were obtained for the duration of the 56-hour study period in 20 patients. No side effects were observed. Inadequate blood levels may be predicted from a single blood level eight hours after the first dose, which could allow for dosage adjustment.

The relationship between the metabolism of procainamide and sulfamethazine

The metabolism of sulfamethazine (SMZ), which is acetylated by a binodally distributed enzyme, and procainamide (PA) was compared in 21 normal volunteers, each given a single oral dosted metabolites, N-acetyl-procainamide (NAPA) and Ac-SMZ, were measured. Subjects with less than 64% Ac-SMZ in the 0-8 hour collection were termed "slow" and those with more than 64% were termed "fast" SMZ acetylators. Slow SMZ acetylators had 9.8 to 43.8% (24.1 +/- 10.13) NAPA recovered, and fast SMZ acetylators, 22.0 to 42.6% (33.7 +/- 7.29) NAPA, P less than 0.01. In addition, the calculated half-life of PA metabolism for slow SMZ acetylators was 9.0 to 33.8 hours (18.4 +/- 8.82) and for fast SMZ acetylators was 8.1 to 14.4 hours (10.9 +/- 2.19), P less than 0.01. For four subjects, SMZ acetylation phenotype did not correlate with the half-life of SMZ or PA metabolism; and in two, SMZ acetylation phenotype and half-life of metabolism did not correlate with the same PA indices. Even though slow SMZ acetylators have less NAPA recovered than fast SMZ acetylators, it is not yet clear that procainamide is metabolized by a bimodally distributed enzyme as is sulfamethazine.

Comparison of the acetylation of procainamide and sulfadimidine in man

The acetylation of procainamide and sulfadimidine has been measured simultaneously in plasma and urine in 20 healthy human volunteers by a specific G.L.C. method, after single and multiple oral dral doses of procainamide retard tablets. A distinct bimodality (9 rapid and 11 slow acetylators) was apparent from the concentrations of procainamide and N-acetylprocainamide both in urine and plasma, which was in complete agreement with data about sulfadimidine acetylation. The influence of acetylator phenotype on the relative concentrations of procainamide and N-acetylprocainamide in plasma as cn 5 additional healthy subjects after a single oral dose of procainamide. The present results show that acetylator phenotype can now be determined using procainamide as the test substance, and for this purpose multiple doses offer hardly any advantage over a single dose of the drug. However, because the separation between rapid and slow acetylators is less pronounced for procainamide than for sulfadimidine, precise criteria must be established for the conditions of the test, and the influence of diseases, such as renal insufficiency, should be taken into consideration.

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