Serum procainamide levels as therapeutic guides

Procainamide pharmacokinetics during extracorporeal membrane oxygenation

Procainamide is a useful agent for management of ventricular arrhythmia, however its disposition and appropriate dosing during extracorporeal membrane oxygenation (ECMO) is unknown. We report experience with continuous procainamide infusion in a critically ill adult requiring venoarterial ECMO for incessant ventricular tachycardia. Pharmacokinetic analysis of procainamide and its metabolite, N-acetylprocainamide (NAPA), was performed using serum and urine specimens. Kidney function was preserved, and sequencing of the N-acetyltransferase 2 gene revealed the patient was a phenotypic slow acetylator. Procainamide volume of distribution and half-life were calculated and found to be similar to healthy individuals. However, despite elevated serum procainamide concentrations, NAPA concentrations remained far lower in the serum and urine. The magnitude of procainamide and NAPA discordance suggested alternative contributors to the deranged pharmacokinetic profile, and we hypothesized NAPA sequestration by the ECMO circuit. Ultimately, the patient received orthotopic cardiac transplantation and was discharged home in stable condition. Procainamide should be used cautiously during ECMO, with close therapeutic drug monitoring of serum procainamide and NAPA concentrations. The achievement of therapeutic NAPA concentrations while maintaining safe serum procainamide concentrations during ECMO support may be challenging.

Continuous intravenous antiarrhythmic agents in the intensive care unit: strategies for safe and effective use of amiodarone, lidocaine, and procainamide

The development of cardiac arrhythmias in the intensive care unit is common and associated with poor prognoses and outcomes. Because of the complexity of patients admitted to the intensive care unit, the management of arrhythmias is often difficult and may require multiple therapeutic interventions. In order for clinicians to appropriately manage arrhythmias, a thorough understanding of all available therapies, including intravenous antiarrhythmic agents, is essential. Suitable antiarrhythmic agents for use in the critical care setting include amiodarone, lidocaine, and procainamide. While these agents can be effective in managing cardiac arrhythmias, they also possess significant disadvantages and require additional monitoring during use. Therapy with these agents is often complicated because of the presence of significant associated adverse effects, clinician unfamiliarity, variable dosing strategies, and the potential for drug-drug interactions. The purpose of this review is to discuss indications and strategies for safe and effective use of amiodarone, lidocaine, and procainamide.

Excretion and ecotoxicity of pharmaceutical and personal care products in the environment

The presence and fate of pharmaceutical and personal care products (PPCPs) in the environment is undergoing increasing scrutiny. The existing clinical pharmacokinetics and pharmacodynamics data for 81 common compounds were examined for cues of ecotoxicity. Of these the proportions excreted were available for 60 compounds (i.e., 74%). The compounds had a low (< or =0.5%), a moderately low (6-39%), a relatively high (40-69%), or a high (> or =70%) proportion of the parent compound excreted. More than half of the compounds evaluated have low or moderately low proportions of the parent compound excreted. However, the proportions excreted were negatively but moderately correlated (r = -0.50; n = 13; P = 0.08) with the concentrations of the compounds in the aquatic environment, suggesting that the compounds that have low proportions excreted may also have inherently low degradability in the environment. Solubility, logK(ow), and pKa work well in predicting the behavior of PPCPs under clinical conditions and have been used in the environmental assessment of PPCPs prior to approval. However, these parameters did not correlate with the proportion of PPCPs excreted in the environment or their concentration in the environment, underscoring the need for research into the behavior of PPCPs in the environment. PPCPs occur in low concentrations in the environment and are unlikely to elicit acute toxicity. An ecotoxicity potential that is based on chronic toxicity, bioavailability, and duration of exposure to nontarget organisms is described as a guide in assessing the potency of these compounds in the environment.

High-performance liquid chromatographic drug analysis by direct injection of whole blood samples. II. Determination of hydrophilic drugs

The determination of hydrophilic drugs in whole blood by direct injection high-performance liquid chromatography was investigated. A pre-column equipped with an inlet filter of pore size 40 microns and an outlet filter of pore size 2 microns was packed with Butyl Toyopearl 650-M. A whole blood sample was injected directly into the pre-column to trap proteins, hydrophobic compounds and blood cytomembranes, and hydrophilic compounds emerged into an analytical column (Nucleosil 5SA, particle size 5 microns) and were determined after column switching. Proteins in 40 microliters of rabbit whole blood were adsorbed in the pre-column (0.63 ml of wet gel) in 0.4% perchloric acid solution. The recovery of procainamide and N-acetylprocainamide from whole blood was quantitative with good reproducibility (coefficient of variation less than 4%). It was shown that procainamide added to rabbit whole blood was subjected to N-acetylation by N-acetyltransferase in blood cells.

Drug concentrations. A guide to their usefulness in clinical practice

When used properly, measurements of plasma drug levels in the clinical setting may provide valuable information. Optimally the drug level will permit the clinician to devise a therapeutic regimen on the basis of an individual patient's handling of the drug and thus obtain maximal drug efficacy while minimizing the risk of drug toxicity. However, the technology that permits the measurement of drug levels has often outpaced the clinical data base that allows proper interpretation of the level. Thus, the physician should be aware of both the potential and the limitations of therapeutic drug monitoring and apply the technique critically with respect to individual drugs in individual patients.

Short-term myocardial uptake of lidocaine and mexiletine in patients with ischemic heart disease

Determination of short-term myocardial drug uptake and subsequent redistribution was performed in 27 patients with ischemic heart disease for the antiarrhythmic agents lidocaine and mexiletine, using frequent simultaneous measurements of drug concentration in aortic and coronary sinus blood, combined with measurement of coronary sinus blood flow after intravenous bolus injection of the drug. Maximal myocardial drug content per unit resting coronary sinus blood flow (MDC:F) was significantly greater in patients in whom coronary sinus pacing at 100 beat/min was performed during the initial period of drug uptake. Maximal myocardial drug content occurred after 2.4 +/- 0.2 (SEM) for lidocaine and after 5.5 +/- 0.6 min for mexiletine (p less than .001), and pacing did not affect time to maximum myocardial drug content. In nonpaced, but not paced, patients maximal MDC:F was greater in the lidocaine group than that in the mexiletine group. The subsequent efflux of lidocaine from the myocardium was more rapid that that of mexiletine in both paced and nonpaced groups.

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.

Dose and concentration dependent effect of ranitidine on procainamide disposition and renal clearance in man

The pharmacokinetics of oral procainamide (1 g) were investigated in six healthy subjects during chronic dosing with ranitidine 150 mg twice daily, and in three of the subjects when ranitidine 750 mg was administered over 12 h. The procainamide area under the plasma concentration-time curve was significantly (PQ0.02) increased by ranitidine (27.761.5 vs 31.561.8 mg l-1 h) with a significant reduction in renal clearance (379632 vs 309630 ml/min, PQ0.02). There was no change in half-life. The N-acetylprocainamide (NAPA) area under the plasma concentration-time curve was also significantly (PQ0.02) elevated by ranitidine (8.661.2 vs 9.761.3 mg 1-1 h) due to a reduction in renal clearance from 187630 to 168628 ml/min. The larger dose of ranitidine produced greater alterations in the procainamide and NAPA pharmacokinetics. Ranitidine reduced the absorption of procainamide by 10% and by 24% at the higher dose level. Two-hourly renal clearance values of procainamide were significantly (PQ0.05) reduced in the 2 to 10 h period and for NAPA between 0 to 6 and 8 to 10 h. The larger ranitidine dose reduced the renal clearances of procainamide and NAPA over the control period at each 2-hourly time period. The reductions in renal clearance are most likely mediated by competition for the renal tubular cationic secretory pathway. Clinical implications arising from this study suggest a reduction in procainamide dosage may be necessary in a small, select number of patients with high plasma ranitidine concentrations, e.g., the elderly; furthermore, failure of therapeutic response for some drugs may be due to ranitidine-induced impaired gastrointestinal absorption.

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.

Cimetidine-procainamide pharmacokinetic interaction in man: evidence of competition for tubular secretion of basic drugs

The hypothesis that basic drugs can compete for active tubular secretion by the kidney was tested in six healthy volunteers by comparing the single dose pharmacokinetics of oral procainamide before and during a daily dose of cimetidine. The area under the procainamide plasma concentration-time curve was increased by cimetidine by an average of 35% from 27.0 +/- 0.3 micrograms/ml X h to 36.5 +/- 3.4 micrograms/ml X h. The elimination half-life increased from an harmonic mean of 2.92 to 3.68 h. The renal clearance of procainamide was reduced by cimetidine from 347 +/- 46 ml/min to 196 +/- 11 ml/min. All these results were statistically significant (p less than 0.016). The area under the plasma concentration-time curve for n-acetylprocainamide was increased by a mean of 25% by cimetidine due to a significant (p less than 0.016) reduction in renal clearance from 258 +/- 60 ml/min to 197 +/- 59 ml/min. The data suggests that cimetidine inhibits the tubular secretion of both procainamide and n-acetylprocainamide, and, if so, represents the first documented evidence for this type of drug interaction in man. The clinical implications from this study necessitate dosage adjustments of procainamide in patients being concomitantly treated with cimetidine. The interaction is pertinent not only for basic drugs that are cleared by the kidney, but also for metabolites of basic drugs and endogenous substances which require active transport into the lumen of the proximal tubule of the kidney for their elimination.

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.

Development of Fluoroimmunoassays for the determination of individual or combined levels of procainamide and N-acetylprocainamide in serum

A fluoroimmunoassay has been developed for the simultaneous determination of serum levels of procainamide and its active metabolite N-acetylprocainamide. It employs procainamide linked through its aromatic amino group to fluorescein isothiocyanate as tracer and an antiserum raised against procainamide conjugated to human thyroglobulin through the same position. Separation is rapidly and simply achieved by covalently linking the antiserum to magnetisable microparticles and use of a magnet. Specific magnetisable particle fluorimmunoassays were also developed for procainamide and for N-acetylprocainamide by the use of suitable immunogens and fluorescein-labelled tracers. That for procainamide uses an antiserum raised to a procainamide-enzyme conjugate and fluorescein-labelled p-aminobenzoic acid while the fluoroimmunoassay for N-acetylprocainamide employs an antiserum against a N-acetylprocainamide-enzyme conjugate and fluorescein-labelled p-acetamidobenzoic acid.