Hemodialysis for severe procainamide toxicity: clinical and pharmacokinetic observations

Pediatric toxicologic concerns

Pediatric poisonings account for significant morbidity in the United States each year. Clinicians must keep current with advances in toxicology to be familiar with the latest recommended treatment regimens and antidotes. They also must be familiar in identifying toxidromes and important physical examination findings. Having these skills can enable the clinician to determine who is at risk for significant morbidity or mortality and to provide the appropriate medical care.

Transport of paraquat and mexiletine from the blood into the rat intestinal lumen and peritoneal cavity

Transport of paraquat and mexiletine from the blood into the intestinal lumen and the peritoneal cavity was examined after their intravenous administration (paraquat: 20 mg kg-1, mexiletine: 10 mg kg-1) to rats. The average amounts of paraquat transferred into the intestinal lumen and the peritoneal cavity were 1.39 and 22.8% of the dose in 120 min, respectively. The average amounts of mexiletine transferred into the intestinal lumen and the peritoneal cavity were 6.1 and 2.5% of the dose in 120 min, respectively. The transfer rate of 3H2O into the peritoneal cavity after intravenous administration (1.85 MBq) was greater than that into the intestinal lumen. In view of the hydrophilic nature of paraquat cation, a solvent drag effect due to movement of water might contribute to transport of paraquat from the blood to the peritoneal cavity. Differences in transport behaviour across the two membranes could be due to differences in the geometrical factors such as the surface area and the distribution of blood vessels. Differences might also be due to differences in physicochemistry and pharmacological effects of both substances.

Combined high-efficiency hemodialysis and charcoal hemoperfusion in severe N-acetylprocainamide intoxication

Several extracorporeal techniques have been used to remove N-acetylprocainamide (NAPA), the major metabolite of procainamide, in patients intoxicated with this substance. We report a patient with life-threatening NAPA intoxication who was rapidly and successfully treated with combined high-efficiency hemodialysis and charcoal hemoperfusion. The hemodialyzer and hemoperfusion cartridge were placed in series such that the patient's blood was dialyzed before reaching the cartridge. Overall clearance of NAPA was 153 mL/min, with clearance due to hemodialysis averaging 102 mL/min and that due to hemoperfusion averaging 88 mL/min. Thus, addition of the hemoperfusion cartridge into the extracorporeal circuit resulted in a 50% increase in clearance over that obtainable by high-efficiency hemodialysis alone. In comparison to other modalities, this technique is more effective than either hemodialysis or charcoal hemoperfusion alone and can achieve a more rapid reduction of serum NAPA levels than that observed with slow continuous hemofiltration or hemodiafiltration.

Therapeutic monitoring and pharmacokinetic evaluation of procainamide in neonates

Past experience with the disposition of procainamide hydrochloride (PA) in neonates is restricted to a single case study involving placental transfer. We studied aspects of PA pharmacokinetics in three neonates who received constant-rate infusion therapy. Results indicated that the total serum clearance of PA is similar to the adult value, but elimination half-lives of both PA and N-acetylprocainamide (NAPA) were slightly prolonged and volume of distribution was variable. Pharmacokinetic evaluations in a renally compromised neonate confirmed that total PA clearance and the renal clearance of both PA and NAPA were reduced, although not to the extent expected for the degree of renal impairment. Peritoneal dialysis was used concurrently and may have contributed to the elimination process. We believe that our experience provides important preliminary guidelines for the management of PA therapy in neonates.

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)

Pharmacokinetics of N-Acetylprocainamide

Shortly after Dreyfus and his colleagues demonstrated that procainamide was metabolized by acetylation to N-acetylprocainamide (NAPA), Drayer, Reidenberg and Sevy reported that NAPA had antiarrhythmic activity in an animal model. We confirmed these findings and found that plasma levels of NAPA were high enough to warrant consideration in managing patients requiring procainamide therapy. However, the actual impetus for developing NAPA as an antiarrhythmic drug in its own right was provided by the initial studies of NAPA pharmacokinetics in normal subjects. In these studies, we showed that NAPA has an elimination-phase half-life that is more than twice as long as procainamide and suggested that patient compliance and arrhythmia suppression might be improved if NAPA were used to circumvent the inconvenience of the frequent dosing schedule that has been recommended for procainamide.

From the standpoint of managing individual patients with NAPA, the pharmacokinetics of this drug continue to provide the scientific basis for designing dose regimens that will have maximal antiarrhythmic efficacy and minimal toxicity. This review summarizes the salient features of NAPA pharmacokinetics and outlines an approach for individualizing therapy with this drug.

Poisoning by antidysrhythmic drugs

This article discusses the management of antidysrhythmic drug overdoses in children and adolescents.

Procainamide toxicity in a patient with acute renal failure

A patient developed acute renal failure while receiving oral procainamide (PA). This lead to severe PA and N-acetyl procainamide (NAPA) toxicity. Rebound of NAPA plasma levels postdialysis prolonged the toxicity, which was treated with hemodialysis, hemoperfusion, and combined hemodialysis-hemoperfusion. Because of the potential for PA and NAPA toxicity in patients with renal insufficiency, especially in patients with changing renal function due to acute renal failure, it is recommended that the use of PA be curtailed in this population and that another substitute antiarrhythmic agent be used.

Clinical pharmacokinetics of N-acetylprocainamide

Since N-acetylprocainamide was identified in the urine of patients receiving procainamide, this compound has been studied both as a metabolite of procainamide and as a separate antiarrhythmic agent. N-acetylprocainamide absorption following oral administration is more than 8-% complete. 59 to 89% of N-acetylprocainamide is excreted unchanged in the urine in subjects with normal renal function. Deacetylation of N-acetylprocainamide to procainamide is a minor route of N-acetylprocainamide elimination. The half-life of N-acetylprocainamide in patients with normal renal function has been reported to vary between 4.3 and 15.1 hours. Total body clearance (mean +/- SD) of N-acetylprocainamide in patients with normal renal function has been reported to range from 2.08 +/- 0.36 ml/min/kg to 3.28 +/- 0.52 ml/min/kg. There is a linear relationship between N-acetylprocainamide clearance and creatinine clearance. The half-life of N-acetylprocainamide in functionally anephric patients may be as long as 42 hours; however, it can be effectively cleared from plasma by haemodialysis. N-acetylprocainamide is 10% protein-bound. There is an age-related decline in N-acetylprocainamide clearance, mostly due to the decrease in creatinine clearance that occurs with ageing. In the neonate, the half-life of acetylprocainamide is prolonged. Several therapeutic trials carried out to assess the effectiveness of N-acetylprocainamide in suppressing chronic ventricular premature beats have now been reported. If there is a therapeutic response to N-acetylprocainamide it will probably occur at a plasma concentration between 15 and 25 micrograms/ml. A high degree of overlap has been reported between the concentration range associated with arrhythmic suppression and the range of concentrations where intolerable side effects begin to occur. No severe cardiac toxicity has been reported with oral therapy despite plasma concentrations as high as 40 micrograms/ml. However, hypotension has been reported in association with a rapid intravenous bolus of N-acetylprocainamide. A maximum intravenous infusion rate of 50 mg/min has been recommended. N-acetylprocainamide in patients receiving procainamide; however, N-acetylprocainamide concentrations remain below the therapeutic range in patients with normal renal function. In patients with renal failure receiving procainamide, N-acetylprocainamide concentrations rise dramatically. The dose of N-acetylprocainamide must be adjusted in patients with renal insufficiency, and it should be used more cautiously in the very old and very young. N-acetylprocainamide plasma concentration monitoring would be valuable clinically in patients with renal insufficiency receiving either N-acetylprocainamide or procainamide, and in the very young and the aged.

Metabolism of procainamide in patients with chronic heart failure, chronic respiratory failure and chronic renal failure

Fractional hydrolysis and acetylation of procainamide, acetylation of procainamide-derived p-aminobenzoic acid and plasma hydrolysis of procaine were studied in 20 patients with chronic heart failure (CHF), 20 patients with chronic respiratory insufficiency (CRI) and 20 patients with chronic renal failure (RF). The results were compared with those obtained in a group of 20 normal volunteers. Hydrolysis of procainamide and procaine were reduced in patients with CHF and CRI, but not in patients with RF. Moreover, more marked decreases in procainamide and procaine hydrolysis were seen in subgroups with secondary hepatic dysfunction. The diminution of hydrolysis of procainamide was not paralleled by changes in acetylation of procainamide or p-aminobenzoic acid. It is concluded that in patients with hepatic involvement secondary to advanced CHF or CRI, hepatic and plasmatic hydrolysis activity is decreased to a degree equivalent to primary liver failure.

Digoxin removal from an anephric patient by hemoperfusion over XAD-4

Removal of digoxin by hemoperfusion over Amberlite XAD-4 was determined in a functionally anephric patient. During four hours of hemoperfusion, 50.45 microgram of digoxin were removed by the column and serum digoxin concentrations decreased by 0.2 ng/ml after the post-hemoperfusion reequilibration was complete.

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.