Disposition of bretylium in man and rat. A sensitive chemical method for its estimation in plasma and urine

Simple, rapid and selective method using high-performance liquid chromatography for the determination of bretylium in plasma

A high-performance liquid chromatographic method with ultraviolet detection has been developed for the determination of bretylium in plasma. Following a single-step solid-phase extraction procedure, bretylium is selectively isolated and well recovered from plasma. The assay sensitivity is 0.156 micrograms/ml from 250-microliters plasma samples and its linearity was assessed up to 40 micrograms/ml. The method is accurate (101.0 +/- 5.4%) and precise (maximum coefficient of variation of 8%). It provides a simple and time-saving alternative to existing methods and is particularly suitable for pharmacokinetic studies.

Therapy with conventional antiarrhythmic drugs for ventricular arrhythmias

Conventional antiarrhythmic drugs are an important tool for the clinical cardiologist for the treatment of ventricular arrhythmias. Knowledge of the different properties of these drugs will help decrease the incidence of adverse effects and increase the frequency of successful therapy.

Antiarrhythmic and electrophysiologic actions of bethanidine sulfate in primary ventricular fibrillation or life-threatening ventricular tachycardia

Antiarrhythmic and electrophysiologic actions of bethanidine sulfate, a chemical analog of bretylium tosylate, were studied using programmed cardiac electrical stimulation in 14 survivors of out-of-hospital cardiac arrest unassociated with acute myocardial infarction. Before bethanidine sulfate was administered sustained ventricular tachyarrhythmias (VT) were inducible in 11 patients and reproducible nonsustained VT was induced in 3 patients. Bethanidine sulfate shortened sinus cycle length and absolute and relative ventricular refractory periods measured during sinus rhythm, but did not alter ventricular effective refractory period measured during ventricular pacing. Bethanidine sulfate prevented inducible VT in 8 patients (57%), increased the number of extrastimuli needed to induce VT in 2 patients, and was ineffective in 4 patients. In contrast, in only 1 of 26 trials with other conventional and investigational antiarrhythmic drugs in these patients was VT prevented. Orthostatic hypotension was a prominent side effect of bethanidine sulfate therapy, but could be reversed in most patients by concomitant administration of protriptyline. Five patients in whom bethanidine sulfate was effective in the laboratory have been treated chronically (400 to 600 mg 4 times daily), and all are alive at 3 to 40 months. In the remaining 9 patients, 8 were treated empirically because no drug was effective in the laboratory and 1 was treated with quinidine, which appeared to be protective during testing. Four of these 9 patients, including the patient treated with quinidine, died suddenly during follow-up. Thus, although bethanidine sulfate therapy is difficult to initiate because of orthostatic hypotensive side effects, it may be useful in treating patients at high risk of recurrent cardiac arrest.

Tissue distribution of [14C]bretylium tosylate in rats

The distribution of [14C]bretylium tosylate in the body and the relationship between tissue and plasma concentrations was determined following intravenous administration of the drug to Charles River rats. The renal excretion of bretylium was rapid in rats and follows an active process. On the average, 50% of the administered dose was excreted in the urine within 1 hr. In the postequilibrium phase, the plasma concentration declined with a half-life of 5 hr. Bretylium concentrations in all tissues, except the heart, declined rapidly according to a triexponential equation. The liver and kidney bretylium concentrations declined in parallel to the plasma concentration with mean tissue-plasma concentration ratios of 6.04 and 12.3, respectively, in the beta phase. However, the concentration of bretylium in the heart increased gradually and peaked at 2 hr, with a tissue-plasma concentration ratio of 121, which, in turn, declined to a value of greater than 60 after 8 hr. The data indicated that (a) bretylium is rapidly distributed into the liver and kidney immediately after reaching the systemic circulation; (b) the distribution into the heart occurs at a slower rate compared with the other organs, and the drug has a high affinity to the myocardium; and (c) since the heart is the site of action and there is no direct correlation between the concentrations in myocardium and plasma, the antiarrhythmic effect of bretylium may not be related to the plasma concentration.

Pharmacokinetics of bretylium in dogs and the effect of hemoperfusion on elimination

The pharmacokinetics of bretylium in dogs and the efficacy of hemoperfusion with a resin column in its removal from the body following intravenous administration of bretylium tosylate were investigated. Five mongrel dogs weighing 18-26 kg were given a bolus dose of 15 mg/kg. Serial blood samples were taken for 24 hr. Hemoperfusion, through a resin column, was then initiated and continued for 4 hr under pentobarbital anesthesia. During hemoperfusion, arterial and venous blood samples were collected several times; venous blood samples were then withdrawn for an additional 8 hr. Urine was collected from each dog in three portions for up to 48-54 hr. Pharmacokinetics of bretylium in dogs could be characterized by a two-compartment open model with a distribution half-life of 7 min and biological half-life of 15.9 +/- 1.9 hr. Plasma levels declined rapidly from approximately 20 microgram/ml at 6 min to less than 2 microgram/ml within 1 hr. The ratio of intercompartmental rate constants, k12/k21, was 16.7, and the volume of the central compartment and apparent volume of distribution were 0.245 and 5.22 liter/kg, respectively, indicating a wide distribution of bretylium into the tissues. Plasma dialysis clearance averaged 29.7 ml/min, which is 30% of the total body clearance (98.8 ml/ min). These data suggest that resin hemoperfusion may not be useful in the treatment of bretylium intoxication.

Antiarrhythmic, antifibrillatory, and hemodynamic actions of bethanidine sulfate: an orally effective analog of bretylium for suppression of ventricular tachyarrhythmias

Bethanidine sulfate is a chemical and pharmacologic analog of bretylium tosylate that has virtually identical antifibrillatory and inotropic actions on the heart. Bretylium is the only drug approved by the Food and Drug Administration specifically for the "prophylaxis and treatment of ventricular fibrillation." Unlike bretylium, which is poorly absorbed from the gut and limited to parenteral use, oral bethanidine is absorbed rapidly. Bethanidine was given to 23 patients with recurrent multiple drug refractory ventricular tachycardia and fibrillation. Eighteen patients (78%) had complete suppression of spontaneous or electrophysiologically inducible tachyarrhythmias; 3 were improved and 2 had no benefit. In 6 of a 9 patient subgroup studied by programmed electrophysiologic drug testing, bethanidine completely prevented previously inducible ventricular tachyarrhythmias at the maximal stimulus tested (including 4 extrastimuli and burst-pacing at 10 times threshold). Cardiac output measured in 6 patients 1 to 2 hours after bethanidine was increased in 4, unchanged in 2, and decreased in 1. Ten patients on long-term therapy with bethanidine and protriptylene (to prevent orthostatic hypotension) have been free of arrhythmias from 2 to 26 (average 13) months.

Bretylium pharmacokinetics and bioavailabilities in man with various doses and modes of administration

The pharmacokinetics and bioavailabilities of bretylium tosylate were studied in 9 male normal volunteers by 60 min constant rate intravenous infusions of 200, 300, and 400 mg, by intramuscular injection of 300 and 400 mg, by oral administration of 100, 200, and 400 mg in solution, and by oral administration of 200 mg tablets. The latter studies were repeated in the same 5 volunteers which were also studied by all modes of administration and at several doses. Intravenous studies showed a sum of 3 exponentials to characterize plasma level-time studies with a terminal half-life of 535 +/- 32 (S.E.M.) min (n = 12). The urinary recovery of unchanged drug was 77 +/- 4(S.E.M.)(n = 14). Half-lives within a subject were correlated and independent of dose. Intramuscular administration showed an apparent half-life of first-order invasion of 79 +/- 13 (S.E.M.) min (n = 6) with no apparent dose dependency and a urinary recovery of unchanged drug of 95.4 +/- 3.2 (S.E.M.) per cent with a terminal half-life similar to the intravenous studies. Oral solutions had smaller lag times of absorption [17 +/- 4(S.E.M.) min] than tablets [56 +/- 9 (S.E.M.) min] and longer apparent half-lives of first-order absorption [231 +/- 23 (S.E.M.) min] than tablets [87 +/- 15 (S.E.M.) min]. The tablets had slightly greater bioavailabilities [27 +/- 2.3 (S.E.M.) per cent] than the oral solutions [22.1 +/- 2.2 (S.E.M.) per cent] but with no apparent dose dependencies. Renal clearances were the same for all modes of administration. Means +/- S.E.M. were 735 +/- 32, i.v., 686 +/- 38, i.m., and 623 +/- 57 ml min-1, p.o. Apparent overall volumes of distribution were 589 +/- 401, i.v. and 450 +/- 671 (S.E.M.), i.m. The i.v. studies in three dogs confirmed the three-compartment body model and the high overall volumes of distribution, had terminal half-lives similar to humans and had renal clearances of 84, 164, and 207 ml min-1 that were in excess of glomerular filtration. There were no significant changes of cardiovascular parameters with the time course of the drug in the body and no significant drug-affected clinical parameters. The only consistent side effect was a generally transient nasal congestion at plasma peak time on intravenous administration.

Suppression of ventricular fibrillation and positive inotropic action of bethanidine sulfate, a chemical analog of bretylium tosylate that is well absorbed orally

Bethanidine sulfate is a closely related chemical analog of bretylium that has virtually identical pharmacologic and antifibrillatory actions on the ventricle. Unlike bretylium, which is very poorly absorbed from the gut, bethanidine is rapidly and effectively absorbed after oral administration. Bethanidine increased ventricular fibrillation threshold in the normal dog heart from an average control value of 28.5 mA to an average peak value of 66.5 mA, an increase of 150 percent. In the infarcted heart, bethanidine increased ventricular fibrillation threshold from an average postinfarction level of 14.4 mA to an average peak value of 55.3 mA, an increase of 327 percent. Like bretylium, the antifibrillatory action of bethanidine was manifested by the appearance of nonsustained ventricular fibrillation when superthreshold shocks induced episodes of ventricular fibrillation lasting from 2 to 120 seconds and converting spontaneously to sinus rhythm. In contrast, the untreated dog heart must always be defibrillated electrically. The onset of antifibrillatory action began as early as 2 minutes after intravenous administration and 15 to 30 minutes after oral administration; peak action occurred in approximately 60 minutes. Bethanidine had prolonged positive inotropic action in the isolated heart as reflected by an increase in cardiac output and blood pressure lasting up to 60 minutes. Bethanidine lowered coronary vascular resistance and increased coronary blood flow. The oral efficacy and rapid onset of action gives bethanidine a potential role in the prevention of out-of-hospital ventricular fibrillation.

Pharmacokinetics of [14C]bretylium tosylate in rats

The pharmacokinetics of bretylium tosylate were investigated in eight male Charles River rats. Each animal received an intravenous dose (10 mg/kg) of [14C)bretylium tosylate. Serial blood samples, urine, and feces were collected for up to 72 hr. Bretylium concentrations in plasma and amounts excreted in urine and feces were determined by scintillation counting. On the average, 88 and 95% of the dose were recovered in urine and feces in 24 and 72 hr, respectively. Urinary recovery accounted for 65.6 of the dose while 29.7% was excreted in the feces. Bretylium concentrations in plasma declined triexponentially and were fitted to a three-compartment open model. Bretylium has a very high apparent volume of distribution (15 liters/kg), and its beta half-life averaged 5.5 hr. Mean values of the apparent volume of the central compartment, plasma clearance, renal clearance, and excretion rate constants of bretylium in rats were 1 liter/kg, 1.93 liters/hr/kg, 1.27 liters/hr/kg, and 1.24 hr-1, respectively. The results indicate that: (a) bretylium is strongly bound to the tissues and is eliminated by active urinary secretion and by biliary excretion in rats, and (b) there are strong similarities between the pharmacokinetics of bretylium in humans and rats and that this animal model might be suitable for interaction studies with other drugs.

Massive intravenous bolus bretylium tosylate

A 30 mg/kg (2-gm) intravenous bolus of bretylium tosylate was administered to a patient with recurrent ventricular tachycardia and fibrillation. After successful defibrillation the patient exhibited marked hypertension followed by protracted refractory hypotension. There was no further ventricular ectopy in spite of a very low cardiac index. A bretylium level of 8,800 ng/ml is the highest reported in man from a single bolus injection. This case demonstrates the exaggerated hemodynamic response to massive intravenous bolus bretylium tosylate.

Pharmacokinetics of bretylium in man after intravenous administration

The pharmacokinetic profile of bretylium was studied in four normal male volunteers using a new sensitive EC-GC procedure for its quantitative in biological fluids. The plasma concentrations and urinary excretion rates following the constant i.v. infusion of a single 4 mg/kg dose of bretylium tosylate declined biexponentially and the data were fitted to a two-compartment model with a renal and a nonrenal route of elimination. The drug had a mean half-life (t1/2 beta) of 7.8 hr and apparent volume of distribution (Vd, beta) of 8.18 liters/kg. The renal clearance, which was 6 times that of the glomerular filtration rate, accounted for almost 84% of the total body clearance and correlated linearly with the subjects' creatinine clearance. The observed side effects of bretylium were mild and similar to those of other adrenergic blocking agents.

GLC determination of bretylium in biological fluids

Bretylium [(o-bromobenzyl)ethyldimethylamine] is a quaternary ammonium compound used as the tosylate salt for treatment of ventricular fibrillation in humans. A sensitive assay was developed for the determination of low bretylium concentrations in plasma and urine. The internal standards were (p-bromobenzyl)ethyldimethylammonium p-toluenesulfonate and (o-methoxybenzyl)ethyldimethylammonium p-toluenesulfonate. Samples were deproteinized with acetonitrile and extracted with methylene chloride. After the evaporation of the organic phase, the residue was reacted with sodium 2,4,5-trichlorothiophenolate in methanol. This procedure yielded volatile compounds with excellent electron-capture capabilities for the GLC analysis. The assay sensitivity is 5 ng/ml. The extraction recovery of bretylium as determined by a direct radioactivity measurement was 90 and 97% for plasma and urine, respectively. The method is highly reproducible with no significant day-to-day variations. Comparisons of 60 standard plasma samples, 25 standard urine samples, and plasma samples from a dog that received [14C]bretylium showed excellent agreement between the GLC method and direct radioactivity measurement of bretylium.

Sensitive gas chromatographic assay for the quantitation of bretylium in plasma, urine and myocardial tissue

A sensitive analytical method has been developed for the quantitation of bretylium in plasma, urine and myocardial tissue. Bretylium and the internal standard, UM-360 (o-iodobenzyltrimethylammonium), are extracted and isolated as the iodide salts. Sodium benzenethiolate is added and the mixture heated to 100 degrees for one hour. This results in the formation of 2-bromobenzyl phenyl thioether and 2-iodobenzyl phenyl thioether, which can be separated and quantitated by gas chromatography. Good reliability and reproducibility can be obtained using electron-capture detection with quantities of bretylium as small as 1 ng.

Effects of chronic bretylium treatment on the sympathetic neuron and the smooth musculature of the rat

The effects of chronic i.p. injection of high doses of bretylium on sympathetic nerves on the smooth musculature of the vas deferens of adult and newborn rats were examined using fluorescence histochemistry, light and electron microscopy and organ bath physiological techniques. Bretylium treatment caused mitochondrial swelling, loss of cristae and the formation of electron-dense inclusions in the mitochondria of sympathetic neurons. However, neuron degeneration was not observed and fluorescent histochemical appearance of adrenergic neurons was normal. A small transient supersensitivity of the isolated vas deferens of bretylium-treated rats to noradrenaline, but not to acetylcholine, occurred. There was, however, considerable increase in the maximal contractile response to both noradrenaline and acetylcholine. In high calcium concentrations acetylcholine-induced contractions of vasa deferentia from bretylium-treated rats were significantly greater than control; there was no difference in magnitude of noradrenaline-induced contractions.

Molecular weight as a factor in the excretion of monoquaternary ammonium cations in the bile of the rat, rabbit and guinea pig

1. The excretion in the bile and urine of intraperitoneally injected (14)C-labelled monoquaternary ammonium or pyridinium cations was measured in bile-duct-cannulated rats (ten compounds) and in guinea pigs and rabbits (six compounds). 2. Seven of these, namely N-methylpyridinium, tetraethylammonium, trimethylphenylammonium, diethylmethylphenylammonium, methylphenyldipropylammonium, dibenzyldimethylammonium and tribenzylmethylammonium, were excreted largely unchanged in the bile and urine. 3. 3-Hydroxyphenyltrimethylammonium, 3-bromo-N-methylpyridinium and cetyltrimethylammonium were metabolized to an appreciable extent in the rat. 4. In intact rats intraperitoneally injected trimethylphenylammonium (mol.wt. 136) was excreted mainly in the urine, dibenzyldimethylammonium (mol.wt. 226) was excreted in roughly equal amounts in the urine and faeces, and tribenzylmethylammonium (mol.wt. 302) was excreted mainly in the faeces. The faecal excretion of these compounds corresponded to their biliary excretion in bile-duct-cannulated rats. About 3-4% of tribenzyl[(14)C]methylammonium was eliminated as (14)CO(2). 5. In rats the extent of biliary excretion of four cations with molecular weights in the range 94-164 was less than 10% of the dose, whereas that of five cations with molecular weights 173-302 was greater than 10%. These results and other data from the literature suggested that the molecular weight needed for the biliary excretion of such cations to an extent of 10% or more of the dose was about 200+/-50. Studies with six cations in guinea pigs and rabbits suggest that this value applies also to these species. 6. The results suggest that the threshold molecular weight for the appreciable (>10%) biliary excretion of monoquaternary cations is different from that for anions (Millburn et al., 1967a; Hirom et al., 1972b). With rats, guinea pigs and rabbits, no significant species difference was noted, whereas with anions there is a marked species difference.

Effectiveness of bretylium tosylate against refractory ventricular arrhythmias

Thirty patients with ventricular tachyarrhythmias, which had not responded to intensive therapy with up to five antiarrhythmic drugs, were treated with bretylium tosylate. All patients had recurrent ventricular tachycardia, and 12 had repeated episodes of ventricular fibrillation. In 17 patients the arrhythmias followed acute myocardial infarction. Bretylium was administered intramuscularly or intravenously, and most patients received 4-5 mg/kg every 6 hours. Eighteen patients responded satisfactorily to bretylium and suffered no further ventricular tachyarrhythmias while receiving the drug. Bretylium partially suppressed ventricular arrhythmic activity in five patients and had no beneficial effects in seven patients. Administration of bretylium soon after the development of arrhythmias and withholding of other antiarrhythmic drugs during bretylium therapy favored a good antiarrhythmic response. Hypotension followed bretylium administration in 19 patients but exceeded 20 mm Hg in only one patient. Transient initial increases in blood pressure and ventricular arrhythmic activity occurred in five and four patients, respectively. Six patients were discharged from the hospital on oral bretylium 600 mg every 6 hours, and all have remained free from major ventricular arrhythmias for up to 15 months. In these patients postural hypotension was a transient and parotid pain a persistent side effect.

Evaluation of bretylium tosylate for the treatment of premature ventricular contractions

In a controlled setting bretylium tosylate was evaluated for efficacy, toxicity, onset, and duration of action in eight patients with frequent premature ventricular contractions (PVC). Four patients received a single im dose of bretylium, 4 mg/kg, with before and after control days; the other four patients received bretylium, 2 and 4 mg/kg, on different days with before and between control days. PVC were quantified from stored continuous ECG tape recordings by an automated arrhythmia-detection system. Five patients had 50% or more reduction of PVC frequency with bretylium 4 mg/kg, and one with 2 mg/kg. Bretylium 4 mg/kg but not 2 mg/kg reduced mean PVC frequency by half beginning at the sixth hour and continuing for 12 hours. Hypotension began within 1 hour. Maximum fall in mean supine blood pressure was 17/6 mm Hg with 2 mg/kg, and 25/12 mm Hg with 4 mg/kg. Plasma bretylium concentration was maximum at about 1 hour with a mean elimination half-life of 10 hours. A controlled quantitative method for evaluation of antiarrhythmic drugs in man demonstrated that bretylium can be effective in suppressing PVC frequency. The dissociation between hypotensive and antiarrhythmic effects of bretylium suggested that its antiarrhythmic effect was independent of adrenergic neuronal blockade.