LC/MS/MS analysis of quaternary ammonium drugs and herbicides in whole blood.

Quaternary ammonium drugs (atracurium, bretylium, edrophonium, ipratropium, mivacurium, neostigmine, pancuronium and rocuronium) and herbicides (difenzoquat, diquat and paraquat) in human whole blood were analysed by LC/MS/MS with positive electrospray ionisation (ESI), following extraction with Bond Elut LRC-CBA cartridges. Internal standards were benzyldimethylphenylammonium chloride monohydrate and ethyl viologen for drug and herbicide analysis, respectively. Ion-pair chromatography used heptafluorobutyric acid (15 mM)-ammonium formate (20 mM) buffer adjusted to pH 3.30 with formic acid and a linear gradient from 5 to 90% methanol run over 18 min. Recoveries ranged from 79.7 to 105.1%, detection limits were between 3.6 and 20.4 ng/ml and the intra- and inter-day precisions were less than 18.6% at a concentration of 10 ng/ml. The method was applied to a case of accidental paraquat poisoning in which the concentration of paraquat in blood was 0.64 mg/l, which is within the range associated with fatal paraquat poisoning.

Clinical pharmacokinetics of bretylium.

Bretylium is a class III antiarrhythmic agent which is used for the management of serious and refractory ventricular tachyarrhythmias. It exhibits a complex pharmacokinetic profile which is poorly understood. The drug is poorly absorbed following oral administration, and its oral bioavailability is in the region of 18 to 23%. Peak plasma concentrations occur at 1 to 9 hours after oral ingestion, and following oral doses of 5 mg/kg average 76 ng/ml, which is 28-fold lower than those achieved after equivalent intravenous doses. Approximately 75% of a bretylium dose is absorbed within 24 hours of intramuscular administration. Peak plasma concentrations occur at 30 to 90 minutes after intramuscular administration and range from 670 to 1500 ng/ml in subjects receiving 4 mg/kg. Bretylium is negligibly bound to plasma proteins (1-6%). Although drug tissue concentrations have not been reported in humans, high values for the apparent volume of distribution suggest extensive tissue binding. In animals, bretylium is progressively taken up by the myocardium over a period of 12 hours, and at 12 hours after bolus administration, myocardial concentrations exceed plasma concentrations 6 to 12 times. It is also avidly taken up by adrenergic nerves in animals. Bretylium is almost entirely cleared by the renal route and its total body clearance is closely correlated with renal clearance. Available data suggest that bretylium exhibits a complex pharmacokinetic profile which has been described by a 3-compartment model in subjects receiving intravenous dosing. The terminal elimination half-life ranges from 7 to 11 hours following oral, intramuscular and intravenous administration, and renal clearance is about 600 ml/min after intravenous administration.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Influence of ion-pair formation on the pharmacokinetic properties of drugs. Pharmacokinetic interactions of bretylium and hexylsalicylic acid in rabbits.

The simultaneous i.v. administration of equimolar doses of bretylium and hexylsalicylic acid results in an increase in plasma area under the curve value of both substances in comparison with their separate administration. The higher plasma levels of both compounds were associated with a reduced renal excretion and an increased biliary elimination. However, the increase in biliary excretion did not compensate for the reduced elimination of bretylium and hexylsalicylic acid via the kidney. The results presented in this paper give further evidence that ion-pairing in-vivo may result in altered pharmacokinetics of drugs particularly due to changes in biliary or renal excretion.

Influence of the ion-pair-formation on the pharmacokinetic properties of drugs. Part 5: Influence of ion-pair-formation on elimination of bretylium and hexylsalicylic acid in rats.

Following i.v. administration of the hydrophilic drug bretylium (1) and the lipophilic hexylsalicylic acid (2) in rats the plasma levels of 2 were increased due to an increased intestinal reabsorption of 2. Under these conditions the biliary eliminated amount of 2 was 8 times higher than that following the administration of 2 alone. The eneteroheptic circulation of 2 was found to be interrupted following i.v. administration of 1 and 2 and additional oral administration of an anionic exchanger. Then the plasma levels of 2 were not influenced by 1. On other hand the plasma levels of 2 appear to be too low in order to influence those of 1.

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.

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.

Serial electrophysiologic effects of bretylium in man and their correlation with plasma concentrations.

The serial electrophysiologic effects of bretylium were studied in 10 patients undergoing cardiac catheterization before giving the drug, at the end of bretylium tosylate-loading infusion (5 mg/kg/15 min), and after 1 h of intravenous drug maintenance (1.5 mg/min). Mean blood pressure increased during drug loading from 93.6 +/- 10.9 mm Hg to 121.1 +/- 16.2 mm Hg (p less than 0.01, t = 15 min) but returned toward control (100.9 +/- 18.7 mm Hg, p = NS) during drug maintenance (t = 75 min). Small changes in PR, QRS, QTc, AH, and HV intervals during spontaneous and paced rhythms were not significant. Comparison of the control electrophysiologic study with early and late postdrug studies showed no significant changes in corrected sinus node recovery times and in Wenckebach cycle lengths, but small decreases in refractory periods occurred. After drug loading, decreases in mean effective refractory periods of atrium, AV node, and right ventricle of 12, 2, and 16 ms, respectively, occurred (p = NS); during drug maintenance (t = 75 min), these refractory periods had decreased with respect to control by 21, 36, and 13 ms, respectively (p less than 0.05, 0.05, and 0.01). Functional refractory period of the AV node decreased at 75 min by 31 ms (p less than 0.01). The observed shortening of refractory periods contrasts with the direct effects of bretylium in isolated ventricular muscle and Purkinje fibers, which consist of prolongation of effective refractory periods and action potential duration. Thus, indirect (adrenergic) effects may be more important to overall clinical electrophysiologic actions not only acutely during loading but also during at least the first 60-90 min of maintenance therapy, which spans the expected time of initial clinical antifibrillatory response.

Bretylium decreases and verapamil increases defibrillation threshold in pigs.

BACKGROUND: Patients with ischemic heart disease may require antianginal and/or antiarrhythmic regimes. These patients may also be candidates for implantable defibrillators. The effects of antiarrhythmics, such as bretylium, or calcium antagonists, such as verapamil, nifedipine, or diltiazem on internal defibrillation efficacy have been inconsistent or are unknown. METHODS AND RESULTS: The effects of bretylium and verapamil on the energy requirements for ventricular defibrillation threshold (DFT) were determined in 92 open-chest anesthetized pigs. Triplicate DFTs were determined before and after intravenous administration of saline or one of four doses of verapamil, or saline or one of three doses of bretylium, in a balanced random order. Bretylium elicited a dose dependent reduction of DFT (F = 2.72 at 3 degrees and 36 degrees of freedom). DFT was significantly reduced with the highest dose of bretylium, (from 5.9 +/- 0.6 J to 4.7 +/- 0.6 J, mean +/- S.E.M.; P < 0.01). However, cardiac massage was sometimes needed at this dose due to low blood pressure immediately after defibrillation. In contrast, there was a positive correlation between DFT and serum verapamil concentration (r = 0.54, P < 0.001). The highest dose of verapamil significantly increased DFT (from 6.3 +/- 0.6 J to 8.2 +/- 1.1 J; P < 0.05), at a serum verapamil concentration of 86.6 +/- 6.8 ng/mL. CONCLUSIONS: These data indicate that bretylium decreases while verapamil increases the minimum energy requirement for internal defibrillation. Caution is warranted in patients who may be hemodynamically comprised and may be candidates for bretylium therapy or in patients who have marginal DFT value who might be candidates for verapamil therapy.