G. L. Garrison

Electrophysiological and inotropic characterization of a novel class III antiarrhythmic agent, GLG-V-13, in the mammalian heart

GLG-V-13, a novel 3,7-diheterabicyclo(3.3.1)nonane, was examined both in vivo and in vitro to characterize its electrophysiological, hemodynamic, and inotropic properties. In anesthetized guinea pigs, GLG-V-13 [0.5-500 micrograms/kg intravenously (i.v.), n = 6] lengthened the epicardial monophasic action potential (MAP) duration, the atrioventricular (AV) conduction time and the RR interval in a dose-dependent manner. At the highest dose, these variables were increased by 30, 13, and 23%, respectively. No significant effects were noted on QRS duration or blood pressure (BP). In rabbit atrial and papillary muscle preparations, GLG-V-13 (0.32-3.2 mg/L) did not exert a negative inotropic action and in isolated rabbit cardiomyocytes the agent blocked the rapidly activating delayed rectifier K+ current (IKr, EC50 = 48 micrograms/L). In 10 intact anesthetized mongrel dogs, the left ventricular (LV) endocardial MAP was measured during atrial pacing before and after administration of GLG-V-13 (3 and 6 mg/kg i.v.). As compared with the drug-free state, the agent induced a significant prolongation of the MAP at all pacing frequencies (2.0-4.5 Hz). In 15 anesthetized dogs studied 1-4 days after two-stage ligation of the left anterior descending coronary artery (LAD), the antiarrhythmic/proarrhythmic potential of GLG-V-13 was compared with that of lidocaine. ECG, His bundle, LV (IZepi), and composite and normal zone composite electrograms were recorded. Programmed electrical stimulation (PES) and burst pacing (4.0-7.0 Hz) were delivered to the right ventricular outflow tract. In the drug-free state, sustained monomorphic ventricular tachycardia (SMVT) was inducible in 6 dogs (6 of 15). After lidocaine, SMVT was induced in 7 other dogs (13 of 15). GLG-V-13 prevented induction of SMVT in 5 of 6 dogs; a proarrhythmic action was noted in 1 dog only. GLG-V-13 slowed the heart rate (HR), increased the AH and the HV intervals, prolonged the paced (2.5 Hz) QT interval, and increased the ventricular effective refractory period (VERP). These effects were associated with 2:1 block of late potentials in the IZepi electrograms, a phenomenon also observed during rapid atrial pacing (2.5-3.5 Hz), suggestive of a marked prolongation of refractoriness in the ischemically damaged myocardium. In light of the recent Cardiac Arrhythmia Suppression Trial (CAST) study, the antiarrhythmic efficacy, together with the low proarrhythmic potential and lack of cardiodepressant properties of GLG-V-13, may merit further investigation of this novel class III antiarrhythmic agent.

Metabolism and metabolite pharmacokinetics of BRB-I-28, a class Ib antiarrhythmic agent

SummaryThe metabolism of BRB-I-28 (7-benzyl-3-thia-7-azabicyclo[3.3.1]nonane), a novel class Ib antiarrhythmic agent, was characterized in vivo in dogs and rats and in vitro with rat liver microsomal preparations containing a NADPH-generating system. In dogs, rats and the in vitro hepatic microsomal oxidation system, BRB-I-28 was extensively metabolized to form 7-benzyl-3-thia-7-azabicyclo [3.3.1]nonane-3-oxide (I), a major metabolite. The metabolite I was produced via S-oxidation, presumably by the hepatic P-450 system. Formation of a minor metabolite, 7-benzoyl-3-thia-7-azabicyclo[3.3.1]nonane (II) via the oxidation of the benzylic site was also identified in rats. Following intravenous and oral administration of BRB-I-28 to dogs, the plasma concentration of major metabolite I could be best described by a 1-compartmental model. The plasma AUC of metabolite I was 20% (i.v.) and 179.4% (oral) of that of the parent BRB-1-28, respectively, suggesting that BRB-I-28 was metabolized significantly by the first pass effect following oral administration. Extensive metabolism of BRB-I-28 to form metabolites I and II, which have demonstrated much lower antiarrhythmic activities, further supports previously observed pharmacodynamic and pharmacokinetic findings.

High-performance liquid chromatographic determination of SAZ-VII-23, a novel antiarrhythmic agent, in dog plasma and urine

Abstract A HPLC method has been developed to determine the concentrations of SAZ-VII-23 (3-benzoyl-7-isopropyl-3,7-diazabicyclo[3.3.1]nonane HClO4), a novel antiarrhythmic agent, in dog plasma and urine. Plasma treated with acetonitrile and alkalinized urine were extracted with chloroform- propanol (9:1). An aliquot was injected on to HPLC system using a C6 reversed-phase column and acetonitrile-methanol-37.5 mM phosphate buffer, pH 6.8 (28.5:28.5:43 v/v) containing 4.0 mM triethylamine as mobile phase. Detection wavelength was 255 nm. The linear range were 0.04–8 μg/ml, and the lower limit of quantitation was 0.04 μg/ml in plasma and urine, respectively. The method was applied to determine plasma and urine concentrations and preliminary pharmacokinetic profiles of SAZ-VII-23 in a dog.

High-performance liquid chromatographic determination of BRB-I-28, a novel antiarrhythmic agent, in dog plasma and urine

A sensitive reversed-phase high-performance liquid chromatographic (HPLC) technique with ultraviolet detection has been developed to determine the concentration of BRB-I-28 (I), a novel antiarrhythmic agent, in dog plasma and urine. The mobile phase was acetonitrile-methanol-37.5 mM phosphate buffer, pH 6.8-triethylamine (50:50:75:0.1, v/v). The compound was extracted from dog plasma and urine with chloroform after alkalinization with sodium hydroxide. The extraction recovery was 83% from plasma and 84% from urine. Good linearity (r > 0.996) was observed throughout the ranges 0.1-12.0 micrograms/ml (plasma) and 0.1-8.0 micrograms/ml (urine). Intra- and inter-assay variabilities were less than 4%. The lower limit of quantitation was 0.08 microgram/ml in either plasma or urine. HPLC analysis of plasma and urine samples from a dog treated with I has demonstrated that the method was accurate and reproducible.

Determination of GLG-V-13, a Novel Antiarrhythmic Agent, in Plasma and Urine by High-Performance Liquid Chromatography

Abstract A sensitive reversed-phase HPLC technique with UV detection has been developed to determine the concentration of GLG-V-13 (3-[4-(1H-imidazol-1-yl)benzoyl]-7-isopropyl-3,7-diazabicyclo[3.3.1]nonane dihydroperchlorate) (I), a novel combined class I and class III antiarrhythmic agent, in dog plasma and urine. Alkalinized plasma and urine samples were extracted with chloroform, and the extracts were reconstituted in methanol. An aliquot was injected on to a Waters HPLC system with a 250 × 4.6 mm Ultramex 5 C6 analytical column (5 μm) and 30 × 4.6 mm Ultramex 5 C6 guard column (5 μm). The elute was detected by a UV detector at 256 nm. Acetonitrile-methanol-37.5 mM phosphate buffer. pH6.8 (27:27:46 v/v) containing 3.6 mM triethylamine was used as the mobile phase. The average extraction recovery was 89% from plasma and 93% from urine. Good lineary (r > 0.999) was observed throughout the range of 8–8000 ng/ml in plasma and in urine with the quantitation limit of 8 ng/ml. Intra- and inter-assay variabili...

Disposition of BRB-I-28 (7-benzyl-7-aza-3-thiabicyclo[3.3.1]nonane hydroperchlorate), a Novel Antiarrhythmic Agent

SummaryThe aim of this study was to characterise the pharmacokinetic disposition and tissue distribution of BRB-I-28 (7-benzyl-7-aza-3-thiabicyclo[3.3.1]nonane hydroperchlorate) in rats. The pharmacokinetic disposition was studied by collecting blood samples before and at frequent intervals after intracardiac or oral administration of 14C-labelled BRB-I-28. Two-compartment and 1-compartment pharmacokinetic models were used to describe blood concentration-time profiles after intracardiac and oral administration, respectively. After intracardiac administration, the half-life of elimination (t1/2β)from blood ranged from 4.66 to 9.91 hours and the apparent volume of distribution (Vd(area)) ranged from 3.131 to 6.239 L/kg. Oral dosing resulted in rapid and extensive absorption (bioavailability ± 80%). Distribution of radioactivity into heart, kidney, brain, liver, and perirenal fat was measured by sacrificing rats at various time intervals after oral administration of 14C-labelled BRB-I-28. Extensive distribution of radioactivity occurred in highly perfused organs, particularly liver, kidney and heart. However, levels of radioactivity in brain were low.

Simultaneous determination of a novel antiarrhythmic agent, 7-benzyl-3-thia-7-azabicyclo[3.3.1]nonane and its sulfoxidation metabolite in plasma and urine by HPLC

Abstract A HPLC method was developed for the simultaneous determination of the concentrations of 7-benzyl-3-thia-7-azabicyclo[3.3.1]nonane (I) as the hydrochloride and the corresponding sulfoxide (II), the major metabolite, in dog plasma and urine. Plasma and urine samples were alkalinized and extracted with chloroform. An aliquot was injected on to a HPLC system with a C6 reversed-phase column and an UV detector. Acetonitrile-methanol-37.5 mM phosphate buffer, pH 6.8 (28:28:44 v/v) containing 4.0 mM triethylamine was used as a mobile phase. The compounds I and II were detected at 261 nm. The extraction recovery for I and II was 85% and 94% from plasma and 89% and 91% from urine, respectively. Good linearity (r<0.994) was observed throughout the range of 0.1–10.0 μg/ml for I and 0.04–10 μg/ml for II in plasma and in urine. Intra- and inter-assay variabilities were less than 8%. The accuracy of this method was < 95% for both compounds, and the limits of quantitation were 0.08 μg/ml for I and 0.03 μg/ml for...

The acute and subchronic toxicity of BRB-I-28, a novel class Ib antiarrhythmic agent, in CD-1 mice.

The acute and subchronic toxic effects of BRB-I-28 (7-benzyl-3-thia-7-azabicyclo[3.3.1]nonane HCl), a novel class Ib antiarrhythmic agent, were investigated in male and female mice. The estimated oral LD(50) for BRB-I-28 was 128 mg/kg (male mice) and 131 mg/kg (female mice). In subchronic oral studies, four groups of mice (15/sex/group/dose) were fed daily with diets containing BRB-I-28 for 90 consecutive days. The equivalent daily doses were approximately 0, 16, 32, 76 (male) and 0, 18, 37, 89 mg/kg (female). All mice survived. Food consumption per day was decreased, but water consumption per day was increased (in a non-dose-dependent manner). However, both mean body weight and mean body weight gain were not significantly changed as were true for hematological and clinical chemistry profiles, except for serum Na(+) concentration (male) and serum K(+) concentration in male and female mice (high dose levels). Hepatocellular necrosis occurred in male and female mice (in a dose-dependent fashion). Renal cortical vacuoles and myocardial necrosis with low numbers of lymphocytic infiltrations were present in female mice (middle and high doses). Lesions in the liver, kidney and heart were mild with (very small) changes in serum biochemical values. These data suggest that BRB-I-28 has limited toxic potential, and coupled with low proarrhythmic and other desirable cardiovascular effects, makes BRB-I-28 worthy of further development.

Electrophysiologic actions of d,l-sotalol and GLG-V-13 in ischemically injured canine epicardium.

The electrophysiologic actions of the class III antiarrhythmic agents, GLG-V-13 and d,l-sotalol, were examined in superfused normal and ischemically injured epicardium. Both drugs produced concentration and reverse-use dependent prolongation of the action potential duration in normal myocardium without altering resting potential, action potential amplitude, or Vmax. Both drugs increased the slope of restitution curves in normal epicardium but prevented action potential alternans at short cycle lengths. The response of superfused ischemically injured left ventricular epicardium to drug 4 days after coronary artery ligation was determined by the extent of ischemic injury, with no electrophysiologic changes produced within epicardial cells characterized by prominent action potential shortening and no further action potential shortening with pacing. Cells demonstrating less severe injury (as evidenced by less severely depressed action potential amplitudes, Vmax, and action potential durations) retained a limited ability to respond to drug administration with action potential prolongation. A concentration-dependent, increased disparity of action potential duration was observed concurrent with the ability of single premature stimuli to induce monomorphic tachycardia. The present data demonstrate a variable response of ischemically injured canine epicardial cells to action potential prolongation with GLG-V-13 and d,l-sotalol, facilitating localized reentry in vitro, despite a failure of the same drugs to facilitate reentrant tachycardia in vivo.

Pharmacokinetics and Plasma Protein Binding of BRB-I-28, a Novel Antiarrhythmic Agent, in Dogs

SummaryThe pharmacokinetics and plasma protein binding of BRB-I-28, a novel antiarrhythmic agent, were investigated in dogs. The plasma concentration-time profile of BRB-I-28, following an intravenous bolus dose of 10 mg/kg, can be adequately described by a 2-compartment open model. The mean volume of distribution at steady-state (Vdss) was 8.759 L/kg, the mean total systemic clearance (CL) was 1.289 ml/h/kg, and the mean elimination half-life (t½β) was 4.645 hours. Following intravenous administration, approximately 1.85% of the dose was excreted in the urine (0 to 48 hours) as parent drug. Changes in plasma concentrations, after oral administration of BRB-I-28 20 mg/kg, were best described by a 1-compartment open model. BRB-I-28 was rapidly absorbed (tmax = 1.22 hours and Cmax =1.59 mg/L) with a rapid elimination rate (t½kel = 1.583 hours). Oral bioavailability was estimated to be 44.5%. Only 2.56% of the 20 mg/kg oral dose was excreted via the urine (0 to 48 hours). In vitro binding of BRB-I-28 to plasma protein was 29.7 ± 10.3% at concentrations of 4 to 16 mg/L. In vivo binding of BRB-I-28 to plasma protein was 24.0 ± 8.7%. Extensive distribution of BRB-I-28 may be due to its low binding to plasma protein. Low oral bioavailability and limited elimination of free parent BRB-I-28 in urine indicates that BRB-I-28 may undergo extensive metabolism, which may be the reason for its short duration of pharmacological effects.