Polymorphic metabolism of flestolol and other ester containing compounds by a carboxylesterase in New Zealand white rabbit blood and cornea.

Flestolol, N(1,1-dimethyl-2-ureidocthyl)-2-hydroxy-3-(o-fluorobenzoyloxy++ +) propylamine, (F), is an ester containing an ultra short-acting beta blocker intended for the treatment of myocardial dysfunctions. In vitro incubation of F, procaine, chloroprocaine, and atropine with blood from different New Zealand White (NZW) rabbits resulted in a bimodal distribution (70% fast, 30% slow) of ester hydrolysis rates. Using F as a model substrate, bimodal hydrolysis rates were also observed in NZW rabbit cornea but not aqueous humor, iris-ciliary body complex and ocular tissues of pigmented rabbits. In addition, the bimodal distribution of esterase activity was not observed in blood from rats, dogs, and humans. Incubation of esters at various positions of the phenoxypropanolamine nucleus of beta blockers with NZW rabbit blood indicated structural specificity of the carboxylesterase in terms of unimodal or biomodal distribution of activity. These results strongly suggest that the carboxylesterase in NZW rabbit blood that hydrolyzes F and similar compounds is atropine esterase as described in the literature.

Determination of DMP 728, a IIb/IIIa receptor antagonist, in rat and dog plasma by high-performance liquid chromatography with fluorimetric detection.

A specific and sensitive HPLC assay for the determination of DMP 728 in dog and rat plasma has been developed. The method involves solid-phase extraction of DMP 728 and the internal standard from plasma using a C2 column. The extracted compounds are derivatized with benzoin under alkaline conditions. Using a mixture of acetonitrile and 0.1 M potassium phosphate buffer (25:75, v/v, pH 7.4) as mobile phase, the derivatized products are separated on a Regis semipermeable surface C8 column and monitored fluorometrically using 325 nm and 425 nm as excitation and emission wavelengths, respectively. The assay is linear from 2.5 to 1000 ng/ml in dog plasma and from 5 to 1000 ng/ml in rat plasma. The limit of quantitation is 2.5 ng/ml using 0.5 ml of dog plasma and 5 ng/ml using 0.5 ml of rat plasma. The assay has been used in pharmacokinetic studies of DMP 728 in dogs and rats.

Biochemical characterization of flestolol esterase.

The blood esterase that mediates the metabolism of flestolol, an ultra short-acting beta blocker, was characterized. Esterase activity occurred in plasma of human, dog, rat, and guinea pig and not in erythrocytes of the same species. The esterase activity was greatest in humans and guinea pigs followed by dogs and rats. Purified human serum cholinesterase was very active against flestolol while human serum albumin was slightly active. Human and bovine erythrocyte membrane acetylcholinesterases, electric eel acetylcholinesterase, human hemoglobin, dog, rat, chicken, and bovine serum albumin were all inactive. Esterase activity with flestolol was inhibited in human, dog, and rat blood by echothiophate, eserine, and sodium fluoride. Guinea pig blood esterase activity was inhibited by echothiophate and sodium fluoride, but not by eserine. Metabolic interaction studies indicated that succinylcholine, procaine, and chloroprocaine interfere with the metabolism of flestolol in human blood. Succinylcholine prolonged the in vitro half-life of flestolol in dog blood, but acetylcholine, procaine, and chloroprocaine had no effect. Flestolol did not affect the metabolism of procaine or chloroprocaine in human and dog blood. The metabolism rate of flestolol decreased in individuals with atypical, fluoride-resistant and silent forms of serum cholinesterase.

Mono- and bis(aminomethyl)phenylacetic acid esters as short-acting antiarrhythmic agents. 2.

The synthesis, antiarrhythmic activity, and blood hydrolysis properties of a series of mono- and bis(aminomethyl)phenylacetic acid esters related to a previously reported class Ic antiarrhythmic agent (ACC-9358) are described. Of the various oxa-, aza-, thia-, and carbacyclic esters initially prepared in the bis(pyrrolidinomethyl)-4-hydroxyphenylacetic acid series, the 1,4-benzodioxanyl-2-methyl(3q) and the thienyl-2-methyl(31) esters were evaluated in vivo for antiarrhythmic efficacy. In addition, a number of monoappended phenylacetic esters of 3q with or without the 4-hydroxy group were also prepared for evaluation of antiarrhythmic, lipophilic, and metabolic properties. Of these compounds, 3q possessed the most desirable pharmacological and pharmacokinetic profile.

An evaluation of 2-benzyl-1-naphthol (DuP 654) analogs as systemic anti-inflammatory agents.

DuP 654 (2-benzyl-1-naphthol) is a topically active anti-inflammatory agent that was evaluated in phase II clinical trials as an anti-psoriatic agent. The compound is a potent 5-lipoxygenase inhibitor and exhibits inhibitory activity against lipopolysaccharide-stimulated release of interleukin-1 from human monocytes. DuP 654 cannot be used as a systemic anti-inflammatory compound due to its rapid and extensive metabolism. Fifteen analogs were synthesized in an attempt to block the systemic route(s) of metabolism. The compounds were evaluated (IP and PO) in the rat carrageenan paw edema inflammation model with plasma samples taken at 1, 2, 3, and 4 hours post-dose. Substitutions at the 4- and/or 8-positions on the naphthol, and/or on the benzyl group of the DuP 654 molecule were unsuccessful in achieving an analog which displayed both oral activity in the inflammatory model and high plasma levels without manifesting toxicity. The low plasma levels of some analogs may indicate poor absorption, high volume of distribution, or that the substitution did not inhibit the high hepatic "first-pass" metabolism observed with DuP 654. Other compounds not studied but similar in structure to DuP 654 may exhibit rapid and extensive metabolism.

Ester derivatives of 2,6-bis(1-pyrrolidinylmethyl)-4-benzamidophenol as short-acting antiarrhythmic agents. 1.

In an effort to find a replacement for the iv antiarrhythmic drug lidocaine having reduced systemic and central nervous system effects, activity against supraventricular as well as ventricular arrhythmias, and a biological half-life of less than 15 min, derivatives of the orally active class Ic clinical agent 2,6-bis(1-pyrrolidinylmethyl)-4-benzamidophenol, 1 (ACC-9358), were synthesized and tested. Compounds with ester groups attached to the phenyl ring were either weakly active or toxic. Replacement of the formanilide function with alkyl esters afforded compounds with antiarrhythmic activity in the range of 1. When the ester carboxyl was separated from the bis(aminomethyl)phenol by methylene units, very short half-lives were observed in human blood. In general, these compounds also had low lipophilic character.

Species differences in the stereoselective hydrolysis of esmolol by blood esterases.

The stereoselective hydrolysis of esmolol was examined in blood from several species including humans. Blood esmolol esterase activity was in the order of guinea pigs greater than rats greater than rabbits greater than dogs greater than rhesus monkeys greater than humans. Dog and rat blood esterases hydrolyzed the (-)-enantiomer of esmolol faster than the (+)-enantiomer whereas rhesus monkey, rabbit, and guinea pig blood esterases hydrolyzed the (+)-enantiomer faster. Human blood esterases did not demonstrate stereoselectivity. Dog liver esterases also showed stereoselectivity towards the (-)-enantiomer but dog skeletal muscle esterases did not. Studies in mongrel dogs indicated that during esmolol infusions the concentration ratio of (-)-esmolol/(+)-esmolol was approximately 0.85. After termination of the esmolol infusion the (-)/(+) concentration ratio continuously decreased until (-)-esmolol was no longer quantifiable. These results indicate that stereoselective hydrolysis of esmolol occurs in vitro and in vivo.

Biochemical properties of blood esmolol esterase.

The blood esterase mediating the hydrolysis of esmolol was characterized in several different species including man. In contrast to most ester-containing drugs, hydrolysis of esmolol was mediated by an esterase in the cytosol of red blood cells (RBC) in man and dogs and not in plasma or RBC membrane. Species differences in the esterase activity existed. Guinea pig and rat blood esterase activities were much greater than those in the dog followed by those in man. In addition, the esterase activity in rat and guinea pig blood was localized in plasma and not in RBC. Purified human serum cholinesterase, human RBC membrane acetylcholinesterase, human hemoglobin, human carbonic anhydrases A and B, and human and dog serum albumin were all inactive against esmolol. Esmolol esterase activity in human and dog blood was inhibited by sodium fluoride, EDTA, and p-hydroxymercuribenzoate, but not by echothiophate, eserine, and acetazolamide. In contrast, echothiophate and sodium fluoride, but not eserine, inhibited the esterase activity in rat and guinea pig plasma. Metabolic interaction studies indicated that acetylcholine, succinylcholine, procaine, and chloroprocaine did not interfere with the metabolism of esmolol by human and dog blood. Based on the results, it appeared that an arylesterase in human and dog RBC cytosol mediated the hydrolysis of esmolol while an aliphatic esterase mediated the hydrolysis of esmolol in guinea pig and rat plasma.

[(Arylcarbonyl)oxy]propanolamines. 1. Novel beta-blockers with ultrashort duration of action.

Novel [(arylcarbonyl)oxy]propanolamines were synthesized and investigated as potential ultrashort-acting beta-adrenergic receptor blockers. Many of these analogues exhibited good potency and short duration. The N-ureidoalkyl analogue 85 (ACC-9089) has a potency equal to propranolol and a duration of action of about 21 min in the dog. It has been selected as a candidate for further clinical study. Structure-activity relationships and structure-duration relationships for these new beta-blockers are also discussed.

Age-related pharmacokinetics of N-acetylprocainamide in rats.

The pharmacokinetics of N-acetylprocainamide, administered orally or intravenously, were studied in 3-, 6-, and 12-month-old rats using a two-way crossover study design. At 3, 6, and 12 months of age, the half-life values of N-acetylprocainamide were 1.66, 1.82, and 2.29 hr, respectively; the apparent volumes of distribution were 4.75, 3.35, and 1.98 liter/kg, respectively. The elimination rate constant, clearance, and absolute bioavailability of the drug (determined by AUC measurements and the amounts excreted unchanged in the urine) decreased significantly with age. The rate of absorption remained unchanged. The amounts of N-acetylprocainamide in the liver and kidneys were significantly higher in the 12-month-old animals. These results clearly demonstrate a significant alteration with age in the bioavailability, distribution, and elimination of N-acetylprocainamide in rats. In long-term toxicity studies of this and other drugs that show age-dependent pharmacokinetics, an adjustment in the chronically administered dose is essential.

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 [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.

Tissue distribution of N-acetylprocainamide in rats.

The purpose of this study was to determine the distribution of N-acetylprocainamide (NAPA) in heart, kidney, and liver tissues of rats and their relationship to the plasma concentration after intravenous administration of the drug (100 mg/kg) to 24 Charles River rats. A specific HPLC procedure was used. The plasma and tissue concentrations of NAPA declined biexponentially in parallel, with an elimination half-life of about 1.8 hr. The equilibrium between plasma and the organs tested in this study was attained within 5 min. The tissue/plasma concentration ratio remained constant throughout the study. The tissue/plasma ratios for heart, kidney, and liver were 2.1, 7.9, and 2.4, respectively. The data indicate that: a) these organs have greater affinity to NAPA than do plasma proteins, and b) plasma concentrations may be reliable measures of the therapeutically effective concentrations at the site of action, i.e., the heart tissues.