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Biomedical subjects

R A Ronfeld

Publications and source records attributed to R A Ronfeld.

At least 19 recordsLinked to original sources
PubMed1997

Pharmacokinetics of sertraline and its N-demethyl metabolite in elderly and young male and female volunteers.

A nonblinded study was conducted to compare the pharmacokinetic properties of the selective serotonin reuptake inhibitor sertraline in 22 young (aged 18 to 45 years) and 22 elderly (> 65 years) volunteers, of whom half were male and half were female. In this study, sertraline was administered at a dosage of 200mg once daily (the maximum recommended daily dosage) for 21 days after upward dosage titration from 50 mg/day over a 9-day period. Thus, this study was designed to measure the effect of age and gender on the pharmacokinetic properties of sertraline at the maximum dosage recommended for clinical use. The terminal elimination half-life (t1/2 beta ) of sertraline was similar in young females, elderly males and elderly females (mean t1/2 beta ranged from 32.1 to 36.7 hours in these groups) but shorter (22.4 hours) in the young males. The mean maximum plasma sertraline concentration (Cmax) and the mean steady-state area under the plasma concentration-time curve from time zero to 24 hours postdose (AUC24) were also similar between the young females, elderly males and elderly females, but were approximately 25% lower in the young males. The time to Cmax was unaffected by age or gender and ranged from 6.4 to 6.9 hours. N-Demethylsertraline is the principal metabolite of sertraline and does not contribute significantly to its serotonergic actions. The mean values for N-demethylsertraline trough plasma concentrations, AUC24 and Cmax were comparable in elderly males and females and young females but lower in young males. The ratios of mean AUC24 and Cmax for N-demethylsertraline to the AUC24 and Cmax for sertraline were similar between the 4 groups.

1-Naphthylamine↗
PubMed1997

Sertraline. Chronopharmacokinetics and the effect of coadministration with food.

Two nonblinded single-dose randomised 3-way crossover studies were conducted in healthy male volunteers to determine the effect of the time of administration (morning vs evening) and the effect of food on the pharmacokinetics of sertraline tablets. There were no significant treatment effects on the mean area under the plasma concentration-time curve (AUC), mean peak plasma sertraline concentration (Cmax), mean time to reach Cmax (tmax), mean terminal elimination half-life, or the mean elimination rate constant in either study. The results of these 2 studies show that the bioavailability and elimination of sertraline tablets are not influenced by the time of administration or administration with or without food. Thus, sertraline tablets offer the flexibility of morning or evening administration, to patients in the fasting or nonfasting state.

1-Naphthylamine↗
PubMed1997

Disposition and metabolism of tenidap in the rat.

Tenidap is a new antirheumatic drug currently undergoing clinical evaluation. It inhibits production and activity of cytokines in vivo and causes significant reductions in plasma markers of disease activity in rheumatoid arthritis. After the oral administration of C-14 labeled tenidap, bile, urine and plasma were examined by HPLC and atmospheric pressure tandem mass spectrometry. Label is excreted primarily in bile/feces and the remainder in urine, with good recoveries. Numerous metabolites were identified and the structures of most were confirmed by comparison with authentic synthetic samples. Hydroxylation in several positions on both the oxindole and thienyl rings of tenidap represents the major routes of metabolism; most of these metabolites are subsequently conjugated. The glucuronide of 5'-hydroxytenidap, excreted primarily in bile, is the major metabolite, constituting about one third of the oral dose recovered. Other pathways include dihydroxylation and methoxylation on the thienyl ring. An unusual reduction of hydroxytenidap took place, resulting in the formation of a novel thiolactone analog. Anaerobic incubation with rat cecal contents generated the thiolactone metabolite, suggesting the involvement of gut microflora.

Animals↗
PubMed1994

Pharmacokinetics of the aldose reductase inhibitor, zopolrestat, in humans.

The pharmacokinetics of zopolrestat, an aldose reductase inhibitor that may be useful for the treatment of complications of diabetes, have been investigated using oral doses ranging from 50 to 1200 mg administered to healthy male volunteers. In a single-dose study, Cmax, AUC(0-48), and urinary elimination of zopolrestat increased linearly with increasing dose. The amount of zopolrestat excreted unchanged in the urine within 48 hours ranged from 34 to 45% of the administered dose. Renal clearance ranged from 2.6 to 5.6 mL/min, and appeared to decrease as the dose was increased. In a 2-week multiple dose study, the mean steady-state minimum and maximum plasma concentrations, Cmin and Cmax, were 91.5 and 196 micrograms/mL for subjects administered 800 mg/day, and 131 and 281 micrograms/mL for subjects administered 1200 mg/day. Steady-state AUC(0-24) was also dose proportional. The mean steady state half life of about 30.3 hours was consistent with the observed 2.2-fold accumulation in plasma. Apparent oral clearance (Clpo) was 5.2 mL/min, and apparent volume of distribution (Vdss/F) was 12 L. Mean renal clearance was 2.2 mL/min, and approximately 45% of the administered dose was excreted into the urine at steady state. There was no effect of food consumption during dosing on the extent of absorption of zopolrestat. In in vitro studies, extensive, concentration-dependent binding of zopolrestat to plasma proteins was observed. These data indicate that once-daily dosing of zopolrestat will provide suitable exposure in the treatment of diabetic complications.

Administration, Oral↗
PubMed1991

Pharmacokinetics of zopolrestat, a carboxylic acid aldose reductase inhibitor, in normal and diabetic rats.

The pharmacokinetics of zopolrestat, a carboxylic acid aldose reductase inhibitor, were examined in normal male rats dosed intravenously at 2 mg/kg and in normal and streptozotocin-diabetic male rats after oral administration at 50 mg/kg. After oral dosing, Cmax was 127 micrograms/ml for normal rats and 144 micrograms/ml for diabetic rats. AUC(0-infinity), however, was lower for diabetic rats than for normal rats and plasma half-life was longer in normal rats (8.0 vs 6.6 hr). Half-lives of zopolrestat in nerve, kidney, and lens were longer than plasma half-life and were similar for both diabetic and normal rats. Less than 2% of the dose was excreted in the urine as unchanged zopolrestat during the 48-hr period following dosing by diabetic or normal rats. Protein binding of zopolrestat was less extensive in plasma from diabetic rats than in plasma from normal rats. Similar kinetics were observed in diabetic animals receiving five daily doses of zopolrestat at 50 mg/kg/day. There was no plasma or liver accumulation of zopolrestat at steady state, consistent with the observed half-lives. However, zopolrestat did accumulate in nerve, kidney, and lens to varying degrees during multiple dosing, reflecting the longer half-lives of zopolrestat in these tissues.

Administration, Oral↗
PubMed1983

Effect of external cardiopulmonary resuscitation on lidocaine pharmacokinetics in dogs.

Lidocaine pharmacokinetics were studied in five fibrillated dogs undergoing external cardiopulmonary resuscitation (CPR) and five comparable control dogs. All animals were anesthetized with sodium pentobarbital and their electrocardiogram, arterial blood pressure, left ventricular pressure and carotid blood flow were monitored continuously. All dogs received a 2 mg/kg i.v. bolus dose of lidocaine. Multiple blood samples from venous, arterial, left ventricular and right atrial sites were obtained for determination of blood lidocaine concentration. At 60 min, the dogs were sacrificed. Lung, liver, kidney, brain, skeletal muscle and heart tissue samples were collected. There were dramatic differences between the control and CPR groups in arterial pressure, left ventricular pressure and carotid blood flow. In the CPR dogs, lidocaine blood concentrations for the entire 60 min were significantly higher than the control dogs and lidocaine clearance was reduced at least by 8-fold. A comparison of extraction ratios across skeletal muscle demonstrated that the phase of tissue uptake was prolonged in the CPR group. In each of the tissue samples, significantly higher tissue concentrations were observed in the CPR group. The results of our study show that lidocaine disposition is greatly altered during CPR and this is most likely due to a tremendous reduction of cardiac output and blood flow during CPR.

Animals↗
PubMed1982

On the kinetics and dynamics of tocainide and its metabolites.

The kinetics of tocainide, a new antiarrhythmic, and two of its metabolites, lactoxylidide (LX) and tocainide carbamoyl glucuronide (TG), were examined in patients given tocainide for 7 days following an acute myocardial infarction. In these patients kinetics were much the same as those reported for volunteers and for patients treated with tocainide for chronic extra ventricular beats. Mean half-life for tocainide, LX, and TG were 13.6, 29.1 and 13 hr. At steady state mean metabolite to tocainide ratios in serum were 0.48 for LX and 0.28 for TG. Using animal models, we examined the relative antiarrhythmic, direct cardiac, and central nervous system (CNS) effects of tocainide and LX. LX, the deaminated alcohol metabolite, had no antiarrhythmic, direct cardiac, or CNS toxic effects. These data suggest that tocainide, unlike many antiarrhythmic drugs, has no active metabolites.

Aged↗
PubMed1981

New antiarrhythmic agents. 4. 1'-(Aminoalkyl)-1,2,3,4-tetrahydronaphthalene-1-spiro-3'-pyrrolidine-2',5'-dione derivatives.

A series of 33 1'-(Aminoalkyl)-1,2,3,4-tetrahydronaphthalene-1-spiro-3'-pyrrolidine-2',5'-dione derivatives was tested for antiarrhythmic and toxic effects in mice and dogs. In mice, 31 compounds produced some protection against chloroform-induced tachyarrhythmias at subcutaneous doses of 100 mg/kg, and 6 compounds produced no detectable toxicity at doses protecting 80% or more of the animals. Seven of the more potent and nontoxic derivatives were tested in dogs with surgically induced myocardial infarctions. All produced distinct antiarrhythmic effects at doses considerably lower than doses of lidocaine or tocainide producing comparable effects. The principal toxic effects observed in dogs were convulsion and depression of intracardiac conduction; they occurred generally at higher doses than those leading to antiarrhythmic effect. Several compounds also suppressed digitalis-induced arrhythmias in anesthetized dogs. Half-lives and total body clearance in dogs were determined for three compounds; two had half-lives comparable to that of tocainide, a long-acting, orally active antiarrhythmic agent, in clinical trials.

Animals↗
PubMed1981

New antiarrhythmic agents. 6. Quantitative structure-activity relationships of aminoxylidides.

The synthesis and pharmacological evaluation of primary and tertiary aminoxylidides with the amino group in the 2-7 position of the acyl chain are described. 2,6-Xylidine was acylated with haloacyl halides and converted to the target compounds by direct amination or by the Gabriel procedure. Alternatively, 2,6-xylidine was coupled with keto acids, and the ketoxylidides were converted to the amines by reductive amination. The target compounds were evaluated in mice both for antiarrhythmic efficacy against chloroform-induced tachycardia and for central nervous system toxicity. Experimentally determined values of partition coefficients and pKa values were used for quantitative structure-activity analyses. While the antiarrhythmic activity could be described as a function of log P alone, the CNS toxicity was best described as a function of both log P and pKa. The results suggest that antiarrhythmic potency can be increased by increasing lipophilicity, while the therapeutic index can be improved by increasing the pKa.

Animals↗
PubMed1980

Tocainide conjugation in humans: novel biotransformation pathway for a primary amine.

The metabolism of tocainide, an experimental antiarrhythmic drug, was studied in humans. Urinary excretion of unchanged drug was 28-55% in 24 hr after oral dosing. Urine hydrolysis with hydrochloric acid or beta-glucuronidase increased tocainide recovery to 55-79%. Saccharo-1,4-lactone inhibited the beta-glucuronidase-mediated tocainide recovery increase. Adjustment of urine to pH 13 produced a compound identified as 3-(2,6-xylyl)-5-methylhydantoin. Evidence suggests that it was derived from the same metabolite that formed the additional tocainide after acid or beta-glucuronidase treatment. Tocainide carbamoyl O-beta-D-glucuronide is the structure proposed for the metabolite. The suggested pathway for its formation involves the addition of carbon dioxide to the amino nitrogen of tocainide followed by uridine diphosphate-glucuronic acid conjugation.

Anilides↗
PubMed1979

Pharmacokinetics of lidocaine in fetal and neonatal lambs and adult sheep.

The pharmacokinetics of lidocaine were studied in fetal and neonatal lambs and in pregnant and nonpregnant adult sheep. Catheters were implanted in the femoral vessels and in the urinary bladders of animals prepared for chronic study. Lidocaine, 5--10 mg/kg, was injected intravenously either into the fetus or newborn lamb or into nonpregnant adult sheep. Serial samples of arterial blood and urine were obtained over four hours and analyzed for unchanged lidocaine using a gas chromatographic technique. The elimination half-lives of lidocaine in the bloods of nonpregnant ewe, neonate and fetus were 31, 51 and 33 min, respectively. Total-body clearances in the neonate and adult were 53 and 41 ml/min/kg. The metabolic clearances of lidocaine were the same in both, and approximated hepatic blood flow. Renal clearance was greater in the neonate, which was attributed to differences in urinary pH values and extents of protein binding. Thus, despite differences in half-lives, the newborn lamb is as capable as the adult of clearing lidocaine.

Age Factors↗
PubMed1977

Interpretation of plasma concentration-time curves after oral dosing.

The pharmacokinetic information obtained after oral administration is examined using the two-compartment model. Data were obtained by simulation and experimentally by administering sulfisoxazole by an exponential infusion to rabbits. When the absorption rate constant is allowed to approach alpha, a typical two-compartment oral absorption curve is obtained, which is described by a triexponential equation. However, if the absorption rate constant approaches E2 (the sum of the elimination rate constants out of the peripheral compartment), the data are adequately fit by a one-compartment model, with the calculated absorption rate equal to alpha. The relative error in using a one-compartment model to calculate absorption rate constants for two-compartment data is also evaluated.

Administration, Oral↗