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PubMed1988

Influence of age on the pharmacokinetics of butorphanol.

Butorphanol kinetics were studied in 8 young (23-34 years of age) and 9 elderly (65-79 years of age) healthy male subjects following a single, intravenous 2-mg dose of butorphanol tartrate. Plasma and blood concentrations collected over 24 h were analyzed by a second antibody radioimmunoassay for unchanged drug. Systemic blood clearance (21.29 +/- 7.18 ml/min/kg), apparent steady-state volume of distribution (9.02 +/- 2.40 liters/kg), distribution half-life (7.67 +/- 4.66 min), and the blood/plasma concentration ratio (1.21 +/- 0.36) in the elderly did not differ from those in the younger subjects. However, the terminal elimination half-life was significantly prolonged in the elderly (5.51 +/- 2.49 versus 3.67 +/- 0.52 h, p less than 0.05). Positive correlations between age and terminal elimination half-life and volume of distribution were noted. Our data suggest that young and old subjects attain similar plasma concentrations after single doses; however, longer dosing intervals may be necessary for multiple dosing in the elderly. The appropriate dosing interval for butorphanol needs to be assessed in elderly patients.

Adult↗

PubMedDate not supplied

Dose-dependent kinetics of quinidine in the perfused rat liver preparation. Kinetics of formation of active metabolites.

The disposition of quinidine and the kinetics of metabolite formation were studied in the once-through perfused rat liver preparation by the stepwise increase in quinidine concentration. Dose-dependent kinetics of quinidine were observed; the steady-state hepatic extraction ratio decreased from 0.97 to 0.37 when input quinidine concentration varied from 1.34 to 33.9 micrograms/ml. Moreover, the formation of 3-hydroxyquinidine (detected only in perfusate as unconjugated 3-hydroxyquinidine) remained relatively linear while the formation of O-desmethylquinidine (present in bile and perfusate mostly as conjugates) apparently approached saturation kinetics within the quinidine concentrations used. The dose-dependent character of quinidine elimination cannot be attributed to changes in drug binding, as the blood/plasma ratio (4.07) and the degree of drug unbound in plasma (66.5%) remained unaltered for the quinidine concentrations used.

Animals↗

PubMed1984

Pharmacokinetic parameters: which are necessary to define a drug substance?

Pharmacokinetics describe what the body does to the drug, as opposed to pharmacodynamics which describe what the drug does to the body. Pharmacokinetic information is required to optimize the pharmacodynamic response. The primary pharmacokinetic disposition parameter is clearance. Knowledge of this value and its major constituent parts, i.e. fractional renal and hepatic elimination, allows the clinician to prescribe the correct dosage regimen to obtain a mean therapeutic concentration and to predict the effects of various disease states. The other primary disposition parameter, volume of distribution at steady-state, may also vary with changes in physiologic and pathologic conditions. Both clearance and volume of distribution as well as the correlation of concentration measurements with pharmacodynamics would be expected to vary with changes in plasma protein binding. Although plasma concentration measurements are usually easiest to perform, interpretation of parameters in physiologic terms requires blood concentration, so the blood/plasma partition parameter should be determined. Although half-life is a composite parameter reflecting changes in both clearance and volume of distribution, it is a value which defines the maximum and minimum blood concentrations obtained for a particular dosage regimen, important quantities in defining the pharmacodynamic response. The major pharmacokinetic input parameter is the extent of availability as a function of route of administration. This parameter, as well as all of the disposition parameters discussed above, may be determined without designating a particular pharmacokinetic model. Only the rate of availability requires a model, although peak time and peak concentration are reasonable noncompartmental substitutes.

Biological Availability↗

PubMed1983

Pharmacokinetic model of diltiazem.

The pharmacokinetic profile of D-3-acetoxy-cis-2,3-dihydro-5-(2-dimethylamino-ethyl)-2-(p-methoxy-phenyl)-1, 5-benzothiazepin-4(5H)-one hydrochloride (diltiazem . HCl) following i.v. and p.o. administration has been studied in six healthy subjects using a new sensitive GLC method. The volunteers received an i.v. infusion of 20 mg in 20 min, a peroral solution of 120 mg and two 60-mg tablets (Dilzem) in a randomized sequence. The plasma level time courses of the unchanged compound following infusion and peroral solution were simultaneously evaluated by nonlinear regression analysis. The best model was chosen by means of statistical criteria. In all subjects the experimental data could be adequately described by an open three-compartment model with zero order input following infusion and first order absorption following p.o. solution. Using this procedure the following common disposition parameters were obtained for both routes of administration: t1/2 alpha = 0.1 h, t1/2 beta = 2.1 h, t1/2 gamma = 9.8 h (harmonic means derived from individualized fits), Vc = 0.9 +/- 0.4 l/kg, Vss = 5.2 +/- 2.4 l/kg, Cltot = 11.5 +/- 1.8 ml/min/kg. Compared to the beta-phase the terminal gamma phase represents a smaller contribution to the total AUC. The blood/plasma distribution ratio was found to be 1.00 +/- 0.08 (N = 4), the mean hepatic extraction ratio was 0.54. Peak levels appeared 0.6 +/- 0.3 h after the p.o. solution. The mean absolute bioavailability of diltazem based on the individual AUC infinity 0 of the p.o. solution and the infusion was 0.44 +/- 0.10. Following tablet administration, delayed maximum levels were found after 2.8 +/- 0.9 h. Comparing the AUC infinity 0 of tablets and p.o. solution, there was no significant difference between both dosage forms.

Adult↗

PubMedDate not supplied

An overview of assay methods for D-penicillamine.

The stability and biotransformation of D-penicillamine as it relates to assay development is discussed. A review of published literature on assays is presented with respect to blood/plasma levels of D-penicillamine in man and to statistical evaluation of assays. Also, the paper describes gas chromatographic assay for D-penicillamine disulfide and L-cysteine D-penicillamine disulfide in urine and plasma, as well as a new high performance liquid chromatography assay for D-penicillamine in plasma.

Biological Assay↗

PubMedDate not supplied

Disposition of morphine and its 3- and 6-glucuronide metabolites during morphine infusion in the sheep.

A sheep preparation was used to examine the regional formation and extraction of morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G), relative to the regional extraction of morphine, at four morphine dose rates. On separate occasions, four ewes received a 15-min loading infusion of morphine sulfate, followed by a constant infusion at 2.5, 5, 10, or 20 mg/hr for an additional 5.75 hr. During the 5th to 6th hr of infusion, blood samples were collected simultaneously from the aorta, pulmonary artery, hepatic vein, hepatic portal and renal veins, posterior vena cava, and coronary and sagittal sinuses. Urine was collected for 48 hr. Morphine, M3G, and M6G in plasma and urine were determined simultaneously by HPLC. The blood/plasma concentration ratio (lambda) for morphine, M3G, and M6G was determined in spiked "blank" blood. Steady-state plasma concentrations were achieved during the sampling period, and dose-normalized concentrations were independent of the infusion rate. There was significant (p < 0.05) extraction (mean +/- SD) of morphine by the liver (0.676 +/- 0.014) and kidney (0.602 +/- 0.039), net extraction of M3G (0.106 +/- 0.046) and M6G (0.104 +/- 0.030) by the kidney, and net formation of M3G (-0.057 +/- 0.017) by the gut. The mean lambda for morphine, M3G, and M6G was 1.25 +/- 0.17, 0.80 +/- 0.03, and 0.82 +/- 0.09, respectively. The mean total body clearance of morphine with respect to blood was 1.58 +/- 0.27 liters/min. Mean (+/-SD) percentage urinary recoveries as morphine, M3G, and M6G were 14.7 +/- 8.5, 75.4 +/- 11.1, and 0.49 +/- 0.39, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Biotransformation of fluvastatin sodium in humans.

The metabolic pathways of fluvastatin sodium (FV; Lescol, Sandoz compound XU 62-320), [R*,S*-(E)]-(+-)-sodium-3,5-dihydroxy-7-[3- (4-fluorophenyl)-1-(1-methylethyl)-1H-indole-2-yl]-hept-6-enoate, a potent inhibitor of hydroxy-methylglutaryl-CoA reductase (HMG-CoA reductase)--the rate-limiting enzyme in cholesterol biosynthesis--were determined in normal male volunteers at steady state. The metabolite profiles were determined in pooled human blood/plasma, urine, and feces obtained from healthy male volunteers after a single dose of 2 and 10 mg of [3H]FV and at steady state after a single 40 mg daily dose of [3H]FV for 6 sequential days utilizing HPLC coupled with radioactivity monitoring. The two major components in plasma were FV and the desisopropylpropionic acid (4) derivative of FV, the latter a result of oxidative removal of the N-isopropyl group and beta-oxidation of the side chain. Minor amounts of the 4,5-pentenoic acid derivative of FV, the threo-isomer of FV, the trans-lactone of FV, and conjugates of 5-hydroxy FV and 6-hydroxy FV were also present in plasma. Parent FV was not present in feces, the major excretory route, or in urine. In urine, 4 and conjugates of 5-hydroxy FV, and 6-hydroxy FV were present, and each represented < 1% of the dose. In feces 5-hydroxy FV, 6-hydroxy FV, and desisopropyl-FV represented the only peaks of significance. The metabolism of FV leading to the 5-hydroxy FV and 6-hydroxy FV was not stereospecific.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1998

Species differences in sirolimus stability in humans, rabbits, and rats.

Species differences in the in vitro stability of sirolimus was assessed in plasma and whole blood in relation to red blood cell distribution. Fresh blood and plasma samples obtained from humans, rabbits, and rats were aliquoted and spiked with sirolimus. After incubation from 0 to 144 hr in a shaking water bath maintained at 37 degrees C, sirolimus concentrations were quantified by a specific high-liquid performance chromatographic method. Sirolimus was unstable in both plasma and whole blood. Sirolimus degradation half-life in whole blood was 135 hr (vs. 7.2 hr in plasma) in humans, 62 hr (vs. 3.1 hr) in rabbits, and 15 hr (vs. 2.2 hr) in rats. Sirolimus stability is greater in whole blood compared with plasma in proportion to the whole blood/plasma ratio and hematocrit. In vivo instability may account for up to 36% of sirolimus clearance in humans and 13% in rabbits, and this is an important factor in the pharmacokinetics of this drug.

Animals↗

PubMed1976

Rapid fluorometric analysis of unbound salicylate in whole blood.

A method has been developed for the analysis of unbound salicylate by membrane cone ultrafiltration of either whole blood or plasma with quantitation by spectrofluorometry. The method was used to study the distribution of salicylate in whole blood over a wide range of concentrations. It was found that at a concentration of 50 ug/ml in whole blood only 9% of the salicylate is present as free drug in the plasma water, while at a concentration of 500 ug/ml, 23% is free. At concentrations exceeding 500 ug/ml the plasma protein binding sites appear to be fully satrated since the free drug concentration increases linearly with respect to the whole blood concentration. Changes in hematocrit have a relatively minor effect on the ultrafiltrate salicylate concentration. The blood/plasma salicylate concentration ratio was found to vary widely over the blood salicylate range studied, 50-1000 ug/ml.

Humans↗

PubMed1946