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Biomedical subjects

H L Fung

Publications and source records attributed to H L Fung.

At least 163 records · Page 9Linked to original sources
PubMed1978

Effects of L-cysteine, L-cysteine derivatives and ascorbic acid on lead excretion in rats.

Urinary and fecal excretion of lead in rats were compared after intravenous administration of L-cysteine and a number of its derivatives. In terms of increasing total lead excretion, L-cysteine ethyl ester was about half as effective as D-penicillamine, whereas L-cysteine and all other derivatives tested were only marginally effective. Interestingly, L-cysteine ethyl ester appeared to increase lead depletion mainly through biliary excretion. This compound may, therefore, have lower renal toxicity than other chelating agents which promote lead excretion principally by increasing urinary elimination. Dietary supplements containing 1% cysteine, 1% ascorbic acid of 1% of both substances did not dramatically increase lead elimination.

Animals↗
PubMed1978

Improved pharmacological activity via pro-drug modification: comparative pharmacokinetics of sodium gamma-hydroxybutyrate and gamma-butyrolactone.

Although gamma-butyrolactone (GBL) rapidly converts to gamma-hydroxybutyrate (GHB) in vivo, the lactone gave significantly more prolonged hypnotic effects than GHB when equimolar doses were compared both parenterally and orally in rats. Plasma drug concentrations were higher after GBL administration through both routes, consistent with the observed differences in the pharmacological activity of these two compounds. Oral GBL was absorbed much faster than oral GHB, with the dual effects of decreasing potential first-pass metabolism and elevating plasma drug concentrations to the region where capacity-limited elimination is operative. Parenteral GBL produced a slower initial drug plasma clearance than parenteral GHB. In spite of the rapid metabolism of GBL to GHB, the apparent tissue distribution of these two compounds may be different.

4-Butyrolactone↗
PubMed1976

Development of a stable sublingual nitroglycerin tablet II: formulation and evaluation of tablets containing povidone.

Stable and pharmaceutically elegant sublingual nitroglycerin tablets were formulated using povidone to retard volatilization of the drug. Formulation and processing variables were investigated to produce an acceptable product. A blend of two grades of povidone, of different degrees of cross-linkage and water solubility, provided stable tablets which exhibited rapid disintegration. Directly compressed sublingual tablets made in this study retained over 80% of the initial nitroglycerin when exposed to the atmosphere at room temperature for 2 months. The direct compression tablets are of good appearance and low friability, and the formulation is readily compressed without problems. An interesting relationship among the hardness, disintegration time, and compaction pressure is described.

Drug Compounding↗
PubMed1976

Dose-dependent pharmacokinetics of laevodopa and its metabolites in the rat.

1. Plasma levels of total radioactivity, unchanged laevodopa, dopamine, 3-O-methyldopa and non-amino phenolic acids were measured in rats treated orally with [3H]laevodopa at total laevodopa doses of 1, 10, 20 and 100mg/kg while the radioactive dose was maintained at 100muCi/kg for all animal groups. 2. Within the dosage range studied, non-linear pharmacokinetics were observed for unchanged laevodopa, non-amino phenolic acids and dopamine but not for 3-O-methyldopa. 3. The area under the plasma concentration-time curve for laevodopa increased exponentially with linear increments in the oral dose. This non-linear increase in laevodopa bioavailability is consistent with the hypothesis that high oral doses of laevodopa are required to saturate gastro-intestinal metabolism of the drug. 4. At the lower doses (1 and 20 mg/kg), only 2-3% of total radioactivity could be attributed to dopamine. At 100mg/kg, the dopamine metabolite fraction amounted to about 1/3 of total radioactivity in the plasma.

Animals↗
PubMed1976

Absorption and first-pass metabolism of 14C-gamma-hydroxybutyric acid.

The recovery of radioactivity from plasma, urine and feces was determined in rats after administration of oral and intravenous doses (200 mg/kg) of 14C-labeled sodium gamma-hydroxybutyric acid. Very small portions of the radioactive dose were recovered in the urine (5.5%, oral; 7.1%, intravenous) and feces (1.5% oral; 0.6%, intravenous) collected between 0-48 hours after drug administration. Considerable levels of radioactivity were found in the plasma after oral dosing. The area under the plasma radioactivity time curve after an oral dose was found to be 65% of that observed after an equivalent intravenous dose. This value is much larger than the relative area value (8%) calculated on the basis of free gamma-hydroxybutyric acid. Results of this study strongly indicate that first-pass metabolism, rather than lack of absorption, is responsible for the apparently poor oral bioavailability of gamma-hydroxybutyric acid.

Absorption↗
PubMed1975

Fluorescence reactions of fluorescamine with levodopa and its derivatives: fluorescence assay of 3-methoxy-4-hydroxyphenylalanine in levodopa dosage forms.

A simple fluorometric method for the quantitation of 3-methoxy-4-hydroxyphenylalanine, either alone or in the presence of levodopa, is presented. Fluorescence is developed by reaction with fluorescamine. The interactions of this reagent with levodopa and a number of its derivatives under various experimental conditions were studied. Negligible fluorescence was obtained with levodopa, dopamine, levodopa benzyl ester, and 6-hydroxydopamine.

Chemical Phenomena↗
PubMed1975

Effects of chronic oral administration on the disposition of laevodopa and its major metabolites in the plasma of the rat.

1. Plasma levels of total radioactivity , unchanged laevodopa, catecholamines, 3-O-methyldopa and non-amino phenolic acids were measured in rats treated orally with [3H]laevodopa (100 mg/kg, 100 muCi/kg) for different periods of time. 2. Chronic oral administration of laevodopa for two months significantly delayed the appearance of peak plasma levels and decreased the overall plasma concentrations of the unchanged drug as compared to controls. The extent of absorption of an oral dose of [3H]laevodopa was not significantly impaired on chronic treatment and/or ageing. The decrease in the levels of unchanged laevodopa appeared to be due to an increase in the apparent volumes of distribution of the drug and its metabolites upon ageing. 3. The plasma levels of the catecholamine metabolite fraction, which included dopamine, noradrenaline, etc., were much higher in chronically dosed animals. 4. These findings may be relevant in the understanding of such clinical observations as decreasing therapeutic effects and increasing toxicity after long-term laevodopa treatment in human patients.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1975

Comparative bioavailability of anhydrous griseofulvin and its chloroform solvate in man.

Using a crossover experimental design, the absorption profile of griseofulvin was assessed in human volunteers after oral administration of a 500 mg dose of the antifungal antibiotic as capsules of the anhydrous (nonsolvated)-and monochloroform solvate forms of the drug. The maximum body level of drug and the rate and extent of griseofulvin absorption (or bioavailability) were significantly increased after administration of the chloroform solvate as compared to that observed after administration of the nonsolvated form of the drug. The enhanced absorption of griseofulvin chloroformate correlated well with its enhanced solubility and dissolution rate at 37 degrees C in simulated intestinal fluid (20 mM sodium deoxycholate, pH 7.5). This is the first demonstration of a drug-organic solvate displaying improved gastrointestinal absorption characteristics over the anhydrous form of a drug.

Biological Availability↗
PubMed1975

Factors affecting the kinetic assay of nitroglycerin in dosage forms.

Parameters affecting the spectrophotometric kinetic assay for nitroglycerin are described. It is shown that the assay is highly specific; results are not significantly affected by many of the tablet diluents found in commercially-available nitroglycerin tablets. Further, the assay is insensitive to glycerol, nitrate, nitrite and glyceryl dinitrates. This simple, precise and specific nitroglycerin assay is well suited for routine analysis of the drug in commercial tablets and parenteral solutions in hospital pharmacies.

Chemistry, Pharmaceutical↗