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Biomedical subjects

Y W Chien

Publications and source records attributed to Y W Chien.

At least 91 records · Page 5Linked to original sources
PubMed1976

Controlled drug release from polymeric delivery devices IV: in vitro--in vivo correlation of subcutaneous release of norgestomet from hydrophilic implants.

The in vitro and in vivo releases of norgestomet from hydrophilic implants were found to follow a matrix-controlled (Q - t1/2) process. The sorption of drug onto the implants was observed to obey the same mechanism but with a much smaller magnitide of the Q/t1/2 value. The effect of the extent of cross-linking on the magnitude of drug release (Q/t1/2) profiles was analyzed both theoretically and experimentally. The release of norgestomet from hydrophilic implants was found to be an energy-linked process. Two energy terms were calculated; the activation energy for matrix diffusion was 7.71 kcal/mole, and the heat of drug crystal solvation was 25-28.6 kcal/mole.

Adsorption↗
PubMed1976

Binding of spirolactones to human plasma proteins.

The lipophilicity and plasma binding of 16 spirolactones and 4 hydroxy acid analogs were determined. Mathematical expressions were derived to correlate quantitatively the extent of plasma binding to the lipophilicity of the drugs. The nonspecific binding of these spirolactones and their hydroxy acid analogs was also analyzed using purified serum albumin. A computer program was developed to examine the mechanism of drug-serum protein interactions. One class of binding sites was observed for the range of concentrations used. The number of binding sites and the equilibrium binding constant were computed and were sensitive to substitution at the C-6 and C7 positions. Hydrolysis of the C-17 lactone ring in spirolactones to form hydroxy acid analogs resulted in a decrease in the lipophilicity and, hence, the equilibrium constant for binding.

Binding Sites↗
PubMed1976

Electrochemistry of drug action I: electrooreduction of ferredoxins.

Ferredoxin serves as an electron carrier in the oxidation-reduction system in anaerobic microorganisms, transferring electrons from a low potential donor to electron-accepting biochemicals. The anaerobicidal activity of some drugs may be due to their interference with the electron transport function of ferredoxin. Two types of ferredoxins (isolated from Clostridium pasteurianum and spinach) were studied, and their electrochemical reduction and biochemical properties were analyzed using a sensitive ac polarographic technique. The reduction potential of both ferredoxins was linearly related to pH. The mechanisms of electron transport in ferredoxin molecules were found to be related to their sulfur-iron bonds. The dissociation of the sulfur-iron bonds resulted in the formation of a free sulfhydryl group and the interruption of the electroactivity of ferredoxin. This sulfur-iron dissociation process was found to be pH dependent. The electroreduction of ferredoxins was an energy-requiring, pH-dependent process.

Clostridium↗
PubMed1975

Interaction of metronidazole with metallic ions of biological importance.

The possibility tht metronidazole exerts several of its biological actions via interaction with important metal ions was investigated. NMR spectroscopy and polarography (ac) were used to test for any interaction, to locate the probable sites for complexation, and to determine the molecular stoichiometry of any complexes formed. Of the series of divalent metal ions tests, only cupric ion showed detectable interaction with metronidazole. The predominant site of interaction of cupric ion was the unsubstituted nitrogen atom (N-3) on the metronidazole molecule. The stoichiometry of the complex was (Cu-(metronidazole)4)+2. A likely structure for the complex is presented.

Chemical Phenomena↗
PubMed1975

Linear relationships between plasma binding and lipophilicity of disopyramide derivatives.

The extent of plasma binding and the partition coefficient of disopyramide and 20 disopyramide derivatives were determined. Structural variations on the four functional groups around the tetrahedral carbon in the disopyramide molecule was found to influence both parameters to varying degrees. Three linear equations were developed to correlate the observed effects, depending on the type of chemical modification. The linear correlation between drug-plasma interaction and lipophilic character was analyzed theoretically. A simple model was derived to relate quantitatively the variation in the extent of plasma binding to the change in lipophilicity of disopyramide derivatives.

Arrhythmias, Cardiac↗
PubMed1975

Effect of pKb on lipophilic binding of disopyramide derivatives to human plasma.

The extent of plasma binding, the partition coefficient, and the pKb of 13 disopyramide derivatives were determined. The structural variation on the diisopropylaminoethyl group of disopyramide molecules influenced these physical parameters to varying degrees. Results demonstrated that the extent of interaction between drugs and human plasma was a linear function of their lipophilicity and inversely proportional to the magnitude of the pKb value.

Blood Proteins↗
PubMed1975

Solution-solubility dependency of controlled release of drug from polymer matrix: mathematical analysis.

Two types of drug release mechanisms-matrix controlled (Q - t1/2 relationship) and partition controlled (Q - t relationship)-were reported previously. The dependency of the transition between these two processes on the solution solubility of drug is now analyzed. Mathematical expressions are derived to treat the systemic effects of the addition of varying volume fractions of the cosolvent system on the concentration gradients across both the drug depletion zone and hydrodynamic diffusion layer as well as on the partitioning behavior at the polymer-solution interface. The results are in excellent agreement with reported experimental observations.

Delayed-Action Preparations↗
PubMed1975

Controlled drug release from polymeric delivery devices. III: In vitro-in vivo correlation for intravaginal release of ethynodiol diacetate from silicone devices in rabbits.

Forty female rabbits were implanted with silicone vaginal devices containing ethynodiol diacetate for up to 8 weeks. As predicted from in vitro studies, a Q - t1/2 (matrix-controlled) release profile was observed in vivo. The in vivo drug release profile was compared with in vitro data measured at three hydrodynamic conditions, and the diffusional resistance across the vaginal wall was estimated. Drug released from silicone devices yielded a prolonged plasma level when compared with data following intravaginal or intravenous administration of a solution dose. The rate constant for elimination was unchanged. The plasma concentration of the drug was related to the intravaginal drug release profile both theoretically and experimentally and was above the concentration required to inhibit fertilization.

Animals↗
PubMed1975

Binding of metronidazole and its derivatives to plasma proteins: an assessment of drug binding phenomenon.

Metronidazole and four derivatives were studied in vitro to investigate the differences in the extent of their binding to plasma proteins. Modification at the terminal portion of the alkyl side chain resulted in wide differences in the extent of binding. Molecular orbital calculations were performed by the CNDO and MINDO/2 methods to estimate the frontier electron density on the hetero atom at the 3'-position of the alkyl side chain. A linear correlation between the protein binding parameter (loge P) and the frontier electron density (qr) was observed for the binding of this group of trichomonicidal drugs. NMR spectroscopy was used to demonstrate that the alkyl side chain participated in the binding of these compounds to plasma proteins.

Blood Proteins↗