Biomedical subjects

N A Armstrong

Publications and source records attributed to N A Armstrong.

33 records · Page 2Linked to original sources

PubMed1979

Inter-relationships between solubilities, distribution coefficients and melting points of some substituted benzoic and phenylacetic acids.

Ten 4-hydroxy and 4-alkoxy benzoic and phenylalkanoic acids have been investigated. Solubilities in aqueous buffer at pH 1.2 were determined, together with distribution coefficients between the buffer and either octanol or isopropyl myristate. When plotted against the total number of carbon atoms in the side chains, log octanol/water distribution coefficients gave two parallel straight lines, one for the substituted benzoic acids, and the other for the substituted phenylalkanoic acids. The slopes approximated to 0.5, the generally accepted value for methylene. Similar plots could be obtained with isopropyl myristate, provided the hydroxy acid results were ignored, and also when log aqueous solubilities were plotted against carbon number, although there was considerable scatter. The differences between the distribution coefficient results were explained in terms of solute-solvent interactions, and the scatter attributed to variations in the heats of fusion of the solutes. Yalkowsky's equation (1977), linking aqueous solubilities and melting points with distribution coefficients, was applied to the results, and found to be of limited predictive value.

Benzoates↗

PubMed1979

An in vitro model for assessing drug availability from lipophilic vehicles.

An apparatus for studying the rate of release of a solute from a water-immiscible solvent into an acidic, aqueous liquid, followed by permeation through a simulated lipid membrane, is described. The object was to imitate the absorption of a drug after oral administration in a soft gelatin capsule. Rate constants of transfer were determined for a series of substituted benzoic acids, using octanol and isopropyl myristate as solvents. The quantity of solute in the acidic phase did not correlate with the solvent-water distribution coefficient, but was linearly related to the rate constant for transfer from solvent to water. A dynamic system was therefore postulated, rather than one in which the two phases are in equilibrium. In vivo studies on two of the solutes confirmed the in vitro observations. No simple relationship could be derived between blood concentrations and any in vitro parameter, but the rank order of magnitude of the blood concentrations fitted the postulated dynamic mechanism.

Benzoates↗

PubMed1976

Quantitative assessment of factors contributing to mottling of colored tablets I: manufacturing variables.

By using a recently developed method for quantifying the degree of mottling of colored tablets, the effects of manufacturing variables such as the method and temperature of granule drying, granule size, and compaction pressure were investigated. Tablets of dibasic calcium phosphate colored with FD&C Blue No. 1 dye were used. Drying temperature had little effect, but the method of granule drying, granule size, and compaction pressure were major influences on mottling. Mechanisms to explain these results, based on the migration of dye during the drying process, are proposed.

Color↗

PubMed1976

Quantitative assessment of factors contributing to mottling of colored tablets II: formulation variables.

The effects of several formulation variables were quantified with respect to factors affecting tablet mottling. Tablet mottling occurred with several commonly used binders and could not be prevented by using highly viscous binding solutions. However, mottling was reduced initially by increasing granule strength. Tablet diluents and dye-adsorbent materials had a profound effect on mottling, not by preventing dye migration but by affecting granule fragmentation on compression and the extent to which the dye-deficient material at the center of the granule was revealed. The lake form of FD&C Blue No. 1 was found to bleed in the presence of diluents that raised the pH of the granulating fluid above 6.4. Anionic impurities in the diluents also caused leaching of free dye and, consequently, increased tablet mottling. The conclusions from this study and previous papers were drawn together to give general principles for the production of uniformly colored tablets by aqueous granulation techniques.

Adsorption↗

PubMed1976

Adsorption sites of kaolin.

The electrophoretic mobility and adsorptive properties of kaolin and kaolin pretreated with anionic and cationic materials were examined over a range of pH values. Pretreatment with anionic compounds had little effect on mobility, while adsorption of cationic species markedly reduced mobility. These results are explained by reference to the structure of kaolin, and the interdependence of adsorption properties and electrophoretic mobility are discussed.

Adsorption↗

PubMed1976