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Biomedical subjects

J H Collett

Publications and source records attributed to J H Collett.

18 recordsLinked to original sources
PubMed1979

Relationships between poloxamer structure and the solubilization of some para-substituted acetanilides.

Saturation solubilities of several para-substituted acetanilides have been measured at 37 degrees C in aqueous solutions of structurally related polyoxyethylene-polyoxypropylene block copolymers-poloxamers L62, L63, L64, P65 and F68. These poloxamers differ only in the amount of ethylene oxide in the hydrophil. Solubilities increased with increasing poloxamer concentration. As the oxyethylene chain length of the poloxamer increased, then the solubilizing capacity per equivalent of oxyethylene decreased. The moles of acetanilide derivative solubilized per mole of poloxamer increased with poloxamer oxyethylene content in the case of the less hydrophobic acetanilides but was invariant in the more hydrophobic ones. The solubilizing capacities have been discussed in terms of the inter-relationships between the hydrophobic nature of the solubilizate and solubilizer and the site of solubilization on the poloxamer molecule.

Acetanilides↗
PubMed1979

Biological effectiveness, in goldfish, of some p-substituted acetanilides alone and in the presence of poloxamers.

The death times of goldfish have been measured in aqueous solutions containing different concentrations of p-substituted acetanilides alone or in the presence of poloxamers. Plots of reciprocal death time versus concentration were linear with a positive concentration intercept, the minimum effective concentration (MEC). The MEC values were directly related to the pi value (hydrophobic-lipophilic constant) of the functional group on the acetanilide indicating that activity is directly related to lipophilicity. Slopes of reciprocal death time versus drug concentration were linearly related to pi values but there was no direct dependence. The presence of poloxamers in aqueous acetanilide solutions reduced the goldfish death time. The effect of the poloxamers is believed to be one of rendering the goldfish membrane more permeable to drugs.

Acetanilides↗
PubMed1976

Correlations between substituent parameters of 4-substituted benzoic acids and their in vitro dissolution and partitioning.

The in vitro dissolution and partitioning of some 4-substituted benzoic acids from nondisintegrating disks was investigated using a water-octanol system. The rates of appearance of benzoic acids in the aqueous phase differed from the rates of appearance in octanol, probably due to back-transfer from the octanol phase. The suitability of the procedure for investigating the influence of molecular modification on in vitro dissolution and partitioning is considered. Correlations among the rates of appearance in octanol, the rates of appearance in an aqueous phase, and substituent parameters of benzoic acids were investigated. The best statistical fit was obtained using molecular orbital substituent indexes.

Benzoates↗
PubMed1976

Some effects of urea on drug dissolution.

Solubilities and dissolution rates of salicylic acid have been determined in urea solutions at different pH values. Solubilities increased with pH and urea concentration; a solubilization mechanism was considered to be operating. The solubilization effect of urea was greatest on the non-ionzed moieties of the solute. Dissolution rates of salicylic acid increased with pH and urea concentration. The increase in dissolution rate paralleled increases in solubility. The role of solubilizing effect in the enhancement of dissolution rate by urea is discussed.

Hydrogen-Ion Concentration↗
PubMed1976

Some factors influencing dissolution from salicylic acid-urea solid dispersions.

Solid dispersion systems of salicylic acid-urea have been prepared using a fusion method. Two different methods of cooling the melt were employed, rapid cooling in liquid nitrogen and slow cooling in air. Differential scanning calorimetry and an X-ray diffraction technique were employed to investigate the nature of the fused mixture. Evidence was found of compound formation between the constituents. Dissolution rates of drug from non-disintegrating discs of solid dispersion systems were measured. Rapid cooling of the melt resulted in a much faster drug dissolution rate than from a corresponding mixture prepared by a slow cooling method. This phenomenon is explained by a difference in the sizes of drug particles produced under the different cooling conditions. Rapid cooling favoured the generation of many nucleation sites for the solid drug particles as the liquid was cooled, and hence many small particles were obtained. Conversely, slow cooling favoured the growth of the first few nuclei or solid drug particles, rather than the production of new nuclei, and hence large drug particles were obtained.

Calorimetry↗
PubMed1975

Interaction of substituted benzoic acids with polysorbate 20 micelles.

Equilibrium solubilities of a series of substituted benzoic acids in different concentrations of polysorbate 20 at controlled pH were measured. The maintenance of pH was achieved using a pH-stat assembly. A linear relationship was found between the amount of benzoic acid solubilized and surfactant concentration. As solubilizate polarity increased, the amount solubilized also increased. Solubility data were analyzed, and the interaction between solubilizate molecules and micelles was calculated in terms of partition coefficients of ionized and unionized molecules between aqueous and micellar phases. A linear relationship between pi values (log partition coefficients) of functional groups and aqueous-micellar partition coefficient was found.

Benzoates↗
PubMed1975

Some relations between dissolution rates and physical parameters of a drug in aqueous micellar solutions of a non-ionic surfactant.

Dissolution rates of salicylic acid from a constant surface area into a series of aqueous micellar polysorbate 20 solutions at pH 1-0 to 4-0 have been measured using two different methods; a stirred beaker and a rotating disc technique. The micellar molecular weight of polysorbate 20 has been obtained from light scattering and differential refractometry data and used with other independently determined physical data to calculate diffusion coefficients of the diffusing species. Linear multiple regression analysis was used to assess the dependence of drug dissolution rate on the diffusion coefficient and the viscosity of the dissolution medium.

Colloids↗