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Biomedical subjects

M Donbrow

Publications and source records attributed to M Donbrow.

At least 19 recordsLinked to original sources
PubMed1979

Sustained release of drugs from ethylcellulose--polyethylene glycol films and kinetics of drug release.

Cast films composed of different ratios of polyethylene glycol and ethylcellulose containing salicylic acid, caffeine, and tripelennamine as model dispersed drugs were prepared and exhibited sustained release. The drug content of the film declined at an apparent first-order rate initially, whereas the drug quantity released was proportional to the square root of time. Data analysis validated the latter treatment, which is in accordance with the diffusional matrix model, and disproved the validity of the apparent first-order conformity. The release rates were independent of film thickness and proportional to drug concentration in pure ethylcellulose films; in polyethylene glycol--ethylcellulose films, a positive deviation from linearity was observed. The logarithm of the rate constant was proportional to the fraction of polyethylene glycol in the film. Unlike in pure ethylcellulose films, the release rate in mixed films was altered by a change in the external fluid pH.

Caffeine↗
PubMed1979

Placebo granules as cores for timed release drug delivery systems.

A drug delivery system is proposed constituted of spherical placebo granules as cores with polymeric surface films containing drug. This timed release dosage form has been prepared by means of a fluidized bed coating technique using ethyl cellulose as the polymeric film and caffeine and salicylic acid as model drugs. The release of the drugs from the dosage form (a) at different drug concentrations and (b) into solutions of different pH showed that drug release was linearly related to the square root of time. Good agreement was found between the theoretical release rate of caffeine, calculated according to Higuchi's equation for a homogenous matrix using membrane permeation parameters measured on linear films, and the experimental results in the case of low drug concentrations. Deviation of the release rate from the homogenous model at high drug concentrations could be explained by crystallization of the drug from the film.

Caffeine↗
PubMed1978

Estimation of dissolution rate of salicylamide in complexing media using a theoretical diffusion model.

Dissolution rates of salicylamide in water and caffeine solutions under perfect sink conditions were predicted by theoretical diffusion equations applicable to dissolution in complexing media. Experimental dissolution rates were measured using a compartmentalized rotating-basket apparatus under two sets of conditions. Agreement was found between experimental and predicted rates. Use of the theoretical equation for estimating dissolution rates involves simple calculations of diffusion coefficients and diffusion layer thickness under the operative dissolution conditions. The increase in dissolution rate caused by addition of the complexant can be calculated for diffusion-controlled dissolution directly if the stability constant and the drug solubility in water are known or measured.

Caffeine↗
PubMed1978

Autoxidation of polysorbates.

Aqueous solutions of polysorbate 20 undergo autoxidation on storage, with the peroxide number increasing and subsequently decreasing again, the acidity increasing continuously, the pH and surface tension falling and tending to level off, and the cloud point dropping sharply until turbidity begins at room temperature. The changes are accelerated by light, elevation of temperature, and a copper sulfate catalyst. At the same time, hydrolysis occurs, liberating lauric acid. Analysis of the alterations in these properties leads to the conclusion that hydrolysis has the major influence near room temperature and that oxyethylene undergoes chain shortening at temperatures above 40 degrees. However, evidence of degradation is detectable even in previously unopened commercial samples of polysorbates 20, 40, and 60, warranting attention to the stability of and standards for these surfactants as compared with the solid alkyl ether type of nonionic surfactant.

Chemical Phenomena↗
PubMed1977

The dissolution mechanism in a system undergoing complexation: salicylamide in caffeine solution.

The dissolution rate of compressed salicylamide discs has been measured in water and in caffeine solutions of increasing concentration at 15, 25, 37 and 45 degrees in an apparatus rotating at 48 rev min-1 or more. Dissolution rate profiles showed breaks indicative of a shift in the mechanism of dissolution from interfacial towards transport control. The shifts occurred at higher caffeine concentrations on increasing the agitation rate or temperature. The dependencies of dissolution rates on agitation rates typified the intermediate type of dissolution and Arrhenius plots indicated that interfacial and transport processes participated in salicylamide dissolution.

Caffeine↗
PubMed1976

Stability of salicylamide-caffeine complex at different temperatures and its thermodynamic parameters.

The stability constants for formation of complexes of salicylamide with caffeine have been measured between 15 and 45degrees, by means of the solubility method. There was a linear solubility increase at all temperatures but phase diagrams indicated that at 15 and 25degrees an additional phase was formed which was found to be an insoluble 1 : 1 complex. The enthalpies and entropies of interactions were evaluated. They indicate that the interaction is exothermic and enthalpy controlled.

Caffeine↗
PubMed1975

Timed release from polymeric films containing drugs and kinetics of drug release.

The preparation of cast films of ethylcellulose containing caffeine and salicylic acid is described. These films exhibit timed release of drugs. Release rates were found to agree with both the classical first-order equation (log drug retained against time) and diffusion-controlled release models, as exemplified by Higuchi's equations (drug release linearly related to square root of time). Mathematical analysis of the data shows that the release behavior actually conforms with the diffusion-controlled model. Literature results, reported as first order, for the release of cetylpyridinium chloride and benzalkonium chloride from polyamide films were analyzed similarly and shown to be diffusion controlled. Recommendations are made for presentation and routine treatment of drug release data to avoid ambiguity and provide useful biopharmaceutical information.

Caffeine↗
PubMed1975

Surface tension and cloud point changes of polyoxyethylenic non-ionic surfactants during autoxidation.

Changes in the surface tension-concentration curves of the non-ionic surfactant cetomacrogol, a polyoxyethylenic (POE) hexadecyl ether containing about 24 ethylene oxide (EO) groups, have been examined during autoxidation of aqueous solutions. The curves exhibit decreases in cmc values and changes in the slopes below and above the cmc which lead to the loss of the sharp break characteristic of micelle-formation. There is also a progressive decrease in the cloud point during autoxidation. Surface tensions and cloud points of a series of known POE hexadecyl ethers containing from 10 to 60 EO units have been measured and related to the number of EO units present. From these data, it is apparent that autoxidation of cetomacrogol is accompanied by degradation of POE chain rather than the hydrocarbon chain, the number of EO units lost up to the time at which the solution becomes turbid being about 14. The significance of such measurements is discussed in relation to the detection of decomposition and pending rapid decomposition in synthesized and commercial surfactants.

Catalysis↗
PubMed1975

Enhancement of permeability of ethyl cellulose films for drug penetration.

Permeability constants of salicylic acid, caffeine and benzoic acid have been measured at 37 degrees for heterogeneous films of ethyl cellulose containing up to 50% PEG 4000, the latter component undergoing leaching out. For the first two compounds, steady state constants were independent of film thickness and solute concentration but increased linearly and sharply with PEG content and were reproducible. The films were impermeable to NaOH and permeation rates were independent of receiver compartment pH. Solubility coefficients and diffusion coefficients of the substances in the films were measured using sorption and/or time lag methods and were low as compared with polyethylene films. High solubility seemed to be associated with the presence of a free activated hydrogen, shown by sorption studies on other substances. From the evidence, it appeared that mass transfer was controlled by the solubility diffusion process in the ethyl cellulose of the membranes with all three substances. Enhancement of permeability by PEG thus seemed due to increased porosity, equivalent to reduction in the effective thickness of the matrix, which nevertheless retained its barrier properties. Enhancement coefficients calculated from the slopes of PEG concentration plots may be useful for predicting the increased mass transfer of drugs through such membranes and could enable the porosity and thickness factors to be balanced against each other for formulation of coated products.

Absorption↗