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Biomedical subjects

M B Fawzi

Publications and source records attributed to M B Fawzi.

8 recordsLinked to original sources
PubMed1994

Mechanism of drug release from an acrylic polymer-wax matrix tablet.

An acrylic polymer-wax matrix system was evaluated for oral sustained-release tablets of diphenhydramine HCl. A desirable release profile of diphenhydramine was achieved by incorporating Eudragit L in a carnauba wax matrix. In this polymer-wax system, carnauba wax maintained the integrity of the matrix, whereas Eudragit L slowly eroded in the matrix as the drug was released. Thus, the area-to-volume ratio of the tablet remained constant over the duration of the drug release. In vitro drug release studies were conducted at physiological pHs that exist in the gastrointestinal tract. Drug release rates decreased as the polymer:drug ratio increased from 1:2 to 2:1. The drug release rate was faster in pH 7.5 phosphate buffer than in 0.1 N HCl solution. The drug release from these polymer-wax matrices is described by a combination diffusion/erosion mechanism. Based on the typical pH encountered in intestinal fluids, complete dissolution of the drug and polymer at pH 7.5 in 8-10 h would ensure good bioavailability of the drug following oral administration.

Diphenhydramine↗
PubMed1988

In vitro release characteristics of hard shell capsule products coated with aqueous- and organic-based enteric polymers.

In this article, an overview of the rationale for the use of enteric coated (EC) dosage forms is presented. The benefits and disadvantages inherent in the use of aqueous dispersions and organic solutions of the various polymers to generate these products are discussed. The comparative dissolution stability of a hard shell capsule product coated with enteric polymers applied as either aqueous dispersions, or as organic solutions, were assessed under accelerated conditions of storage. Polymethacrylic acid methacrylate copolymer, cellulose acetate phthalate (CAP) and polyvinyl acetate phthalate (PVAP), along with the corresponding commercially available aqueous dispersions, Eudragit L30D, Aquateric, and Coateric, were employed in these studies as enteric polymers. Diethyl phthalate (DEP) was used as the plasticizer and procainamide HCl 250 mg capsules served as the substrate. Storage of the coated capsules at 37 degrees C/80% RH and at 45 degrees C for 2 months revealed that, while the stability of Eudragit L30D coatings are comparable or superior to the corresponding organic-based coatings, Coateric films are markedly unstable when compared with PVAP coatings applied through the use of organic vehicles. After storage at 37 degrees C/80% RH, Aquateric-based capsules demonstrated stability comparable to CAP organic-based coatings only when a protective seal coat was present. The performance failures of the capsules that occur upon storage primarily result in a loss of gastric resistance. Scanning Electron Microscopy (SEM) and thermomechanical analysis (TMA) of the different coatings revealed differences in the film-forming properties of the polymer films and provide an explanation for the changes that occur during storage of the coated capsules.

Capsules↗
PubMed1980

Gentisic acid: a new stabilizer for low tin skeletal imaging agents: concise communication.

In vitro stabilization of low-tin bone-imaging agents has previously been achieved with ascorbic acid. In this study gentisic acid is shown to be an equally effective antioxidant for the (1-hydroxyethylidene) diphosphonate (HEDP) and hydroxymethylenediphosphonate (HMDP) skeletal agents. In vitro studies show less than 2% free sodium [99mTc] pertechnetate at 24 hr with the gentisic acid stabilizer. Studies in guinea pigs at 3 and 24 hr--whether with C-14 or H-3-labeled gentisic acid as stabilizer--show no alteration in the biodistribution of either skeletal imaging agent by the addition of the gentisic acid. Gentisic acid is a safe and effective stabilizer, and clinical studies have shown bioequivalency with ascorbic acid.

Animals↗
PubMed1977

Synchronized crystal dissolution behavior for tooth enamel and synthetic (NBS) hydroxyapatite.

The synchronized cyrstal dissolution hypothesis previously proposed to explain the unusual dissolution behavior of human dental enamel and hydroxyapatite in partially saturated acidic media has been critically examined with dissolution-dialysis transport experiments. The findings are in accord with the hypothesis. A model based upon a variable effective solubility for the hydroxyapatite crystal is proposed.

Chemical Phenomena↗
PubMed1977

Unusual dissolution behavior of tooth enamel and synthetic HAP crystals under high partial saturation conditions.

The dissolution behavior of enamel and synthetic hydroxyapatite in acidic media possessing a high degree of partial saturation was found to be neither simple surface dissolution nor linear with time. Instead, a repetitive, stepwise dissolution pattern was observed. To explain this phenomenon, a model based upon a hypothesis that the crystals dissolve in a synchronized fashion was proposed.

Buffers↗