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Biomedical subjects

S A Howard

Publications and source records attributed to S A Howard.

8 recordsLinked to original sources
PubMed1979

Hydrodynamic characterization of a spin-filter dissolution device.

The spin-filter dissolution device was characterized using a two-dimensional convective diffusion model. Experimental model testing involved analysis of dissolution rates from nondisintegrating salicylic acid disks. The disks were prepared as double-layer tablets, with an ethylcellulose layer as a nondissolving surface. For each dissolution run, the disk was positioned so that the dissolving salicylic acid surface was parallel to the flow of the circulating fluid. Experimental variables included the stirring speed, the tablet radius, and the distance of the tablet from the stirring source. At the farthest distance from the stirring source, the average numerical exponents for stirring speed and tablet radius were 0.58 and 1.54, respectively, which compare favorably with the values of 0.50 and 1.50 from the model. When the dissolving salicylic acid surface was positioned closer to the stirring source, the numberical exponent for the stirring speed increased significantly, while the average numerical exponent for the tablet radius was lowered to 1.07, indicating a change is dissolution mechanism as a function of distance from the stirring source. These data indicate that dissolution rates are not necessarily proportional to surface area as predicted by the Nernst equation and that distance from the stirring source is significant.

Chemistry, Pharmaceutical↗
PubMed1979

Suspending agent effects on steroid suspension dissolution profiles.

Dissolution profiles and particle-size analyses were determined for two lots of prednisolone acetate. The effects of common suspending agents on dissolution and particle-size distributions of these suspensions also were investigated. Lot-to-lot variation in the prednisolone acetate dissolution rate was observed and was apparently related to the percentage of fine particles within the distribution. Carboxymethylcellulose sodium inhibition of prednisolone acetate dissolution occurred with only one lot of raw material and seemed to be related to aggregation of the fine particles. Hydroxypropyl methylcellulose inhibited both prednisolone acetate lots and was observed with or without small particle aggregation. The dissolution variations observed have important implications in suspension formulation.

Excipients↗
PubMed1979

Tablet position and basket type effects in spin-filter dissolution device.

The effects of stirring and basket placement on tablet dissolution using the previously developed Shah spin-filter device were investigated. Visualization of flow and dissolution patterns was possible by testing nondisintegrating colored tablets. Dissolution experiments were conducted on nondisintegrating double-layered tablets containing salicylic acid as the dissolving layer and ethylcellulose as an inert nondissolving layer. Visual observations revealed that color was drawn more rapidly from the tablet face resting on the bottom of the basket. Dissolution data from multilayered tablets revealed that when the salicylic acid face was resting on the bottom of the basket, the dissolution was appreciably more rapid than when it was facing up in the basket. This phenomenon was found for several stirring speeds.

Diffusion↗
PubMed1978

Separation of multisized drug suspensions into narrow distributions by centrifugal elutriation.

A centrifugal elutriator rotor was used to separate suspensions of micronized hydrocortisone acetate and prednisolone acetate. Up to five distinct particle fractions could beisolated from a single parent suspension, and reasonable reproducibility was exhibited between various elutriator runs. Arithmetic means and associated standard deivations, based on volume, were calculated for each isolated fraction. These data demonstrate the narrowness and uniqueness of each fraction. The particle-size data show an apparent log-normal distribution for each isolate. The uniqueness of each fraction also was demonstrated by dissolution experiments where Fraction 1, the smallest fraction of prednisolone acetate, dissolved much more rapidly than Fraction 4, the largest fraction. The substantial difference in dissolution behavior of these two fractions of prednisolone acetate powder was biopharmaceutically significant.

Centrifugation↗
PubMed1977

Dissolution profiles for multisized prednisolone acetate suspensions.

Particle-size measurements and in vitro dissolution characteristics of commercial and formulated suspensions of prednisolone acetate were determined using a resistance particle counter and a spinning filter apparatus, respectively. Significant differences in dissolution rates were noted for the commercial suspensions. Particle size affected dissolution but did not account for all observed variations in the dissolution rate. Formulation differences, specifically the presence of hydroxypropyl methylcellulose, in suspensions seemed to be important in dissolution.

Chemistry, Pharmaceutical↗