The effect of Carbopol 934 rheological properties on the dissolution rate of sulphadamidine crystals.

This thesis investigates possible mechanisms by which a binding agent reduces the dissolution rate of a drug. For this the polymer Carbopol 934 (BF Goodrich) and a model drug, sulphadimidine, were chosen because their physicochemical properties could be changed by experimental variables, namely pH, temperature and salt concentration. Three forms of sulphadimidine were produced; recrystallized, coated by coprecipitation from aqueous solution and coated by coprecipitation from organic solvent. Their physical characteristics were elucidated using particle size analysis (Coulter), chemical analysis, X-ray diffraction and optical and scanning electron microscopy. The saturation solubility of sulphadimidine was determined for each of the experimental variables and in the presence of Carbopol. The rheological properties of Carbopol dispersions, using the variables, were determined using flow (to simulate bulk flow in a dissolution process) and oscillatory (to simulate stationary layer properties in dissolution) modes of controlled stress rheometer (Carrimed). The dissolution rates of the three forms of sulphadimidine were determined using a flow-through dissolution system (Copley). The pH-dissolution rate and pH-saturation solubility profiles for plain sulphadimidine indicated that a diffusion controlled dissolution process was involved. The presence of Carbopol in aqueous coprecipitate reduced the dissolution rate. The effect was more marked at low pH where Carbopol solubility was at its lowest. The dissolution rates of the organic coprecipitate indicate the same behaviour at low pH. At high pH, where Carbopol dissolves readily, it has no effect on dissolution rate. Thus an occlusion of sulphadimidine surface by Carbopol was observed at low pH. There was no evidence that the rheological properties of Carbopol, in either the bulk liquid or stationary layer, had a controlling effect on dissolution rate of sulphadimidine.

Grantor dc:publisher.institution

Robert Gordon University

Year dc:date.issued

1995

Author dc:creator

• Muungo, Lungwani Tyson Makoye

Advisor dc:contributor.advisor

• A.J. Winfield

• Sulphadimidine dissolution
• Carbopol 934
• Coprecipitation
• pH‑dependent solubility
• Rheological properties
• Diffusion controlled dissolution

Language dc:language

en

Identifier

oai:rgu-repository.worktribe.com:2807503
https://doi.org/10.48526/rgu-wt-2807503

OAI identifier oai:identifier

oai:rgu-repository.worktribe.com:2807503