Rosin-glycerol ester microcapsules containing sulphadiazine were prepared by solvent evaporation technique. The goodness of fit of the release data was tested with first order, Higuchi matrix model and Hixon-Crowell cube root law. All these models were sufficiently linear. Application of the differential rate treatment showed that release from most of the microcapsules followed first order equation. Whereas up to 40-50 per cent of release, a zero order, membrane controlled kinetics was observed, the release is apparently first order under nonsteady, state conditions.
Shellac was chemically modified to alter its permeability and to prevent its 'after hardening'. Various shellac derivatives such as with succinic anhydride, phthalic anhydride, ethylenediamine and myristic acid were prepared. Salicylic acid granules were coated and evaluated for flow properties, moisture absorption and release characteristics before and after ageing. These derivatives imparted better flow properties and showed excellent ageing properties.
Free flowing, spherical rosin microcapsules were prepared by a method based on phase separation by solvent evaporation. Bentonite was used to prevent the agglomeration and coalescence of the dispersed polymer droplets. The effect of varying the core to coat ratio on micrometric and dissolution properties has been described.
Rosin was esterified with pentaerythritol and intermediate reaction products with different acid values were isolated. Microcapsules containing sulphadiazine were prepared by a solvent evaporation technique using these esters as wall materials. The microcapsules were evaluated for their size, drug content, and release characteristics in simulated gastric and intestinal fluids. The microcapsule size increased as the acid value of the ester decreased. The release of the drug was studied by using first-order, Higuchi and Hixon-Crowell cube root models. The release mechanism of the microcapsules is discussed.
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