Control of encapsulation efficiency in polymeric microparticle system of tolmetin.

Ethylcellulose microparticles containing tolmetin sodium, an anti-inflammatory drug, were prepared by a solvent diffusion method based on the formation of multiple W/O(1)/O(2)-emulsion. The drug used was TOL, which is water-soluble and n-hexane was used as the non-solvent. Important parameters in the evaluation of a microencapsulation technique are actual drug loading, the encapsulation efficiency, the yield, solvent systems, dispersed phase to continuous phase ratio (DP/CP ratio), composition of continuous phase, drug distribution in microparticles and stability of primary emulsion. A small volume of internal aqueous phase and volume of organic solvent were favorable to achieve high drug encapsulation efficiencies. Since drug release during the initial stages depends mostly on the diffusion escape of the drug, major approaches to prevent the initial burst have focused on efficient encapsulation of the drug within the microparticles. For this reason, control of efficiency and the extent of initial burst are based on common formulation parameters. Most parameters affect encapsulation efficiency and initial burst by modifying solidification rate of dispersed phase. In order to prevent many unfavorable events such as pore formation, drug loss, and drug migration that occur while the dispersed phase is in the semi-solid state, it is important to understand and optimize these variables.