SIMPLE COACERVATION OF HYDROXYPROPYL METHYLCELLULOSE PHTHALATE (HPMCP) .2. MICROENCAPSULATION OF IBUPROFEN

Microencapsulation with hydroxypropyl methylcellulose phthalate (HPMCP ) through simple coacervation by the addition of 20% (w/w) sodium sulp hate solution was investigated on the basis of the temperature-depende nt coacervate formation of the polymer. The nonsteroidal antirheumatic drug ibuprofen was used as model substance. This paper describes the microencapsulation process and the resulting microcapsules. Furthermor e, the influence of docusate sodium present during encapsulation was i nvestigated with respect to the phase separation behaviour of HPMCP an d the wall characteristics of the microcapsules. Simple coacervation o f HPMCP is a suitable method for the microencapsulation of ibuprofen. The coacervate enveloped the suspended drug which had no effect upon t he phase separation of the polymer owing to the low solubility of ibup rofen in the HPMCP solution, The microencapsulation process was contro lled by temperature increase: additional coacervate for the coating of the drug crystals was formed and the resulting coacervate shells were subsequently prehardened by jelling. This enabled the recovery and is olation of the microcapsules to be performed. The coating of the drug crystals occurred as twins and multiples when microencapsulation was p erformed without surfactant; SEM micrographs demonstrated the high she ll quality of the microcapsules and polymer yield calculations showed the almost complete utilization of the coacervate for enveloping the d rug crystals in surfactant-free systems. Small amounts of docusate sod ium present during microencapsulation resulted in a more individual en capsulation of the ibuprofen crystals; however, coating by the coacerv ate was incomplete and the microcapsules showed clod-like polymer shel l deficiencies. As a consequence, an increased release rate of ibuprof en at pH 4.0 was observed compared to microcapsules prepared without u sing surfactant. Since docusate sodium had no effect upon the phase se paration behaviour of HPMCP under the conditions used for microencapsu lation, the incomplete polymer coating was attributed to competition b etween surfactant and coacervate for the solid/liquid interface.