[Effect of morphological properties on drug release from biodegradable microspheres]

Uniformity and physical states of troglitazone in solid dispersions determined by electron probe microanalysis and microthermal analysis

Solid dispersions of troglitazone with PVP K30 in a weight ratio of 1:2 were prepared by the closed melting method. Solid dispersions that exhibit different degrees of crystallinity (0 and 36%) were prepared by changing the charged amount of water, which functions as a plasticizer for PVP K30. Electron probe microanalysis (EPMA) and microthermal analysis (micro TA) of the solid dispersions were performed to investigate the uniformity and physical state of troglitazone in the solid dispersions. The EPMA study confirmed that troglitazone was dispersed homogeneously in the sample whose apparent crystallinity was 0%. However, the sample with a 36% crystallinity was heterogeneous. The micro TA study showed that the sample with a 36% crystallinity was present in two states, crystal and amorphous. EPMA and micro TA would be useful tools to confirm the uniformity and physical states, respectively, of solid dispersions.

Modification of release rates of cyclosporin A from polyl(L-lactic acid) microspheres by fatty acid esters and in-vivo evaluation of the microspheres

Biodegradable microspheres containing cyclosporin A (CyA, cyclosporine) were prepared using poly(L-lactic acid) (PLA) and poly(lactide-co-glycolide)(PLGA) by a solvent evaporation method. CyA was efficiently entrapped in PLA, PLGA(50/50) and PLGA(75/25) microspheres in a range of 81-85%. CyA released constantly from PLA microspheres without any lag time, whereas the drug from PLGA(50/50) and PLGA(75/25) microspheres was released after lag time of about 1 and 3 weeks, respectively. Addition of fatty acid esters enhanced the release rates of CyA from PLA microspheres. In-vivo study was performed using rats with adjuvant-induced arthritis. PLA microspheres with ethyl myristate sustained high blood levels of CyA compared with the microspheres with no additives over 4 weeks. In addition, the PLA microspheres improved the symptoms such as the decrease in body weight and the increase in paw swelling occurred by adjuvant-induced arthritis in rats. Consequently, the release rate of CyA from PLA microspheres can be improved by adding fatty acid esters and PLA microspheres with fatty acid esters seem to be a useful dosage form for autoimmune disease therapy.