Abstract
The releasing rate of poly(3-hydroxybutyrate)-P(3HB)-microspheres containing Lastet, an anti-cancer agent, was investigated both in vitro and in vivo. The rate of the release of Lastet from P (3HB) microspheres was very small and only 20% was released during a 15-day period. The addition of glycerol tristearate (GTS) to P (3HB) increased the releasing rate of Lastet and P (3HB) microspheres which contained 25% GTS released 100% of the Lastet during a 10-day period. P (3HB) microspheres which contained 25% GTS and 10% Lastet were administered intraperitoneally to rats and the change of Lastet concentration in blood and tissue was investigated. Although in low levels, Lastet was detected in the blood up to day 3 after administration but not on day 7. Lastet was detected in high levels in the peritoneal tissue up to day 3, but not on day 7, although the microspheres were confirmed histologically. The change of the surface property of microspheres confirmed by scanning electron micrographs suggested that the decomposition of P (3HB) in vivo may be accelerated by some enzyme to increase the release of drugs.
