Investigation on the in vitro and in vivo release of biodegradable PLGA (9:1) microspheres containing levonorgestrel

OBJECTIVE: To evaluate the release of PLGA (9:1) microspheres containing levonorgestrel in vitro and in vivo. METHODS: The pharmacokinetics of levonorgestrel(LNG) in the form of injectable biodegradable PLGA (9:1) microspheres containing LNG were tested in rats by means of RIA method. The drug release in vitro was determined by means of LTV spectrophotometry. RESULTS: The release profiles of microspheres showed a similar pattern in vitro and in vivo. A similar two-peak release was observed: the first peak of the release was diffusion controlled, and a secondary rise in the drug level related to the onset of degradation of the PLGA. Between the first peak and the second, there was about 70% steady release in vitro and in vivo. The first peak of plasma LNG of the microspheres was significantly lower than that of LNG microcrystal, but MRT of the microspheres was about 6 times as long as that of LNG microcrystal. CONCLUTION: The drug release from PLGA (9:1) microspheres in vitro correlated well with that in vivo. The microspheres have remarkablely long control release action.