Objective: To investigate the release characteristics and mechanism of oridnonin self-microemulsifying drug delivery system (SMEDDS) in vitro.
Method: The concentration of oridonin was determined by HPLC. In vitro release studies were conducted by reverse dialysis technique. The effects of release medium, agitation rate and preparations on the oridonin release were studied. The similarity factor (f2) was applied to the release profile comparisons. Model fitting was used to determine the kinetics and mechanism.
Result: The release media and agitation rate from 50-100 r x min(-1) had no distinctive effect on the oridonin release kinetics, which the similarity factors were greater than 50. The oridonin release profiles for oridonin SMEDDS and oridonin ethanol solution were similar. 65% of oridonin were released in 30 min for oridonin SMEDDS in pH 7.8 PBS. Oridonin SMEDDS fit the Hixson-Crowell model best.
Conclusion: The release data from oridonin SMEDDS showed it release fast. The deduced release mechanism is that the surface and particle sizes of self-microemulsion in water solution are changing during the process of release and the drug penetration through membrane is a passive diffusion process.