Studies On Injectable,Biodegradable,and Sustained-Release Microspheres Loaded With Estradiol

Estradiol (E2) was chosen as a lipophilic model drug and Poly (D,L-lactic acid) (PLA) or D,L-lactide/glycolide copolymer (PLGA) were used as carriers to prepare biodegradable and biocompatible microspheres (MS) with sustained release of drug for parenteral application in this paper. Furthermore, drug release behavior in vitro and in vivo and release mechanism of different types of MS were deeply studied.An emulsification-solvent extraction method, an emulsification-mixed solvent extraction method or an emulsification-solvent evaporation method was used to prepare MS separately. The criteria to evaluate the MS included the appearance, particle's size and size distribution, the drug loading percent, drug entrapment efficiency, the yield percent, and so on. An analysis of variance (ANOVA) was used to test the effect of various factors on results. Then multiple comparisons were done with a Turkey's method (T-method) between levels to see the significance of difference further. All the results were considered statistically significant if p<0.05. Then the principle component analysis was used to standardize the results and systemic analysis was done. Optimal formulation was chosen and MS were formed with good properties. Results of comparison showed that MS with different interior structure were formed when prepared with different method. MS formed with the emulsification-solvent evaporation method were in good appearance and had porous matrix inside like "honeycomb", while MS formed with the emulsification-solvent extraction method had a dense surface layer and their inner structure was hollow, but some deflects were seen on the surface. When emulsification-mixed solvent extraction method was used with tetrahydrofuran added at some volume ratio and the drug loaded percent increased, MS had good appearance although drug crystals were seen on the surface.Since there was no consensus on which method should be selected, different methods were used in this paper to study the drug release behavior in vitro and comparisons were done. First, commonly used dialysis method was studied comprehensively. Models were established, mathematic formula were derived and the permeation constant (K) of free drug through dialysis membrane was determined. Model fitting was done and the character of drug release kinetics and the drug release rate constants (km or km' ) were obtained. Second, based on the sample and separate techniques, a modified direct drug release method in vitro was created, and phosphate buffer saline (PBS, pH 7.4) containing hydroxypropyl-p-cyclodextrin (HP-CD) as the solubilizer was used as the release media. Through the model fitting, thedrug release mechanisms at various periods were judged, and the fraction (a) of drug released in the initial burst release phase and the drug release rate constant (k') controlled by a polymer degradation mechanism and time to maximum drug release rate (Tmax) were determined for MS with various formula. It was proved that the established direct drug release method was suitable for evaluation of drug release in vitro from injectable MS loaded with lilophilic estradiol. The establishment of this method was of innovative significance internationally. Finally, study was done on the accelerated drug release in vitro. The results showed that when done in solutions with various concentration of NaOH (37), it had good ability to predict the real-time drug release in vitro controlled by polymer degradation mechanism through introduction of time scale factor. Furthermore the accelerated drug release in vitro could response rapidly to the changes in the formulation, technology and various drug release mechanisms. The corresponding references regarding the accelerated drug release method in vitro based on the drug release mechanism for MS depots could not been found domestically. In addition, the results of stability experiments indicated that this product was stable when stored tightly, dryly and under low temperature (4-8) .In the pharmacokinetics and pharmacodynamics study of M...