| Thymopentin was a synthet(?)c penta-peptide corresponding to the active site of thymopoietin, a 49 amino acid hormone of the thymus. Its biological acitivity was similar to that of thymopoietin, and it had been used clinically as a modulator of the immune response or a co-adjuvant for serious illnesses. So far, the pharmaceutical products of TP-5 were injections, with the specification of 1mg. Once or twice per day by s.c. or i.v., and the course of treatment lasted from one month to 24 months. Frequent injections for long time impared the compliance of the patients and therapeutical efficacy. To overcome the shortcomings referred to, our research team prepared PLGA based micro-spheres with a water-oil-water emulsion solvent evaporation technique for 15～60 days controlled release. For the high solubility of TP-5 in water, significant burst effect(＞40%) happened in this sustained-release inject-able micro-spheres, which was an obstacle to the development of sustained-release inject-able micro-spheres.Objective: Prepare tp-5-loaded microspheres having the characteristics of low burst effect, well-distributed particle size, controlled release and good quality to break through the bottle-neck of sustained-release inject-able micro-spheres.Method: to establish the quality control method for items including the appearance,dispersibility,particle size and distribution,drug content,encapsulation efficiency,drug loading and release profile. Set the encapsulation efficiency and the burst effect as the main indexes, to investigate the influence of kinds of addictives on the characteristics of the microspheres. Further study was conducted on the mechanism about the burst effect reduced by addictive. Furthermore, different specifications and manufacturers of the PLGA, the production process for controlling particle size, drying process andγirradiation process were investigated. An orthogonal experiment was undertaken to optimize the formulation and production process. Evaluate the stability of TP-5 microspheres in influential factors experiment and long-term storage experiment. The drug release kinetics of TP-5/PLGA microspheres was studied by determining the residue drug in the injection site. Results: [1] burst effect controlling strategies add Tween-20,glucose to the inner water phase, or zinc carbonate,glycerol,acetoacetate to the oil phase, or sodium chloride to the outer water phase all could reduce the burst effect. Interestingly, the sodium chloride has better results than other addictives. The extent of reducing the burst effect was correlated with the osmotic pressure. When the concentration of sodium chloride in the external water phase was adjusted within 10～15mg/ml, low initial release (＜13%) was achieved. PLGA(50:50,0.55～0.75dl/g) provided by BPI or COCC could prepare high encapsulation and low initial release microspheres. Increasing the power of the homogenizers,the second emulsifying speed,extending the emulsifying time or adjusting the PVA concentration were benefit for the homogenicity of the particle size distribution. Freezing-drying was the best drying process, and theγirradiation would impact the stability, so sterile operation was suggested as the sterilization process. The results from the orthogonal experiment showed that the PLGA concentration was the most striking influential factor for the burst effect and the encapsulation efficiency, the secondly influential factor was the sodium chloride concentration. The optimization combination was comprised by the PLGA 250mg/ml, sodium chloride 10 or 15mg/ml, the second emulsifying speed 13000r·min-1, PVA 0.5%. [2] Stability Under the conditions of high temperature, high humidity and highlight, the microspheres became to agglomerate to different extent, and the dispersibility turned bad. But in the long-term storage experiment, no change on the particle size, the drug content or the burst effect was found. [3] The study of pharmacokinetics Determining the residual drug in the injection site by HPLC, with the addition of methanol to destroy the enzyme in the subcutaneous tissue. The PLGA (provided by the COCC) based microspheres, could controlled release for one month, and the initial release in vitro and in vivo were 12.03% and 3.70% respectively. The release profile in vivo meted the zero order equation. Good relativity was detected between the in vivo drug release and in vitro drug release.Conclusions: The normal distribution of particle size, D(4,3) within 30～65μm, high encapsulation(＞85%), low initial release (＜5%) and controlled release for one month are achieved by the optimization of the formulation and production process. This study have obtained the proposed objects.
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