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Periodontal disease is one of the world's most common chronic diseases, and is thought to lead to some systemic disease risk factors, periodontal disease is a serious threat to people's quality of life. Traditional delivery method - systemic administration, side effects, and low bioavailability. The local administration allows the retention of the drug in the periodontal pocket, but the use of some preparations to patients suffering, compliance is poor, resulting in poorer treatment outcomes. A novel sustained release drug delivery system - in situ gel to resolve the many issues. In situ gel (in situ gel, ISG) is the use of polymer material in response to external stimulation, the dispersion state or conformation of the polymer to occur under physiological conditions a reversible change, complete conversion from a solution to the gel. Accordingly, in situ gel can be divided into the temperature-sensitive, pH-sensitive, ion-sensitive or removal of the solvent precipitation type and many other types. Wherein removing the solvent precipitation in situ gel suitable for use in the treatment of periodontal disease. Situ gels can be injected through a small needle into the periodontal pocket, solidified after contact with the gingival sulcus fluid (GCF), and adheres to the periodontal pocket, sustained release drug, the drug concentration in the periodontal pocket, improved bioavailability, increased efficacy and reduce the adverse reactions. After completion of the drug release, it is not necessary to remove the self-degradation, thereby increasing patient compliance. Combined with a simple preparation, in situ gel has a very good value and broad prospects for development. This study selected the doxycycline drug of choice for treatment of periodontal hydrochloride as a model drug to biodegradable the good biocompatibility PLGA accessories, a safe, non-toxic NMP as solvent hydrochloride doxycycline in situ gel. Through the needle and solidification of the different components of the preparation of hydrochloric multi doxycycline situ gel initial visits. Major factor in determining the impact hydrochloride doxycycline situ gel in vitro release single factor, and the results are analyzed and discussed. By orthogonal test, as the marker of in vitro release formulation optimization. Ultimately determine the prescription: PLGA (Mn = 10000), a concentration of 25%, the NMP concentration of 65%, a drug concentration of 10%. In this study, the quality evaluation of multi-the doxycycline situ gel hydrochloric acid prepared in accordance with the best prescription. Its appearance is transparent, uniform color, yellow liquid with good fluidity. The rheological study results show that the in situ gel as a Newtonian fluid, good liquidity. More hydrochloric acid prepared in accordance with the optimal prescription doxycycline situ gel at 37 ℃, the burst release of about 20% within 2 hours, followed by slow release up to 10 days, the cumulative release rate of 90%. The in situ gel to a release by the release mechanism of preliminary research shows that the main line Fick diffusion mechanism. HPLC determination of doxycycline hydrochloride content, the results show the content to meet the requirements. Initially investigated hydrochloride doxycycline situ gel stability and irritating. The results show that the in situ gel sensitive to light should be dark; \
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