Current Advances in Sustained-release Injectable Preparations

In recent years, there has been a great deal of interests in developing sustained-release systems which can prolong the therapeutic effect, decrease adverse side effects, and reduce administration frequency. Nowadays, the oral sustained-release preparations account for a larger market share comparing to other sustained-release forms, mainly because of its noninvasive pain-free administration. However, the hostile environment of gastrointestinal tract and first-pass effect may lead to low bioavailability of some drugs, such as some proteins, peptides, and hormones. In this paper, the latest research progresses of some new-model sustained-release injectable dosage forms were introduced, including microsphere, microcapsule, liposome, polymeric micelle, and in situ forming system. INTRODUCTION: Since 1960s, sustained-release preparations have been widely studied because of the prominent advantages: less administration frequency, low toxicity, and longer action time enhancement . Recently, many types of sustained-release preparations have been marketed and accepted by most patients; in addition, the oral sustained-release preparations exhibited more superiority in market share compared with other formulations. However, sometimes oral administration cannot achieve a good absorption mainly due to the hostile environment of gastrointestinal tract and first-pass effect 2, . Therefore, more and more researchers focus on the investigations of the sustained-release injectable preparations. Except for the common advantages of the sustainedrelease preparations, injectable preparations exhibited some special merits when compared with others. Generally, injectable preparations have a better bioavailability than oral preparations, so are the sustained-release preparations. The sustained effects of oral sustained-release preparations are restricted by the gastrointestinal tract, so the sustained-release injectable preparations can reach a much longer action time than the oral sustained-release preparations and some sustainedrelease injectable preparations could attain a consistent drug release for a period of more than one month. However, the more important virtue is that the sustained-release injectable preparations can improve targeting effects and reduce systemic toxicity through local steroid injection. Nowadays, sustained-release injectable preparations have developed rapidly and been widely used in contraception , tissue repair , oncotherapy 6 and treatment in patients with bipolar disorder .