Time-and pH-dependent colon-specific drug delivery for orally administered diclofenac sodium and 5-aminosalicylic acid

AIM: To investigate Time- and pH-dependent colon-specific drug delivery systems (CDDS) for orally administered diclofenac sodium (DS) and 5-aminosalicylic acid (5-ASA), respectively. METHODS: DS tablets and 5-ASA pellets were coated by ethylcellulose (EC) and methacrylic acid copolymers (Eudragit L100 and $100), respectively. The in vitro release behavior of the DS coated tablets and 5-ASA coated pellets were examined, and then in vivo absorption kinetics of DS coated tablets in dogs were further studied. RESULTS: Release profile of time-dependent DS coated tablets was not influenced by pH of the dissolution medium, but the lag time of DS release was primarily controlled by the thickness of the coating layer. The thicker the coating layer, the longer the lag time of DS release is. On the contrary, in view of the pH-dependent 5-ASA coated pellets, 5-ASA release was significantly governed by pH. Moreover, the 5-ASA release features from the coated pellets depended upon both the combination ratio of the Eudragit~ L100 and S100 pH-sensitive copolymers in the coating formulation and the thickness of the coating layer. The absorption kinetic studies of the DS coated tablets in dogs demonstrated that in vivo lag time of absorption was in a good agreement with in vitro lag time of release. CONCLUSION: Two types of CDDS, prepared herein by means of the regular coating technique, are able to achieve site-specific drug delivery targeting at colon following oral administration, and provide a promising strategy to control drug release targeting the desired lower gastrointestinal region.

A Survey and Statistics of Interstellar OH and H_2O Masers

We present a statistical analysis of a sky survey of interstellar H2O and OH masers. These masers can be classified into three categories: isolated H2O masers, isolated OH masers, and simple OH/H2O maser associations. The total number of sources in each category is of the same order of magnitude, and as an evolutionary phase they can maintain ~ 105 yr. An improved radiative pumping mechanism is proposed. This model avoids some of the deficiencies of previous radiative models, such as shortage of exciting photons. The statistical results obtained from the survey can be interpreted by the new mechanism together with the evolutionary model in which the gravitational force of the central stellar objects is responsible for the HII region.

A Possible Pumping Mechanism for Interstellar Class Ⅱ107 GHz Methanol Masers

It is recognized that the interstellar methanol-107GHz masers and OH-4.765 GHz masers towards Class II sources are associated with each other and coexist towards ultracompact HII regions. Therefore we suggest a new pumping mechanism - methanol masers without population inversion. It can explain the formation of 107GHz methanol masers, with the 4.765 GHz OH masers acting as a driving coherent microwave field. It is argued that this mechanism is compatible with the astronomical conditions.