Masataka Katsuma

Studies on lactulose formulations for colon-specific drug delivery

A novel, colon-targeted delivery system (CODES), which uses lactulose, was investigated in this study. Lactulose is not absorbed in the upper GI tract, but degraded to organic acids by enterobacteria in the lower gastrointestinal tract, especially the colon. A CODES consists of three components: a core containing lactulose and the drug, an inner acid-soluble material layer, and an outer layer of an enterosoluble material. When a CODES containing a pigment was introduced into the rat cecum directly after shaking in JP 2nd fluid for 3 h, pigment release was observed 1 h after introduction. A CODES containing 5-aminosalicylic acid (5-ASA) was orally administered to fasting and fed dogs to evaluate its pharmacokinetic profiles. 5-ASA was first detected in plasma after 3 h, which is the reported colon arrival time for indigestible solids, after dosing to fasting dogs. The T(max) in fed dogs was delayed by 9 h when compared to fasting dogs. This corresponds to the gastric emptying time. However, the C(max) and AUC under fed conditions were almost as same as those under fasting conditions. The results of this study show that lactulose can act as a trigger for drug release in the colon, utilizing the action of enterobacteria.

In vitro evaluation of dissolution behavior for a colon-specific drug delivery system (CODES™) in multi-pH media using United States Pharmacopeia apparatus II and III

United States Pharmacopeia dissolution apparatus II (paddle) and III (reciprocating cylinder) coupled with automatic sampling devices and software were used to develop a testing procedure for acquiring release profiles of colon-specific drug delivery system (CODES™) drug formulations in multi-pH media using acetaminophen (APAP) as a model drug. System suitability was examined. Several important instrument parameters and formulation variables were evaluated. Release profiles in artificial gastric fluid (pH 1.2), intestinal fluid (pH 6.8), and pH 5.0 buffer were determined. As expected, the percent release of APAP from coated core tablets was highly pH dependent. A release profile exhibiting a negligible release in pH 1.2 and 6.8 buffers followed by a rapid release in pH 5.0 buffer was established. The drug release in pH 5.0 buffer increased significantly with the increase in the dip or paddle speed but was inversely related to the screen mesh observed at lower dip speeds. It was interesting to note that there was a close similarity (f2=80.6) between the release profiles at dip speed 5 dpm and paddle speed 100 rpm. In addition, the release rate was reduced significantly with the increase in acid-soluble Eudragit E coating levels, but lactulose loading showed only a negligible effect. In conclusion, the established reciprocating cylinder method at lower agitation rates can give release profiles equivalent to those for the paddle procedure for CODES™ drug pH-gradient release testing. Apparatus III was demonstrated to be more convenient and efficient than apparatus II by providing various programmable options in sampling times, agitation rates, and medium changes, which suggested that the apparatus II approach has better potential for in vitro evaluation of colon-specific drug delivery systems.

A new stressed test to predict the foreign matter formation of minodronic acid in solution

A formulation containing 0.5 mg/ml minodronic acid, 40 mM citrate, pH 4.5, and sodium chloride, stored in regular flint glass ampoules, was stable without particulate increase under high temperature conditions, such as 40 degrees C for 6 months, or 50 or 60 degrees C for 3 months. However, when stored at 25 degrees C, there was an increase in >or=2 microm particles at the 5-month timepoint. This demonstrated that long-term stability cannot simply be predicted by the evaluation of samples just stored at higher temperatures. Therefore, a new stressed test was designed which is useful in the rapid selection of formulations that are stable and without particulate increase. Since the particulate matter is apparently a complex of minodronic acid and aluminum ions leaching from ampoules, samples were placed at 80 degrees C for up to 4 weeks to accelerate aluminum leaching. Although no particulate increase was observed directly after storage at 80 degrees C, 4 freeze-thaw cycles following the storage caused a drastic particulate increase. The evaluation of samples subjected to the freeze-thaw cycles indicated that the following formulation modifications have inhibitory effects on particulate generation: (1). addition of meglumine, diethanolamine, mannitol, or glycerol to the formulation; (2). increase of citric acid concentration; (3). decrease of minodronic acid concentration. These modifications also worked well for samples stored at 25 degrees C for 6 months, and particulate increase did not occur. This method is a powerful tool for predicting the stability of minodronic acid in solution.