Recently,
tacrolimus was shown to be effective in mitigating
inflammatory bowel disease (IBD). In the treatment of IBD, oral
drug delivery using pH-dependent
polymers is one of the most successful therapeutic strategies.
Eudragit P-4135F, a pH-sensitive
polymer for colonic delivery was used to prepare
tacrolimus microparticles using an oil/oil emulsification or an oil/water emulsification technique combined with a
solvent extraction or evaporation step. Although the pH-dependent drug release was similar for all types of
microspheres, it was generally found that encapsulation rates of oil/water systems (extraction 38.8 +/- 9.4%; evaporation 56.3 +/- 1.9%) were superior to the oil/oil emulsification (4.8 +/- 0.4%).
Eudragit P-4135F was found to limit
drug leakage at pH 6.8 to levels lower than 10% within 6 h. At pH 7.4, almost immediate release (within 30 min) was observed. From differential scanning calorimetry and X-ray analyses, the
drug inside the polymeric
microsphere matrix was concluded to be present in a molecular dispersion. Generally, all formulations proved their applicability in vitro as a promising device for pH-dependent colonic delivery of
tacrolimus, however, the oil/water technique was found to be superior to the oil/oil approach and among them
solvent evaporation seemed to be more advisable, due to the higher encapsulation rate.