Aminoalkyl methacrylate copolymers for improving the solubility of tacrolimus. I: Evaluation of solid dispersion formulations

The aim of this study was to investigate the effect of Eudragit E®/HCl (E-SD) on the reprecipitation of a poorly water-soluble drug, tacrolimus. To evaluate the inhibition of reprecipitation of E-SD, reprecipitation studies on tacrolimus were conducted using a dissolution test method. Solubility of tacrolimus was measured at regular intervals in a dissolution media, in which tacrolimus was dissolved in ethanol, and the test media contained additives for inhibiting precipitation. Supersaturation profiles of tacrolimus were observed, and were maintained for 24 h only with E-SD. Solid dispersion formulations of tacrolimus prepared with hydroxypropylmethylcellulose (HPMC) or E-SD in different drug/carrier ratios were also investigated. Solid dispersions prepared with E-SD showed higher solubility of tacrolimus compared with that of HPMC. In the E-SD formulation, the drug solubility influences to drug/carrier ratio. The formulation of drug/E-SD (1/5) showed the highest drug solubility. Thus, it may be inferred that a definite drug/carrier ratio exists to increase drug solubility. Further, by mixing E-SD the solid dispersion prepared with HPMC showed enhanced drug solubility.