A Novel Approach to Evaluate Amorphous-to-Crystalline Transformation of Active Pharmaceutical Ingredients in Solid...

The aim of this study was to demonstrate the usefulness of the time-domain NMR (TD-NMR) method to characterize the crystalline state of active pharmaceutical ingredients (APIs) containing a solid dispersion. In this study, indomethacin (IMC) was used as a model for poorly water-soluble API. Solid dispersions of IMC were prepared with polyvinylpyrrolidone (PVP) at different weight ratios. First, we measured the T₁ relaxation behavior of solid dispersions. From the result, the T₁ relaxation time (T₁) changed according to the API content; the T₁ tended to increase with increasing API content because the T₁ value of amorphous IMC was longer than that of PVP. Next, we tried to monitor the amorphous-to-crystalline transformation of IMC in the solid dispersion during the thermal stress test. In the case of solid dispersion containing 90% IMC, a clear prolongation of the T₁ could be observed during the thermal stress test. From the powder X-ray diffraction patterns, the change in T₁ relaxation behavior must be caused by the IMC transformation from amorphous to crystalline. From these findings, we were successful in monitoring the IMC amorphous-to-crystalline transformation by the changes in T₁ relaxation behavior. Our findings led us to conclude that TD-NMR is a novel approach for the evaluation of crystalline state of APIs in solid dispersions.