We use terahertz (THz) time-domain spectroscopy (TDS) to assess the crystalline state of indomethacin (IM) when loaded in smartFilms®. We found that smartFilms favour the amorphous IM (A-IM) for low loading concentrations. For higher concentrations, IM recrystallizes in its $$\alpha$$ α - crystalline form and the amount of A-IM in the smartFilms reduces. Both, $$\alpha$$ α - and A-IM are preferred over the more common $$\gamma$$ γ - crystalline form, as they exhibit better water solubility, which can increase the oral bioavailability of the drug.

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We use terahertz time-domain spectroscopy for non-destructive crystallinity investigation of poorly soluble drugs loaded into paper. Our results underline the great potential of terahertz spectroscopy as an analytical tool to study pharmaceutical formulations.

(1) Background: Amorphous drug systems are an intensively studied approach to overcome the insufficient bioavailability of poorly soluble drugs. Here, paper tablets were studied, which were made from cellulose-based paper matrices loaded with norfloxacin. Moreover, wet granulation was introduced as an additional processing step for improving the flowability of the solids, which is necessary when considering production on an industrial scale. (2) Methods: The possible impact of the wet granulation on the crystallinity of norfloxacin was studied by examining granulated and non-granulated samples. Crystallinity investigations were performed using X-ray powder diffraction (XRD) and terahertz time-domain spectroscopy (THz TDS). (3) Results: THz TDS allowed for a more straightforward crystallinity assessment than XRD. Moreover, using THz TDS, it was possible to detect minor changes in the crystallinity of the API after the granulation, whereas this was not possible with the XRD analysis. (4) Conclusions: THz TDS results indicate a partial crystallization of norfloxacin due to the wet granulation. Depending on the formulation, THz TDS can serve as a beneficial and advantageous tool to determine the crystallinity of an API.

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