This study reports the appearance and characterization of multiple new polymorphic forms of indomethacin. Considering the interest in amorphous suspensions for toxicology studies of poorly water-soluble drugs, we sought to investigate the crystallization behavior of amorphous indomethacin in aqueous suspension. Specifically, the effect of pH and temperature on crystallization behavior was studied. Quench cooled amorphous powder was added to buffered media at different pH values (1.2, 4.5, and 6.8) at 5 and 25 °C. Both the solid and the solution were analyzed at different time points up to 24 h. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy (with principal component analysis) was used to study solid-phase transformations and ultraviolet (UV) spectroscopy used to probe solution concentration. The crystallization onset time decreased and rate of crystallization increased with increasing pH and temperature. Diverse polymorphic forms were observed, with three new forms being identified; these were named ε, ζ, and η. At 25 °C, the amorphous form recrystallized directly to the α form, except at pH 6.8, where it initially converted briefly into the ε form. At 5 °C, all three new polymorphic forms were observed sequentially in the order ε, ζ, and then η, with the number of these forms observed increasing sequentially with decreasing pH. The three new forms exhibited distinct X-ray powder diffraction (XPRD), differential scanning calorimetry (DSC), and FTIR and Raman spectroscopy profiles. The solution concentration profiles suggest that the relative physical stabilities of the polymorphs at 5 °C from lowest to highest is ε < ζ < η < α. The appearance of new polymorphs in this study suggests that amorphous suspensions are worth considering when performing polymorphic screening studies.

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Traditionally, the development of a new solid dosage form is formulation-driven and less focus is put on the design of a specific microstructure for the drug delivery system. However, the compaction process particularly impacts the microstructure, or more precisely, the pore architecture in a pharmaceutical tablet. Besides the formulation, the pore structure is a major contributor to the overall performance of oral solid dosage forms as it directly affects the liquid uptake rate, which is the very first step of the dissolution process. In future, additive manufacturing is a potential game changer to design the inner structures and realise a tailor-made pore structure. In pharmaceutical development the pore structure is most commonly only described by the total porosity of the tablet matrix. Yet it is of great importance to consider other parameters to fully resolve the interplay between microstructure and dosage form performance. Specifically, tortuosity, connectivity, as well as pore shape, size and orientation all impact the flow paths and play an important role in describing the fluid flow in a pharmaceutical tablet. This review presents the key properties of the pore structures in solid dosage forms and it discusses how to measure these properties. In particular, the principles, advantages and limitations of helium pycnometry, mercury porosimetry, terahertz time-domain spectroscopy, nuclear magnetic resonance and X-ray computed microtomography are discussed.

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PurposeA 3D printer was used to realise compartmental dosage forms containing multiple active pharmaceutical ingredient (API) formulations. This work demonstrates the microstructural characterisation of 3D printed solid dosage forms using X-ray computed microtomography (XμCT) and terahertz pulsed imaging (TPI).MethodsPrinting was performed with either polyvinyl alcohol (PVA) or polylactic acid (PLA). The structures were examined by XμCT and TPI. Liquid self-nanoemulsifying drug delivery system (SNEDDS) formulations containing saquinavir and halofantrine were incorporated into the 3D printed compartmentalised structures and in vitro drug release determined.ResultsA clear difference in terms of pore structure between PVA and PLA prints was observed by extracting the porosity (5.5% for PVA and 0.2% for PLA prints), pore length and pore volume from the XμCT data. The print resolution and accuracy was characterised by XμCT and TPI on the basis of the computer-aided design (CAD) models of the dosage form (compartmentalised PVA structures were 7.5 ± 0.75% larger than designed; n = 3).ConclusionsThe 3D printer can reproduce specific structures very accurately, whereas the 3D prints can deviate from the designed model. The microstructural information extracted by XμCT and TPI will assist to gain a better understanding about the performance of 3D printed dosage forms.Electronic supplementary materialThe online version of this article (doi:10.1007/s11095-016-2083-1) contains supplementary material, which is available to authorized users.

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