Long-acting injectables are a unique drug formulation strategy, providing a slow and sustained release of active pharmaceutical ingredients (APIs). In this study, a novel approach that combines liquid antisolvent precipitation with seeding to obtain a stable form of the API indomethacin while achieving the desired particle size distribution is described. It was proven that when a metastable form of indomethacin was initially nucleated, the rate of its transformation to the stable form was influenced by the presence of excipients and seeds (17.10 ± 0.20 μm), decreasing from 48 to 4 h. The final particle size (D50) of the indomethacin suspension produced without seeding was 7.33 ± 0.38 μm, and with seeding, it was 5.61 ± 0.14 μm. Additionally, it was shown that the particle size distribution of the seeds and the time point of seed addition were critical to obtain the desired solid-state form and that excipients played a crucial role during nucleation and polymorphic transformation. This alternative, energy-efficient bottom-up method for the production of drug suspensions with a reduced risk of contamination from milling equipment and fewer processing steps may prove to be comparable in terms of stability and particle size distribution to current industrially accepted top-down approaches.

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