Impact of stabilizers on particle size and dispersion behavior in biorelevant media in solid nanocrystal formulations

Nanocrystalline formulations typically contain stabilizing additives to minimize the risk of particle growth or agglomeration. This risk is particularly relevant when the nanosuspension is converted into a solid drug product as the original state of the nanosuspension should be restored upon redispersion of the drug product in vivo. In this work, the behavior of different nonionic and anionic surfactants in solid nanocrystalline formulations and their effects on redispersibility under biorelevant conditions were investigated. For this purpose, nanocrystalline formulations of basic (itraconazole, ritonavir), acidic (naproxen), and neutral (fenofibrate) API containing nonionic polymers acting as steric stabilizers combined either with anionic (sodium dodecyl sulfate, deoxycholate sodium, docusate sodium) or non-ionic surfactants (polysorbate 80, vitamin E-TPGS) were manufactured by nano-milling. These formulations were turned into a solid drug product by lyophilization and their redispersibility was tested by dispersing them in biorelevant media with different pH values and by characterizing their particle size distribution (PSD) and surface charge. In the absence of an anionic surfactant, it was difficult to achieve particle sizes below 500 nm. However, formulations stabilized anionically were at risk of agglomeration in gastric media. For basic API, the agglomeration was reversible for formulations containing sodium deoxycholate after increasing the pH from acidic to neutral levels, but it was found to be irreversible for those containing sodium dodecyl sulfate and docusate sodium. In summary, the type of anionic stabilizer and its interplay with the physicochemical properties of the API (basic, acidic, or neutral) should be considered in the development of solid nanocrystal formulations.