Mechanism of nanoparticle formation from ternary coground phenytoin and its derivatives

The mechanism of drug nanoparticle formation of phenytoin (DPH) and its derivatives monomethylphenytoin (MDPH) and dimethylphenytoin (DMDPH) was investigated. The drug, polyvinylpyrrolidone K17 (PVP), and sodium dodecyl sulfate were coground to obtain the ground mixture (GM). The DPH GM was amorphous; however, MDPH and DMDPH GMs contained drug crystals. Spectral changes in infrared and (13)C solid-state nuclear magnetic resonance were observed in the DPH GM, partially observed in the MDPH GM, and hardly observed in the DMDPH GM. Mean particle sizes of the DPH, MDPH, and DMDPH GM nanosuspension were almost the same; however, stability after storage differed in the order of DPH > MDPH > DMDPH. The intermolecular interaction between the drug and PVP reflected not only the crystallinity of the drug in the GM but also the stability of the GM suspension. The size and stiffness of drug nanoparticles were evaluated using atomic force microscopy. Crystallization of the amorphous GM and agglomeration of the primary nanocrystals were observed in the DPH GM suspension. In contrast, primary nanocrystals were observed in the DMDPH GM suspension. The size of the drug nanocrystals formed from the different molecular states of the drug in the GM reflects the agglomerated states in water and stability.