Nanocrystal Preparation of Poorly Water-Soluble Drugs with Low Metal Contamination Using Optimized Bead-Milling Technology

Nanocrystal preparation using bead milling is an important technology to enhance the solubility of poorly water-soluble drugs. However, there are safety concerns regarding the metal contaminants generated during bead milling. We have previously reported optimized bead-milling parameters that could minimize metal contamination and demonstrated comparable performance to NanoCrystal^®, a world-leading contamination-free technology. This study aimed to investigate the applicability of optimized milling parameters for preparing nanocrystals of several poorly water-soluble drugs exhibiting various physicochemical properties. Using our optimized bead-milling parameters, we found that all the tested drugs could be ground into nanosized particles within 360 min. Notably, fenofibrate, which has a low melting point, could be ground into nanosized particles owing to the low level of heat generated during bead milling. Additionally, the concentration of metal contaminants in all the drugs prepared using the optimized milling parameters were approximately ten to twentyfold lower than those prepared without the optimized parameters and were comparable to those prepared using polycarbonate beads, known to minimize metal contamination during bead milling. Our results provide insights into the development of drug nanocrystals with low metal contamination using bead milling.

Development of Novel Bead Milling Technology with Less Metal Contamination by pH Optimization of the Suspension Medium

To develop novel contamination-less bead milling technology without impairing grinding efficiency, we investigated the effect of the formulation properties on the grinding efficiency and the metal contamination generated during the grinding process. Among the various formulations tested, the combination of polyvinylpyrrolidone and sodium dodecyl sulfate was found to be suitable for efficiently pulverizing phenytoin. However, this stabilization system included a relatively strong acid, which raised the concern of possible corrosion of the zirconia beads. An evaluation of the process clearly demonstrated that acidic pH promoted bead dissolution, suggesting that this could be suppressed by controlling the pH of the suspension. Among the various pH values tested, the metal contamination generated during the grinding process could be significantly reduced in the optimized pH range without significant differences in the particle size of the phenytoin suspension after pulverization. In addition, the contamination reduction by pH optimization in the presence of physical contact among the beads was approximately 10-times larger than that without bead contact, suggesting that pH optimization could suppress not only bead dissolution but also the wear caused by bead collisions during the grinding process. These findings show that pH optimization is a simple but effective approach to reducing metal contamination during the grinding process.