All chemical entities that are developed for drug applications, regardless of whether they include nanoscale materials, possess unique characteristics and properties and therefore can, and do, present the FD A with novel challenges. Other than a comprehensive physicochemical characterization of nanoscale containing drugs, pharmacokinetic and biodistribution studies are crucial to help assess the safety and efficacy as well as to estimate clinical doses, dose linearity and species differences of such products [6]. It is important to note that there is a close relationship between the biodistribution profile and the physicochemical properties of the nanoparticles. Therefore, identification of whether nanoparticles can accumulate in target and non-target tissues is crucial for designing adequate safety studies. Because of the unique features in each product, there may be additional parameters that may require characterization depending on the nanomaterial. Such features have been reported to influence the biodistribution of nanomaterial containing drugs and possibly their safety [150]. Some of the important and critical evaluation parameters that are required for nanoscale product characterization are measurement of particle size, size distribution, shape, surface charge, stability, density, crystallinity, surface characteristics, solubility and aggregation state [151]. The aggregation/agglomeration state is evaluated as any change in the agglomeration may contribute to unpredictable variations in the PK profile [152].