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eye on counterfeiting and product diversion. This is done through track-and-trace technologies. To date, the majority of PI has been at the package level, using barcodes, holograms, and other pro- prietary security features on the bottle or printed on the label. However, because packaging has proven to be relatively easy to counterfeit, there is great interest in using a PI technology at the dose (tablet, capsule) level. For dose-level PI, companies have relied on composition-measurement tech- nologies, which seek to determine what is in the dose under examination. Oftentimes, however, there is no way to confirm the production details (lot number, date of manufacture, location of manufacture) nor to identify diverted products in a case of goods in which authentic drug products are dis- covered in unexpected or unsanc- tioned channels or territories. Because of the limitations of current package- level and dose-level identification, and industry demand for more advanced dose-level solutions, the FDA pub- lished a Guidance in 2011 on incorpo- rating on-dose anti-counterfeiting technologies, referred to as physical- chemical identifiers (PCIDs), for use in solid oral dosage forms (SODFs) [1]. The approach outlined in the Guidance is to introduce a trace amount of an inactive ingredient to an SODF product so it can be detected to authenticate the product and thus identify counterfeits. This Guidance has helped to accelerate the development of poSi-based mate- rials and technologies. SiO 2 is affirmed as Generally Recognized as Safe (GRAS) by the FDA, so it is considered edible and can be added at substantial levels (2 percent w/w, according to the FDA). Moreover, as noted above, silica has been used extensively in the pharmaceutical and nutraceutical industries, so it is well-accepted as a common excipi- Tablets & Capsules October 2017 43 Craig Leidholm TruTag Technologies excipients This edition of the column discusses how porous silica provides on-dose product identification and improves patient compli- ance with targeted, sustained drug release. Silica is well known in the phar- maceutical industry as an excipient. While pure silica, SiO 2 , is common, there are silicates of calcium, magne- sium, and aluminum that are widely used as anti-caking agents, glidants, opacifiers, and viscosity modifiers. These silicas are considered bulk solids and come in many forms, including flakes, pellets, granules, and even nanoparticles. There is another class of silica excipients that are of interest in pharmaceuticals: porous silica (poSi). PoSi, as the name implies, is sim- ply silica that has some level of pores throughout the solid body. These poSi materials are typically catego- rized by pore size, where silica with pores of less than 2 nanometers (nm) are considered microporous, and sil- ica with pores 2 to 50 nm are meso- porous, and when the pores exceed 50 nm, they are called macroporous. Sometimes the bulk of these three categories are more generally called "nanoporous," which indicates pores smaller than 100 nm. The pore size, as well as the level of porosity, are important to the silica's functional- ization and applications. Applications in product identification Pharmaceutical and nutraceutical companies have focused on product identification (PI) to reveal and deter Silica is a common excipient, which makes porous silica particles excellent candidates for use in pharmaceutical and nutraceutical products as unique identifiers.