PT  - JOURNAL ARTICLE
AU  - Stern, Stephan T.
AU  - Martinez, Marilyn N.
AU  - Stevens, David M.
TI  - When Is It Important to Measure Unbound Drug in Evaluating Nanomedicine Pharmacokinetics?
AID  - 10.1124/dmd.116.073148
DP  - 2016 Dec 01
TA  - Drug Metabolism and Disposition
PG  - 1934--1939
VI  - 44
IP  - 12
4099  - http://dmd.aspetjournals.org/content/44/12/1934.short
4100  - http://dmd.aspetjournals.org/content/44/12/1934.full
SO  - Drug Metab Dispos2016 Dec 01; 44
AB  - Nanoformulations have become important tools for modifying drug disposition, be it from the perspective of enabling prolonged drug release, protecting the drug molecule from metabolism, or achieving targeted delivery. When examining the in vivo pharmacokinetic properties of these formulations, most investigations either focus on systemic concentrations of total (encapsulated plus unencapsulated) drug, or concentrations of encapsulated and unencapsulated drug. However, it is rare to find studies that differentiate between protein-bound and unbound (free) forms of the unencapsulated drug. In light of the unique attributes of these formulations, we cannot simply assume it appropriate to rely upon the protein-binding properties of the traditionally formulated or legacy drug when trying to define the pharmacokinetic or pharmacokinetic/pharmacodynamic characteristics of these nanoformulations. Therefore, this commentary explores reasons why it is important to consider not only unencapsulated drug, but also the portion of unencapsulated drug that is not bound to plasma proteins. Specifically, we highlight those situations when it may be necessary to include measurement of unencapsulated, unbound drug concentrations as part of the nanoformulation pharmacokinetic evaluation.