Unbound Brain-to-Plasma Partition Coefficient, K(p,uu,brain)—a Game Changing Parameter for CNS Drug Discovery and Development

PURPOSE: More than 15 years have passed since the first description of the unbound brain-to-plasma partition coefficient (K(p,uu,brain)) by Prof. Margareta Hammarlund-Udenaes, which was enabled by advancements in experimental methodologies including cerebral microdialysis. Since then, growing knowledge and data continue to support the notion that the unbound (free) concentration of a drug at the site of action, such as the brain, is the driving force for pharmacological responses. Towards this end, K(p,uu,brain) is the key parameter to obtain unbound brain concentrations from unbound plasma concentrations. METHODS: To understand the importance and impact of the K(p,uu,brain) concept in contemporary drug discovery and development, a survey has been conducted amongst major pharmaceutical companies based in Europe and the USA. Here, we present the results from this survey which consisted of 47 questions addressing: 1) Background information of the companies, 2) Implementation, 3) Application areas, 4) Methodology, 5) Impact and 6) Future perspectives. RESULTS AND CONCLUSIONS: From the responses, it is clear that the majority of the companies (93%) has established a common understanding across disciplines of the concept and utility of K(p,uu,brain) as compared to other parameters related to brain exposure. Adoption of the K(p,uu,brain) concept has been mainly driven by individual scientists advocating its application in the various companies rather than by a top-down approach. Remarkably, 79% of all responders describe the portfolio impact of K(p,uu,brain) implementation in their companies as ‘game-changing’. Although most companies (74%) consider the current toolbox for K(p,uu,brain) assessment and its validation satisfactory for drug discovery and early development, areas of improvement and future research to better understand human brain pharmacokinetics/pharmacodynamics translation have been identified. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11095-022-03246-6.