The concept of fraction of drug transported (ft) with special emphasis on BBB efflux of CNS and antiretroviral drugs.

The fraction of drug transported (f_t) into or out of a tissue is a concept useful to understand the impact of transporters on absorption, distribution, metabolism, and excretion (ADME) and tissue distribution of a drug. Here, f_t is utilized to explain the impact of transporters on central nervous system (CNS) distribution of drugs, drug interactions (DDI), and to predict the unbound brain concentration (C_u,b) of the drug. The latter is important to ascertain if C_u,b is sufficient for efficacy. [ABSTRACT FROM AUTHOR]