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

Clin Pharmacol Ther. 2015 Apr;97(4):320-3. doi: 10.1002/cpt.72. Epub 2015 Feb 13.


The fraction of drug transported (ft) 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, ft 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 (Cu,b) of the drug. The latter is important to ascertain if Cu,b is sufficient for efficacy.

MeSH terms

  • Animals
  • Antiretroviral Therapy, Highly Active*
  • Antiviral Agents / pharmacokinetics*
  • Biological Transport
  • Blood-Brain Barrier / metabolism*
  • Carrier Proteins / metabolism
  • Central Nervous System / metabolism*
  • Drug Interactions
  • Humans
  • Membrane Transport Proteins / metabolism
  • Pharmaceutical Preparations / metabolism*


  • Antiviral Agents
  • Carrier Proteins
  • Membrane Transport Proteins
  • Pharmaceutical Preparations