I knew what is is Distribution of drug but I think somewhere along my medical school I might have missed reading about REdistribution of drug. Here's what it is:
It applies to lipid soluble drugs only.
I will explain with an example:
You inject thiopentone. It goes into the blood. Everyone knows how quickly it crosses the Blood brain barrier because of its really quick onset of action. Despite this, its halflife is about 9hrs! How? Redistribution. After its effect, the drug comes back to blood, gets redistributed in adipose tissue. Some of it may even go back to the blood and cross BBB.
Why is this important?
If increasing concentrations of the drug is given, drug builds up in adipose tissue, and eventually rising concentrations enter the BBB with time.