Drug accumulation ratio

The accumulation ratio of a specific drug in humans is determined by clinical studies. According to a 2013 analysis, such studies are typically done with 10 to 20 subjects who are given one single dose followed by a washout phase of seven days (median), and then seven to 14 repeated doses to reach steady state conditions. Blood samples are drawn 11 times (median) per subject to determine the blood concentration of the studied drug.[1]

The drug accumulation ratio, according to one common definition, is the ratio of the green area to the blue area.

There are various competing calculation methods for the drug accumulation ratio, yielding somewhat different results. A commonly used formula defines R_ac as the ratio of the area under the curve (AUC) during a single dosing interval under steady state conditions to the AUC during a dosing interval after one singe dose:[1]

${\displaystyle R_{ac}={\frac {\operatorname {AUC} (\tau ,ss)}{\operatorname {AUC} (\tau ,1)}}}$

where ${\displaystyle \tau }$ is the dosing interval, ss means steady state and 1 stands for a single-dose application.

Another definition sets R_ac to the ratio of the average drug concentration during one day under steady state conditions to the concentration after a single dose.[2]