Partition coefficient

![Drug permeability in brain capillaries (y-axis) as a function of partition coefficient (x-axis).[27]](/uploads/202502/01/Log_P_examples_012943.png)
In the physical sciences, a partition-coefficient (P) or distribution-coefficient (D) is the ratio of concentrations of a compound in a mixture of two immiscible phases at equilibrium. Hence these coefficients are a measure of the difference in solubility of the compound in these two phases.