Erythrocyte uptake of drugs and its impact on volume of distribution (VD) determinations

In most volume of distribution (VD) determinations the drug partitioned in to erythrocytes (C ery ) occupying 45% of blood volume is disregarded. The VD determinations can be erroneous on two accounts. The first is the indiscriminate reference to plasma (C p ), whole blood (C b ) or serum (C s ) concentrations. The second is when C ery values are not considered in calculations. Isolated erythrocytes were incubated in plasma water (C pw ) represented by physiological saline drug solutions, the C pw , C ery and C b values were experimentally determined in vitro . Aberrations to the VD determinations are demonstrated using both theoretically and practically determined values of C pw , C ery and C b . Widely varying VD values 125 L to 2.55 L resulted when C p data alone is used while the values differed marginally from 4.56 L to 5.53 L when C b values were used for two setting using same amount of drug.