Erythrocyte Uptake of Drugs and Its Impact on Volume of Distribution (VD) Determinations

Abstract

In most volume of distribution (VD) determinations the drug partitioned in to erythrocytes (Cery) 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 (Cb) or serum (C s) concentrations. The second is when Cery values are not considered in calculations. Isolated erythrocytes were incubated in plasma water (Cpw) represented by physiological saline drug solutions, the C p W, Cery and C b values were experimentally determined in vitro. Aberrations to the VD determinations are demonstrated using both theoretically and practically determined values of Cpw, Cery and Cb. Widely varying Vd values 125 L to 2.55 L resulted when Cp data alone is used while the values differed marginally from 4.56 L to 5.53 L when Cb values were used for two setting using same amount of drug