Concentration (of drug) in the plasma at t=0

The concentration in the plasma at zero time (C0 or Cp0) is the theoretical concentration of a one-compartment drug in the plasma at time = 0, following instantaneous mixing throughout the compartment and before any drug has been eliminated. Cp0 is equal to the Y-axis intercept of a first-order elimination curve following bolus IV administration of a one-compartment drug. Since there is no point that can be plotted at t=0 because instantaneous mixing can not occur, the intercept is typically found by back-extrapolating the straight line obtained when data are plotted on a logarithmic Y-axis.

The theoretical concentration of drug in plasma at time = 0 for a one-compartment drug may be found by plotting the first-order exponential data (left panel) on a logarithmic concentration axis (right panel), generating a straight line which can then be extrapolated back to the Y-axis. The semilogarithmic plot shown here uses natural logarithms, but the same outcome will be achieved through plotting base 10 logarithms. The benefit to using natural logarithms is the ease with which a first order rate constant can be obtained directly from the slope.

 

License

Icon for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

An ABC of PK/PD Copyright © 2023 by Dr. Andrew Holt is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

Share This Book