Introduction To Pharmacokinetics
Steady State, Models And Other Terminology
TWO COMPARTMENT MODEL CONTINUED
When a drug is administered, initially the concentration in the central compartment falls rapidly. This is because the drug is being eliminated from the central compartment but also being distributed from the central compartment to the peripheral compartment with little drug transferring back to the central compartment.Over time, the concentration in the peripheral compartment reaches a maximum level and then declines as the amount transferred back to the central compartment increases. Eventually a distribution equilibrium is reached between the peripheral and central compartments.
Assuming first order kinetics, if you plot the log of the plasma drug concentration against time (or the equivalent semilog graph of concentration against time), you will obtain a biphasic graph. The first phase of the graph is the distribution phase, the second phase is the elimination phase.
