Kinetics of Drug Accumulation and Disappearance

If a drug is administered to a patient, the drug concentration in the plasma will rise to a value and then decay away with time (see Brody fig.5-4, or handout fig.1). If we could monitor the drug concentration in the blood in real time, we’d see that it would rise to some value, the shape of the rise would depend on the way you administered the drug (via IV, it would rise very quickly; if given orally it would rise slower). The way that it dies away with time is the same no matter which way you administer the drug. This is called the elimination phase (the down-slope of the curve). Elimination means redistribution through the body, metabolism and excretion. We can talk about the total amount of the drug, or the plasma concentration—usually they’re proportional to each other.

Category: Pharmacology Notes