What is one characteristic of a drug that exhibits first-order kinetics?

A drug that exhibits first-order kinetics is characterized by the fact that its elimination rate is directly proportional to its concentration in the bloodstream. This means that as the concentration of the drug increases, the rate of elimination also increases. In practical terms, when the concentration of the drug is high, more of it is being metabolized and eliminated from the body per unit of time compared to a lower concentration. This relationship is often illustrated with a logarithmic graph or a plot of concentration versus time, where the decline in drug levels is exponential.

This characteristic of first-order kinetics is fundamental to understanding how many medications behave in the body. For instance, at different points in time after drug administration, measurements will show that more drug is cleared as the concentration at that moment is higher.

The other characteristics mentioned do not apply to drugs with first-order kinetics in the same way. For example, in zero-order kinetics, the elimination occurs at a constant rate regardless of concentration, which stands in contrast to the behavior described in first-order kinetics. Also, while dosage can impact how much drug is present initially, the first-order proportionality specifically speaks to how the concentration affects elimination rate rather than requiring a constant dosage or indicating fixed amounts eliminated over time.