What is the key characteristic of 1st order drug kinetics?

The key characteristic of first-order drug kinetics is that the rate of drug elimination is proportional to the drug concentration in the body. This means that as the concentration of the drug increases, the amount of drug eliminated per unit time also increases—resulting in a linear relationship when graphed. Thus, the higher the drug level, the greater the amount removed over time, following an exponential decay pattern.

In practical terms, if a patient receives a higher dose of a medication, the body will eliminate a larger amount of that drug over a specified time frame, which is a fundamental principle for understanding how most drugs behave in the body at therapeutic doses. This proportional relationship allows clinicians to predict how changes in dosage will affect drug levels and clearance rates.

In contrast, the other options do not describe first-order kinetics accurately. For example, constant amount of drug eliminated regardless of dose pertains to zero-order kinetics, where the elimination process is saturated and does not change with concentration. Immediate drug effect onset is more related to the pharmacodynamic properties of a drug rather than its kinetics. The concept of drug elimination being independent of drug concentration doesn’t align with how first-order kinetics operates, as it is fundamentally based on concentration-dependent processes.