Pharmacy PEBC Practice Exam

What defines a drug's half-life?

1. The time for the body to eliminate the drug

2. The duration drugs remain effective

3. The time it takes for the blood concentration to decrease by half

4. The overall lifespan of the drug in the body

The correct answer is: The time it takes for the blood concentration to decrease by half

A drug's half-life is defined as the time it takes for the blood concentration of the drug to decrease by half. This is a critical pharmacokinetic parameter because it informs healthcare professionals about how quickly a drug is eliminated from the body and helps in determining dosing schedules. Knowing the half-life helps in predicting how long the drug will exert its effects, influencing both efficacy and safety. The half-life can also aid in understanding drug accumulation and the steady state, especially when medications are taken on a regular schedule. For instance, a drug with a short half-life may need to be administered more frequently to maintain therapeutic levels, while drugs with longer half-lives may allow for less frequent dosing. While the concept of drug elimination is related, it is measured specifically by half-life and does not encompass the process in its entirety. Other choices, such as the duration of effectiveness or the overall lifespan, are more broad and do not specifically define the pharmacokinetic concept that is half-life.