FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam

What does the distribution half-life (t1/2a) represent?

1. Time for plasma concentration to decline by 50% during distribution

2. Time for plasma concentration to stabilize

3. Time for the drug to be eliminated completely

4. Time for therapeutic effects to begin

The correct answer is: Time for plasma concentration to decline by 50% during distribution

The distribution half-life (t1/2a) represents the time required for the plasma concentration of a drug to decline by 50% during the distribution phase. This is an important concept in pharmacokinetics, as it focuses specifically on the initial phase after a drug is administered, where the distribution of the drug throughout the body occurs. During this time, the drug moves from the central compartment (such as the bloodstream) into peripheral tissues. Understanding this concept helps inform healthcare professionals about how quickly a drug disperses and equilibrates in the body after administration, which can influence both dosing strategies and monitoring of the drug’s effects. The distribution half-life provides critical information that is distinct from the elimination half-life, which pertains to the time it takes for the drug to be cleared from the body overall, or other timelines related to stabilization or onset of therapeutic effects.