In a two-compartment model, which statement correctly identifies the alpha phase?

• A. The beta rate constant governs distribution between central and peripheral compartments.
• B. The alpha phase reflects elimination from the central compartment.
• C. The AUC determines the distribution rate.
• D. The alpha rate constant governs distribution between central and peripheral compartments.

Answer: (D)

In a two-compartment model after an IV bolus, the early, rapid decline in concentration is the distribution phase (alpha phase), while the slower, later decline is the elimination phase (beta phase). The rates that shape these phases come from the transfer between the central and peripheral compartments. The alpha rate constant specifically describes how quickly drug moves between these compartments, governing the distribution process. The beta rate constant, on the other hand, describes elimination from the central compartment. AUC reflects overall exposure, not the rate of distribution. Therefore, the alpha rate constant governing distribution between central and peripheral compartments is the correct interpretation.