In the two-compartment model, the beta (distribution/elimination) phase is best described as:

• A. Rapid distribution between central and peripheral compartments
• B. Equilibration with no elimination
• C. Immediate clearance from plasma
• D. Slower distribution with elimination, culminating in terminal elimination

Answer: (D)

In the two-compartment model, after the initial rapid spread of drug between the central compartment (blood/plasma) and the peripheral tissues, the next, slower phase reflects the combined process of distribution continuing at a slower pace while elimination from the body also occurs. This results in a gentler, terminal decline in plasma concentration—the terminal elimination phase. That’s why the beta phase is described as slower distribution with elimination, culminating in terminal elimination. The other descriptions don’t fit: the very fast transfer between compartments is the alpha (distribution) phase, not beta; there is elimination during the beta phase, so it isn’t just equilibration with no elimination; the decline isn’t instantaneous clearance from plasma.