After intravenous administration in a two-compartment model, the concentration-time profile typically shows a rapid distribution phase followed by a slower elimination phase.

• A. True
• B. False
• C. Only distribution.
• D. Only elimination.

Answer: (A)

In a two-compartment model after an IV bolus, the plasma concentration-time curve is typically biexponential, reflecting two processes happening in sequence. First, the drug rapidly distributes from the central (plasma) compartment to the peripheral tissues, causing a quick drop in plasma concentration—the distribution phase. Once distribution slows and equilibrium between compartments is approached, elimination from the central compartment becomes the dominant process, producing a slower decline—the elimination phase. Mathematically, the profile is described by two exponentials with rate constants alpha (distribution) and beta (elimination), where alpha is larger than beta. So the statement captures the common pattern seen in two-compartment IV kinetics. (Note: if distribution is very fast relative to elimination, the curve can appear nearly monophasic, but the usual behavior is a rapid distribution phase followed by a slower elimination phase.)