In a two-compartment pharmacokinetic model, what do the α and β phases represent?

• A. α-phase is slow elimination; β-phase is rapid distribution.
• B. α-phase is distribution; β-phase is distribution.
• C. α-phase is rapid distribution between central and peripheral compartments; β-phase is slower elimination phase.
• D. α-phase is excretion; β-phase is absorption.

Answer: (C)

In a two-compartment model after an IV bolus, the initial rapid drop in concentration (α-phase) comes from quick distribution of the drug between the central (blood) and peripheral (tissue) compartments. Once distribution reaches near-equilibrium, the remaining drug is cleared from the body more slowly, producing the β-phase, which reflects elimination. So the α-phase represents rapid distribution between compartments, while the β-phase represents the slower elimination phase. The other descriptions mix up distribution and elimination or introduce absorption/excretion, which don’t describe the two-compartment IV bolus pattern.