Differentiate between one-compartment and two-compartment models in terms of their distribution phases.

Differentiate between one-compartment and two-compartment models in terms of their distribution phases.

• A. One-compartment models assume instantaneous uniform distribution; two-compartment models have a rapid distribution to a central compartment (alpha phase) followed by slower distribution to a peripheral compartment (beta phase).
• B. One-compartment models require two distribution phases; two-compartment models assume instant distribution.
• C. One-compartment models have no distribution phase; two-compartment models have two distribution phases.
• D. One-compartment models show only elimination; two-compartment models include absorption.

Answer: (A)

In pharmacokinetics, how the drug distributes after dosing distinguishes one- and two-compartment models. A one-compartment model treats the body as a single, well-mixed space, so after administration the drug equilibrates almost instantly and the plasma concentration declines in a single exponential due to elimination—there’s no separate distribution phase to observe. In a two-compartment model, the body has a central compartment (plasma and highly perfused tissues) and a peripheral compartment (less perfused tissues). After a dose, the drug rapidly moves between these compartments, producing a quick initial fall in plasma concentration (the alpha distribution phase) as it distributes to the peripheral tissues, followed by a slower phase (the beta distribution phase) as redistribution between compartments continues. Elimination occurs from the central compartment, shaping the later part of the curve. This results in a biexponential plasma concentration-time profile with two distinct distribution phases, unlike the single-phase decline seen in the one-compartment model.

In pharmacokinetics, how the drug distributes after dosing distinguishes one- and two-compartment models. A one-compartment model treats the body as a single, well-mixed space, so after administration the drug equilibrates almost instantly and the plasma concentration declines in a single exponential due to elimination—there’s no separate distribution phase to observe. In a two-compartment model, the body has a central compartment (plasma and highly perfused tissues) and a peripheral compartment (less perfused tissues). After a dose, the drug rapidly moves between these compartments, producing a quick initial fall in plasma concentration (the alpha distribution phase) as it distributes to the peripheral tissues, followed by a slower phase (the beta distribution phase) as redistribution between compartments continues. Elimination occurs from the central compartment, shaping the later part of the curve. This results in a biexponential plasma concentration-time profile with two distinct distribution phases, unlike the single-phase decline seen in the one-compartment model.