In a two-compartment pharmacokinetic model, what are the names of the distribution and elimination phases?

• A. Alpha phase and Beta phase
• B. Gamma phase and Delta phase
• C. Delta phase and Gamma phase
• D. Initial and Terminal phase

Answer: (A)

In a two-compartment pharmacokinetic model, the early, rapid change in drug concentration reflects distribution between the central and peripheral compartments and is called the alpha phase. The later, slower decline represents the elimination of drug from the body and is called the beta phase. Mathematically, the concentration over time is described by two exponential terms, with alpha governing the distribution and beta governing elimination. In this two-compartment scenario there isn’t a separate gamma or delta phase—that terminology appears in more complex multi-compartment models.