Figure 4.

Schematic illustration of the two-compartment model with first-order input and elimination rate used to describe the median concentration-time profiles of all kratom alkaloids. Compartments 1 and 2 represent the central and peripheral compartments, respectively. The model was parameterized with the microconstants k₀₁, k₁₂, k₂₁, and k₁₀; k₀₁ (or k_abs) is the rate constant for absorption into the central compartment constant, k₁₂ and k₂₁ are the intercompartmental distribution rate constants, and k₁₀ is the rate constant for loss from the central compartment.