Figure 2.

Pharmacokinetic–pharmacodynamic model diagram of ropinirole for the treatment of hyperprolactinaemia. The pharmacokinetics of ropinirole are characterized with a one compartment model with linear absorption and linear elimination. The concentration in the central compartment is used as the driving force for the inhibition of prolactin secretion. The indirect response model is used to capture the exposure response relationship. Xa is the dosing compartment (absorption compartment), Ka is the first order absorption rate constant, Tlag is the lag time for absorption, Cp is the concentration in the central compartment, Vc is the central compartment volume and CL is the clearance ropinirole (l h^–1) from the central compartment. Prolactin is the concentration of prolactin in plasma. I_max is the maximum fractional ability of the ropinirole to inhibit prolactin production, which is defined as a function of desensitization slope α and time (t) in patients exhibiting time‐dependent dopamine receptor desensitization (n = 3). IC₅₀ is the plasma concentration of ropinirole that results in 50% of the maximum inhibition. K_in and K_out are the zero‐order production rate and first order elimination rate of prolactin, respectively.