4.1. Pharmacokinetic Equation

The PK profile of most of the SMKIs is characterized by first-order elimination [26,27,28,29]. Therefore, the concentration at a random time point during the elimination phase (T2) can be estimated based on the concentration measured at another time point during the elimination phase (T1) using the following pharmacokinetic equation:

And this equation can be rewritten to:

In this equation C_t1 represents the plasma drug concentration measured at the moment of blood withdrawal (i.e., a random time-point). T¹/₂ represents the elimination half-life and is taken from the SMPC for each drug. The factor ∆t represents the time between the moment of blood withdrawal (i.e., known and measured drug concentration) and the moment of the next drug intake (time point of C_trough). By filling in the aforementioned factors the product C_t2 is calculated which represents the estimated trough concentration.