Fig. 1.
Schematic diagram of the minimal physiologically-based model for tubular reabsorption of drugs in the kidney. The nephron is represented by a glomerulus compartment in addition to four compartments representing different regions of the nephron tubule (proximal tubule (PT), loop of Henle (LoH), distal tubule (DT) and collecting duct (CD) in descending anatomical order). Physiological parameters, tubular flow rate (TFRi) and tubular surface area (TSAi), for each individual tubular region are indicated. Tubular filtrate flow (Q) is represented by grey arrows connecting tubular compartments and used to calculate TFRi (average midpoint flow rates). The intrinsic reabsorption clearance of each individual region (CLR,int,reab,i) is calculated using the corresponding TSAi. Total renal excretion clearance (CLR) is obtained from the filtration clearance (CLR,filt) and the overall fraction reabsorbed (Freab), by rearrangement of Eq. (9).