Simultaneous tubular excretion and reabsorption of pindolol in man

The plasma concentrations of pindolol have been examined following the administration of single doses of 15 mg tablets to eight healthy male subjects. The apparent half-life of elimination in plasma (t1/2 = 4.05 h) and in urine (t1/2 = 3.21 h) was calculated using conventional pharmacokinetic methods. The renal clearance was estimated by plotting urinary excretion rates versus plasma concentrations; for all subjects these plots were curved. In addition to these graphical estimations, the plasma concentrations of pindolol and the urinary excretion data for each volunteer were simultaneously fitted using a one or two-compartment open body model; a computer program using non-linear regression algorithms was used. This procedure did not give an adequate fit to the data. Another type of data analysis, using a population - based model, permitted us to show that the renal elimination of pindolol in man comprises of two separate processes - tubular secretion and reabsorption, which was partially saturable under the experimental conditions. The theoretical relevance and clinical significance of these findings are discussed.