Measuring drug concentrations using pulsatile microdialysis: Theory and method development in vitro

A novel method of rapidly sampling drug concentrations, based on pulsatile microdialysis (PMD), was developed. In PMD, a dialysate fluid is pumped into a microdialysis probe, allowed to occupy the probe while at rest for some time, and then flushed at a high rate. A model that is based on a Fick's Laws was solved and tested, using methazolamide (MTZ) as the test drug in a variety of experimental setups, including time-dependent donor concentrations. Calibration plots of the donor versus sample concentrations were linear. There was excellent agreement between the calculated and experimental values of the fraction recovered obtained from the calibration plots. In a system for which the donor concentration declined in a first order manner, the data obtained using PMD and direct sampling of the donor were in nearly exact agreement with the theoretical value of k = 0.09 min−1. PMD was also able to collect data points quickly enough to characterize the rapid binding kinetics of MTZ by activated charcoal. It was concluded that PMD is an accurate method of sampling drug concentrations, and can obtain samples over shorter time intervals and more frequently than previously available methods.