Validation protocol of an automated in-line flow-through diffusion equipment for in vitro permeation studies

Transdermal drug delivery experiments are often tedious and time consuming in terms of sampling, labor, etc. In this way, the automation of such experiments has increased in the last few years. A protocol suitable to validate an automated diffusion equipment with seven in-line flow-through cells is described. The proposed protocol was divided into two parts. First, validation of each component which makes up the whole equipment, including the study of the statistical variability of the internal volumes between the cells, the temperature into the different chambers, the time and sample volumes, etc. In the second part, a series of permeation studies were carried out comparing the performance of the system against a classical Franz-type diffusion cell. Ketoprofen was used as a model drug. It was proved the low variability of the replicates obtained with the automated flow-through diffusion cells. The best work conditions as flow rate into the receptor chamber, temperature, etc., as well as the best mathematical approach for the diffusion data, were determined. The advantages in terms of time saved and easiness of validation of the flow-through cell design in comparison to the Franz-type cell were evidenced.