Abstract
The vertical diffusion cell is an in vitro laboratory device for the study of drug release and permeation of semi-solid topical formulations and topical patches. Both static and dynamic versions of the diffusion cell are used in practice, the operation of which can be automated. The device is available at a reasonable cost for smaller, mainly transdermal patches, the amount of sampling fluid is replenished at the same time as the sample, in the same amount as the amount sampled without automation of the system, and simultaneous replenishment of acceptor fluid by hydrostatic pressure helps keeping the acceptor chamber bubble-free.