AIMTo illustrate the non-equilibrium properties of drug permeation through stratum corneum (SC) to provide theory and method for transdermal drug delivery.

METHODSThe system of side-by-side permeation chambers in vitro was isolated, thus conditions for equilibrium state were decided. And a network thermodynamic model was established. Non-equilibrium and leakage experiments were completed with which tinidazole was pattern drug.

RESULTSThe properties of non-equilibrium including: long term to reach equilibrium state; delay-start of the permeation; uncertainty of initial drug permeable flux. The properties of leakage including: degression of drug permeable flux; changeability of permeation time constant.

CONCLUSIONThe permeation cell is believed to be a non-linear and time variable system.