Flow‐through versus static in vitro percutaneous penetration at 50 years: Possible relevance for bioequivalence

OBJECTIVE: Compare the relevance of flow‐through versus static diffusion cells data as relates to bioequivalence. METHODS: Search was conducted on PubMed and Google Scholar. Keywords utilized: static cells, flow‐through cells, percutaneous permeation, percutaneous absorption, dermal absorption, and types of permeation. RESULTS: Fifteen articles were identified with no consistent significant differences between flow‐through and static diffusion cells identified; any differences could exist for two main reasons. (1) Sampling time differences and (2) physical chemistry (lipophilic vs hydrophilic) of the penetrant examined. CONCLUSION: Even though there was no consistent significant difference observed, labs have generally adapted to the method they regularly use, which is usually stated in their respective articles. Well‐designed multicentered prospective comparative experiments should clarify potential advantages and disadvantages for each. For flow‐through systems, the flow rate that most approximates to comparable in vivo data for animals and humans may be preferable.