In the Pharmacopeial Forum 41(1) a "stimulus to the revision process" article on pharmaceutical packaging has been published. This article proposes a new method for the determination of the permeability of water vapour for the General Chapter <671>.
The determination of the permeability rate for water vapour ("water vapour transmission rate", WVTR) applies for solid dosage forms such as tablets or capsules that are packed in plastic bottles or blister packs.
The conclusion of the article is as follows:
WVTR can be measured by the weight gain of a desiccant or by the weight loss of water in a packaging system in an environment with constant temperature and relative humidity (RH). Packaging materials to be tested, which are filled with water, show a constant vapour pressure difference along the walls of the containers. This constitutes an improvement in comparison to the current WVTR testing according to <671>, in which the containers are filled with desiccant and where the vapour pressure inside neither starts nor remains at 0% rel. humidity.
When containers are filled with water, many of the challenges can be avoided occurring with the use of desiccants and with the handling of containers which must be filled with desiccants - which is another advantage of the new method.
All other information about the USP proposal can be found on the USP Website of the Pharmacopeial Forums (PF).