Fill volume as an indicator of surface heterogeneity in glass vials for parenteral packaging.

The chemical durability of glass vials for parenteral packaging is typically assessed by completely filling the vial with a medium of interest. This testing approach can mask the heterogeneous dissolution behavior of vials produced by conversion of glass tubing. In this study, the corrosion behavior of vials provided by four suppliers was evaluated as a function of fill volume. Vials were filled with incrementally increasing volumes of water for injection (WFI) up to near-maximum capacity and then autoclaved. The pH and levels of extracted ions were measured. The pH of autoclaved WFI generally increased for low fill volumes relative to pure WFI, presumably because of extraction of alkali from the heel region. The pH was found to generally decrease with increasing fill volume as the concentration of extractables was diluted. Analysis of dissolution profiles supports the altered surface chemistry of the heel region relative to the body. The results of this study demonstrate the potential limitations of conventional hydrolytic resistance tests and the susceptibility of the heel region to aqueous corrosion.