A parenteral vial stopper and cap assembly comprises a vial having a body defining an interior and an opening leading to the interior. The assembly further comprises a stopper configured to sealingly engage the opening a cap configured to cover the opening and the stopper. The stopper and the cap fit together to form an integral unit configured to cap the vial. The cap moves with respect to the vial between a partially engaged position that permits gas flow out from the vial interior and a fully engaged position in which the stopper sealingly engages the opening.
