In certain embodiments, a vial adaptor for removing liquid contents from a vial comprises a housing and a bag. In some embodiments, an initial volume of a regulating fluid can be contained within the bag. In some embodiments, the regulating fluid flows into the vial as liquid is removed from the vial via the adaptor, thereby regulating pressure within the vial. In some embodiments, a vial adaptor is coupled with the vial in order to remove the liquid. In some embodiments, as the liquid is removed from the vial via the adaptor, the bag expands, and in other embodiments, the bag contracts.