A vial adaptor (110) may comprise a body portion (120). The body portion includes a vial connection port (122), a syringe connection port (124), an access passageway (126) between the vial connection port and the syringe connection port, and a regulation passageway (128). The vial adaptor may further comprise an expandable and/or contractible chamber (140) comprising one or more membranes impermeable to gas and/or liquid, the regulation passageway being between the vial connection port and the chamber, and a housing (150) casing the chamber. The chamber may comprise a two-way air resistor (146) arranged on the one or more membranes. Such a vial adaptor constitutes an improved vial adaptor.
