The invention concerns a method and an apparatus for transferring an amount of a liquid drug (11) from a supply container (1) having stored the liquid drug (11) to a collapsible reservoir (2), the method including and the apparatus enabling the steps of:a) providing a fluid connection (3) between the supply container (1) and the collapsible reservoir (2)；b) subjecting the liquid drug (11) stored in the supply container (1) to an environmental pressure；c) subjecting the collapsible reservoir (2) to a positive pressure relative to the environmental pressure, thereby collapsing the collapsible reservoir (2) and transferring gas comprised in the collapsible reservoir (2) from the collapsible reservoir (2) to the supply container (1)；d) subjecting the collapsible reservoir (2) to a negative pressure relative to the environmental pressure, thereby expanding the collapsible reservoir (2) and transferring the amount of the liquid drug (11) from the supply container (1) to the collapsible reservoir (2).
