The present disclosure refers to drug administering devices that may include a casing front portion in which a cavity is formed and which includes front connecting means, a drug container received in the cavity, a casing rear portion comprising a piston rod which is displaceable into the cavity, and rear connecting means for releasably connecting to the front connecting means, wherein said casing front portion comprises at least two members which, in locking engagement with each other, delimit a front portion of the cavity and a rear portion having a cross section which is narrower than that of the front portion and too narrow for the drug container to pass.
