A multi-use injection device (100) for multiple subcutaneous injections, wherein the injection device comprises a device main portion (110) and a multi-use needle unit (150) adapted to prevent unintended introduction of living microorganisms into a reservoir (114) of the device main portion during use of the injection device, and thereby promote bacteriostasis of a multiple-use drug preparation (115) during a use period with multiple injections. The drug delivery device (100) is adapted to enable multiple injections, without accidentally introducing living microbial contaminations into the reservoir during use, by adapting the multi-use needle to: (i) sterilize contaminations introduced into the distal needle after each exposure of a distal injection needle (156), (ii) restrict diffusion and flow from the distal needle (156) to the reservoir (114) with a valve (170), (iii), and by allowing the needle unit to remain mounted in the in-use configuration during the use period with multiple injections.