A cannula cartridge for receiving a cannula, comprising: a) a needle unit having a needle hub and a needle attached to the needle hub; b) a cannula; and c) a protective element, - wherein the needle unit is movable within the protective element from at least one first position to at least one second position and vice a versa, - wherein in the first position the needle is covered by the protective element, - wherein in the second position the needle at least partially extends from the protective element, - wherein in the first position a retaining member of the protective element engages with an engagement element of the needle hub by a form fit connection, - wherein the needle unit is configured to be moved by an inserter from the first position to the second position and back to a the first position in which the retaining member again engages with the engagement element of the needle hub, - wherein the retaining member and the engagement element of the needle hub are configured such that a holding force of the retaining member is overcome by applying forces parallel to the axis of the needle, characterized in that the retaining member contains at least one latch, wherein the latch is configured to engage with at least one cavity in at least one surface of the engagement element, wherein the latch comprises at least one latch arm, the latch arm being connected to a housing of the protective element at a fixed end, the latch arm further having at least one free end configured to engage with the engagement element of the needle hub, wherein the free end contains an interlocking element having at least two sloped surfaces (170, 172) configured for engaging the engagement element of the needle hub, wherein the at least two sloped surfaces (170, 172) have different slopes, wherein the at least two sloped surfaces (170, 172) comprise at least one first sloped surface interacting with at least one edge of the engagement element when the needle unit moves from the first position to the second position, and at least one second sloped surface interacting with at least one proximal edge of the needle hub when the needle unit moves back from the second position to the first position. a) a needle unit having a needle hub and a needle attached to the needle hub; b) a cannula; and c) a protective element, - wherein the needle unit is movable within the protective element from at least one first position to at least one second position and vice a versa, - wherein in the first position the needle is covered by the protective element, - wherein in the second position the needle at least partially extends from the protective element, - wherein in the first position a retaining member of the protective element engages with an engagement element of the needle hub by a form fit connection, - wherein the needle unit is configured to be moved by an inserter from the first position to the second position and back to a the first position in which the retaining member again engages with the engagement element of the needle hub, - wherein the retaining member and the engagement element of the needle hub are configured such that a holding force of the retaining member is overcome by applying forces parallel to the axis of the needle, characterized in that the retaining member contains at least one latch, wherein the latch is configured to engage with at least one cavity in at least one surface of the engagement element, wherein the latch comprises at least one latch arm, the latch arm being connected to a housing of the protective element at a fixed end, the latch arm further having at least one free end configured to engage with the engagement element of the needle hub, wherein the free end contains an interlocking element having at least two sloped surfaces (170, 172) configured for engaging the engagement element of the needle hub, wherein the at least two sloped surfaces (170, 172) have different slopes, wherein the at least two sloped surfaces (170, 172) comprise at least one first sloped surface interacting with at least one edge of the engagement element when the needle unit moves from the first position to the second position, and at least one second sloped surface interacting with at least one proximal edge of the needle hub when the needle unit moves back from the second position to the first position. - wherein the needle unit is movable within the protective element from at least one first position to at least one second position and vice a versa, - wherein in the first position the needle is covered by the protective element, - wherein in the second position the needle at least partially extends from the protective element, - wherein in the first position a retaining member of the protective element engages with an engagement element of the needle hub by a form fit connection, - wherein the needle unit is configured to be moved by an inserter from the first position to the second position and back to a the first position in which the retaining member again engages with the engagement element of the needle hub, - wherein the retaining member and the engagement element of the needle hub are configured such that a holding force of the retaining member is overcome by applying forces parallel to the axis of the needle,