Delay device for a medical administration appliance

A plunger rod unit for an administration appliance for administering a medical substance, wherein the plunger rod unit delays a release of a mechanism of the administration appliance, the plunger rod unit comprising:

• a. an outer plunger rod with a contact face on a distal end of the outer plunger rod for interacting with a stopper, in order to discharge the substance from a product container,
• b. an inner plunger rod mounted in the outer plunger rod in such a way that a cavity is formed at the distal end of the outer plunger rod, said cavity being at least partially filled with a viscous fluid,
• c. a fluid displacement element that is located at least partially in the cavity and that is operably or integrally connected to the inner plunger rod and wherein the fluid displacement element is moved relative to the outer plunger rod in a delay movement,
• d. wherein, in a relative movement between the fluid displacement element and the outer plunger rod by displacement of the fluid, a movement resistance is generated, so that the fluid displacement element is delayed in reaching a release position that releases the mechanism of the administration appliance, and
• e. wherein the outer plunger rod comprises a distal first plunger rod part that comprises the contact face and forms the cavity for the fluid displacement element, and a second plunger rod part adjoining the first plunger rod part.