Safe medical-drug injector and collapsible plunger combination thereof

摘要

A safe medical-drug injector with a collapsable plunger combination thereof is proposed. The injector includes a hub connected with a needle, a hollow barrel, and a collapsable plunger combination including a hollow cannula and a retractable plunger that is telescoped with the hollow cannula. At least a stress adjustable notch is formed at the core of the retractable plunger or in an upper edge of the hollow cannula, and at least one raised portion is formed on an outer lateral side of the retractable plunger near the stress adjustable notch to be correspondingly embedded with at least a depression formed on an inner lateral side of the hollow cannula. The engagement between the raised portion and the depression is released to make the retractable plunger drawn back to the hollow cannula when a following press is applied on the hollow cannula after the safe medical-drug injector completes an injection.