Safe medical-drug injector and collapsible plunger combination thereof

A safe medical-drug injector comprising:

• a needle hub connecting a needle;
• a hollow barrel connected with the needle hub for guiding the needle hub to be drawn back to the hollow barrel after an injection is completed;
• and
• a collapsible plunger combination inserted into the hollow barrel, the collapsible plunger combination comprising a hollow cannula and a retractable plunger partly connected with the cannula, there being at least one raised portion formed on outside wall of the retractable plunger near the connection part to be correspondingly embedded in at least one depression formed on the inside wall of the hollow cannula;
• wherein the connection between the hollow cannula and the retractable plunger is released to make the retractable plunger drawn back to the hollow cannula when a following press is applied on the hollow cannula after an injection is completed, and thereby spare space of the hollow barrel for accommodating the needle hub.

A collapsible plunger combination for medical-drug injection comprising:

• a hollow cannula;
• and
• a retractable plunger partly connected with the cannula, there being at least one raised portion formed on outside wall of the retractable plunger near the connection part to be correspondingly embedded in at least one depression formed on the inside wall of the hollow cannula;
• wherein the connection between the hollow cannula and the retractable plunger is released to make at least one part of the retractable plunger drawn back to the hollow cannula when a following press is applied on the hollow cannula after an injection is completed.

A safe medical-drug injector comprising:

• a needle hub connecting a needle;
• a hollow barrel connected with the needle hub and one-piece formed with a narrow barrel having its diameter smaller than that of the hollow barrel near the needle hub, there being a block set adjacent to the opening of the narrow barrel for preventing the needle hub from escaping and guiding the needle hub to retract after an injection is completed;
• and
• a collapsible plunger combination inserted into the hollow barrel, the collapsible plunger combination comprising a hollow cannula and a retractable plunger partly connected with the cannula, there being at least one raised portion formed on outside wall of the retractable plunger near the connection part to be correspondingly embedded in at least one depression formed on the inside wall of the hollow cannula;
• wherein the connection between the hollow cannula and the retractable plunger is released to make the retractable plunger drawn back to the hollow cannula when a following press is applied on the hollow cannula after an injection is completed, and thereby spare space of the hollow barrel for accommodating the needle hub.