Injection pens for medicine administration and tracking

A medicine injection pen, comprising:

• a body;
• a drive member disposed within the body and configured to move relative to the body upon actuation of the drive member;
• a cartridge housing releasably engageable with the body and configured to retain a medicine cartridge therein, the medicine cartridge configured to retain a liquid medicine therein and including a piston configured to slide within the medicine cartridge, wherein the drive member is configured to move relative to the body upon actuation thereof to urge the piston to slide within the medicine cartridge to thereby dispense at least some of the liquid medicine through a dispensing end of the medicine cartridge;
• at least one sensor configured to sense movement of the drive member relative to the body upon actuation of the drive member to enable determination of an amount of the liquid medicine dispensed based on the sensed movement;
• and
• at least one detector configured to detect a gap between the drive member and the piston, wherein the at least one detector is configured to detect the gap by determining a position of the piston based on an amount of the liquid medicine in the medicine cartridge.