Subcutaneous drug delivery device

Claim 1

A surgical instrument comprising: a) a housing with a bore extending along a longitudinal axis of the housing and a track extending parallel to the bore, said track having an elongate proximal housing slot and an elongate distal housing slot extending along the longitudinal axis; b) a piston having a distal tip end and a cannula mounted coaxially thereto and within the bore extending along the longitudinal axis thereof; c) a driving member slideably engaged in said track for longitudinal movement therein, the driving member having a proximal elongate slot with a notch formed therein and a distal elongate slot with a notch formed therein, said slots extending along the longitudinal axis; d) a piston drive pin for engaging the piston with the driving member, the piston drive pin extending from the piston in a direction perpendicular to the longitudinal axis through the proximal housing slot and the proximal driving member slot, the piston drive pin engaging the piston with the driving member by movement of the driving member distally long the track toward the piston tip end, the piston capable of being extended until the piston drive pin reaches the distal end of the proximal housing slot; and e) a cannula drive pin for engaging the cannula with the driving member, the cannula drive pin extending from the cannula in a direction perpendicular to the longitudinal axis through the distal housing slot and the distal driving member slot, the piston drive pin engaging the cannula with the driving member when the piston drive pin is at the distal end of the proximal housing slot, the cannula capable of being extended by movement of the driving member further along the track toward the piston tip end until the cannula drive pin reaches the distal end of the distal housing slot.