Patent ID: 7604613

Claim:
A medical device for delivering a medicament to a patient, comprising: a barrel having a forward end and a rear end and defining a reservoir within which the medicament may be contained; a needle cannula having a forward tip and a rear end; a needle cannula hub connected to said rear end of said needle cannula and providing fluid communication of said needle cannula with said reservoir, said needle cannula hub being selectively movable between an initial position in which said forward tip of said needle cannula is exposed, and a retracted position in which said forward tip of said needle cannula is disposed in said device; a barrel hub member coupled to said forward end of said barrel over said needle cannula hub and dimensioned to provide retractable telescoping movement of said needle cannula hub with respect to said barrel hub member to allow said needle cannula hub to move to said retracted position; a retaining member seated between said forward end of said barrel and said barrel hub member for releasably securing said needle cannula hub at said barrel forward end when said needle cannula hub is in said initial position, said retaining member having a forward face and rear end defining a bore therethrough, said forward face dimensioned for seating at said barrel forward end; an urging member in contact with said needle cannula hub and said barrel hub for exerting a force to bias said needle cannula hub from said initial position to said retracted position; and a plunger rod having a hollow first end bounded by a cutting edge and supporting a stopper and positioned in said reservoir, and a second end having a thumb pad for receiving medicament delivery pressure for causing said plunger rod to move within said reservoir to cause the medicament to be expelled from said reservoir, said plunger rod cutting edge configured for cutting away a portion of said stopper when said stopper is fully inserted into said barrel and for thereafter interacting with said retaining member to elastically radially expand the bore to a size sufficient to release said needle cannula hub from said retaining member and enable said needle cannula hub to move, by said urging member, to said retracted position though said hollow first end of said plunger rod.