Patent ID: 7344517

Claim:
A medical device for delivering a medicament to a patient, comprising: a syringe 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 and being connected to a needle cannula hub movable in said barrel between an initial position in which said forward tip is exposed and a retracted position in which said forward tip is contained within said barrel, said rear end of said needle cannula being in fluid communication with said reservoir through said needle cannula; a plunger having a first end with a stopper positionable in said reservoir and a second end having a thumb pad for receiving medicament delivery pressure for causing said plunger to move within said reservoir to cause the medicament to be expelled from said reservoir; a retainer engaging an annular groove defined in an inner surface of said barrel and releasably securing said needle cannula hub at said initial position proximate the front end of said barrel, said retainer being ring-shaped and having a cross-sectional shape with a radially outward projection engaging the groove defined in said barrel, a first leg facing said forward end of said barrel, and a second leg facing said rear end of said barrel; and an urging member arranged between said front end of said barrel and said needle cannula hub and having an urgency for urging said needle cannula hub with said needle cannula toward the retracted position in said barrel, said second leg interacting with one of said needle cannula hub and said stopper to release said radially outward projection from said groove in response to the application of medicament delivery force to said thumb pad when said stopper is in a fully inserted position in said reservoir to allow said urging member to move said needle cannula hub from said initial position to said retracted position upon release of medicament delivery pressure from said thumb pad.