Pre-filled injection ampoules for administering a readily-available dose of fluid medication, are provided with a retractable needle. The needle is held in a projecting configuration from a barrel against a rearward bias exerted on the needle by a spring located within a spring housing. A piston is positioned...http://www.google.ca/patents/US7300416?utm_source=gb-gplus-sharePatent US7300416 - Pre-filled retractable needle injection ampoules
