Patent ID: 7097634

Claim:
An injection device comprising a syringe cartridge including a needle for delivery of a medicament, a trigger mechanism, a drive mechanism and a bias mechanism, wherein the injection device is configured to provide automatic injection of a desired dose of the medicament followed by automatic retraction of the needle associated with the syringe cartridge and the drive mechanism includes a compound plunger, wherein the compound plunger comprises an outer plunger forming a first reservoir, a hydraulic fluid contained within the first reservoir, a hydraulic orifice, and an inner plunger positioned at least partially within the outer plunger, the inner plunger being positioned and configured such that, as the drive mechanism operates, the inner plunger acts against the hydraulic fluid and the hydraulic fluid is expelled from the first reservoir through the hydraulic orifice, wherein the injection device further comprises a second reservoir configured to contain the hydraulic fluid expelled from the first reservoir, wherein the second reservoir is at least partially formed by a sealing member included on an outer surface of the outer plunger.