| CPC A61M 5/3158 (2013.01) [A61M 5/2033 (2013.01); A61M 5/31501 (2013.01); A61M 5/31511 (2013.01); A61M 5/3157 (2013.01); A61M 5/3202 (2013.01); A61M 5/3204 (2013.01); A61M 5/3245 (2013.01); A61M 5/3257 (2013.01); A61M 5/326 (2013.01); A61M 5/5086 (2013.01); A61M 2005/2013 (2013.01); A61M 2005/206 (2013.01); A61M 2005/208 (2013.01); A61M 2005/3247 (2013.01); A61M 5/46 (2013.01); A61M 2205/581 (2013.01); A61M 2205/582 (2013.01); F04C 2270/0421 (2013.01); Y10T 403/32501 (2015.01)] | 20 Claims |

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1. An autoinjector comprising:
a carrier;
a plunger releasably engaged to the carrier to form a ramped interface between the carrier and the plunger, wherein the plunger, when released from the carrier, is arranged to be driven in a proximal direction relative to the carrier for a delivery operation;
a drive spring biasing the plunger in the proximal direction relative to the carrier to drive the delivery operation, wherein the autoinjector is configured such that the plunger rotates relative to the carrier under load of the drive spring due to the ramped interface when the plunger engages the carrier; and
a chassis that is movable relative to the carrier and the plunger between a first position and a second position, wherein, when the chassis is in the first position, rotation of the plunger relative to the carrier is prevented by a longitudinal rib abutting the plunger, and wherein the autoinjector is configured such that a relative axial movement between the plunger and the longitudinal rib is required to release the plunger from the carrier for the delivery operation.
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