A medical injector (10) including a body (32) having a distal end and a proximal end, and a plunger (12) displaceably disposed in the body (32). The plunger (12) includes a plurality of spaced-apart ratchet teeth (20) disposed along the length thereof. The plunger (12) selectively displaces a stopper to dispense a medicament from said medical injector (10). The medical injector (10) also includes an indexer (38) disposed within the body (32) to engage the plunger (12) to permit distal displacement of the plunger (12) and substantially prevent proximal displacement of the plunger (12), an actuator (48) having an engagement portion (50) to engage the plunger (12) to permit proximal displacement of the actuator (48) relative to the plunger (12) and substantially prevent distal displacement of the actuator (48) relative to the plunger (12), and a rotating member (48B) for proximally displacing the engagement portion (50) relative to the plunger (12) and the body (32). Upon proximal displacement of the actuator (48) relative to the body (32) to a ready state, one or more of the ratchet teeth (20) bypass the engagement portion (50) to proximally displace the actuator (48) relative to the plunger (12). Upon distal displacement of the actuator (48) relative to the body (32) from the ready state, the actuator (48) engages one or more of the ratchet teeth (20) to distally displace the plunger (12) relative to the indexer (38) to distally displace the stopper to dispense medicament from the medical injector (10).
