A medical injector, comprising: a body having a distal end and a proximal end; a plunger displaceably disposed in the body, the plunger having a plurality of spaced-apart ratchet teeth disposed along the length thereof, the plunger selectively displacing a stopper to dispense a medicament from said medical injector; an indexer disposed within the body to engage the plunger to permit distal displacement of the plunger and substantially prevent proximal displacement of the plunger; and an actuator (48A, 48) having an engagement portion to engage the plunger to permit proximal displacement of the actuator relative to the plunger and substantially prevent distal displacement of the actuator relative to the plunger; characterized in that: the medical injector further comprises a rotating member (48B, 100) adapted to proximally displace the engagement portion relative to the plunger and the body upon rotation of the rotating member relative to the body; wherein upon proximal displacement of the actuator relative to the body to a ready state, one or more of the ratchet teeth bypass the engagement portion to proximally displace the actuator relative to the plunger; and wherein upon distal displacement of the actuator relative to the body from the ready state, the actuator engages one or more of the ratchet teeth to distally displace the plunger relative to the indexer to distally displace the stopper to dispense medicament from the medical injector. a body having a distal end and a proximal end; a plunger displaceably disposed in the body, the plunger having a plurality of spaced-apart ratchet teeth disposed along the length thereof, the plunger selectively displacing a stopper to dispense a medicament from said medical injector; an indexer disposed within the body to engage the plunger to permit distal displacement of the plunger and substantially prevent proximal displacement of the plunger; and an actuator (48A, 48) having an engagement portion to engage the plunger to permit proximal displacement of the actuator relative to the plunger and substantially prevent distal displacement of the actuator relative to the plunger; characterized in that: the medical injector further comprises a rotating member (48B, 100) adapted to proximally displace the engagement portion relative to the plunger and the body upon rotation of the rotating member relative to the body; wherein upon proximal displacement of the actuator relative to the body to a ready state, one or more of the ratchet teeth bypass the engagement portion to proximally displace the actuator relative to the plunger; and wherein upon distal displacement of the actuator relative to the body from the ready state, the actuator engages one or more of the ratchet teeth to distally displace the plunger relative to the indexer to distally displace the stopper to dispense medicament from the medical injector. the medical injector further comprises a rotating member (48B, 100) adapted to proximally displace the engagement portion relative to the plunger and the body upon rotation of the rotating member relative to the body; wherein upon proximal displacement of the actuator relative to the body to a ready state, one or more of the ratchet teeth bypass the engagement portion to proximally displace the actuator relative to the plunger; and wherein upon distal displacement of the actuator relative to the body from the ready state, the actuator engages one or more of the ratchet teeth to distally displace the plunger relative to the indexer to distally displace the stopper to dispense medicament from the medical injector.