A medical injector, including a body with a displaceable plunger, which has at least one set of ratchet teeth, each set having a plurality of spaced-apart ratchet teeth disposed along the length thereof. At least one indexer is formed to engage the plunger. The indexer is configured to allow the plunger to displace distally toward the distal end of the body but not proximally toward the proximal end of the body. An actuator has a rocker pivotally connected thereto, the rocker being of single-piece construction and having an engagement portion formed to engage the ratchet teeth. The indexer and the rocker engage the same set of ratchet teeth. The rocker is pivotally connected at a first portion thereof to the body to rotate about an axis disposed on the body and pivotally connected at a second portion thereof to a link to rotate about an axis disposed on the link.