Dosing mechanism

A pen injector apparatus, that includes a dosing mechanism, for delivering a plurality of single metered doses, the dosing mechanism of the pen injector apparatus comprising:

• a linearly actuated dose delivery mechanism arranged to deliver a metered dose of therapeutic material from a cartridge;
• a non-return mechanism, arranged to prevent the dose delivery mechanism from returning toward a primed position until a full metered dose has been delivered,
• the non-return mechanism including
• a track defining an actuation path and a return path, and
• an engagement member arranged to be received within said track,
• the track and engagement member being relatively rotationally moveable such that the engagement member is arranged to move along the actuation path during actuation of the dose delivery mechanism and along the return path during priming of the dose delivery mechanism, and
• at least a portion of the actuation path being provided with a toothed profile to prevent reverse movement of the engagement member in the actuation path;
• and
• a cam arranged to provide relative rotational movement between the track and the engagement member in response to a linear movement of the dose delivery mechanism.