A medication dispensing apparatus (20, 220) comprising: a housing; a drive member (60, 280) within said housing and movable in a distal direction; a fluid container defining a medicine-filled reservoir with a movable piston at one end and an outlet at the other end, said piston engageable by said drive member to be advanced toward said outlet a distance equal to a distal movement of said drive member when said drive member is moved distally; a plunger element (90, 260); a gear set (52, 270) including first and second toothed pinions (160, 166); a first toothed rack meshed with said first pinion and axially stationary within said housing; a second toothed rack meshed with said second pinion and movable within said housing on a pinion-engaging piece clutchably connected to said drive member; characterized in that: said gear set is pivotal on said plunger element and shiftable proximally and distally with said plunger element to convert motion of the plunger element into motion of the drive member; and said apparatus further comprises a latching element (180, 225) including a latching lip (186, 240) and a skid (190, 236); said drive member including an axially extending, skid-engaging surface (71, 71') along which said skid is slidable as said drive member passes distally during advancement during plunger element shifting in the distal direction, said skid-engaging surface having an axial length and a proximal end, said drive member along said axial length structured and arranged with said skid so as to maintain said latching lip against a spring force in a first position free of a latchable element (117, 266) disposed on said plunger element during dose preparing and injecting prior to a final dose administration; and wherein said skid-engaging surface shifts distally of said skid such that said skid passes beyond the proximal end upon administration of a final dose allowing said latching lip to be urged by said spring force from said first position to a second position for engagement with said latchable element to physically lock said plunger element to prevent further dose preparing and injecting. a housing; a drive member (60, 280) within said housing and movable in a distal direction; a fluid container defining a medicine-filled reservoir with a movable piston at one end and an outlet at the other end, said piston engageable by said drive member to be advanced toward said outlet a distance equal to a distal movement of said drive member when said drive member is moved distally; a plunger element (90, 260); a gear set (52, 270) including first and second toothed pinions (160, 166); a first toothed rack meshed with said first pinion and axially stationary within said housing; a second toothed rack meshed with said second pinion and movable within said housing on a pinion-engaging piece clutchably connected to said drive member; characterized in that: said gear set is pivotal on said plunger element and shiftable proximally and distally with said plunger element to convert motion of the plunger element into motion of the drive member; and said apparatus further comprises a latching element (180, 225) including a latching lip (186, 240) and a skid (190, 236); said drive member including an axially extending, skid-engaging surface (71, 71') along which said skid is slidable as said drive member passes distally during advancement during plunger element shifting in the distal direction, said skid-engaging surface having an axial length and a proximal end, said drive member along said axial length structured and arranged with said skid so as to maintain said latching lip against a spring force in a first position free of a latchable element (117, 266) disposed on said plunger element during dose preparing and injecting prior to a final dose administration; and wherein said skid-engaging surface shifts distally of said skid such that said skid passes beyond the proximal end upon administration of a final dose allowing said latching lip to be urged by said spring force from said first position to a second position for engagement with said latchable element to physically lock said plunger element to prevent further dose preparing and injecting. said gear set is pivotal on said plunger element and shiftable proximally and distally with said plunger element to convert motion of the plunger element into motion of the drive member; and said apparatus further comprises a latching element (180, 225) including a latching lip (186, 240) and a skid (190, 236); said drive member including an axially extending, skid-engaging surface (71, 71') along which said skid is slidable as said drive member passes distally during advancement during plunger element shifting in the distal direction, said skid-engaging surface having an axial length and a proximal end, said drive member along said axial length structured and arranged with said skid so as to maintain said latching lip against a spring force in a first position free of a latchable element (117, 266) disposed on said plunger element during dose preparing and injecting prior to a final dose administration; and wherein said skid-engaging surface shifts distally of said skid such that said skid passes beyond the proximal end upon administration of a final dose allowing said latching lip to be urged by said spring force from said first position to a second position for engagement with said latchable element to physically lock said plunger element to prevent further dose preparing and injecting.