A medication injection pen (51, 200, 300, 400), comprising: a housing (1)； a dose setting control (2) comprising at least one internal tooth (22)； a brake member (5) having a plurality of axially extending ridges (52)； and an impeller (9) that includes at least one outer tooth (92) for engaging said at least one inner tooth (22) of said dose setting control (2) and at least one ratchet arm (96) which is coupled to said plurality of axially extending ridges (52), characterized in that during dose setting and dose correction by means of rotation of said dose setting control, said outer tooth (92) of said impeller (9 ) is decoupled from said inner tooth (22) of said dose setting control (2) and said ratchet arm (96) is coupled with said axially extending ridges (52) of said brake member (5) to prevent that said impeller (9) rotates with said dose setting control (2) and with a spindle (4) while moving axially with said dose setting control (2) and said impeller (9) moves axially with respect to said spindle, said spindle (4) is in a fixed state so that e during an injection a button is pressed causing said external tooth (92) of said impeller (9) to be rotatably coupled with said internal tooth (22) of said dose setting control (2) that is rotationally coupled to said spindle ( 4) to axially move a hollow piston rod (6) and said ratchet arm (96) slides from said axially extending ridges (52) of said brake member (5).Un pluma de inyección de medicación (51, 200, 300, 400), que comprende: un alojamiento (1)； un mando de establecimiento de dosis (2) que comprende al menos un diente interno (22)； un miembro de freno (5) que tiene una pluralidad de lomas que se extienden axialmente (52)； y un impulsor (9) que incluye al menos un diente externo (92) para acoplarse a dicho al menos un diente interno (22) de dicho mando de establecimiento de dosis (2) y al menos un brazo de trinquete (96) que se acopla a dicha pluralidad de lomas que se extienden axialmente (52), caracterizado
