US Patent 9421334 Multiple use disposable injection pen

A medication injection pen (51) includes a housing (1) and a dose set knob (2) having at least one internal tooth (22). A brake member (5) has a plurality of axially extending splines (52). A driver or setback member (9) includes at least one external tooth (92) engaging the at least one internal tooth (22) of the dose set knob (2) and at least one ratchet arm (96) engaging the plurality of axially extending splines (52). The driver (9) is prevented from rotating with the dose set knob (2) while moving axially with the dose set knob (2) during dose setting and dose correcting, and the driver (9) rotates with the dose set knob (2) during an injection.