US Patent 9295782 Multiple use disposable injection pen

A medication injection pen (11) includes a housing (1) and a dose set knob (2) rotatable with respect to the housing (1). A brake assembly (68) is disposed in the housing (1) and has a ratchet member (43). A driver (21) includes at least one external tooth (57) engaging the ratchet member (43). The engagement between the ratchet member (43) and the at least one external tooth (57) substantially prevents the driver (21) from rotating with respect to the dose set knob (2) during dose setting and dose correcting. The engagement between the ratchet member (43) and the at least one external tooth (57) allows the driver (21) to rotate with the dose set knob (2) during an injection.