PEN-TYPE DRUG INJECTION DEVICE WITH PARTICULAR DOSE SCALE AND DOSE DISPLAY WINDOW COMPRISING OPTICAL FILTER FOR UNAMBIGUOUS DISPLAY OF SET DOSE VALUE

摘要

The present invention relates to a pen-type drug injection device, comprising a dose scale drum (22) and having a housing (12) with a window (14) covered by an optical filter (50), the dose scale drum being displaceable axially relative to the housing during dose setting such that the dose value set can be read through the window while at least a portion of the dose scale drum protrudes from the housing. The dose values (42) are printed on an information surface (40) of the drum as an illegible pattern (48) together with a coding pattern (44), wherein the dose values (42) and the coding pattern (44) are designed such that light (52) reflected by or emanating from the illegible pattern (48) interacts with the optical filter (50) in such a way that the dose values (42) are exclusively recognizable through the optical filter (50) but not on the part of the dose scale drum protruding from the housing. The optical filter can be a color filter or a polarization filter in order to achieve the desired effect. In this way confusion of the actually set dose value and dose values which would otherwise be visible on the part of the dose scale drum protruding from the housing can be avoided during dose setting.