DRUG DELIVERY INJECTION PEN WITH ADD-ON DOSE CAPTURING AND DISPLAY MODULE

A drug injector (1) comprising expelling means for expelling a dose of drug from a reservoir, a release member (13) for releasing the drug expelling means, and an actuation member (33) adapted to be moved by a user between an initial, intermediate and actuated position in which the release member is moved to release the drug expelling means. The injector further comprises an electronic capturing system for capturing data representing a dose of drug to be expelled, and a switch (38) for starting initialization of the data capture system, the switch being actuated when the actuation member is positioned in its intermediate position. A spring (34) provides a biasing force against movement of the actuation member between its initial and intermediate position. Thereby the electronic data capturing system is allowed to initialize during the actuation member's movement between the intermediate and the actuated position.