A cartridge interface assembly drives a stopper in a drug reservoir or a drug delivery device. An anti-rotational guide optionally moves along an axis of a cavity of the reservoir. The anti-rotational guide is optionally slidably anti-rotationally coupled to a housing of the drug delivery device. A telescoping plunger driver may include a proximal shaft and distal shaft that telescope by relative rotation. The distal shaft is optionally slidably anti-rotationally coupled to the anti-rotational guide. The shafts are optionally oriented along said axis. In some embodiments, rotating the proximal shaft with respect to the anti-rotational guide moves the guide along said axis with respect to the housing and moves the distal shaft along the axis with respect to the anti-rotational guide.