An infusion device for a drug delivery system comprises an infusion needle (1) having a tip end (2) and a drive unit (D) coupled to the infusion needle and arranged for advancing the tip end of the infusion needle to penetrate any fibrosis when the infusion device is implanted in a patient's body. The infusion needle and drive unit are designed for implantation in a patient's body. Other components of the drug delivery system may be part of the implantable infusion device or, alternatively, be for extracorporal use cooperating with the implanted infusion device. Preferably, the infusion needle can be advanced and retracted with each infusion cycle. Furthermore, upon each advancement and/or retraction, the needle may be moved laterally so as to vary the injection site. Needle (1) and drive unit (D) are preferably disposed within a body (15), with the infusion needle being arranged for penetrating a self-sealing penetration membrane (18).
