An extended use self-contained, wearable medical device is provided. The device may be configured with an infusion needle deployment mechanism to variably insert and retract an infusion needle to different depths, or to completely retract the infusion needle from the infusion site and then re-insert the needle after a predetermined period of time, during an infusion cycle in order to extend the viability of the infusion site. The device may also comprise dual needle deployment mechanisms that variably insert and retract the infusion needles. A flow sensor may be provided to detect the stoppage of flow through the infusion cannula and signal the needle deployment mechanism to attempt infusion at a different depth or to deploy a second infusion needle. A re-fillable reservoir assembly may be provided to supply a drug over the extended use of the device. The device may also be partially reusable or partially-disposable.
