An extended use self-contained, wearable medical device is provided. Thedevice may be configured with aninfusion needle deployment mechanism to variably insert and retract aninfusion needle to different depths, or to completely retract theinfusion needle from the infusion site and then re-insert the needle after apredetermined period of time, during an infusion cyclein order to extend the viability of the infusion site. The device may alsocomprise dual needle deployment mechanisms thatvariably insert and retract the infusion needles. A flow sensor may beprovided to detect the stoppage of flow through the infusioncannula and signal the needle deployment mechanism to attempt infusion at adifferent depth or to deploy a second infusionneedle. A re-fillable reservoir assembly may be provided to supply a drug overthe extended use of the device. The device may also bepartially reusable or partially-disposable.
