An implantable medical device is provided for controlled drug delivery within the bladder, or other body vesicle. The device may include at least one drug reservoir component comprising a drug; and a vesicle retention frame which comprises an elastic wire having a first end, an opposing second end, and an intermediate region therebetween, wherein the drug reservoir component is attached to the intermediate region of the vesicle retention frame. The retention frame prevents accidental voiding of the device from the bladder, and it preferably has a spring constant selected for the device to effectively stay in the bladder during urination while minimizing the irritation of the bladder.