Current available medicine can increase bone strength by making bones wider and "filling in" the holes in the bone walls that weaken it. These medicines are bisphosphonates, given either by a drip intravenously (eg pamidronate), or taken by mouth (eg risedronate). Their major action is to prevent bone breakdown by stopping the normal process of removing and then replacing old bone tissue, so in some parts of the bone, new bone formation is actually reduced. Most studies of bisphosphonates in children with OI have shown increased bone mineral density and improved exercise tolerance that could positively affect new bone formation; some have shown reduced fracture rate. Bone is highly responsive to mechanical stimulation. Whole body vibration (WBV) is a form of mechanical stimulation that has been shown to improve bone mineral density in some individuals with narrow bones.