susanjohnston,
the bisphosphonates stop the acid producing cells that break bone down. But these bone dissolving cells are attracted to bone that has weakened or fissured and should be replaced. In the natural order the bone is removed and replaced by fresh bone. When the cells that replace bone aren't produced in sufficient number we lose bone density and resilience.
For a long time the only way we had to reduce fracture was to decrease the acid producing cells, while the problem was that there weren't enough cells to replace the lost bone. We didn't know how to increase those bone building cells until Forteo and then Tymlos.
Both of these drugs increase the cells that produce new bone.
Bisphosphonates are pretty amazing. They prevent the osteoclasts-- the acid producing cell from forming the ruffled border necessary for adhering to the bone; the newer bisphosphonates induce death in the osteoclasts and the bisphosphonates adhere to the bone themselves preventing the osteoclasts from attaching.
They attach to the bone for a very long time. They are finding Fosamax remaining on bone ten years after it is taken as a medication.
If you take a drug that builds bone after you take a bisphosphonate, the effect of the bone building drug is less than if you take the anabolic first.
If I had to stop Forteo, I'd prefer a bisphosphonate that had the least effect and stayed on my bones for the least amount of time because I'd always be looking for a way to get back on Forteo or Tymlos.
Susan, I can manage to be pretty unclear. If any of this is questionable, I'm happy to give it another try.