From the link posted by @amrh: and why are docs prescribing Tymlos or Forteo after Prolia? Is it mostly PCP's?

"In postmenopausal osteoporotic women switching from teriparatide to denosumab, BMD continued to increase whereas switching from denosumab to teriparatide results in progressive or transient bone loss. Combination denosumab/teriparatide therapy followed by denosumab alone results in the largest 4-year increases in hip and wrist BMD. These results should be considered when choosing the initial and subsequent management of postmenopausal osteoporotic patients."