Some future antiresorptive drugs that are not yet improved by US food and drug administration (FDA), include calcitriol, genistein, other bisphosphonates (etidronate, pamidronate, and tiludronate), PTH (1-84), sodium fluoride, strontium ranelate, and also tibolone.

Nonapproved agents include:

• Calcitriol: This synthetic vitamin D analogue, which promotes calcium absorption, has been approved by the FDA for managing hypocalcemia and metabolic bone disease in renal dialysis patients. It is also approved for use in hypoparathyroidism, both surgical and idiopathic, and pseudohypoparathyroidism. No reliable data demonstrate a reduction of risk for osteoporotic fracture.
• Genistein: An isoflavone phytoestrogen which is the main ingredient in the prescription “medical food” product Fosteum® and generally regarded as safe by the FDA. Genistein may benefit bone health in postmenopausal women but more data are needed to fully understand its effects on bone health and fracture risk.
• Other bisphosphonates (etidronate, pamidronate, tiludronate): These medications vary chemically from alendronate, ibandronate, risedronate, and zoledronic acid but are in the same drug class. At this time, none is approved for prevention or treatment of osteoporosis. Most of these medications are currently approved for other conditions (e.g., Paget’s disease, hypercalcemia of malignancy, myositis ossificans).
• PTH (1-84): This medication is approved in some countries in Europe for treatment of osteoporosis in women. In one clinical study, PTH (1-84) effectively reduced the risk of vertebral fractures at a dose of 100 mcg/ day.
• Sodium fluoride: Through a process that is still unclear, sodium fluoride stimulates the formation of new bone. The quality of bone mass thus developed is uncertain, and the evidence that fluoride reduces fracture risk is conflicting and controversial.
• Strontium ranelate: This medication is approved for the treatment of osteoporosis in some countries in Europe. Strontium ranelate reduces the risk of both spine and nonvertebral fractures, but the mechanism is unclear. Incorporation of strontium into the crystal structure replacing calcium may be part of its mechanism of effect. These effects have only been documented with the pharmaceutical grade agent produced by Servier. This effect has not been studied in nutritional supplements containing strontium salts.
• Tibolone: Tibolone is a tissue-specific, estrogen-like agent that may prevent bone loss and reduce menopausal symptoms. It is indicated in Europe for the treatment of vasomotor symptoms of menopause and for prevention of osteoporosis, but it is not approved for use in the USA.^[1]

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