PTH analog · osteoporosis
Teriparatide is made by a genetically modified strain of E. coli and has the same sequence as the 34 N-terminal amino acids of human parathyroid hormone, which hold the biological activity of the 84-amino-acid hormone1. Its approved uses are in osteoporosis with a high risk of fracture, given by injection under the skin1. Doctors class it as an anabolic (bone-building) agent because it stimulates new bone formation1; antiresorptive drugs such as bisphosphonates, the more common choice, work mainly by slowing bone loss.
Parathyroid hormone is the body's main regulator of calcium and phosphate, acting on bone and kidney through cell-surface receptors that teriparatide binds just as the full hormone does. Its effect on bone depends on the pattern of exposure. A continuous excess, as in an overactive parathyroid gland, lets bone-removing cells outpace bone-building ones and weakens the skeleton. Brief, intermittent exposure from an injection does the opposite: it stimulates osteoblasts, the cells that lay down bone, more than osteoclasts, which resorb it. The result is new bone on both the spongy inner (trabecular) and dense outer (cortical) surfaces, with higher bone mass, higher markers of bone turnover and greater bone strength. Teriparatide is not expected to accumulate in bone or other tissues.
Its fracture benefit comes from large randomized trials in people. In a trial of 1,637 postmenopausal women with prior vertebral fractures, new vertebral fractures occurred in 14% on placebo versus 4% to 5% on teriparatide, nonvertebral fragility fractures fell from 6% to 3%, and spine bone density rose substantially2.
In VERO, 1,360 women with severe osteoporosis were randomized to teriparatide or the oral bisphosphonate risedronate for two years; new vertebral fractures occurred in 5.4% versus 12.0%, and clinical fractures were also less frequent3. In 428 adults on long-term glucocorticoids, teriparatide raised spine bone density more than alendronate and was followed by fewer new vertebral fractures (0.6% vs 6.1%), though more patients had raised blood calcium4. Rats given teriparatide developed osteosarcoma, the finding behind the label's bone-tumor warning1.
FDA-approved in 2002 as Forteo (Eli Lilly); other teriparatide products have since been approved, including Bonsity (2019) and several generics (from 2023). It is indicated for postmenopausal women and men with osteoporosis at high risk for fracture and for osteoporosis linked to long-term glucocorticoid use.
Per the FDA label, the most common effects are joint pain, general pain and nausea; dizziness and leg cramps also occur more often than with placebo. Warnings cover serious allergic reactions, osteosarcoma (seen in rats and reported after marketing, though observational studies have not shown higher risk in people; avoided in those at higher baseline risk, such as those with open growth plates, Paget's disease or prior skeletal radiation), raised blood calcium, kidney stones, a drop in blood pressure on standing with early injections, and digoxin toxicity.
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