Teriparatide

Teriparatide (Forteo, Eli Lilly and Company) is a recombinant form of parathyroid hormone. It is an effective anabolic (i.e., bone growing) agent used in the treatment of some forms of osteoporosis. It is also occasionally used off-label to speed fracture healing. Teriparatide is identical to a portion of human parathyroid hormone (PTH) and intermittent use activates osteoblasts more than osteoclasts, which leads to an overall increase in bone.

Medical uses
Teriparatide is the only anabolic (i.e., bone growing) agent indicated for use in postmenopausal women with osteoporosis at a high risk for fracture or with a history of osteoporotic fracture, patients with multiple risk factors for fracture, and for patients who have failed or are intolerant to other available osteoporosis therapy. It has been FDA-approved since 2002. It is effective in growing bone (e.g., 8% increase in bone density in the spine after one year) and reducing the risk of fragility fractures. Osteoporosis medications are generally safe, but some side effects of teriparatide include headache, nausea, dizziness, and limb pain.

One randomized trial of postmenopausal women who had already fractured vertebra compared teriparatide at either 20 or 40 micrograms per day with placebo. After about 19 months, 14% of the women taking placebo had new vertebral fractures, as compared with 5% of the women taking 20 micrograms of teriparatide and 4% of the women taking 40 micrograms. There were also a statistically significant lower number of non-vertebral fractures in the teriparatide treated group. 20 micrograms of teriparatide increased spine and hip bone mineral density.

Teriparatide is also indicated to increase bone mass in men with primary or hypogonadal osteoporosis at high risk of fracture, patients with multiple risk factors for fracture, and for patients who have failed or are intolerant to other available osteoporosis therapy.

Teriparatide is indicated as well for the treatment of men and women with osteoporosis associated with sustained systemic glucocorticoid therapy.

Teriparatide should not be prescribed for patients who are at increased risks for osteosarcoma. This includes those with Paget's Disease of bone or unexplained elevations of serum alkaline phosphate, open epiphysis, or prior radiation therapy involving the skeleton.

Other
Teriparatide is used as off-label therapy to speed fracture repair and treat fracture nonunions. It has been reported to have been successfully used to heal fracture nonunions. Generally, due to HIPAA regulations, it is not publicized when American athletes receive this treatment to improve fracture recovery. But an Italian soccer player, Francesco Totti, was given teriparatide after a tibia/fibula fracture, and he unexpectedly recovered in time for the 2006 World Cup. It has been reported that Mark Mulder used it to recover from a hip fracture Oakland A's for the 2003 MLB playoffs and Terrell Owens to recover from an ankle fracture before the 2005 Super Bowl.

Administration
Teriparatide is administered by injection once a day in the thigh or abdomen.

Adverse effects
Teriparatide has a theoretical risk of osteosarcoma, which was found in rat studies but not confirmed in humans. This may be because unlike humans, rat bones grow for their entire life. The tumors found in the rat studies were located on the end of the bones which grew after the injections began. After nine years on the market, there were only two cases of osteosarcoma reported. This risk was considered by the FDA as "extremely rare" (1 in 100,000 people) and is only slightly more than the incidence in the population over 60 years old (0.4 in 100,000).

Mechanism of action
Teriparatide is a portion of human parathyroid hormone (PTH), amino acid sequence 1 through 34, of the complete molecule (containing 84 amino acids). Endogenous PTH is the primary regulator of calcium and phosphate metabolism in bone and kidney. PTH increases serum calcium, partially accomplishing this by increasing bone resorption. Thus, chronically elevated PTH will deplete bone stores. However, intermittent exposure to PTH will activate osteoblasts more than osteoclasts. Thus, once-daily injections of teriparatide have a net effect of stimulating new bone formation leading to increased bone mineral density.

Teriparatide is the first, and to date only, FDA approved agent for the treatment of osteoporosis that stimulates new bone formation.

FDA approval
Teriparatide was approved by the Food and Drug Administration (FDA) on 26 November 2002, for the treatment of osteoporosis in men and postmenopausal women who are at high risk for having a fracture. The drug is also approved to increase bone mass in men with primary or hypogonadal osteoporosis who are at high risk for fracture.

Combined teriparatide and denosumab
Combined teriparatide and denosumab increased BMD more than either agent alone and more than has been reported with approved therapies. Combination treatment might, therefore, be useful to treat patients at high risk of fracture.