Teriparatide is a third-line agent in osteoporosis, after calcium/vitamin D supplementation and bisphosphonates. The bisphosphonates are effective in a large majority of osteoporosis patients, and only a minority would normally require teriparatide.

Mechanism of action

Teriparatide is the portion of human parathyroid hormone (PTH),amino acid sequence 1 through 34 of the complete molecule which contains amino acid sequence 1 to 84. Endogenous PTH is the primary regulator of calcium and phosphate metabolism in bone and kidney. Daily injections of teriparatide stimulate new bone formation leading to increased bone mineral density.

Teriparatide is the first FDA approved agent for the treatment of osteoporosis that stimulates new bone formation.

FDA approval

Forsteo was approved by the FDA on 26 November 2002, for the treatment of osteoporosis in 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.

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Teriparatide for osteoporosis
From American Family Physician, 4/15/04 by Oralia V. Bazaldua

Synopsis: Teriparatide (Forteo) is a synthetic human parathyroid hormone labeled for use in men and postmenopausal women with osteoporosis who are at high risk of fractures. It activates osteoblasts to stimulate new bone formation.

Safety: Teriparatide use is not recommended for more than two years because of limited safety data. (1) The labeling states it causes osteosarcomas in rats, but the relevance to humans is unknown. Limited exposure (one to two years) may not increase the risk of osteosarcomas.However, it should not be prescribed for patients at increased risk of bone cancer, including those with Paget's disease, metabolic bone disease, skeletal malignancies, unexplained increased alkaline phosphatase, or prior radiation therapy.Hypercalcemia and hyperparathyroidism also are contraindications. Teriparatide is category C in pregnancy and should not be used by nursing mothers.

Tolerability: Side effects are uncommon with teriparatide. Nausea (8.5 versus 6.7 percent), dizziness (8.0 versus 5.4 percent), and leg cramps (2.6 versus 1.3 percent) were reported more often by patients taking teriparatide than by those taking placebo.1 Discontinuation because of side effects occurred in 5.6 percent of the patients receiving placebo and 7.1 percent of treated patients. Transient hypotension also may occur, especially when therapy is started, but can be relieved by placing the person in a reclining position. Hypotension generally subsides after the first few doses and does not preclude continued treatment.

Effectiveness: Teriparatide increases bone mineral density in men and women. The effect on fracture risk has been studied in women but not in men. One study (2) found a reduction in vertebral fractures but not hip fractures in women at high risk. In this study, women who had one or more vertebral fractures at baseline were treated with teriparatide for an average of 19 months. (2) Treatment reduced the incidence of one or more new vertebral fractures from 14.3 percent in the placebo group to 5 percent in the treatment group (P <.001). Eleven patients will have to receive teriparatide for 19 months to prevent one additional vertebral fracture (number needed to treat = 11). Hip fractures were not reduced, but the study was not large enough to find a difference if one exists. Other therapies that have proven to reduce the risk of hip fractures include alendronate, risedronate, hormone therapy, and calcium with vitamin D either alone or in combination with other agents. Teriparatide has not been studied in women at lower risk of osteoporotic fractures, and fracture risk has not been compared head-to-head with other agents.

Price: A one-month supply of teriparatide costs approximately $560 compared with $67 for alendronate or risedronate, $33 for hormone therapy, $66 for calcitonin, $70 for raloxifene, and $10 for 1,200 mg of calcium with 800 IU vitamin D. (3)

Simplicity: Teriparatide is administered as a subcutaneous injection of 20 mcg once daily. It is available as a prefilled pen and patient education is recommended before its use. The product should be kept refrigerated at all times.

Bottom line: Teriparatide increases bone density in men and women with osteoporosis and has reduced the risk of new vertebral fractures in high-risk women. Its role in therapy is not clear. Due to its uncertain safety profile, lack of long-term experience, and high cost, it makes sense to reserve teriparatide for patients with severe osteoporosis who are intolerant or unresponsive to currently approved therapies.

STEPS drug updates cover Safety, Tolerability, Effectiveness, Price, and Simplicity.

The series coordinator of STEPS is Allen F. Shaughnessy, Pharm.D., director of medical education at Pinnacle Health System, Harrisburg, Pa.

REFERENCES

(1.) Forteo package insert. 2002. Forteo (teriparatide) by Eli Lilly and Company. Accessed online March 10, 2004, at: http://pi.lilly.com/us/forteo-pi.pdf.

(2.) Neer RM, Arnaud CD, Zanchetta JR, Prince R, Gaich GA, Reginster JY, et al. Effect of parathyroid hormone (1-34) on fractures and bone mineral density in postmenopausal women with osteoporosis. N Engl J Med 2001;344:1434-41.

(3.) 2003 Drug topics. Red Book. Montvale, NJ: Medical Economics Data, 2003.

ORALIA V. BAZALDUA, PHARM.D., BCPS, and JAN BRUDER, M.D. The University of Texas Health Science Center at San Antonio, San Antonio, Texas

Oralia V, Bazaldua, Pharm.D., BCPS, is associate professor in the Department of Family and Community Medicine, University of Texas Health Science Center at San Antonio.

Jan Bruder, M.D., is associate professor and director of the osteoporosis metabolic bone clinic, Department of Medicine, University of Texas Health Science Center at San Antonio.

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