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Forteo (human teriparatide parathyroid hormone) a Potential Treatment for High Risk Fracture Patients with Osteoporosis

Forteo (human teriparatide parathyroid hormone, PTH 1-24) is a genetically engineered anabolic drug that increases bone mass and decreasing fracture risk in postmenopausal women with osteoporosis and is currently recommended for patients with a high risk of fracture, according to a recent American review.

Traditional treatments of osteoporosis include antiresorptive drugs that inhibit osteoclast bone resorption, such as oestrogen, selective oestrogen receptor modulators, bisphosphonates, and calcitonin.

The new genetically engineered drug is now available and approved in the United States by the Food and Drug Administration for treatment of osteoporosis. It is a recombinant form of the parathyroid hormone, which naturally regulates calcium in the body. It uses a different mode of action for treating osteoporosis than the antiresorptive agents in that it increases bone turnover and stimulates osteoblasts.

Chad Deal, MD, and James Gideon, MD, PhD, with the Cleveland Clinic Foundation, Cleveland, Ohio, United States, and Eli Lilly and Company, reviewed the pharmacology and efficacy of Forteo.

In a clinical trial funded by Eli Lilly and Company, the researchers compared the efficacy of Forteo 20 mcg or 40 mcg daily for an average 19 months in comparison and placebo in 1,637 postmenopausal women with low bone mass and prior vertebral fractures.

Results show that bone density increased and fracture risk decreased to a greater extent in the Forteo-treated group than in the placebo group. An 18-month follow up study also found that the protective effect persisted even after cessation of treatment.

Side effects associated with Forteo treatment include leg cramps, dizziness, and hypercalcaemia. Reports that Forteo also caused osteosarcoma in rats have not been confirmed in humans.

Forteo is not recommended for patients with open epiphyses, such as children, teenagers and young adults, and patients with Paget disease, metabolic bone diseases, primary hyperparathyroidism, history of osteosarcoma, and renal impairment.

The authors recommend using the drug "as initial therapy for 2 years (the FDA-approved interval) in high-risk patients, followed by an antiresorptive agent to maintain and further the increase in bone mass achieved with Forteo." For patients already taking antiresorptive agents, he recommends stopping this treatment before starting Forteo.

They add, "the drug is much more expensive than antiresorptive agents," ($600 a month for treatment) and will therefore likely be restricted to patients with high fracture risk that can pay or have insurance coverage for the treatment.
Cleveland Clinic Journal of Medicine 2003;70:7:585-601. "Recombinant human PTH 1-34 (Forteo): An anabolic drug for osteoporosis"

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