A review of teriparatide and its clinical efficacy in the treatment of osteoporosis.

Until recently, antiresorptive medications such as bisphosphonates and raloxifene represented the main pharmacological treatment options for patients with osteoporosis. With the introduction of teriparatide (rhPTH (1-34) ), a recombinant formulation of parathyroid hormone (PTH) consisting of the first 34 amino acids of the N -terminal region, bone-forming therapy has now become possible. Preclinical, as well as human studies, have shown increases in trabecular as well as cortical bone mass with subsequent improvements in bone microstructure and cortical thickness. The subcutaneous daily dose of teriparatide 20 microg has been shown to decrease the occurrence of new vertebral fractures in caucasian women (70 years of age) by 65%, in a large randomised, double-blind placebo-controlled trial. Moderate-to-severe fractures or multiple vertebral fractures could be reduced by 90 and 77%, respectively. There was also a significant beneficial effect on new nonvertebral fractures (-35%) by the end of the 21-month treatment period. The reduction in nonvertebral fractures became evident after approximately 8 - 12 months of treatment. Smaller studies in men with low bone mass showed similar effects on bone mineral density and changes in bone turnover markers when compared to the results obtained in postmenopausal women. Recent data suggest that teriparatide is best given as monotherapy and not in combination with a bisphosphonate. Previous bisphosphonate treatment is also likely to diminish the bone anabolic potential of teriparatide. In order to preserve bone mass gained during the recommended 18- to 24-month treatment period, antiresorptive medication should be prescribed following teriparatide treatment. Studies so far have not shown serious PTH-related side effects. Hypercalcaemia is usually mild and transient and the osteosarcoma risk reported in rat toxicology studies is very unlikely to be predictive of a similar risk in humans. As teriparatide is expensive, its use at the moment should be limited to patients with more severe forms of osteoporosis, usually with the presence or history of one or more fractures because of those patients' high risk for subsequent fractures.