Teriparatide: Bone Building Treatment for Severe Osteoporosis
Teriparatide is the synthetic 1-34 amino acid fragment of human parathyroid hormone (PTH), representing the biologically active portion of the naturally occurring hormone. Unlike antiresorptive drugs that slow bone loss, teriparatide is an anabolic agent that actively stimulates new bone formation. It remains one of the most potent treatments available for severe osteoporosis with fracture risk.
Approved in Europe and the United States, teriparatide is indicated when other osteoporosis therapies are inappropriate or have failed. Its unique mechanism of building bone rather than simply preserving it distinguishes it from bisphosphonates and denosumab. Due to preclinical findings of osteosarcoma in rats with long-term high-dose exposure, treatment duration is limited to a maximum of 24 months.
Mechanism of Action
Intermittent subcutaneous administration of teriparatide mimics the pulsatile physiological secretion of endogenous PTH, which has anabolic effects on bone in contrast to the catabolic effects of continuously elevated PTH levels seen in primary hyperparathyroidism. Teriparatide activates PTH-1 receptors on osteoblasts, increasing their proliferation, differentiation, and survival while reducing osteoblast apoptosis. The net result is stimulation of bone formation on both trabecular and cortical surfaces, increasing bone mineral density and improving bone microarchitecture and quality beyond what density measurements alone reflect.
Indications
Teriparatide is indicated for the treatment of osteoporosis in postmenopausal women and in men with primary or hypogonadal osteoporosis at high risk of fracture. It is approved for glucocorticoid-induced osteoporosis in both sexes. Key patient profiles include those with very low bone mineral density (T-score below minus 3.0), multiple vertebral fractures, or those who have experienced fractures despite adequate antiresorptive therapy. The maximum lifetime treatment duration is 24 months, after which antiresorptive therapy must follow to preserve the gains achieved.
Dosage and Administration
The approved dose is 20 micrograms administered once daily by subcutaneous injection into the thigh or abdomen. The prefilled injection pen is stored in the refrigerator and should be allowed to reach room temperature before injection. Patients can self-administer after proper training. The first injection should be given under medical supervision due to the risk of orthostatic hypotension. Treatment duration must not exceed 24 months in a lifetime. Upon completion of teriparatide therapy, antiresorptive treatment such as a bisphosphonate or denosumab should begin promptly to maintain bone density gains.
Side Effects
Nausea, pain in the extremities, headache, and dizziness are the most commonly reported adverse effects. Orthostatic hypotension can occur within the first hours after injection, typically resolving within a few hours. Hypercalcaemia has been observed in some patients; monitoring of serum calcium and urinary calcium excretion is recommended, particularly in patients prone to hypercalcaemia. Mild increases in serum uric acid have been noted. Injection site reactions including pain, erythema, and bruising occur in a small proportion of patients. Osteosarcoma was observed in rats treated with very high doses over a lifetime; the relevance to humans at therapeutic doses is considered low, but the drug is contraindicated in patients with elevated baseline osteosarcoma risk.
Interactions
Digitalic glycosides (digoxin) may be sensitized to hypercalcaemia induced by teriparatide; monitoring is required in patients taking digoxin. No clinically relevant pharmacokinetic drug interactions have been identified. Concomitant calcium and vitamin D supplementation is generally recommended to support bone mineralisation; doses should be adjusted based on dietary intake and serum levels to avoid hypercalcaemia. Antiresorptive agents are not combined with teriparatide during the treatment period, as combination has not demonstrated superiority over teriparatide alone.
Special Notes
Teriparatide is contraindicated in Paget's disease of bone, unexplained elevations of alkaline phosphatase, prior radiation therapy involving the skeleton, pre-existing hypercalcaemia, severe renal impairment, and skeletal malignancies. It is not approved for use in children or adolescents with open epiphyses. The drug should not be used in pregnancy. The 24-month lifetime limit applies regardless of whether the two years are consecutive or interrupted. After completing teriparatide, patients must transition to antiresorptive therapy; bone density can decrease significantly without follow-on treatment.
Related Topics
Frequently Asked Questions
Why can teriparatide only be used for 24 months?
In rat studies, lifetime treatment with high doses of teriparatide caused osteosarcoma. Although the doses were much higher than therapeutic human doses and the relevance to humans is considered low, regulatory agencies set a precautionary 24-month lifetime limit. No osteosarcoma cases attributable to teriparatide have been confirmed in decades of human use.
What happens to bone density after stopping teriparatide?
Without follow-on antiresorptive therapy, bone density gained during teriparatide treatment is progressively lost within the first year after stopping. Bisphosphonates or denosumab taken immediately after the teriparatide course preserve and can further increase bone density. This sequential strategy is strongly recommended in all guidelines.
Is teriparatide suitable for men with osteoporosis?
Yes, teriparatide is approved for osteoporosis in men with primary or hypogonadal osteoporosis at high fracture risk. Clinical trials demonstrated significant reductions in vertebral fracture risk in male patients comparable to the effects seen in postmenopausal women.
Sources
- EMA: Teriparatide (Forsteo) Summary of Product Characteristics 2023
- DVO Leitlinie Osteoporose 2023
- Neer RM et al: Effect of Teriparatide on Fractures. N Engl J Med 2001