Teriparatide adverse effects

Teriparatide contains the first 34 amino acids in human parathyroid hormone and represents a novel approach to osteoporosis treatment. Although hyperparathyroidism leads to bone loss (see Fig. 88-3), therapeutic doses (for shorter periods of time) conversely improve BMD and rednce fractnre risk. Parathyroid hormone is currently the only approved osteoporosis medication that works by stimulating bone formation. Becanse of adverse effects and cost concerns, teriparatide is reserved for treating those at high risk of osteoporosis-related fracture who cannot or will not take or have failed bisphosphonate therapy. 

Candidates for teriparatide treatment include women who have a history of osteoporotic fracture, who have multiple risk factors for fracture, or who failed or are intolerant of previous osteoporosis therapy. Teriparatide should not be used in patients who are at increased baseline risk for osteosarcoma (including those with Paget s disease of bone, unexplained elevations of alkaline phosphatase, open epiphyses, or prior radiation therapy involving the skeleton). Full-length PTH(l-84), which is in clinical trials, has not been associated with osteosarcomas. Other adverse effects have included exacerbation of nephrolithiasis and elevation of serum uric acid levels. 

Administered as a once-daily, 20-pg SC injection in the thigh or abdominal wall, teriparatide is a clear, colorless liquid that is available as a 750 pg/3 ml, prefilled, disposable pen that requires refrigeration. Concurrent calcium (1,000 mg) and vitamin D (400 lU) supplementation is recommended. Treatment for longer than 2 years is not recommended. Teriparatide is rapidly absorbed, demonstrates 95% bioavailability, and is quickly eliminated via both hepatic and extrahepatic routes. The half life is 1 hour when administered SC. Metabolic studies have not been performed on teriparatide however, the entire PTH preprohormone has been shown to undergo enzyme-mediated transformations in the liver. Dizziness and leg cramps are the most commonly reported adverse side effects. 

Tumorigenidty Osteosarcoma is postulated as a potential adverse reaction to parathyroid hormone analogues, based on animal studies, and another case has been reported in a 67-year-old man who took teriparatide 20 micrograms/day subcutaneously for 2 months, 7 years after a course of radiotherapy for recurrent prostate cancer [65 ]. However, the osteosarcoma occurred within the field of previous radiotherapy and the time course suggested that the osteosarcoma may have been present before teriparatide administration. The authors noted that 430 000 patients have been treated with teriparatide for osteoporosis and that there have been only two reported cases of osteosarcoma, which is consistent with the expected population incidence of 4-5 per million. However, the effect of teriparatide on the growth of an undiagnosed osteosarcoma is unknown, and so teriparatide should be used with caution in patients who have had previous radiotherapy. 

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