Regarding teriparatide therapy for severe osteoporosis, which statement is correct?
- A It acts primarily by inhibiting RANK ligand
- B It should be limited to a maximum of 24 months of lifetime exposure ✓
- C It is the first-line agent in patients with active malignancy
- D It decreases bone formation markers during the first month of use
Correct answer: B. It should be limited to a maximum of 24 months of lifetime exposure
Explanation
Teriparatide, recombinant human PTH 1-34 given as 20 micrograms subcutaneously daily, stimulates bone formation when given intermittently. Because it caused osteosarcoma in rats, cumulative lifetime use is capped at 24 months. Its action is anabolic through osteoblast stimulation, not RANKL inhibition, so formation markers such as P1NP rise early. It is avoided in active malignancy, prior skeletal radiotherapy and hypercalcaemia, making option C incorrect rather than supportive.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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