A 69-year-old woman with severe osteoporosis and multiple vertebral fragility fractures is being considered for teriparatide. Which statement about this drug is correct?

• A It is given as a once weekly oral dose and continued indefinitely
• B It increases cortical bone density at the expense of trabecular bone
• C It primarily inhibits osteoclast apoptosis and is safe in Paget's disease
• D It stimulates bone formation preferentially when given by intermittent daily injection, with treatment limited to 2 years ✓

Explanation

Teriparatide, recombinant PTH 1-34, given as a daily subcutaneous injection, preferentially stimulates osteoblastic bone formation over resorption, producing the largest gains in trabecular bone. Duration is limited to 24 months because rat studies showed osteosarcoma at high lifetime exposure, and it is contraindicated in Paget's disease, prior skeletal radiotherapy, and unexplained raised alkaline phosphatase. Continuous PTH exposure causes net resorption, not intermittent dosing, which is why option C fails.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

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Written and medically reviewed by the StethoPrep medical team.