TeriparatideRx

Trade Names: Forteo

Synonyms: Human recombinant parathyroid hormone (1-34)

Drug Class: Hormone

Preparations: Prefilled injection pen 2.4 mL (supplies 20 mcg dose for 28 days)

Dose: 20 mcg daily by subcutaneous injection

Indications: Osteoporosis with high risk of fracture failed alternative therapies; long-term safety not well established; until additional information is available, treatment for >2 years is not recommended.

Mechanism of Action: Mimics action of parathyroid hormone and stimulates new bone formation

Contraindications: Hypersensitivity, hypercalcemia, increased risk of osteosarcoma, avoid in Paget’s disease, previous irradiation, skeletal malignancy, open epiphyses, children

Precautions: Renal stones, unexplained increase in alkaline phosphatase, digoxin therapy, orthostatic hypotension – if occurs, is usually within a few hours of injection, ensure adequate vitamin D and calcium intake

Monitoring: Monitor serum calcium level periodically

Pregnancy Risk: C

Adverse Effects: Causes osteosarcoma in rats; the significance of this as regards risk in humans not established
Common: Arthralgia, nausea, transient increase in serum calcium concentration 4–6 hours after injection, dizziness, leg cramps
Uncommon: Orthostatic hypotension 4–6 hours after injection

Drug Interactions
Digoxin: Increased serum calcium may predispose to toxicity
Bisphosphonates: Impair ability of teriparatide to increase bone density

Patient Instructions: Refrigerate (do not freeze) the injection pen. Follow manual of instructions that comes with the pen. Dizziness on standing can occur after injection.

Comments: Cost, daily injections  and limited duration of therapy  limit use.  A weekly teriparatide preparation is under study. Carries a “black box” warning that it causes osteosarcoma in rats and should only be prescribed for patients for whom benefits outweigh risk. Antiresorptive drugs such as bisphosphonates impair the anabolic effects of teriparatide.  Bone mineral density decreases when drug is  stopped. Case reports of use in bisphosphonate-associated osteonecrosis of the jaw and atypical subtrochanteric fractures.  Reports of increased bone mineral density in combination with denosumab.

Clinical Pharmacology: Good rapid absorption, half-life less than 1 hour after subcutaneous injection

Cost: $$$$$

BIBLIOGRAPHY

Saag KG, Zanchetta JR, Devogelaer JP, et al. Effects of teriparatide versus alendronate for treating glucocorticoid-induced osteoporosis: thirty-six-month results of a randomized,double-blind, controlled trial. Arthritis Rheum 2009;60:3346-55. PMID: 19877063.