Generic Name

Forteo

Mechanism

Forteo (teriparatide) is a recombinant fragment of human parathyroid hormone (PTH[1‑34]). It binds to the PTH/PTHrP receptor on osteoblasts, activating the cAMP‑dependent protein kinase A pathway. This stimulates osteoblast differentiation, increases bone formation, and transiently suppresses osteoclastic bone resorption. The net effect is an anabolic response that raises bone mineral density (BMD) and reduces vertebral and non‑vertebral fractures.

Pharmacokinetics

• Absorption – Subcutaneous injection; ~70 % bioavailability.
• Distribution – Plasma protein binding <10 %.
• Metabolism – Proteolytic cleavage of the peptide; no hepatic CYP interaction.
• Elimination – Primarily renal; half‑life 1–3 h (time to steady state ~8 days).
• Special Populations – No dose adjustment needed for mild‑to‑moderate renal impairment; use cautiously in creatinine clearance <30 mL/min.

Indications

• Postmenopausal osteoporosis – In patients at high risk for fracture, when bisphosphonates or denosumab are unsuitable or ineffective.
• Glucocorticoid‑induced osteoporosis – For patients on high‑dose corticosteroids (≥7.5 mg/day prednisone equivalent for ≥3 months).
• Anabolic therapy – For patients with severe osteopenia or low BMD (T‑score ≤ –2.5).

Contraindications

• Contraindications – Hypercalcemia, hyperparathyroidism, familial hypophosphatemic rickets, osteogenesis imperfecta, Paget disease.
• Warnings –
• Calcitonin‑induced bone loss – Avoid concurrent calcitonin use.
• Bone neoplasia – Teriparatide use is not recommended if malignant bone disease is suspected.
• Metabolic alkalosis – May exacerbate alkalosis.
• Age >65 yr – Not studied beyond 75 yr; caution advised.

Dosing

• Adult dose – 20 µg (0.24 mL) subcutaneously once daily, preferably at the same time each day.
• Injection site – Rotating abdomen, thigh, or upper arm.
• Duration – Maximum of 24 months (18 months in the U.S.) to minimize osteosarcoma risk in animal studies.
• Missed dose – Bypass or reschedule for next dose within 3 days; do not double dose.

Adverse Effects

• Common – Nausea, dizziness, limb edema, transient hypercalcemia.
• Serious –
• Osteosarcoma – Rare, increased risk in rodent models; thus strict duration limit.
• Hypercalcemia – Monitor serum calcium; treat with hydration and calcium‑lowering agents.
• Hypophosphatemia – May occur; monitor phosphate levels.
• Injection‑site reactions – Pruritus, erythema, induration.

Monitoring

Clinical Pearls

• Rotational injections help prevent local skin atrophy; avoid the same anatomical site daily.
• Begin after a period of anti‑resorptive therapy (bisphosphonates or denosumab) to maximize BMD gains—teriparatide is optimally used after a “drug holiday.”
• Adjunct vitamin D (800–1,000 IU/day) and calcium (1,200 mg/day) are essential; suboptimal levels blunt anabolic response.
• Patient education: Emphasize daily adherence—skipping doses reduces therapeutic benefit; do not double‑dose.
• Use in adolescents: Teriparatide is a Category B/Category D agent; only consider when other options are exhausted and after discussing potential risks.
• Osteosarcoma vigilance: No routine imaging needed, but patients should report new bone pain or swelling promptly.
• Switching to denosumab: After teriparatide, transition to denosumab can help consolidate BMD gains and mitigate rebound bone loss.

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• Forteo (teriparatide) offers a powerful anabolic option for high‑risk osteoporosis, but requires careful patient selection, monitoring, and adherence for optimal outcomes.