Teriparatide

• Severe Osteoporosis
• Glucocorticoid-Induced Osteoporosis
• High-Risk Fractures
• Bone Loss Treatment

Teriparatide is a recombinant form of parathyroid hormone (PTH 1-34) used to treat osteoporosis in patients at high risk for fracture. Unlike antiresorptive agents, it stimulates new bone formation, making it an anabolic therapy for osteoporosis.

Mechanism of Action

Teriparatide mimics endogenous parathyroid hormone:

• PTH receptor activation: Binds to PTH/PTHrP receptors on osteoblasts
• Intermittent vs continuous exposure: Once-daily dosing causes anabolic effects; continuous exposure (as in hyperparathyroidism) is catabolic
• Stimulates osteoblast activity: Increases bone formation rate
• Increases bone mineral density: Both trabecular and cortical bone
• Improves bone microarchitecture: Enhances structural integrity
• Reduces fracture risk: Demonstrated reduction in vertebral and nonvertebral fractures

Available Formulations

Teriparatide is available as:

• Prefilled pen (Forteo): 20 mcg/dose (contains 28 daily doses of 20 mcg each in 2.4 mL)

Administered subcutaneously.

Medical Uses

FDA-Approved Indications:

• Postmenopausal women with osteoporosis at high risk for fracture
• Men with primary or hypogonadal osteoporosis at high risk for fracture
• Men and women with glucocorticoid-induced osteoporosis at high risk for fracture

"High risk" includes history of osteoporotic fracture, multiple risk factors, or failure of other treatments.

Dosing Guidelines

Adults:

• 20 mcg subcutaneously once daily in thigh or abdominal wall

Duration:

• Maximum cumulative lifetime use: 24 months
• After teriparatide, transition to antiresorptive therapy to maintain gains

Administration:

• Inject in thigh or abdomen
• Rotate injection sites
• Administer initially where patient can sit or lie down (orthostatic hypotension may occur with first doses)

Important Safety Information

Boxed Warning:

• Osteosarcoma risk: In rats, teriparatide caused dose-dependent increase in osteosarcoma incidence. Risk in humans unknown.
• Not recommended for patients at increased baseline risk for osteosarcoma (Paget's disease, prior radiation, pediatric/young adult open epiphyses, unexplained alkaline phosphatase elevation)

Contraindications:

• Hypersensitivity to teriparatide
• Pediatric and young adult patients with open epiphyses
• Patients with increased baseline risk for osteosarcoma

Warnings and Precautions:

• Orthostatic hypotension: May occur within 4 hours of dose; have patient sit or lie down if symptoms develop
• Hypercalcemia: May transiently increase serum calcium; usually not clinically significant
• Urolithiasis: Use with caution in patients with active or recent urolithiasis
• Cumulative use >24 months not recommended

Drug Interactions

• Digoxin: Hypercalcemia may predispose to digitalis toxicity; monitor if used together
• Calcium supplements/Vitamin D: Typically continued; monitor serum calcium

Special Populations

• Hepatic Impairment: No adjustment needed
• Renal Impairment: No adjustment for mild to moderate; caution in severe (limited data)
• Pregnancy: Limited data; not recommended
• Lactation: Unknown if excreted in milk
• Pediatric: Contraindicated (open epiphyses)
• Elderly: No specific adjustment