Abaloparatide

Also known as: Tymlos, BA058

**Mechanism of Action** Abaloparatide is a synthetic analog of parathyroid hormone-related protein (PTHrP(1-34)) that acts as a selective agonist at the PTH1 receptor. Unlike teriparatide (PTH(1-34)), which induces prolonged receptor activation, abaloparatide exhibits a more transient interaction with the receptor, favoring a conformational state that preferentially stimulates bone formation pathways (e.g., Wnt/β-catenin signaling) over bone resorption. This differential signaling reduces the net efflux of calcium from bone, resulting in a lower incidence of hypercalcemia compared to teriparatide while maintaining robust anabolic effects on trabecular and cortical bone. **Key Research Findings** The pivotal Phase III ACTIVE trial (NCT01343004) demonstrated that daily subcutaneous abaloparatide (80 μg) significantly reduced vertebral (86% risk reduction; p<0.001) and nonvertebral fractures (43% risk reduction; p=0.049) over 18 months in postmenopausal women with osteoporosis, compared to placebo. Bone mineral density (BMD) gains at the lumbar spine (9.2%) and total hip (3.4%) were superior to both placebo and teriparatide. A subsequent extension study (ACTIVExtend) showed that transitioning to alendronate after abaloparatide maintained fracture risk reduction for up to 5 years. Preclinical models also indicate enhanced periosteal bone formation and improved bone microarchitecture, with minimal effects on renal calcium handling. **Clinical Relevance** Abaloparatide is FDA-approved for the treatment of postmenopausal women with osteoporosis at high fracture risk, including those with a history of osteoporotic fracture or multiple risk factors. Its favorable safety profile—particularly lower hypercalcemia rates (3.4% vs. 6.4% with teriparatide)—and once-daily subcutaneous dosing offer a practical alternative to other anabolic agents. Use is limited to a maximum of 2 years due to potential osteosarcoma risk observed in rodent studies, though no such risk has been confirmed in humans. It is contraindicated in patients with Paget’s disease, unexplained alkaline phosphatase elevations, or prior radiation therapy. For research purposes only — not medical advice.

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