Abaloparatide

Abaloparatide is a synthetic 34-amino acid peptide analog of parathyroid hormone-related protein (PTHrP) approved by the FDA in 2017 for the treatment of postmenopausal osteoporosis in women at high fracture risk. While teriparatide is based on PTH(1-34), abaloparatide is based on PTHrP(1-34) with specific amino acid modifications designed to optimize its interaction with the PTH1 receptor in a manner that favors bone formation over bone resorption.

The key pharmacological distinction lies in abaloparatide's preferential binding to the RG (receptor G-protein) conformation of the PTH1 receptor, rather than the R0 (receptor zero) conformation. Binding to the RG conformation produces a more transient intracellular signaling response, which appears to favor anabolic (bone-building) activity while causing less stimulation of bone resorption compared to PTH(1-34). This results in a wider anabolic window — a greater net difference between bone formation and resorption.

The pivotal ACTIVE trial demonstrated that abaloparatide significantly reduced the risk of new vertebral fractures by 86% and non-vertebral fractures by 43% compared to placebo over 18 months in postmenopausal women with osteoporosis. In the same trial, abaloparatide showed a numerically lower incidence of hypercalcemia compared to open-label teriparatide, consistent with its pharmacological profile of reduced resorptive activity.

Like teriparatide, abaloparatide treatment is limited to 2 years due to the theoretical osteosarcoma risk based on animal studies. Patients should transition to antiresorptive therapy after completing abaloparatide to maintain bone density gains. A transdermal delivery system (abaloparatide-sstm) has been investigated, which could offer a needle-free alternative for patients who are averse to daily injections.