Ronacaleret (SB-751689-A) is a calcium-sensing receptor antagonist. This orally administered compound has been evaluated as a drug for treatment of postmenopausal osteoporosis. By antagonizing calcium-sensing receptors on the surface of the parathyroid gland, ronacaleret triggers a transient release of the body's own stores of parathyroid hormone. In patients with osteoporosis, this may increase volumetric bone mineral. In a phase II clinical trial, bone mineral density at the lumbar spine increased. Cardiac disorders (2.3% of patients) and gastrointestinal disorders (>60% of patients) were reported as adverse events. Phase I studies have also been conducted to evaluate the impact of ronacaleret on mobilization of Hematopoietic stem cells (HSCs) and to measure changes in CD34+ cell counts.