MK-5442

MK-5442 is an orally bioavailable small molecule calcium-sensing receptor (CaSR) antagonist, also known as a calcilytic, developed by Merck Sharp & Dohme for the treatment of postmenopausal osteoporosis. The drug's mechanism of action involves blocking CaSRs in the parathyroid gland, which triggers a transient, pulsatile increase in the secretion of endogenous parathyroid hormone (PTH). This pulsatile PTH release is intended to exert an anabolic effect on bone, stimulating bone formation. In Phase 2 clinical trials involving postmenopausal women with osteoporosis, MK-5442 demonstrated dose-dependent increases in PTH levels and biochemical markers of bone formation. However, the drug failed to produce statistically significant improvements in bone mineral density (BMD) compared to placebo after six months of treatment, leading to the cessation of its clinical development for this indication.