Menatetrenone (INN), also known as MK4, is a vitamin K compound used as a hemostatic agent, and also as adjunctive therapy for the pain of osteoporosis. MK4 is marketed for the osteoporosis indication in Japan by Eisai Co., under the trade name Glakay. Has several mechanism of actions: (1) Acceleration of osteogenesis. In human osteoblast cultures, calcification was accelerated by administration of menatetrenone at a concentration of 2.25 × 10-6 mol/L alone or when it was coadministered with 1,25(OH)2D3. The osteocalcin content in the cell layers was increased by coadministration with 1,25(OH)2D3. 2. Inhibition of bone resorption. In organ cultures of mouse calvaria, at concentrations of 3 × 10-6 to 3 × 10-5 mol/L, menatetrenone inhibited bone resorption induced by IL-1α, PGE2, PTH and 1,25(OH)2D3. In mouse bone marrow cell cultures, at concentrations of 3 × 10-6 to 1 × 10-5 mol/L, menatetrenone inhibited the induction of osteoclast release by 1,25(OH)2D3. 3. Effect on serum level of osteocalcin. Menatetrenone was administered to patients with osteoporosis at a dose of 45 mg/day for 2 years. Menatetrenone increased the serum level of osteocalcin and decreased the serum level of Glu-osteocalcin.