Abstract
Romosozumab (RSB) is a monoclonal antibody to sclerostin that is approved for post-menopausal osteoporosis at high fracture risk. It is administered as a monthly 210 mg subcutaneous injection for 12 months. We report the response to half the standard dose of RSB in an underweight patient with severe osteoporosis and primary biliary cholangitis (PBC). Using half dose RSB (approximately 3 mg/kg RSB), she demonstrated significant improvement in lumbar spine BMD, paralleling the results of phase III trials. This case highlights the effectiveness of RSB in a patient with concomitant PBC, in addition to its effectiveness at half the recommended dose in an underweight patient.