SERMs and SERMs with estrogen for postmenopausal osteoporosis

Abstract

Bone loss with aging places postmenopausal women at a higher risk for osteoporosis and its consequences such as fractures, pain, disability, and increased morbidity and mortality. Approximately 200 million patients worldwide are affected. The Third National Health and Nutrition Examination Survey (NHANES III) estimated that up to 18% of US women aged 50 and older have osteoporosis and up to 50% have osteopenia. Greater than 2 million osteoporotic related fractures occurred in the United States with direct healthcare costs exceeding $17 billion. Hormone Replacement Therapy (HRT) was a popular option for postmenopausal women before the Women's Health Initiative (WHI). Several agents are available in the U.S., including bisphosphonates, hormone therapy, calcitonin, parathyroid hormone and the selective estrogen receptor modulator (SERM) raloxifene. There are concerns about long term safety and compliance. Therefore, other agents are under investigation. SERMs are a diverse group of agents that bind to the estrogen receptor and each SERM appears to have a unique set of clinical responses, which are not always consistent with the typical responses seen with other SERMs. This article will discuss the SERMs approved in the United States, tamoxifene and raloxifene, and investigational SERMs. The ideal SERM would include the beneficial effects of estrogen in bone, heart and the central nervous system, with neutral or antagonistic effects in tissues where estrogen effects are undesirable(breast and endometrium). A new target in treating postmenopausal osteoporosis is the tissue estrogen complex or the pairing of a SERM with a conjugated estrogen known as a tissue selective estrogen complex (TSEC). This novel approach is currently being evaluated with bazodoxifene which could yield the beneficial effects of estrogens and SERMS, while potentially being more tolerable and safer than either therapy alone.