Why is alendronate taken once a week?

Alendronate is used to treat and prevent osteoporosis (a condition in which the bones become thin and weak and break easily) in women who have undergone menopause (”change of life,” end of menstrual periods) and to treat osteoporosis in men.

Alendronate (Fosamax, Merck & Co.) is now available in a 70 mg formulation to be taken once a week for osteoporosis. Earlier studies demonstrated that alendronate is highly effective for increasing bone density, reducing bone turnover rate and reducing the risk of fractures. A subsequent clinical trial reported that the once-weekly dosing regimen is therapeutically equivalent to the daily regimen. Administering alendronate (70 mg) once a week effectively provides continuous inhibition of bone resorption because bone resorption by osteoclasts is a slow process that typically requires 2-3 weeks for completion and alendronate remains at active bone remodelling sites for a sustained period and (when present in sufficient concentration) effectively inhibits bone resorption. Bisphosphonates are currently the pre-eminent therapy for osteoporosis. Once-weekly alendronate represents a major advance in convenience because oral bisphosphonates must be taken in the fasting state with water at least 30 minutes before consuming food or beverages. Sales data several months after introduction of once-weekly alendronate into the marketplace demonstrate rapid and extensive acceptance of this new regimen.