Alendronate osteoporosis drug, molecular model. Alendronate is marketed as Fosamax, or as Fosavance when combined with vitamin D. It is a bisphosphonate drug, which works by blocking the resorption of bone by osteoclast bone cells. The treatment requires healthy levels of calcium and vitamin D, so if the underlying problem is with levels of either of those, that must be corrected before the course starts. In this molecule, atoms are shown as blobs and are colour-coded: carbon (green), nitrogen (blue), hydrogen (white), phosphorus (orange) and oxygen (red).