Does the combination of alendronate and parathyroid hormone give a greater benefit than either agent alone in osteoporosis?

In osteoporosis, both the bisphosphonate alendronate and parathyroid hormone (1-34) (PTH (1-34) ) have been shown to reduce the incidence of fractures. As bisphosphonates and PTH have different mechanisms, it has been proposed that their effects in osteoporosis may be additive. However, a major clinical trial of PTH (1-84) and alendronate in postmenopausal women demonstrated that their effects were not additive. A further trial in men with osteoporosis showed that alendronate impaired the ability of PTH (1-34) to increase bone mineral density. The combination of alendronate and PTH does not have greater benefit than either agent alone, and may even be detrimental, thus should not be used.