Potential of alfacalcidol for reducing increased risk of falls and fractures

There are no general accepted strategies for combined drug treatments in osteoporosis, while in other important chronic diseases combinations of different medications are used as a rule to improve therapeutic results and reduce the risk of adverse events. It is suggested that the success of combined treatments is related to the different modes of action of the respective single therapies. On the other hand it was shown that a strong antiresorptive bisphosphonate is able to blunt at least in part the effects of anabolic parathyroid hormone peptides Calcitriol, the active vitamin D-hormone and its prodrug alfacalcidol lead to pleiotropic effects on bone remodelling (antiresorptive, anabolic and enhancing mineralization) and in addition to effects on other important target tissues (e.g. gut, parathyroid glands, muscle). With active D-analogs significant improvements in the therapeutic outcome of osteoporosis can be achieved by the resulting improvements of bone quality, calcium absorption and risk reduction of falling. The same beneficial effects cannot be achieved with plain vitamin D due to feedback controlled, limited renal activation or insufficient conversion in the elderly with impairment of renal function. Accordingly alfacalcidol, approved as a treatment for different forms of osteoporosis, is besides adoption as a mono-therapy an interesting candidate for combined therapies. There are interesting preclinical trials and clinical pilote studies in the literature proving that a parallel therapy with selectively anti-osteoclastic bisphophonates and pleiotropically acting D-analogs is able to optimize therapeutic results in osteoporosis. In the AAC-Trial (Alfacalcidol-Alendronate-Combined) we studied 90 patients with established osteoporosis (57 women, 33 men) over two years after alternate allocation to three treatment arms (alfacalcidol plus calcium, alendronate plus plain vitamin D and Ca, and alendronate plus alfacalcidol and Ca). During the 2-year-study we observed the significantly highest lumbar spine and hip BMD increases in the combined treatment group (p < 0.001). The number of patients with new vertebral and non-vertebral fractures after 2 years was 9 with alfacalcidol alone, 10 with alfacalcidol and plain vitamin D and 2 in the group receiving alendronate plus alfacalidol (p < 0.02). Furthermore there was a lower rate of falls and an earlier reduction in back pain in the patients treated with the active combination. This trial confirms the demonstrated highly significant advantages of this combined treatment regimen used in the pilote studies. Especially in patients with severe osteoporosis this interesting combination of two substances with complete different mechanisms of action should be taken into consideration.