Abstract
Alfacalcidol(1α-OH-D_3) is the prodrug of calcitriol(1α,25(OH)_2D_3), the active form of vitamin D. Sixteen years have passed since 1981 when alfacalcidol was first marketed as a therapeutic agent for bone disease associated with vitamin D metabolic disorders. In 1983, its indications were extended to include the treatment of osteoporosis. During this time, the usefulness of the active form of vitamin D for osteoporosis became accepted among Japanese clinicians, but internationally, researchers remained divided in their views. The positive outcome of the discussions that ensured regarding this issue is reflected directly in the consensus reports compiled at the symposia of 1993 and 1996 in Hong Kong and Amsterdam, respectively. Osteoporotic patients have intestinal calcium malabsorption and renal vitamin D activation dysfunction. Adequate results cannot be expected from the administration of nutritional supply of vitamin D (400-800 I.U.) or high doses of calcium agents. To bring about recovery of physiological function in such patients and maintain bone in normal condition, therefore, it is necessary to administer the active form of vitamin D. The consensus report of 1996 recognized that active vitamin D products are effective under vitamin D replete conditions and in Caucasians. In this review, we introduced the history of the debate surrounding the efficacy of the active form of vitamin D in osteoporosis, as well as the thinking behind the different views. Moreover, we explained how active vitamin D agents compare with the many other agents available for osteoporosis and proposed that their administration should become a basic therapeutic modality for osteoporotic patients.
