Calcitriol 2micrograms/1ml solution for injection ampoules

Calcitriol is a biologically active calcitrophic hormone with anti-osteoporotic, immunomodulatory, anticarcinogenic, antipsoriatic, antioxidant, and mood-modulatory activities. Its main sites of action are the intestine, bone, kidney and parathyroid hormone [FDA Label]. Calcitriol is a ligand for the vitamin D nuclear receptor, which is expressed in, but not limited to, gastrointestinal (GI) tissues, bones, and kidneys [A3366]. As an active form of vitamin D₃, calcitriol elevates the plasma levels of calcium by stimulating intestinal calcium uptake, increasing reabsorption of calcium by the kidneys, and possibly increasing the release of calcium from skeletal stores. The duration of pharmacologic activity of a single dose of exogenous calcitriol is expected to be about 3 to 5 days [FDA Label].

In addition to its important role in calcium metabolism, other pharmacological effects of calcitriol have been studied in various conditions including cancer models. Various studies demonstrated expression of vitamin D receptors in cancer cell lines, including mouse myeloid leukemia cells [A3366]. Calcitriol has been found to induce differentiation and/or inhibit cell proliferation in vitro and in vivo in many cell types, such as malignant cell lines carcinomas of the breast, prostate, colon, skin, and brain, myeloid leukemia cells, and others [A3367]. In early human prostate cancer trials, administration of 1.5 µg/d calcitriol in male participants resulted in a reduction in the rate of PSA rise in most participants, however it was coincided with dose-limiting hypercalcemia in most participants [A3366]. Hypercalcemia and hypercalcuria were evident in numerous initial trials, and this may be due to these trials not testing the drug at concentrations that are active in preclinical systems [A3367]. Findings from preclinical data show an additive or synergistic antineoplastic action of calcitriol when combined with agents including dexamethasone, retinoids, and radiation, as well as several cytotoxic chemotherapy drugs such as platinum compounds [A3367].

Vitamin D deficiency has long been suspected to increase the susceptibility to tuberculosis. The active form of calcitriol, 1,25-(OH)₂-D3, has been found to enhance the ability of mononuclear phagocytes to suppress the intracellular growth of Mycobacterium tuberculosis. 1,25-(OH)₂-D3 has demonstrated beneficial effects in animal models of such autoimmune diseases as rheumatoid arthritis. Vitamin D appears to demonstrate both immune-enhancing and immunosuppressive effects.