Pharmacokinetics: The pharmacokinetics of vitamin D is well known.Ībsorption: Vitamin D is well absorbed from the gastro-intestinal tract in the presence of bile, so the administration with the major meal of the day might therefore facilitate the absorption of Vitamin D.ĭistribution and biotransformation: It is hydroxylated in the liver to form 25-hydroxy-cholecalciferol and then undergoes further hydroxylation in the kidney to form the active metabolite 1, 25-dihydroxycholecalciferol (calcitriol).Įlimination: The metabolites circulate in the blood bound to a specific α - globin, vitamin D and its metabolites are excreted mainly in the bile and faeces.Ĭharacteristics in Specific Groups of Subjects or Patients: A 57% lower metabolic clearance rate is reported in subjects with renal impairment as compared with that of healthy volunteers.ĭecreased absorption and increased elimination of vitamin D occurs in subjects with malabsorption.
PTH secretion is inhibited additionally by the increased calcium uptake in the small intestine under the influence of biologically active vitamin D. The production of parathyroid hormone (PTH) in the parathyroids is inhibited directly by the biologically active form of vitamin D3. In the kidney, it inhibits the excretion of calcium and phosphate by promoting tubular resorption. The passive and active transport of phosphate is also stimulated. In the small intestine it promotes rapid and delayed calcium uptake. Pharmacology: Pharmacodynamics: In its biologically active form Vitamin D stimulates intestinal calcium absorption, incorporation of calcium into the osteoid, and release of calcium from bone tissue.
Pharmacotherapeutic Group: Vitamin D, cholecalciferol.
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