The formulation of choice in hypoparathyroidism is the active form of vitamin D, calcitriol (1.25-OH vitamin D), which is insufficient due to the deficiency of PTH-dependent renal 1α-hydroxylation of 25OH vitamin D. Calcitriol should be preferred to vitamin D2 or D3 (ergocalciferol or cholecalciferol), because these latter agents should be used at very high dosages with the risk of severe intoxication even in the long term, due to their long half-life [73]. Here, PTH is linked to hypoparathyroidism.