Calcitriol (1,25-Dihydroxyvitamin D3) is a metabolite of vitamin D and a vitamin D receptor (VDR) agonist (IC50=0.4 nM). Calcitriol increases intestinal absorption of calcium and phosphorus, and increases bone resorption with parathyroid hormone.

(1S)-Calcitriol (1α,25-Dihydroxy-3-epi-vitamin-D3), a natural metabolite of 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3), exerts potent actions through vitamin D receptor (VDR) activation, including the inhibition of keratinocyte growth and suppression of parathyroid hormone secretion[1].

Ercalcitriol (1α,25-Dihydroxy Vitamin D2) is an active metabolite of vitamin D2. Ercalcitriol, as the physiological activated form of vitamin D, can strengthen immunity via regulation of cathelicidin antimicrobial peptide (CAMP) and defensin β-4 (DEFB4) genes in normal and transformed cells to combat pathogenic infections.