Calcitroic acid (1α-hydroxy-23-carboxy-24,25,26,27-tetranorvitamin D3) is a metabolite of 1α,25-dihydroxyvitamin D3 (calcitriol). Its formation is catalyzed by the enzyme calcitriol 24-hydroxylase. Calcitroic acid is soluble in water and excreted in bile.
