Unremitting itch may trouble the patient with biliary obstructive disease. Recent investigations suggest that levels of bile salts correlate with pruritus and levels on the skin surface correlate better than those in serum. Cholestyramine reduces these levels and relieves pruritus. Its greater avidity for dihydroxy bile salts, and the severalfold over-representation of this group in cutaneous surface film, suggest that they may represent a more significant cause of pruritus than cholate, the trihydroxy compound. Though still poorly understood, the mechanism by which bile salts induce itching may involve release of a secondary mediator, perhaps endogenous protease, in skin.
Herndon JH. Pathophysiology of Pruritus Associated With Elevated Bile Acid Levels in Serum. Arch Intern Med. 1972;130(4):632–637. doi:10.1001/archinte.1972.03650040156014