Intestinal solubilization, absorption, pharmacokinetics and bioavailability of chenodeoxycholic acid

Little is known about the physical state, intestinal solubilization, absorption and bioavailability of chenodeoxycholic acid used in the medical treatment of gallstones. Therefore the concentrations of unconjugated chenodeoxycholic acid were measured in the supernatant and precipitate phases of intestinal contents aspirated from stomach, duodenum and jejunum of nine control subjects who took 500 mg chenodeoxycholic acid (4 X 125 mg gelatin-coated capsules) either fasting or together with a standard liquid meal. Chenodeoxycholic acid solubility was markedly influenced by luminal pH but was little affected by endogenous conjugated bile acids when their concentrations were > 1-2 mmol/l. Systemic bioavailability of 250, 500 and 750 doses of chenodeoxycholic acid was measured in five subjects by comparing areas under 4 h serum concentration-time curves after giving the bile acid first as a bolus intraduodenal aqueous infusion of 3H-labelled chenodeoxycholic acid containing either 14C-polyethylene glycol or bromsulphthalein as non-absorbable markers, and then as gelatin-coated capsules by mouth. Absorption was assessed by measuring the ratio of marker: bile acid in intestinal contents aspirated for 2 h from sites 60 and 120 cm distal to the duodenal infusion port and in three subjects quantitative recovery of marker was measured proximal to an occluding intestinal balloon. Absorption of duodenally-infused chenodeoxycholic acid was 96-99% complete and bioavailability was complete with the 250 and 500 mg doses but fell to 81% with the 750 mg dose.