A major factor in poor bioavailability of cyclosporine in children undergoing orthotopic liver transplantation appears to be poor absorption of the drug. Our hypothesis is that the Roux‐en‐Y choledochojejunostomy used for biliary drainage in these children causes cyclosporine malabsorption by reducing the length of bowel available for absorption and by distally displacing the entry of bile into the intestine. In these experiments, we determined the effect of biliary enteroenterostomy on the pharmacokinetics of enterally administered cyclosporine in Sprague‐Dawley rats. Experimental rats (n = 24) were prepared for study by constructing self‐emptying jejunal blind loops. Sham rats (n = 9) had jejunal transection and reanastomosis. Control rats (n = 26) had no operation. Two to 4 weeks later, chronic biliary‐enteric fistulae were formed in all animals. In experiments, [3H]cyclosporine was delivered into the duodenum while the site of bile delivery varied. Hourly and cumulative [3H]cyclosporine excretion into bile was quantitated, which our preliminary data show to be a valid estimate of absorption. In control rats, bile was delivered into the duodenum or was replaced with saline and sucrose solution. In experimental rats, bile was infused either into the duodenum, which tested bowel shortening only, or into the proximal end of the blind loop, which tested the combined effects of bowel shortening and distal displacement of bile entry. In sham rats, bile was infused into the duodenum, which controlled for previous abdominal surgery, or into the mid‐jejunum, which tested for distal bile entry only. Two effects of biliary enteroenterostomy on cyclosporine absorption were observed. First, distal displacement of bile entry into the intestinal lumen reduced drug absorption by about 50%. Compared to control rats with duodenal bile (n = 15), which excreted 14.8 ± 3.3% of the label into bile in 24 hr, and sham rats with duodenal bile (n = 4), which excreted 14.6 ± 1.3%, experimental animals with loop bile (n = 13) excreted 7.7 ± 2.1% and sham rats with midjejunal bile (n = 5) excreted 7.2 ± 1.8%. Control rats with no bile (n = 11) excreted 3.2 ± 1.6%. Second, reduction of bowel length by constructing the enteroenterostomy reduced absorption by 25%. Experimental rats with duodenal bile (n = 11) excreted 11.2 ± 2.5%. These data suggest that the surgical approach to biliary reconstruction after orthotopic liver transplantation in children can contribute to poor cyclosporine bioavailability.
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