The maintenance of the intestinal mucosal barrier may be energy dependent. Tacrolimus is a potent immunosuppressive drug that decreases mitochondrial adenosine triphosphate production and increases intestinal permeability in animals.

Twelve liver graft recipients receiving tacrolimus, 9 healthy volunteers, and 5 liver graft recipients not receiving immunosuppression underwent a combined absorption-permeability-mitochondrial function test using 5 g lactulose, 1 g L-rhamnose, 0.5 g D-xylose, 0.2 g 3-o-methyl-D-glucose, 1 mg/kg 2-keto[1-¹³C]isocaproic acid ([¹³C]KICA), and 20 mg/kg L-leucine. The respiratory quotient and resting energy expenditure were measured by indirect calorimetry. Tacrolimus pharmacokinetic profiles and levels of endotoxin and IgM and IgG endotoxin core antibodies were determined.

Tacrolimus inhibited the decarboxylation of [¹³C]KICA, the resting energy expenditure, and the respiratory quotient in an exposure-dependent manner, suggesting an inhibition of mitochondrial respiration. Tacrolimus inhibited intestinal absorptive capacity in an exposure-dependent manner. Tacrolimus-treated patients had an increased intestinal permeability and significantly higher endotoxin levels compared with healthy volunteers.

Tacrolimus inhibits cellular energy production in humans at clinically relevant doses. This is associated with an increased intestinal permeability, endotoxemia, and an impaired intestinal absorptive capacity. GASTROENTEROLOGY 1998;115:67-74