Increased tacrolimus levels in a pediatric renal transplant patient attributed to chronic diarrhea

Abstract: Tacrolimus is an immunosuppressant used to prevent rejection of transplanted organs. It is metabolized in both the gut and the liver by the cytochrome P450 (CYP) 3A4 enzyme system and is a substrate for the P‐glycoprotein (P‐gp) drug efflux pump. As CYP3A4 enzymes and P‐gp are present at differing concentrations throughout the gastrointestinal tract, the bioavailability of tacrolimus may be influenced by changes in gastrointestinal transit time in addition to changes in hepatic metabolism. We report the case of a pediatric renal transplant patient who experienced a three‐fold increase in serum tacrolimus concentrations during an episode of gastroenteritis with chronic diarrhea.