Two cases of severe de novo colitis in kidney transplant recipients after conversion to prolonged-release tacrolimus.

Diarrhea is a frequent complication in patients after solid organ transplantation. We describe two cases of severe new onset colitis in kidney transplant recipients that developed shortly after the introduction of the therapy with prolonged-release formulation of tacrolimus replacing standard twice daily formulation of tacrolimus in one case and cyclosporine A in the second case. Both patients developed severe, intermittent bloody diarrhea with abdominal pain, weight loss, dehydration and worsening graft function that required immediate hospitalization. The symptoms did not diminish after dose reduction or withdrawal of mycophenolic acid derivatives. After excluding bacterial, viral, fungal, and parasite infections, colonoscopy with colonic biopsy was performed in both patients, which revealed features typical of colitis. Both patients received mesalazine until the symptoms stopped. In one of the patients, standard formulation of tacrolimus was immediately reintroduced. The second patient was given everolimus in an acute phase of diarrhea. Although the two cases presented in this report cannot fully support a causal relationship between the prolonged-release tacrolimus and colitis, they should increase awareness among transplant physicians and prompt more close monitoring of such potential side effects as a part of the pharmacovigilance plan for a new formulation of the well-established immunosuppressive drug.