A peculiar vacuolization in the kidney transplant of a child treated with tacrolimus.

Tacrolimus (TAC) is a useful immunosuppressive agent in the prevention of rejection. However, the blood level between its therapeutic and toxic levels is narrow such that its nephrotoxicity is a problem. Moreover, its bioavailability and pharmacokinetics are highly variable. We experienced a case of acute nephrotoxicity, in which the blood level rose about 10 times above the expected level. We found a peculiar vacuolization in the transplant biopsy specimen. This change showed a marked vacuolization of the tubular cells, suggestive of acute nephrotoxicity by TAC.