Clinical and histological analysis of chronic tacrolimus nephrotoxicity in renal allografts

Tacrolimus (TAC) is an effective primary immunosuppressive agent in kidney transplantation. Chronic nephrotoxicity due to TAC has been reported to be similar to that of cyclosporine in kidney transplant patients. Since, the severity and influence of chronic TAC nephrotoxicity are not fully elucidated, we studied the clinicohistological characteristics of chronic TAC nephrotoxicity in kidney transplants.

We retrospectively studied the clinicohistological profiles of 15 transplant patients under TAC-based immunosuppression, who were diagnosed as chronic TAC nephrotoxicity by allograft biopsies, showing characteristic arteriolopathy--periodic acid-Schiff PAS--positive hyaline thickening in small arteries--between January 2004 and December 2005. The mean recipient age was 37.3 years and they consisted of 11 men and 4 women. The mean age of their donors was 59.4 years.

The diagnoses of chronic TAC nephrotoxicities were established at an average of 54.7 months postoperatively. The severities of arteriolopathy were moderate in eight cases and severe in eight cases. The mean dosage of TAC at the time of diagnoses was 0.054 mg/kg with mean whole blood trough levels of 5.09 ng/mL, which is recognized to be within the so-called recommended level. Moderate to severe arteriosclerosis of medium-sized arteries were observed in 12 cases (80.0%).

The existence of moderate to severe arteriosclerosis in medium-sized arteries would have the potential of causing chronic TAC nephrotoxicities, rather than the dosage or whole blood trough level of TAC.