Tacrolimus Concentration/Dose Ratio is Associated with Renal Function After Liver Transplantation.

BACKGROUND: The calcineurin inhibitor (CNI) tacrolimus (Tac) is an effective immunosuppressant used after liver transplantation (LTx), but is often associated with CNI nephrotoxicity. Currently, there is no simple clinical predictor for CNI nephrotoxicity after LTx. We hypothesized that the Tac metabolism rate - defined as the blood concentration normalized by its daily dose (the C/D ratio) - is associated with post-LTx renal impairment. MATERIAL AND METHODS: We analyzed the relationship between the C/D ratio and post-transplant renal function in 179 patients who underwent LTx between 2000 and 2012 and were initially immunosuppressed with Tac, mycophenolate mofetil, and prednisolone. Six months after LTx, 115 patients were categorized into 1 of 2 groups based on their Tac C/D ratio (<1.09 or ≥1.09): fast (n=58) or slow (n=57) metabolizers. The renal function was determined 36 months after LTx using the estimated glomerular filtration rate (eGFR) as described by Cockcroft and Gault. RESULTS: At the time of LTx there was no statistically significant difference between the eGFR of fast and slow metabolizers. Six months (P=0.016), 12 months (P=0.001), and 36 months (P=0.018) after LTx, fast Tac metabolizers had significantly more impaired renal function than slow metabolizers. Because of a presumption of CNI nephrotoxicity, 32.8% of fast metabolizers and 14.0% of slow metabolizers were switched from Tac to other immunosuppressants (P=0.027). CONCLUSIONS: In this study, the Tac metabolism rate appears to influence renal function after LTx, suggesting that a C/D ratio of <1.09 is associated with increased CNI nephrotoxicity in LTx recipients.

The tacrolimus metabolism rate influences renal function after kidney transplantation.

The effective calcineurin inhibitor (CNI) tacrolimus (Tac) is an integral part of the standard immunosuppressive regimen after renal transplantation (RTx). However, as a potent CNI it has nephrotoxic potential leading to impaired renal function in some cases. Therefore, it is of high clinical impact to identify factors which can predict who is endangered to develop CNI toxicity. We hypothesized that the Tac metabolism rate expressed as the blood concentration normalized by the dose (C/D ratio) is such a simple predictor. Therefore, we analyzed the impact of the C/D ratio on kidney function after RTx. Renal function was analyzed 1, 2, 3, 6, 12 and 24 months after RTx in 248 patients with an immunosuppressive regimen including basiliximab, tacrolimus, mycophenolate mofetil and prednisolone. According to keep the approach simple, patients were split into three C/D groups: fast, intermediate and slow metabolizers. Notably, compared with slow metabolizers fast metabolizers of Tac showed significantly lower estimated glomerular filtration rate (eGFR) values at all the time points analyzed. Moreover, fast metabolizers underwent more indication renal biopsies (p = 0.006) which revealed a higher incidence of CNI nephrotoxicity (p = 0.015) and BK nephropathy (p = 0.024) in this group. We herein identified the C/D ratio as an easy calculable risk factor for the development of CNI nephrotoxicity and BK nephropathy after RTx. We propose that the simple C/D ratio should be taken into account early in patient's risk management strategies.