Tacrolimus Metabolite M-III May Have Nephrotoxic and Myelotoxic Effects and Increase the Incidence of Infections in Kidney Transplant Recipients

• We quantified tacrolimus metabolites M-I and M-III in kidney transplant recipients.
• Negative correlation between M-III and eGFR was found.
• In the subgroup with infections, we observed higher M-III and Tac concentrations.
• M-III may have a nephrotoxic effect and result in a higher incidence of infections.

BackgroundTacrolimus (Tac) is one of the most commonly used immunosuppressive drugs after solid organ transplantation. Eight Tac metabolites have been described, but their clinical importance remains unclear. The aim of this study was quantification of the 2 major Tac metabolites, 13-O-demethyl (M-I) and 15-O-demethyl (M-III), in kidney transplant recipients and to link them with parameters of kidney and liver function, peripheral blood cell counts, and infection incidence.MethodsIn 81 kidney transplant recipients, concentrations of Tac, M-I, and M-III were measured with the use of liquid chromatography combined with tandem mass spectrometry (LC-MS-MS).ResultsThere was a negative correlation between M-III levels and estimated glomerular filtration rate (eGFR; r = −0.244; P < .05). Also, a negative correlation between M-III concentrations and red blood cell count (RBC) was found (r = −0.349; P < .05). Neither concentrations of Tac nor of M-I correlated with eGFR or RBC. M-I, M-III, and Tac were not related to alanine aminotransferase activity. Significantly higher Tac and M-III concentrations in the group with all types of infections in comparison with the group without infections were observed (6.95 ± 2.09 ng/mL vs 5.73 ± 2.43 ng/mL [P = .03] and 0.27 ± 0.17 ng/mL vs 0.20 ± 0.11 ng/mL [P = .04], respectively).ConclusionsThe results suggest that higher concentrations of M-III may have a nephrotoxic or myelotoxic effect and result in higher incidence of infections. Further studies are needed to confirm if monitoring of M-III could minimalize adverse effects such as nephrotoxicity or infections.