Area under trough concentrations of tacrolimus as a predictor of progressive renal impairment after liver transplantation

BACKGROUND: Tacrolimus minimization is usually restricted to patients with pre-transplant renal impairment and this strategy could result into worse renal outcomes after liver transplantation (LT). METHODS: A consecutive cohort of 455 LT patients receiving tacrolimus-based immunosuppression was studied (2008-2013). Cumulative exposure to tacrolimus was calculated as the area under curve of trough concentrations (AUCtc). Patients were stratified as tacrolimus minimization, conventional or high exposure according to thresholds based in the COMMIT consensus. Estimated glomerular filtration rates (eGFR) were assessed by the MDRD-4 formula up to 5 years post-LT. RESULTS: Seventy patients (15.4%) had pre-transplant eGFR<60 ml/min, which was associated with increased mortality rates, particularly within the first 5 years post-LT (31.4% vs 17.5%; Breslow p= 0.010). After LT, there was an abrupt eGFR decline within the first 3 months (median 18.6 ml/min; p<0.001), further decreasing up to 12 months (additional 3 ml/min), without any improvement thereafter. According to AUCtc, 33.7% of patients received tacrolimus minimization, 44.8% conventional exposure and 21.5% high exposure. Conventional/high exposure to tacrolimus resulted in a more pronounced eGFR decline within the first 3 months as compared with minimization (23.3ml/min vs 9.5ml/min; p<0.001). This gap was even higher in patients with initially preserved renal function. Tacrolimus AUCtc was an independent predictor of eGFR decline within the first 3 months after controlling for potential confounders. CONCLUSIONS: AUCtc is a surrogate of cumulative exposure to tacrolimus and may be helpful for routine dose adjustments. Tacrolimus minimization should be universally attempted after LT in order to preserve renal function

Quantification of Methotrexate in Human Serum and Plasma by Liquid Chromatography Tandem Mass Spectrometry

Mass spectrometry (MS) is a highly specific and sensitive technique that is used for the detection of many different analytes with diverse chemical characteristics. It has been adopted by clinical laboratories for the quantification of small molecules and, by extension, has been widely used for therapeutic drug monitoring. It is an attractive alternative to immunoassay methods, because it is not subject to the same interferences. A limitation of MS (relative to immunoassays) is the turnaround time. However, this can be addressed by workflow parallelization with other assays. Herein we describe a tandem LC-MS/MS method for the detection and quantification of methotrexate in human plasma with a lower limit of quantification of 0.01 μM and within-assay and between-assay coefficients of variation of less than 15%. This method lacks interference from high-abundance metabolites and utilizes kindred chromatography to improve turnaround time in the therapeutic drug monitoring laboratory