Current Biochemical Monitoring and Risk Management of Immunosuppressive Therapy after Transplantation

Use of Pharmacogenetics to Optimize Immunosuppressant Therapy in Kidney-Transplanted Patients

Immunosuppressant drugs (ISDs) are routinely used in clinical practice to maintain organ transplant survival. However, these drugs are characterized by a restricted therapeutic index, a high inter- and intra-individual pharmacokinetic variability, and a series of severe adverse effects. In particular, genetic factors have been estimated to play a role in this variability because of polymorphisms regarding genes encoding for enzymes and transporters involved in the ISDs pharmacokinetic. Several studies showed important correlations between genetic polymorphisms and ISDs blood levels in transplanted patients; therefore, this review aims to summarize the pharmacogenetics of approved ISDs. We used PubMed database to search papers on pharmacogenetics of ISDs in adults or pediatric patients of any gender and ethnicity receiving immunosuppressive therapy after kidney transplantation. We utilized as search term: “cyclosporine or tacrolimus or mycophenolic acid or sirolimus or everolimus and polymorphism and transplant”. Our data showed that polymorphisms in CYP3A5, CYP3A4, ABCB1, and UGT1A9 genes could modify the pharmacokinetics of immunosuppressants, suggesting that patient genotyping could be a helpful strategy to select the ideal ISDs dose for each patient.

Exploring Sirolimus Pharmacokinetic Variability Using Data Available from the Routine Clinical Care of Renal Transplant Patients - Population Pharmacokinetic Approach

Background

Due to wide intra- and inter-individual pharmacokinetic variability and narrow therapeutic index of sirolimus, the therapeutic drug monitoring (TDM) of sirolimus with detailed biochemical and clinical monitoring is necessary for dose individualization in kidney transplant patients. The purpose of the study was to explore and identify factors that contribute to pharmacokinetic variability by developing and validating a population model using routine TDM data and routinely monitored biochemical and clinical parameters.

Methods

The data obtained by routine monitoring of 38 patients over a period of one year from the sirolimus treatment initiation, were collected from patients' records. Population analysis was performed using the software NONMEM^®. The validity of the model was tested by the internal and external validation techniques.

Results

The pharmacokinetic variability was partially explained with patient's age and liver function. CL/F was found to decrease with age. According to the developed model, sirolimus CL/F decreases by, in average, 37% in patients with aspartate aminotransferase (AST) greater than 37 IU/L. The internal and external validation confirmed the satisfactory prediction of the developed model.

Conclusions

The population modeling of routinely monitored data allowed quantification of the age and liver function influence on sirolimus CL/F. According to the final model, patients with compromised liver function expressed via AST values require careful monitoring and dosing adjustments. Proven good predictive performance makes this model a useful tool in everyday clinical practice.

Phase Angle Is Associated With Handgrip Strength but Not With Sarcopenia in Kidney Transplantation Patients

OBJECTIVES

Phase angle (PhA) is a cell health marker and has been associated with muscle mass and strength in non-kidney disease individuals. However, it is unknown whether PhA is a predictor of sarcopenia and its components in kidney transplantation patients. The aim of the present study was to associate PhA with sarcopenia and its components in kidney transplantation patients.

DESIGN AND METHODS

One hundred and twenty-nine kidney transplantation individuals were evaluated in a cross-sectional study. PhA and muscle mass were evaluated using bioelectrical impedance. Handgrip strength (HGS) was performed with a hand dynamometer and functional capacity with 4-m walk test. Sarcopenia was diagnosed according to the European Consensus Diagnostic Criteria for Sarcopenia. Participants were divided according to the PhA tercile, and 2 groups were evaluated: first versus second and third terciles, according to sex. The individuals in the first tercile had PhA values <5.8° and <6.2° for women and men, respectively.

RESULTS

Individuals in the lower tercile of PhA showed lower odds of having higher values of HGS (kg; odds ratio [OR] = 0.89; 95% confidence interval [CI]: 0.82-0.97) and higher odds to have low HGS (OR = 5.97; 95% CI: 1.05-33.98). However, PhA was not associated with sarcopenia (OR = 1.95; 95% CI: 0.71-5.39), low muscle mass index (OR = 1.17; 95% CI: 0.41-3.36), and low functional capacity (OR = 2.47; 95% CI: 0.45-13.48).

CONCLUSION

PhA was associated with HGS but not with sarcopenia and its other components. These results suggest that PhA can be used as a possible predictor of muscle strength in kidney transplantation patients.