Tacrolimus overexposure in kidney transplant recipients during the first post-operative week: caution is required in older patients

CYP3A5 Polymorphism in Renal Transplantation: A Key to Personalized Immunosuppression

BACKGROUND

Tacrolimus is essential for the maintenance of immunosuppression after a kidney transplant. CYP3A5 is the gene that metabolizes tacrolimus, and polymorphism in this gene affects the metabolizing status.

AIM

To assess the genetic polymorphism status of patients undergoing kidney transplantation and determine its impact on graft function and complications in the post-transplant period.

METHODS

We retrospectively included the patients who had undergone a kidney transplant and had positive genetic polymorphism of the CYP3A5 gene. Based on loss of alleles, patients were categorized as non-expresser (loss of both alleles), intermediate expresser (loss of one allele), and expresser (no loss of allele) denoted by CYP3A5*3/*3, CYP3A5*1/*3, and CYP3A5*1/*1, respectively. Data were analyzed with descriptive statistics.

RESULTS

Of 25 patients, 60%, 32%, and 8% were non-expressers, intermediate-expressers, and expressers, respectively. The mean tacrolimus trough concentration to dose ratio after 6 months of the transplant was higher in non-expressers than intermediate-expressers and expressers (213 vs 85 and 46 ng/mL/mg/kg/d, respectively). The graft function was normal in all 3 groups except for graft rejection 1 patient in the expresser group. Compared with expressers, urinary tract infections (42.9% and 62.5%) and new-onset diabetes after transplantation (28.6% and 12.5%) were more frequent in non-expresser and intermediate expressers, respectively. The proportion of patients developing new-onset diabetes after transplantation was lower with the pre-transplant diagnosis of CYP3A5 polymorphism (16.7% vs 23.1%).

CONCLUSION

Genotype-based dosing of tacrolimus helps achieve the desired therapeutic concentrations that can help to optimize graft outcomes and reduce the tacrolimus-related adverse effects. Pre-transplant evaluation of CYP3A5 can be more helpful in planning treatment strategies for optimized outcomes after kidney transplantation.

Therapeutic Drug Monitoring Strategies for Envarsus in De Novo Kidney Transplant Patients Using Population Modelling and Simulations

INTRODUCTION

Tacrolimus, the cornerstone of transplantation immunosuppression, is a narrow therapeutic index drug with a low and highly variable bioavailability. Therapeutic drug monitoring based on trough level assessment is mandatory in order to target a personalised exposure and avoid both rejection and toxicity. Population pharmacokinetic (POPPK) models might be a useful tool for improving early attainment of target range by guiding initial doses until steady state is reached and trough levels can be reliably used as surrogate marker of exposure. Here we present the first POPPK for predicting the initial doses of the once-daily prolonged release tacrolimus Envarsus (LCPT) in adult kidney recipients.

METHODS

The model was developed exploiting the data from a recent pharmacokinetic randomised clinical study, in which 69 de novo kidney recipients, 33 of whom treated with LCPT, underwent an intensive blood sampling strategy for tacrolimus including four complete pharmacokinetic profiles.

RESULTS

The complex and prolonged absorption of LCPT is well described by the three-phase model that incorporates body weight and CYP3A5 genotype as significant covariates accounting for a great proportion of the inter-patient variability: in particular, CYP3A5*1/*3 expressors had a 66% higher LCPT clearance. We have then generated by simulation a personalised dosing strategy based on the model that could improve the early attainment of therapeutic trough levels by almost doubling the proportion of patients within target range (69.3% compared to 36.1% with the standard body weight-based approach) on post-transplantation day 4 and significantly reduce the proportion of overexposed patients at risk of toxicity.

CONCLUSIONS

A POPPK model was successfully developed for LCPT in de novo kidney recipients. The model could guide a personalised dosing strategy early after transplantation. For the model to be translated into clinical practice, its beneficial impact of earlier attainment of therapeutic trough levels should be demonstrated on hard clinical outcomes in further studies.