Severe acute nephrotoxicity in a kidney transplant patient despite low tacrolimus levels: a possible interaction between donor and recipient genetic polymorphisms

Efficacy and outcomes of CYP3A5 genotype-based tacrolimus dosing compared to conventional body weight-based dosing in living donor kidney transplant recipients

Introduction:

Clinical use of tacrolimus has been challenging due to its narrow therapeutic index and highly variable pharmacokinetics. In this study, we compared patients who received body weight-based tacrolimus dosing pre-transplant (transplanted from 2016 to 2018) with those who received CYP3A5 genotype-based dosing (2018 to 2020).

Methods:

Eighty-two renal transplant recipients were non-randomly assigned to genotype-adapted or bodyweight-based tacrolimus dosing groups. The primary end point was to study the proportion of subjects who achieved the target tacrolimus C₀ on post-op day 4. Secondary end points included clinical outcomes and safety.

Results:

The proportion of subjects who achieved the target tacrolimus C₀ on postoperative days 4 and 10 were significantly higher in the adapted group, 53.6% and 47.5%, compared to 24.3% and 17% in controls, respectively (P = 0.01). Adapted group subjects achieved their first target tacrolimus C₀ significantly earlier (4 days) compared to 25 days in controls (P = 0.01). The total number of tacrolimus dose modifications required in the first postop month were lower in the adapted group; 47 compared to 68 in the controls (P = 0.05). The proportion of subjects with sub-therapeutic tacrolimus exposure on postoperative day 4 was significantly higher in the controls, 56% versus 10% in the adapted group (P < 0.001). There were no significant differences between the groups in the rate of biopsy proven acute rejections, adverse events, and graft function at the end of 3 months follow up.

Conclusion:

Genotype-based tacrolimus dosing leads to more subjects achieving the target tacrolimus C₀ earlier. However, there may be a higher risk of tacrolimus nephrotoxicity.

Translational Knowledge Discovery Between Drug Interactions and Pharmacogenetics

Clinical translation of drug-drug interaction (DDI) studies is limited, and knowledge gaps across different types of DDI evidence make it difficult to consolidate and link them to clinical consequences. Consequently, we developed information retrieval (IR) models to retrieve DDI and drug-gene interaction (DGI) evidence from 25 million PubMed abstracts and distinguish DDI evidence into in vitro pharmacokinetic (PK), clinical PK, and clinical pharmacodynamic (PD) studies for US Food and Drug Administration (FDA) approved and withdrawn drugs. Additionally, information extraction models were developed to extract DDI-pairs and DGI-pairs from the IR-retrieved abstracts. An overlapping analysis identified 986 unique DDI-pairs between all 3 types of evidence. Another 2,157 and 13,012 DDI-pairs and 3,173 DGI-pairs were identified from known clinical PK/PD DDI, clinical PD DDI, and DGI evidence, respectively. By integrating DDI and DGI evidence, we discovered 119 and 18 new pharmacogenetic hypotheses associated with CYP3A and CYP2D6, respectively. Some of these DGI evidence can also aid us in understanding DDI mechanisms.

CYP3A5 polymorphisms in renal transplant recipients: influence on tacrolimus treatment

Tacrolimus is a commonly used immunosuppressant after kidney transplantation. It has a narrow therapeutic range and demonstrates wide interindividual variability in pharmacokinetics, leading to potential underimmunosuppression or toxicity. Genetic polymorphism in CYP3A5 enzyme expression contributes to differences in tacrolimus bioavailability between individuals. Individuals carrying one or more copies of the wild-type allele *1 express CYP3A5, which increases tacrolimus clearance. CYP3A5 expressers require 1.5 to 2-fold higher tacrolimus doses compared to usual dosing to achieve therapeutic blood concentrations. Individuals with homozygous *3/*3 genotype are CYP3A5 nonexpressers. CYP3A5 nonexpression is the most frequent phenotype in most ethnic populations, except blacks. Differences between CYP3A5 genotypes in tacrolimus disposition have not translated into differences in clinical outcomes, such as acute rejection and graft survival. Therefore, although genotype-based dosing may improve achievement of therapeutic drug concentrations with empiric dosing, its role in clinical practice is unclear. CYP3A5 genotype may predict differences in absorption of extended-release and immediate-release oral formulations of tacrolimus. Two studies found that CYP3A5 expressers require higher doses of tacrolimus in the extended-release formulation compared to immediate release. CYP3A5 genotype plays a role in determining the impact of interacting drugs, such as fluconazole, on tacrolimus pharmacokinetics. Evidence conflicts regarding the impact of CYP3A5 genotype on risk of nephrotoxicity associated with tacrolimus. Further study is required.

Clinical implementation of pharmacogenetics

In the last decade, pharmacogenetic research has been performed in different fields. However, the application of pharmacogenetic findings to clinical practice has not been as fast as desirable. The current situation of clinical implementation of pharmacogenetics is discussed. This review focuses on the advances of pharmacogenomics to individualize cancer treatments, the relationship between pharmacogenetics and pharmacodynamics in the clinical course of transplant patients receiving a combination of immunosuppressive therapy, the needs and barriers facing pharmacogenetic clinical application, and the situation of pharmacogenetic testing in Spain. It is based on lectures presented by speakers of the Clinical Implementation of Pharmacogenetics Symposium at the VII Conference of the Spanish Pharmacogenetics and Pharmacogenomics Society, held in April 20, 2015.

Effect of CYP3A5*3 on kidney transplant recipients treated with tacrolimus: a systematic review and meta-analysis of observational studies

The highly variable pharmacokinetics of tacrolimus can hamper the optimal management of kidney transplant patients. This variability has been attributed to the genetic polymorphism of CYP3A5 6986A>G, but the evidence is not clear. We conducted a meta-analysis of studies evaluating the effect of CYP3A5 polymorphism on kidney transplant recipients with tacrolimus plasma concentration divided by daily dose per body weight (C/D) and clinical outcomes. We searched in MEDLINE and EMBASE. We found evidence suggesting a significantly lower C/D among CYP3A5*1 allele carriers compared with carriers of the CYP3A5*3/*3 genotype at weeks 1 and 2, and months 1, 3, 6 and 12. We demonstrated that the expresser genotype might have higher risk of acute rejection and chronic nephrotoxicity. In conclusion, CYP3A5 6986A>G polymorphism can affect tacrolimus pharmacokinetics and the incidence of acute rejection and chronic nephrotoxicity on kidney transplant recipients. Patients at high risk of developing tacrolimus-related complications could be detected even before their kidney transplant.