Sustained Inhibition of Calcineurin Activity With a Melt-Dose Once-daily Tacrolimus Formulation in Renal Transplant Recipients

The Effect of Intracellular Tacrolimus Exposure on Calcineurin Inhibition in Immediate- and Extended-Release Tacrolimus Formulations

Despite intensive monitoring of whole blood tacrolimus concentrations, acute rejection after kidney transplantation occurs during tacrolimus therapy. Intracellular tacrolimus concentrations could better reflect exposure at the site of action and its pharmacodynamics (PD). Intracellular pharmacokinetic (PK) profile following different tacrolimus formulations (immediate-release (TAC-IR) and extended-release (TAC-LCP)) remains unclear. Therefore, the aim was to study intracellular tacrolimus PK of TAC-IR and TAC-LCP and its correlation with whole blood (WhB) PK and PD. A post-hoc analysis of a prospective, open-label, crossover investigator-driven clinical trial (NCT02961608) was performed. Intracellular and WhB tacrolimus 24 h time-concentration curves were measured in 23 stable kidney transplant recipients. PD analysis was evaluated measuring calcineurin activity (CNA) and simultaneous intracellular PK/PD modelling analysis was conducted. Higher dose-adjusted pre-dose intracellular concentrations (C₀ and C₂₄) and total exposure (AUC_0-24) values were found for TAC-LCP than TAC-IR. Lower intracellular peak concentration (C_max) was found after TAC-LCP. Correlations between C₀, C₂₄ and AUC_0-24 were observed within both formulations. Intracellular kinetics seems to be limited by WhB disposition, in turn, limited by tacrolimus release/absorption processes from both formulations. The faster intracellular elimination after TAC-IR was translated into a more rapid recovery of CNA. An Emax model relating % inhibition and intracellular concentrations, including both formulations, showed an IC₅₀, a concentration to achieve 50% CNA inhibition, of 43.9 pg/million cells.

Pharmacodynamic Monitoring of Ciclosporin and Tacrolimus: Insights From Nuclear Factor of Activated T-Cell-Regulated Gene Expression in Healthy Volunteers

BACKGROUND

Although therapeutic drug monitoring of calcineurin inhibitor (CNI) concentrations is performed routinely in clinical practice, an identical concentration may lead to different effects in different patients. Although the quantification of nuclear factor of activated T-cell-regulated gene expression (NFAT-RGE) is a promising method for measuring individual CNI effects, CNI pharmacodynamics are as of yet incompletely understood.

METHODS

CNI concentrations and NFAT-RGEs were quantified in 24 healthy volunteers receiving either ciclosporin or tacrolimus in 2 clinical trials. NFAT-RGE was measured using quantitative reverse transcription polymerase chain reaction tests of whole-blood samples. Pharmacokinetics and pharmacodynamics were analyzed using compartmental modeling and simulation. In addition, NFAT-RGE data from renal transplant patients were analyzed.

RESULTS

The average NFAT-RGE during a dose interval was reduced to approximately 50% with ciclosporin, considering circadian changes. The different effect-time course with ciclosporin and tacrolimus could be explained by differences in potency (IC 50 204 ± 41 versus 15.1 ± 3.2 mcg/L, P < 0.001) and pharmacokinetics. Residual NFAT-RGE at the time of maximum concentration (RGE tmax ) of 15% when using ciclosporin and of 30% when using tacrolimus was associated with similar average NFAT-RGEs during a dose interval. Renal transplant patients had similar but slightly stronger effects compared with healthy volunteers.

CONCLUSIONS

Ciclosporin and tacrolimus led to similar average suppression of NFAT-RGE in a dose interval, despite considerably different RGE tmax . Pharmacodynamic monitoring of average NFAT-RGE should be considered. When using NFAT-RGE at specific time points, the different effect-time courses and circadian changes of NFAT-RGEs should be considered.

Immunosuppressive drugs modes of action

The innate and adaptive immune systems work as a complex interplay between different cell types, involving cytokines and chemokines mediating extracellular and paracrine effects. At the intracellular level, the inflammatory cascade is mediated by multifaceted processes that have been better described in the last 10 years. Immunosuppressive agents available in clinical practice act at different points of those cascades at the intracellular or extracellular level. Those drugs can mediate their effects on one or more cell types finally limiting inflammation and immune responses to antigens. Every immunosuppressive agent is characterized by intrinsic toxicity and side effects that may be due to the same therapeutic pathways or to off-target secondary effect of each molecule. We will here review the mechanisms of action of the most widely used immunosuppressive agents in the field of solid organ transplantation and autoimmune disorders, describing the mechanisms underlying both the therapeutic and secondary effects.

Influence of the Circadian Timing System on Tacrolimus Pharmacokinetics and Pharmacodynamics After Kidney Transplantation

Introduction: Tacrolimus is the backbone immunosuppressant after solid organ transplantation. Tacrolimus has a narrow therapeutic window with large intra- and inter-patient pharmacokinetic variability leading to frequent over- and under-immunosuppression. While routine therapeutic drug monitoring (TDM) remains the standard of care, tacrolimus pharmacokinetic variability may be influenced by circadian rhythms. Our aim was to analyze tacrolimus pharmacokinetic/pharmacodynamic profiles on circadian rhythms comparing morning and night doses of a twice-daily tacrolimus formulation. Methods: This is a post-hoc analysis from a clinical trial to study the area under curve (AUC) and the area under effect (AUE) profiles of calcineurin inhibition after tacrolimus administration in twenty-five renal transplant patients. Over a period of 24 h, an intensive sampling (0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 12.5, 13, 13.5, 14, 15, 20, and 24 h) was carried out. Whole blood and intracellular tacrolimus concentrations and calcineurin activity were measured by UHPLC-MS/MS. Results: Whole blood and intracellular AUC_12-24 h and C_max achieved after tacrolimus night dose was significantly lower than after morning dose administration (AUC_0-12 h) (p < 0.001 for both compartments). AUE_0-12 h and AUE_12-24 h were not statistically different after morning and night doses. Total tacrolimus daily exposure (AUC_0-24 h), in whole blood and intracellular compartments, was over-estimated when assessed by doubling the morning AUC_0-12 h data. Conclusion: The lower whole blood and intracellular tacrolimus concentrations after night dose might be influenced by a distinct circadian clock. This significantly lower tacrolimus exposure after night dose was not translated into a significant reduction of the pharmacodynamic effect. Our study may provide conceptual bases for better understanding the TDM of twice-daily tacrolimus formulation.