Meeting Regulatory Requirements for Drugs with a Narrow Therapeutic Index: Bioequivalence Studies of Generic Once-Daily Tacrolimus

Update on Maintenance Immunosuppression in Intestinal Transplantation

Outcomes in intestinal transplantation remain hampered by higher rates of rejection than any other solid organs. However, maintenance immunosuppression regimens have largely remained unchanged despite advances in therapies for induction and treatment of rejection and graft-versus-host disease. Recently, there have been a small number of new maintenance therapies attempted, and older agents have been used in new ways to achieve better outcomes. The authors herein review the traditional maintenance therapies and their mechanisms and then consider updates in new therapies and new ways of using old therapies for maintenance immunosuppression after intestinal transplantation.

Immunosuppression with Generics in Liver and Kidney Transplantation: A Real-World Evidence Study

Purpose

This study evaluates the use, benefit-risk profile, and economic impact of generic immunosuppressants (tacrolimus-TAC, cyclosporine-CsA, and mycophenolate-MYC) in kidney and liver transplant recipients compared to brand-name drugs.

Patients and Methods

A retrospective multicentre observational study, involving four Italian regions, was conducted based on the national transplant Information system and regional healthcare claims data. The analysis focused on incident patients who received kidney and liver transplants between 2013 and 2019 and evaluated the use of generic of CsA, TAC, and MYC during the 30-day period following discharge. For each type of transplant and immunosuppressive agent, the benefit-risk profile of generic vs branded drugs in a two-year window was estimated by multivariate Cox models (HR; 95% CI). Furthermore, the potential cost savings per person associated with one year of treatment using generics were calculated.

Results

The utilization of generic drugs showed a significant increase; over the study years, the proportion of users among kidney recipients ranged from 14.2% to 40.5% for TAC, from 36.9% to 56.7% for MYC, and from 18.2% to 94.7% for CsA. A great variability in generic uptake for region was found. A comparable risk-benefit profile between generic and branded formulations was shown for all immunosuppressors considered. Choosing generic immunosuppressants during maintenance could result in yearly savings of around 2000 euros per person for each therapy ingredient.

Conclusion

The study shows an increasing proportion of patients using generic immunosuppressive drugs over time suggesting a growing acceptance of generics within the transplant community and reveals comparable risk-benefit profiles between the generic and branded formulations of TAC, CsA, and MYC. A significant variability in the use of generics immunosuppressive agents was found both at the regional level and among transplant centers and future research should delve into regional prescribing variations.

Bioequivalence evaluation and blood concentration estimation of generic and branded tacrolimus in healthy subjects under fasting: A randomized, four-periods, two-sequences, complete repeated, crossover study

OBJECTIVE

The demand for generic tacrolimus is enormous. Our randomized trial was an open-label single-dose testing with four-periods and two-sequences; we aimed to evaluate the bioequivalence between a generic and branded tacrolimus by establishing their area under concentration-time curve (AUC) predictive equations. For better comparison, each tacrolimus served either as test vs. reference in sequence 1 or vice versa as reference vs. test in sequence 2.

METHODS

Forty healthy subjects were randomized into two groups, namely a sequence 1 group (N = 20 in test-reference-test-reference) or sequence 2 (N = 20, reference-test-reference-test) received a test tacrolimus (Ruibeirong®; Chengdu Shengdi Medicine Co., Ltd.) and a reference tacrolimus (Astagraf XL®, Astellas Ireland Co., Ltd.) under the fasting condition with a wash-out period of ≥14 days between every two phases. Blood samples were collected sequentially until 120 h after oral administration of tacrolimus.

RESULTS

A 95% upper confidence bound was -0.05% for the peak concentration (Cmax), -0.02% for the AUC from 0 to the last time point (AUC0-t), and - 0.02% for the AUC from 0 to infinity (AUC0-∞). The geometric least square means ratio (test/reference) with 90% of confidence interval (CI)) was 96.10% (90.58%-101.95%) for Cmax, 93.80% (88.52%-99.39%) for AUC0-t, and 94.34% (89.20%-99.77%) for AUC0-∞. Meanwhile, the ratio of within-subject standard deviation of test/reference (σWT/WR) with 90% CI was 0.66 (0.50-0.86) for Cmax, 0.73 (0.55-0.96) for AUC0-t, and 0.75 (0.57-0.98) for AUC0-∞. These results fulfilled the bioequivalence criteria by the Food and Drug Administration. Both products showed acceptable safety. Moreover, the AUC predictive equations (by linear regression plus limited sampling strategy) with 2-5 sampling time point showed the high performance (all R > 0.970, predictive error (PE) >0.5%, absolute PE <5.1%, which were interchangeable between test and reference products.

CONCLUSION

Generic tacrolimus (Ruibeirong®) is bioequivalent to branded tacrolimus (Astagraf XL®) with tolerable safety, which AUC predictive equations work well and are interchangeable between the two products.

Comparative Study of 2 Extended-Release Tacrolimus Formulations in Kidney Transplantation

BACKGROUND

During the 1900s, tacrolimus became the mainstay immunosuppressive agent to prevent rejection after kidney transplant. Subsequently, an extended-release tacrolimus (ER-Tac) formulation was developed to improve adherence, and its generic version has been marketed over the last years. This study examines the differences in efficacy and safety between the generic ER-Tac (Conferoport) and the reference brand-name drug (Advagraf).

METHODS

Prospective, randomized and parallel single-center study (May 2020 to June 2021) with 52 kidney transplant recipients who were randomly assigned to 1 of the following groups: study group (Conferoport, n = 31) and control group (Advagraf, n = 21). The variables of interest were collected and analyzed to compare tacrolimus efficacy and safety between them. Demographic characteristics of the patients and clinical donor data were homogeneous in both groups (P > .05).

RESULTS

No statistically significant differences were found among treatments regarding dosage used, levels, creatinine, and proteinuria (P > .05), with these variables presenting a downward trend during follow-up and, consequently, the improvement of graft function. Analyses also revealed the absence of differences concerning the incidence of acute rejection and intrapatient variability (coefficient of variation) throughout the first year of evolution between both formulations (P > .05). A total of 5 graft losses occurred, 2 resulting from patient death.

CONCLUSIONS

In our experience, we found no significant differences between the measured parameters in relation to the efficacy and safety profile of both drugs, with generic ER-Tac being an alternative comparable with the reference brand-name ER-Tac.

The Use of Machine Learning Algorithms and the Mass Spectrometry Lipidomic Profile of Serum for the Evaluation of Tacrolimus Exposure and Toxicity in Kidney Transplant Recipients

Tacrolimus has a narrow therapeutic window; a whole-blood trough target concentration of between 5 and 8 ng/mL is considered a safe level for stable kidney transplant recipients. Tacrolimus serum levels must be closely monitored to obtain a balance between maximizing efficacy and minimizing dose-related toxic effects. Currently, there is no specific tacrolimus toxicity biomarker except a graft biopsy. Our study aimed to identify specific serum metabolites correlated with tacrolinemia levels using serum high-precision liquid chromatography–mass spectrometry and standard laboratory evaluation. Three machine learning algorithms were used (Naïve Bayes, logistic regression, and Random Forest) in 19 patients with high tacrolinemia (8 ng/mL) and 23 patients with low tacrolinemia (5 ng/mL). Using a selected panel of five lipid metabolites (phosphatidylserine, phosphatidylglycerol, phosphatidylethanolamine, arachidyl palmitoleate, and ceramide), Mg2+, and uric acid, all three machine learning algorithms yielded excellent classification accuracies between the two groups. The highest classification accuracy was obtained by Naïve Bayes, with an area under the curve of 0.799 and a classification accuracy of 0.756. Our results show that using our identified five lipid metabolites combined with Mg2+ and uric acid serum levels may provide a novel tool for diagnosing tacrolimus toxicity in kidney transplant recipients. Further validation with targeted MS and biopsy-proven TAC toxicity is needed.