Equivalence and interchangeability of narrow therapeutic index drugs in organ transplantation

Determination of tacrolimus in human whole blood in kidney transplant recipients using a rapid and specific LC-MS/MS method

OBJECTIVE

To develop and validate an LC-M/SMS method for the determination of tacrolimus in human whole blood.

METHOD

The LC-MS/MS method for the determination of tacrolimus in whole blood was developed and validated according to the guidelines. Concentrations of TAC in 100 kidney transplant patients measured by LC-MS/MS were compared with CMIA using correlation analysis and Bland-Altman plots.

RESULTS

The method had a total chromatographic run time of 5 min. The calibration curves were linear over the range of 0.5-100.0 ng/mL with a lower limit of quantification of 1 ng/mL. The intra- and interday accuracy was within the range of 93.3%-109.2% and 96.0%-108.4%, respectively, with precision ranging from 0.8 to 9.4%. The mean extraction recoveries of TAC ranged from 102.6 to 107.8%. The mean concentrations of TAC in whole blood of kidney transplant patients measured by the two assays were different at 1, 3 months and all time points (p < 0.001), but no significant difference was observed at 6 months (p = 0.094). The correlation of data was good with the correlation coefficients (r2 ) of 0.7581, 0.8811, 0.8777, and 0.8077, respectively. Passing-Bablok regression analysis demonstrated good correlations with r2 values higher than 0.88 between TAC levels measured by LC-MS/MS and CMIA. Using Bland-Altman plots yielded average biases of 1.29, 0.79, 0.11, and 0.65 ng/mL at 1, 3, and 6 months and all time points.

CONCLUSION

The LC-MS/MS method was validated for the accurate determination of TAC in human whole blood. The comparison of tacrolimus concentrations measured by the LC-MS/MS with CMIA showed a good correlation and agreement of two methods, suggesting LC-MS/MS should be used routinely to monitor TAC concentrations in kidney transplant patients.

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.

Comparative safety of generic versus brand calcineurin inhibitors in solid organ transplant patients: a systematic review and meta-analysis

BACKGROUND

Although generic ciclosporin-A (CsA) and tacrolimus (TAC) have been used for the prophylaxis of organ rejection in transplant patients for decades, evidence in their safety profile compared to reference listed drugs (RLDs) in real-world transplant patients remains limited.

OBJECTIVES

To compare safety outcomes of generic CsA and TAC with the reference-listed drugs in solid organ transplant patients.

METHODS

We systematically searched MEDLINE, International Pharmaceutical Abstracts, PsycINFO, and Cumulative Index of Nursing and Allied Health Literature from inception until March 15, 2022, to select randomized and observational studies comparing safety profiles of generic versus brand CsA and TAC in de novo and/or stable solid organ transplant patients. Primary safety outcomes were changes in serum creatinine (Scr) and glomerular filtration rate (GFR). Secondary outcomes included incidences of infection, hypertension, diabetes, other serious adverse events (AEs), hospitalization, and death. Mean difference (MD) and relative risk (RR) with 95% confidence intervals (CIs) were calculated using random-effects meta-analyses.

RESULTS

Of 2612 publications identified, 32 studies met inclusion criteria. Seventeen studies had a moderate risk of bias. Scr was statistically significantly lower in patients using generic CsA compared to brand at 1 month (MD = -0.07; 95% CI: -0.11, -0.04), while there were no statistically significant differences at 4 months, 6 months, and 12 months. No differences were detected in Scr (MD = -0.04; 95% CI: -0.13, 0.04) and estimated GFR (MD = -2.06; 95% CI: -8.89, 4.77) between patients using generic and brand TAC at 6 months. No statistically significant differences between generic CsA and TAC with their RLDs were observed for secondary outcomes.

CONCLUSION

Findings support similarity in safety outcomes between generic and brand CsA and TAC in real-world solid organ transplant patients.

A Phase 1, open-label, crossover study evaluating the effect of a single dose of sodium zirconium cyclosilicate on the pharmacokinetics of tacrolimus and cyclosporin

Background

Sodium zirconium cyclosilicate (SZC) is an oral, highly selective potassium binder approved for the treatment of hyperkalaemia in adults. SZC may change the absorption of co-administered drugs that exhibit pH-dependent bioavailability. This study evaluated whether the pharmacokinetic (PK) profiles of tacrolimus and cyclosporin were altered by concomitant SZC administration in healthy participants.

Methods

This was an open-label, randomised sequence, two-cohort crossover, single-centre study. Healthy adults were assigned to one of two cohorts: Cohort 1 (tacrolimus) received a single dose of tacrolimus 5 mg and tacrolimus 5 mg + SZC 15 g in a random order; Cohort 2 (cyclosporin) received a single dose of cyclosporin 100 mg and cyclosporin 100 mg + SZC 15 g in a random order. Primary PK endpoints were maximum observed blood concentration (C_max) and area under the concentration-time curve (AUC) from time zero to infinity (AUC_inf). Differences in mean C_max and AUC_inf were analysed using a mixed effects model.

Results

Thirty participants in Cohort 1 and 29 in Cohort 2 completed the study. Tacrolimus exposure was lower with tacrolimus + SZC versus tacrolimus alone: C_max geometric mean ratio (GMR) 71.10% [90% confidence interval (CI) 65.44-77.24], AUC_inf 62.91% (55.64-71.13). Cyclosporin exposure was similar with cyclosporin + SZC compared with cyclosporin alone: C_max GMR 102.9% (90% CI 96.11-110.10), AUC_inf 97.23% (92.93-101.70).

Conclusions

Tacrolimus exposure was lower when co-administered with SZC 15 g and should be administered ≥2 h before or after SZC. The PK profile of cyclosporin was not affected by SZC co-administration.

A Prediction Model for Tacrolimus Daily Dose in Kidney Transplant Recipients With Machine Learning and Deep Learning Techniques

Tacrolimus is a major immunosuppressor against post-transplant rejection in kidney transplant recipients. However, the narrow therapeutic index of tacrolimus and considerable variability among individuals are challenges for therapeutic outcomes. The aim of this study was to compare different machine learning and deep learning algorithms and establish individualized dose prediction models by using the best performing algorithm. Therefore, among the 10 commonly used algorithms we compared, the TabNet algorithm outperformed other algorithms with the highest R² (0.824), the lowest prediction error [mean absolute error (MAE) 0.468, mean square error (MSE) 0.558, and root mean square error (RMSE) 0.745], and good performance of overestimated (5.29%) or underestimated dose percentage (8.52%). In the final prediction model, the last tacrolimus daily dose, the last tacrolimus therapeutic drug monitoring value, time after transplantation, hematocrit, serum creatinine, aspartate aminotransferase, weight, CYP3A5, body mass index, and uric acid were the most influential variables on tacrolimus daily dose. Our study provides a reference for the application of deep learning technique in tacrolimus dose estimation, and the TabNet model with desirable predictive performance is expected to be expanded and applied in future clinical practice.

Retrospective Database Analysis to Explore Patterns and Economic Burden of Switchback to Brand After Generic or Authorized Generic Utilization

Background

Despite demonstration of bioequivalence of generics to brands and the potential for reduced costs, some patients switch back from a generic to the brand. A prior retrospective analysis suggested that this switchback rate may be lower among patients that had initially switched to authorized generics (AG), often both produced and marketed by the brand company, compared to those initially switched to another generic.

Objective

Explore switching patterns of brands, AGs, and generics, switchback rates, and the potential impact of switchbacks on healthcare costs.

Methods

An analysis of the Pharmetrics Plus™ database (2007–2019), a United States (US) payer administrative database, was conducted to examine the use of Upjohn medications available as AGs across multiple therapeutic areas. Patients initiating treatment with brand medication in the 6 months prior to generic market entry were identified and switch rates to generics and AGs, as well as switchback rates, were evaluated. Costs were descriptively compared between patients who switched back to brand and those who remained on any generic.

Results

Across 14 brand medications, more than half of the patients initiating treatment with the brand medication were switched to a generic. Generally, switching to AG, which ranged from 0.5 to 39.6%, was lower than switching to non-AG generics (16.7–79.9%). The comparison of switchback rates from AGs to brand and non-AGs to brand showed similar results (AG:1.3–7.5%; non-AG:1.4–12.9%); however, the most substantial differences were observed where non-AG switchbacks were higher. Patients that switched back to brand remained on AG or generic for an average of 1–3 months (32–88 days). The analysis showed a tendency towards increased medical costs in the period immediately preceding switchback for all medications except sildenafil in both indications (erectile dysfunction and pulmonary arterial hypertension). For the remaining medications, medical costs ranged from $63 to $1544 higher for the switchback population. Pharmacy costs similarly tended to be higher for patients who had a switchback, with the exception of sildenafil for pulmonary arterial hypertension and sirolimus.

Conclusion

Patients receiving a brand medication are likely to be switched to a generic upon market availability. Some patients switch back to the brand medication, usually within 1–3 months; this may be associated with increased medical costs. Additional research is needed to understand switching, its potential disruption to patients, and the role of brands, generics, and AGs.

Three new pyrrole alkaloids from the endophytic fungus Albifimbria viridis

Three new pyrrole alkaloids albifipyrrols A-C (1-3), were isolated from the endophytic fungus Albifimbria viridis collected from the Chinese medicinal plant. Their structures were elucidated by extensive NMR and HRESIMS spectrometric analyses. All compounds were evaluated for immunosuppressive activity. Fortunately, compound 2 exhibits certain inhibition specifically against the LPS-induced proliferation of B lymphocyte cells with IC₅₀ value 16.16 μM.

Predicting Blood Concentration of Tacrolimus in Patients With Autoimmune Diseases Using Machine Learning Techniques Based on Real-World Evidence

Tacrolimus is a widely used immunosuppressive drug in patients with autoimmune diseases. It has a narrow therapeutic window, thus requiring therapeutic drug monitoring (TDM) to guide the clinical regimen. This study included 193 cases of tacrolimus TDM data in patients with autoimmune diseases at Southern Medical University Nanfang Hospital from June 7, 2018, to December 31, 2020. The study identified nine important variables for tacrolimus concentration using sequential forward selection, including height, tacrolimus daily dose, other immunosuppressants, low-density lipoprotein cholesterol, mean corpuscular volume, mean corpuscular hemoglobin, white blood cell count, direct bilirubin, and hematocrit. The prediction abilities of 14 models based on regression analysis or machine learning algorithms were compared. Ultimately, a prediction model of tacrolimus concentration was established through eXtreme Gradient Boosting (XGBoost) algorithm with the best predictive ability (R² = 0.54, mean absolute error = 0.25, and root mean square error = 0.33). Then, SHapley Additive exPlanations was used to visually interpret the variable’s impacts on tacrolimus concentration. In conclusion, the XGBoost model for predicting blood concentration of tacrolimus on the basis of real-world evidence has good predictive performance, providing guidance for the adjustment of regimen in clinical practice.

Long-term, Prolonged-release Tacrolimus-based Immunosuppression in De Novo Liver Transplant Recipients: 5-year Prospective Follow-up of Patients in the DIAMOND Study

Background

Immunosuppression with calcineurin inhibitors (CNIs) is reportedly associated with risk of renal impairment in liver transplant recipients. It is believed that this can be mitigated by decreasing initial exposure to CNIs or delaying CNI introduction until 3-4 d posttransplantation. The ADVAGRAF studied in combination with mycophenolate mofetil and basiliximab in liver transplantation (DIAMOND) trial evaluated different administration strategies for prolonged-release tacrolimus (PR-T).

Methods

DIAMOND was a 24-wk, open-label, phase 3b trial in de novo liver transplant recipients randomized to: PR-T 0.2 mg/kg/d (Arm 1); PR-T 0.15-0.175 mg/kg/d plus basiliximab (Arm 2); or PR-T 0.2 mg/kg/d delayed until day 5 posttransplant plus basiliximab (Arm 3). In a 5-y follow-up, patients were maintained on an immunosuppressive regimen according to standard clinical practice (NCT02057484). Primary endpoint: graft survival (Kaplan-Meier analysis).

Results

Follow-up study included 856 patients. Overall graft survival was 84.6% and 73.5% at 1 and 5 y post transplant, respectively. Five-year rates for Arms 1, 2, and 3 were 74.7%, 71.5%, and 74.5%, respectively. At 5 y, death-censored graft survival in the entire cohort was 74.7%. Overall graft survival in patients remaining on PR-T for ≥30 d was 79.1%. Graft survival in patients who remained on PR-T at 5 y was 87.3%. Patient survival was 86.6% at 1 y and 76.3% at 5 y, with survival rates similar in the 3 treatment arms at 5 y. Estimated glomerular filtration rate at the end of the 24-wk initial study and 5 y posttransplant was 62.1 and 61.5 mL/min/1.73 m², respectively, and was similar between the 3 treatment arms at 5 y. Overall, 18 (2.9%) patients had ≥1 adverse drug reaction, considered possibly related to PR-T in 6 patients.

Conclusions

In the DIAMOND study patient cohort, renal function, graft survival, and patient survival were similar between treatment arms at 5 y posttransplant.

Generics in transplantation medicine: Randomized comparison of innovator and substitution products containing mycophenolate mofetil

Objective: Mycophenolate mofetil (MMF) is widely used as an immunosuppressant for the prophylaxis of acute organ rejection in recipients of solid organ transplants. Materials and methods: We have compared, in healthy subjects, the pharmacokinetics of mycophenolic acid when MMF was administered in the form of the innovator product CellCept (F. Hoffmann-La Roche Ltd.) or one of three commercially available generics, Renodapt (Biocon Ltd.), Mycept (Panacea Biotec), or Cellmune (Cipla Ltd.). The study was powered to detect a 20% difference in mean formulation performance measures, but not to formally evaluate bioequivalence. Geometric mean ratios of maximum concentrations (C_max) and areas under plasma concentration-time curves were calculated. Results: Comparing generics against each other, the differences in point estimates of the geometric mean ratios of C_max of two of the comparisons were either borderline within (Renodapt/Cellmune) or clearly outside (Mycept/Cellmune) a region of 80 – 125% around the reference mean, indicating that bioequivalence between these generics may be difficult to show. Conclusion: Physicians in the field of transplantation should be aware of the potential risk of altering the therapeutic outcome when switching from one preparation of MMF to another. ClinicalTrials.gov identifier: NCT02981290.

A high-throughput LC-MS/MS method for the quantification of four immunosu- ppressants drugs in whole blood

BACKGROUND

Immunoassays and liquid chromatography tandem mass spectrometry (LC-MS/MS) are two major methods for therapeutic drug monitoring (TDM) of immunosuppressant drugs. Compared to the relatively limited analytical performance and cross reactivities of immunoassays, the LC-MS/MS method is considered as a gold standard; however, the lack of systematic evaluation and standardization needs to be addressed.

METHODS

A LC-MS/MS method for the determination of cyclosporine A, sirolimus, tacrolimus, and everolimus was developed. One-step protein precipitation was used to prepare blood samples. The newly developed method was systematically evaluated and validated according to the standard guidelines.

RESULTS

The quantitative method for four immunosuppressant drugs in human whole blood was validated according to the guidelines. The lower limits of the measuring interval (LLMI) for cyclosporine A, sirolimus, tacrolimus, and everolimus were 5, 0.5, 0.5, and 0.5 ng/mL, respectively. Linear correlation coefficients were all >0.999. Internal standard-normalized (IS-normalized) matrix correction factor was within the range 0.88-1.17. The average spiked recoveries of five replicates for the four immunosuppressant drugs were in the range 87.4-109.6%.

CONCLUSION

An LC-MS/MS method combined with one-step protein precipitation was developed, providing short sample preparation and chromatographic run time, thus allowing easy clinical diagnosis.

Pharmacokinetics of Prolonged-Release Once-Daily Formulations of Tacrolimus in De Novo Kidney Transplant Recipients: A Randomized, Parallel-Group, Open-Label, Multicenter Study

INTRODUCTION

Different prolonged-release formulations of tacrolimus are available. To date, the pharmacokinetic (PK) profile of LCP-tacrolimus (LCPT; Envarsus^®) has not been compared with PR-Tac (Advagraf^®) in de novo kidney transplant recipients. These profiles will guide clinical recommendations for the initiation and dose titration strategies of once-daily tacrolimus formulations.

METHODS

This randomized, parallel-group, open-label, multicenter PK study randomized 75 de novo, adult, white kidney transplant recipients to LCPT 0.17 mg/kg/day (n = 37) or PR-Tac 0.20 mg/kg/day (n = 38) for 4 weeks. Dose adjustments were permitted to target a pre-defined therapeutic range based on measured trough blood concentrations.

RESULTS

PK analysis (days 1, 3, 7 and 14) included 68 patients (LCPT, n = 33; PR-Tac, n = 35). Similar proportions of patients were within the pre-defined therapeutic tacrolimus trough blood concentration range, with < 12% in each group having below-target trough levels over the study period. LCPT demonstrated ~ 30% greater relative bioavailability [LCPT/PR-Tac adjusted geometric mean ratio: day 3, 1.32 (p = 0.007); day 7, 1.25 (p = 0.051); day 14, 1.43 (p = 0.002)] and ~ 30% lower peak-to-trough percentage fluctuation of blood concentration [LCPT/PR-Tac adjusted geometric mean ratio: day 3, 0.70 (p < 0.001); day 7, 0.68 (p < 0.001); day 14, 0.73 (p = 0.004)] in addition to longer time to maximum blood concentration (t_max), lower maximum concentration (C_max) and a consistently lower daily dose (~ 40% dose reduction with LCPT vs. PR-Tac by day 28). Safety profiles were similar.

CONCLUSION

In de novo kidney transplant recipients, prolonged-release formulations of tacrolimus can reach therapeutic concentrations in the immediate post-transplant period. LCPT has greater relative bioavailability and lower peak-to-trough fluctuation compared with PR-Tac.

TRIAL REGISTRATION

Registered at ClinicalTrials.gov; study number NCT02500212.

FUNDING

Chiesi Farmaceutici S.p.A.

[The use of generics in transplantation: Towards rational and safe solutions!]

Generic immunosuppressive drugs are available in Europe Canada and the United States. Between countries, there are large differences in penetration of generic drugs in general, and for immunosuppressive drugs in particular. The registration for generic immunosuppressive drugs are slightly different, but the criteria for registration of narrow therapeutic index drugs and bioequivalence studies, performed only in healthy volunteers, will remain in the medical landscape. About 50 studies compare the clinical efficacy and bioequivalence of the generic immunosuppressive drugs in patients with solid organ transplants. To allow for safe substitution, a number of criteria need to be fulfilled. Consensus statements were made by most transplant organizations. Authorities and payers should refrain from forcing pharmacists to dispense generic drugs in patients on maintenance immunosuppressive treatment. Generic substitution could be safe if realized by the treating physician, for a well-informed patient. Substitution must be followed by control visits to check if the patient is taking the medication correctly and if the drug exposure, through a close monitoring, remains stable. Substitution from one generic to another generic should be avoided, in all cases.

Generic-reference and generic-generic bioequivalence of forty-two, randomly-selected, on-market generic products of fourteen immediate-release oral drugs

Background

The extents of generic-reference and generic-generic average bioequivalence and intra-subject variation of on-market drug products have not been prospectively studied on a large scale.

Methods

We assessed bioequivalence of 42 generic products of 14 immediate-release oral drugs with the highest number of generic products on the Saudi market. We conducted 14 four-sequence, randomized, crossover studies on the reference and three randomly-selected generic products of amlodipine, amoxicillin, atenolol, cephalexin, ciprofloxacin, clarithromycin, diclofenac, ibuprofen, fluconazole, metformin, metronidazole, paracetamol, omeprazole, and ranitidine. Geometric mean ratios of maximum concentration (C_max) and area-under-the-concentration-time-curve, to last measured concentration (AUC_T), extrapolated to infinity (AUC_I), or truncated to C_max time of reference product (AUC_Reftmax) were calculated using non-compartmental method and their 90% confidence intervals (CI) were compared to the 80.00%–125.00% bioequivalence range. Percentages of individual ratios falling outside the ±25% range were also determined.

Results

Mean (SD) age and body-mass-index of 700 healthy volunteers (28–80/study) were 32.2 (6.2) years and 24.4 (3.2) kg/m², respectively. In 42 generic-reference comparisons, 100% of AUC_T and AUC_I CIs showed bioequivalence, 9.5% of C_max CIs barely failed to show bioequivalence, and 66.7% of AUC_Reftmax CIs failed to show bioequivalence/showed bioinequivalence. Adjusting for 6 comparisons, 2.4% of AUC_T and AUC_I CIs and 21.4% of C_max CIs failed to show bioequivalence. In 42 generic-generic comparisons, 2.4% of AUC_T, AUC_I, and C_max CIs failed to show bioequivalence, and 66.7% of AUC_Reftmax CIs failed to show bioequivalence/showed bioinequivalence. Adjusting for 6 comparisons, 2.4% of AUC_T and AUC_I CIs and 14.3% of C_max CIs failed to show bioequivalence. Average geometric mean ratio deviation from 100% was ≤3.2 and ≤5.4 percentage points for AUC_I and C_max, respectively, in both generic-reference and generic-generic comparisons. Individual generic/reference and generic/generic ratios, respectively, were within the ±25% range in >75% of individuals in 79% and 71% of the 14 drugs for AUC_T and 36% and 29% for C_max.

Conclusions

On-market generic drug products continue to be reference-bioequivalent and are bioequivalent to each other based on AUC_T, AUC_I, and C_max but not AUC_Reftmax. Average deviation of geometric mean ratios and intra-subject variations are similar between reference-generic and generic-generic comparisons.

Trial registration

ClinicalTrials.gov identifier: NCT01344070 (registered April 3, 2011).

Electronic supplementary material

The online version of this article (doi:10.1186/s40360-017-0182-1) contains supplementary material, which is available to authorized users.

New tablet formulation of tacrolimus with smaller interindividual variability may become a better treatment option than the conventional capsule formulation in organ transplant patients

To evaluate the pharmacokinetic (PK) and tolerability profiles of a new tablet formulation of tacrolimus and its interindividual variability (IIV) in the systemic exposure, and to compare them with those of the conventional capsule formulation, a randomized, open-label, two-treatment, two-period, two-sequence, crossover study was performed in 47 healthy males. The capsule or tablet formulation of tacrolimus was orally administered, and serial blood samples were collected up to 96 hours after dosing. Whole-blood tacrolimus concentration was determined using liquid chromatography–tandem mass spectrometry. The maximum whole-blood tacrolimus concentration (C_max) and the area under the whole-blood tacrolimus concentration–time curve from 0 hour to the last quantifiable concentration (AUC_last) were compared between the two formulations. The similarity factor (f₂) of the in vitro dissolution profiles was calculated. The geometric mean ratio (90% confidence interval) of tablet to capsule was 0.9680 (0.8873–1.0560) and 1.0322 (0.9359–1.1385) for C_max and AUC_last, respectively. The IIV of C_max and AUC_last of the tablet was smaller than the capsule. The f₂ values were >50 in all media. Both formulations were well tolerated. Thus, the tablet formulation of tacrolimus has smaller IIV in the systemic exposure than capsule, while having comparable PK and tolerability profiles, which may render it as a better treatment option for organ transplant patients.

Does the placebo effect modulate drug bioavailability? Randomized cross-over studies of three drugs

BACKGROUND

Medication effect is the sum of its drug, placebo, and drug*placebo interaction effects. It is conceivable that the interaction effect involves modulating drug bioavailability; it was previously observed that being aware of caffeine ingestion may prolong caffeine plasma half-life. This study was set to evaluate such concept using different drugs.

METHODS

Balanced single-dose, two-period, two-group, cross-over design was used to compare the pharmacokinetics of oral cephalexin, ibuprofen, and paracetamol, each described by its name (overt) or as placebo (covert). Volunteers and study coordinators were deceived as to study aim. Drug concentrations were determined blindly by in-house, high performance liquid chromatography assays. Terminal-elimination half-life (t_½) (primary outcome), maximum concentration (C_max), C_max first time (T_max), terminal-elimination-rate constant (λ), area-under-the-concentration-time-curve, to last measured concentration (AUC_T), extrapolated to infinity (AUC_I), or to T_max of overt drug (AUC_Overttmax), and C_max/AUC_I were calculated blindly using standard non-compartmental method. Covert-vs-overt effect on drug pharmacokinetics was evaluated by analysis-of-variance (ANOVA, primary analysis), 90% confidence interval (CI) using the 80.00-125.00% bioequivalence range, and percentage of individual pharmacokinetic covert/overt ratios that are outside the +25% range.

RESULTS

Fifty, 30, and 50 healthy volunteers (18%, 10%, and 6% females, mean (SD) age 30.8 (6.2), 31.4 (6.6), and 31.2 (5.4) years) participated in 3 studies on cephalexin, ibuprofen, and paracetamol, respectively. Withdrawal rate was 4%, 0%, and 4%, respectively. Eighteen blood samples were obtained over 6, 10, and 14 h in each study period of the three drugs, respectively. ANOVA showed no significant difference in any pharmacokinetic parameter for any of the drugs. The 90% CIs for AUC_T, AUC_I, C_max, AUC_Overttmax, and C_max/AUC_I were within the bioequivalence range, except for ibuprofen C_max (76.66-98.99), ibuprofen C_max/AUC_I (77.19-98.39), and ibuprofen (45.32-91.62) and paracetamol (51.45-98.96) AUC_Overttmax. Out of the 126 individual covert/overt ratios, 2.0-16.7% were outside the +25% range for AUC_T, 2.0-4.2% for AUC_I, 25.0-44.9% for C_max, 67.3-76.7% for AUC_Overttmax, and 45.8-71.4% for T_max.

CONCLUSIONS

This study couldn't confirm that awareness of drug ingestion modulates its bioavailability. However, it demonstrates the trivial effect of blinding in bioequivalence studies and the extent of bio-variability that would be expected when comparing a drug product to itself.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01501747 (registered Dec 26, 2011).

A Systematic Literature Review Approach to Estimate the Therapeutic Index of Selected Immunosuppressant Drugs After Renal Transplantation

BACKGROUND

Drugs that exhibit close margins between therapeutic and toxic blood concentrations are considered to have a narrow therapeutic index (NTI). The Food and Drug Administration has proposed that NTI drugs should have more stringent bioequivalence standards for approval of generic formulations. However, many immunosuppressant drugs do not have a well-defined therapeutic index (TI).

METHODS

We sought to determine whether safety, efficacy, and pharmacokinetic data obtained from the medical literature through a comprehensive literature search could be used to estimate the TI of cyclosporine, tacrolimus, and sirolimus. In this analysis, we considered TI ≤2 as a criterion to define a drug as having an NTI.

RESULTS

Published literature indicates that cyclosporine has a TI of 2-3, which falls just short of our criteria to be classified as having an NTI. We found sirolimus and tacrolimus to have a therapeutic range of 5-12 ng/mL and of 5-20 ng/mL, respectively, but were unable to calculate the TI.

CONCLUSIONS

Although the current literature does not provide a clear indication that these drugs have an NTI, the routine use of therapeutic drug monitoring in clinical practice suggests that more stringent testing of their pharmacokinetic and pharmacodynamic properties should be performed before the approval of generic formulations.

Medication Adherence After Renal Transplantation-a Review of the Literature

BACKGROUND

Whether or not patients follow the advice given by their healthcare professional is commonly referred to as adherence. In the case of kidney transplantation, transplant recipients need to take immunosuppressive drugs on a regular basis to prevent rejection of their transplant. However, medication adherence can be problematic for many patients.

OBJECTIVES

This critical appraisal of evidence aimed to gain insights into factors contributing to adherence and non-adherence in recipients of kidney transplants, and to explore patients' perceptions regarding adherence to immunosuppression.

METHODS

A comprehensive literature search was performed using Medline, PsycInfo, the Joanna Briggs Institute, CINAHL and the Cochrane Library. Included were primary research studies or reviews of primary research, independent of their research paradigms, on adult kidney or kidney/pancreas transplant recipients published in English or German. Children or adolescents were not considered. No time-frame was applied RESULTS: Fifty-two papers were included in the review. All extracted findings of included papers were organised according to the five factors influencing medication-taking behaviour as defined by the World Health Organisation: social and economic factors; therapy-related factors; patient-related factors; condition-related factors; healthcare team and system-related factors.

CONCLUSION

Reasons for non-adherence after kidney transplantations are diverse. Attention is attracted by the fact that potentially modifiable factors such as social support, experiences on dialysis, side effects, features of the treatment regimen, intentions and beliefs, forgetfulness and mental health issues play a greater role than other factors in the development of medication non-adherence. Factors not related to patient characteristics seem to be under researched.

External evaluation of published population pharmacokinetic models of tacrolimus in adult renal transplant recipients

AIM

Several tacrolimus population pharmacokinetic models in adult renal transplant recipients have been established to facilitate dose individualization. However, their applicability when extrapolated to other clinical centres is not clear. This study aimed to (1) evaluate model external predictability and (2) analyze potential influencing factors.

METHODS

Published models were screened from the literature and were evaluated using an external dataset with 52 patients (609 trough samples) collected by postoperative day 90 via methods that included (1) prediction-based prediction error (PE%), (2) simulation-based prediction- and variability-corrected visual predictive check (pvcVPC) and normalized prediction distribution error (NPDE) tests and (3) Bayesian forecasting to assess the influence of prior observations on model predictability. The factors influencing model predictability, particularly the impact of structural models, were evaluated.

RESULTS

Sixteen published models were evaluated. In prediction-based diagnostics, the PE% within ±30% was less than 50% in all models, indicating unsatisfactory predictability. In simulation-based diagnostics, both the pvcVPC and the NPDE indicated model misspecification. Bayesian forecasting improved model predictability significantly with prior 2-3 observations. The various factors influencing model extrapolation included bioassays, the covariates involved (CYP3A5*3 polymorphism, postoperative time and haematocrit) and whether non-linear kinetics were used.

CONCLUSIONS

The published models were unsatisfactory in prediction- and simulation-based diagnostics, thus inappropriate for direct extrapolation correspondingly. However Bayesian forecasting could improve the predictability considerably with priors. The incorporation of non-linear pharmacokinetics in modelling might be a promising approach to improving model predictability.

Bioavailability, Efficacy and Safety of Generic Immunosuppressive Drugs for Kidney Transplantation: A Systematic Review and Meta-Analysis

BACKGROUND

Concerns exist over the extrapolation of bioavailability studies of generic immunosuppressive drugs in healthy volunteers, regarding their efficacy and safety in kidney transplant recipients. We conducted a meta-analysis of trials examining the bioavailability of generic (test) immunosuppressive drugs relative to their brand (reference) counterparts in healthy volunteers, based on the US Food and Drug Administration requirements for approval of generics, and their efficacy and safety in kidney transplant recipients.

METHODS

Eligible studies were identified in PubMed, Cochrane Central Register of Controlled Trials, Scopus, ClinicalTrials.gov, and conference abstracts.

RESULTS

Twenty crossover trials of healthy volunteers (n = 641) and 6 parallel-arm randomized controlled trials of kidney transplant recipients (n = 594) were identified. The 90% CI of the pooled test-to-reference drug ratio for maximum or peak plasma concentration (Cmax) and area under the plasma concentration time-curve from time 0 to time of last determinable concentration (AUC(0-t)) fell within the required range (0.80-1.25) for cyclosporine (Cmax 0.91; 90% CI 0.86-0.95; and AUC(0-t) 0.97; 90% CI 0.94-1.00), tacrolimus (Cmax 1.17; 90% CI 1.09-1.24; and AUC(0-t) 1.00; 90% CI 0.97-1.03) and mycophenolate mofetil (Cmax 0.98; 90% CI 0.96-1.01; and AUC(0-t) 1.00; 90% CI 0.99-1.01). In subgroup analyses, some generic cyclosporine formulations did not meet criteria for bioequivalence. No significant differences were observed in the time to maximum plasma concentration and terminal plasma half-life between generic and brand drugs. In parallel-arm trials, generic cyclosporine was non-inferior to brand counterpart in terms of acute allograft rejection, infections, and death.

CONCLUSIONS

Not all generic immunosuppressive drugs have similar relative bioavailability to their brand name counterparts. Evidence on their efficacy and safety is inconclusive. Tighter regulatory requirement for approval of generic drugs with narrow therapeutic index is needed.

Advances in pharmacotherapy to treat kidney transplant rejection

INTRODUCTION

Current immunosuppressive combination therapy provides excellent prevention of T-cell-mediated rejection following renal transplantation; however, antibody-mediated rejection remains of high concern and accounts for a large number of long-term allograft losses. The recent development of protocol biopsies resulted in the definition of subclinical rejection (SCR), showing histologic evidence for rejection but unremarkable clinical course.

AREAS COVERED

This review describes the current knowledge and evidence of pharmacotherapy to treat kidney allograft rejections and covers SCR treatment options. Each substance is analyzed with regard to its classical indication and further discussed for the treatment of other forms of rejection.

EXPERT OPINION

Despite a lack of randomized trials, early acute T-cell-mediated rejection can be treated effectively in most cases without graft loss. The necessity to treat SCR is currently unclear. Due to a lack of effective therapies, new treatment approaches for antibody-mediated rejection are an urgent medical need to improve long-term outcomes. Future research should aim to better define pathophysiology and histology, stratify risk, and develop rational treatment strategies from randomized controlled trials, in order to establish the value of novel therapies in the arsenal of rejection pharmacotherapy. However, the effective prevention of rejection with minimal side effects still remains the goal in immunosuppression.

A National Survey Assessing the Current Workforce of Transplant Pharmacists Across Accredited U.S. Solid Organ Transplant Programs

Integration of pharmacists into multidisciplinary transplant patient care has advanced in recent years, with limited data available to evaluate the current status of the profession. This was a national survey developed as an AST Pharmacy COP initiative. Responses were solicited from pharmacists practicing at U.S. transplant programs based on UNOS listing; 176 participants from 113 centers (41%) responded, with 79% practicing ≤10 years. There is a median of 1.4 pharmacist full-time equivalents (FTEs) (range 0.1-7.1) for every 100 transplants. The predominant activities performed by pharmacists during the transplant phase include medication review (95%), lab review (92%), allergy review (88%), medication therapy management (92%), bedside rounds (87%), medication education (79%), documentation (71%), and coordinating discharge medications (58%). Similar activities were reported during the other phases, but participation was less common. The involvement of dedicated transplant pharmacists within multidisciplinary care has become standard at a large number of centers, although expansion is still needed to ensure core pharmaceutical care components are provided to all transplant recipients across all centers. These results inform on the typical responsibilities of pharmacists practicing within the field of transplantation and illustrate that the level of pharmacist involvement significantly varies across transplant centers and the phases of transplantation.

Population pharmacokinetic analysis of tacrolimus in Mexican paediatric renal transplant patients: role of CYP3A5 genotype and formulation

AIMS

The aims of this study were (i) to develop a population pharmacokinetic (PK) model of tacrolimus in a Mexican renal transplant paediatric population (n = 53) and (ii) to test the influence of different covariates on its PK properties to facilitate dose individualization.

METHODS

Population PK and variability parameters were estimated from whole blood drug concentration profiles obtained at steady-state using the non-linear mixed effect modelling software NONMEM® Version 7.2.

RESULTS

Tacrolimus PK profiles exhibited high inter-patient variability (IPV). A two compartment model with first order input and elimination described the tacrolimus PK profiles in the studied population. The relationship between CYP3A5 genotype and tacrolimus CL/F was included in the final model. CL/F in CYP3A5*1/*1 and *1/*3 carriers was approximately 2- and 1.5-fold higher than in CYP3A5*3/*3 carriers (non-expressers), respectively, and explained almost the entire IPV in CL/F. Other covariates retained in the final model were the tacrolimus dose and formulation type. Limustin® showed markedly lower concentrations than the rest of the formulations.

CONCLUSIONS

Population PK modelling of tacrolimus in paediatric renal transplant recipients identified the tacrolimus formulation type as a significant covariate affecting the blood concentrations and confirmed the previously reported significant effect of CYP3A5 genotype on CL/F. It allowed the design of a proposed dosage based on the final model that is expected to help to improve tacrolimus dosing.

Limustin®, a non-innovator tacrolimus formulation, yields reduced drug exposure in pediatric renal transplant recipients

The aim of this study was to evaluate the bioavailability of two oral tacrolimus formulations, the innovator Prograf(®) and a formulation commercialized in Mexico with the brand name Limustin(®), in children. Stable Mexican pediatric renal transplant recipients received the product authorized by their social security provider, being either Prograf(®) or Limustin(®). At steady state, blood samples were drawn and tacrolimus blood concentration against time curves was constructed. CYP3A5 genotype was also determined. There was no significant difference in dose or in trough concentrations between formulations. However, AUC and Cmax were significantly higher with Prograf(®). The lower tacrolimus bioavailability with Limustin(®) was observed in both expressers and non-expressers of the functional CYP3A5 protein. Dose-normalized AUC values in expressers were 12.7 ± 11.9 and 48.7 ± 20.4 ng·h/mL/mg for Limustin(®) and Prograf(®), whereas in non-expressers, dose-normalized AUC was 54.4 ± 49.1 and 110.4 ± 42.9 ng·h/mL/mg for Limustin(®) and Prograf(®), respectively (p < 0.05). Pharmaceutical quality analysis showed that Limustin(®) dissolution at 120 min was 31.1 ± 6.2% while Prograf(®) dissolution was 100 ± 4.8%. Furthermore, the mean percentage of labeled amount of Limustin(®) and Prograf(®) was 91.0 ± 3.1% and 100.0 ± 0.7%, respectively. Hence, Limustin(®) exhibits pharmaceutical characteristics dissimilar to the innovator that likely explain the reduced tacrolimus exposure in children. We consider Limustin(®) is not adequate for pediatric use.