Pharmacokinetics of tacrolimus granules in pediatric de novo liver, kidney, and heart transplantation: The OPTION study

2.1 Study design

This was a multicenter, single-arm, phase IV PK study of tacrolimus granules in children undergoing de novo liver, kidney, or heart transplantation. The study was conducted across 10 sites in six countries: United Kingdom, Spain, Germany, Belgium, Poland, and France (NCT01371331, https://clinicaltrials.gov). The Independent Ethics Committee/Institutional Review Board reviewed the ethical, scientific, and medical appropriateness of the study, and approval for the study protocol was obtained from the relevant competent authorities at each study site, prior to study initiation. For all study subjects, the patient's parent(s) or their legal representative(s) had been fully informed and had given written informed consent to participate in the study. The patient had given assent where applicable. All procedures performed during this study were in accordance with the 1975 Declaration of Helsinki and its later amendments or comparable ethical standards.

2.2 Patients

Eligible patients were ≤12 years of age and first-time recipients of a liver, kidney, or heart transplant. Patients were permitted to have received a multiorgan transplant. Exclusion criteria included: high immunologic risk (panel reactive antibody score >50% in the previous 6 months for kidney transplant recipients); significant renal impairment (serum creatinine ≥230 μmol/L [≥2.6 mg/dL] pretransplantation in liver and heart transplant recipients); or liver disease (elevated alanine aminotransferase, and/or aspartate aminotransferase, and/or total bilirubin levels three times the upper limit of normal during the 28 days prior to transplantation) in kidney and heart transplant recipients.

2.3 Intervention

Transplant recipients were treated with tacrolimus granules (Astellas Pharma, Tokyo, Japan) at an initial daily dose of 0.3 mg/kg per day, given as two doses (0.15 mg/kg twice daily) postoperatively. When the total daily dose was not divisible by 0.2 (the smallest sachet size), the dose was rounded up by 0.1 mg. In cases where it was not possible to divide the daily dose exactly, the higher dose was given in the morning. The first dose of tacrolimus 0.15 mg/kg was administered in the morning within 24 hours of reperfusion (this period could be extended up to 5 days for heart transplant recipients, if required). Subsequent oral tacrolimus doses were adjusted based on clinical evidence of efficacy and the occurrence of TEAEs, aided by TDM, to maintain C_trough in the recommended range of 5-20 ng/mL using site-specific assays.

2.4 Preparation of tacrolimus granules suspension for dosing

Centers were advised to prepare the tacrolimus granules suspension by adding the contents of the tacrolimus granule sachets to a measured volume of water (maximum of 50 mL) in a glass or cup; materials containing polyvinyl chloride were avoided for all dosing procedures. The mixture was then stirred gently until the granules were completely suspended. The suspension was drawn up with a syringe and administered orally; alternatively, the contents of the glass or cup were swallowed directly by the transplant recipient. The glass or cup was then rinsed and filled with an equal amount of water to the suspension to be consumed by the transplant recipient. Other methods of delivery, such as through a gastrostomy tube, were not permitted.

2.5 Concomitant medications

Monoclonal antibodies, polyclonal antibodies (thymoglobulin), mycophenolate mofetil (CellCept^®), and corticosteroids were permitted as concomitant immunosuppressive medications. Concomitant medications with known drug interactions with tacrolimus, which may increase or decrease tacrolimus exposure, were prohibited throughout the study and 7 days prior to the first dose of tacrolimus. The following concomitant medications were prohibited within 24 hours prior to the first administration of tacrolimus granules and throughout the study: omeprazole, esomeprazole, and lansoprazole (pantoprazole or ranitidine were permitted as alternatives). The following concomitant medications were prohibited within 7 days prior to the first administration of tacrolimus granules and throughout the study: ketoconazole, fluconazole, itraconazole, clotrimazole, voriconazole, erythromycin, clarithromycin, josamycin, telithromycin, danazol, ethinyl estradiol, calcium antagonists (except nifedipine), nefazodone, phenobarbital, phenytoin, rifampicin, rifabutin, antacids (eg, aluminium hydroxide, oral sodium bicarbonate, or sucralfate), St John's wort, rapamycin, everolimus, and mycophenolic acid.

2.6 Pharmacokinetic evaluation

Whole blood samples (0.5 mL) were collected in tubes containing ethylenediaminetetraacetic acid as an anticoagulant, to provide two blood concentration–time profiles for PK evaluations. Blood samples for PK analyses were taken after the first dose of tacrolimus (Day 1), and at steady state (Day 7; after a minimum of 4 days without a dose change), 0 hours (predose), and 0.5, 1, 2, 4, 8, and 12 hours (postdose). A 10% deviation from nominal time points was permitted for blood samples taken up to 4 hours after administration with tacrolimus granules. A 30-minute deviation was permitted for blood samples taken at the 8- and 12-hour time points. Samples were frozen and transported to a central laboratory for bioanalysis.

Blood samples were thawed, and 0.2 mL aliquots were taken for analysis. The assay was based on the method developed by Alak et al.13 Aliquots were extracted using protein precipitation and solid-phase extraction using C18 200 mg/3 mL cartridges. Elutes were evaporated to dryness under a stream of nitrogen at 40°C, and residues were re-dissolved in a 50:50 mix (vol/vol) of acetonitrile and water, mixed and centrifuged, before being submitted for HPLC/MS/MS. An analog of tacrolimus (ascomycin) was used as an internal standard. The lower limit of quantification was 0.5 ng/mL. All procedures were performed in compliance with the Principles of Good Laboratory Practice.

Tacrolimus concentrations for TDM were determined using a site-specific HPLC/MS/MS assay or immunoassay at local laboratories.

2.7 Outcomes

The primary objective of this study was to determine the PK of tacrolimus granules after the initial dose and at steady state in children undergoing de novo liver, kidney, or heart transplantation. The PK parameters evaluated were AUC_tau, C_max, t_max, and C_trough. All PK parameters were calculated using noncompartmental methods from concentration–time profiles of tacrolimus in whole blood. Using the WinNonlin software (version 5.0 or later), AUC was estimated using the linear trapezoidal rule with linear interpolation. C_max, t_max, and C_trough were obtained directly from concentration–time profiles.

Secondary objective measures included rejection episodes (according to the histological grading of liver biopsies for rejection, the Banff 97 diagnostic categories for renal allograft biopsies, or the standardized nomenclature of the International Society of Heart and Lung Transplantation), transplant recipient and graft survival, and TEAEs over a 2-week time frame.

A post hoc analysis was conducted to examine the relationship between age and AUC_tau after the first dose of tacrolimus 0.15 mg/kg for all transplant recipients.

2.8 Statistical analyses

No power calculations were performed; however, based on previous experience, and assuming a drop-out rate of 40%, approximately 60 transplant recipients were required to achieve 36 evaluable transplant recipients (12 [±2] from each transplant group), each with two evaluable PK profiles.

The SAF consisted of all transplant recipients who took at least one dose of study medication. The PKAS included all transplant recipients who provided two evaluable PK profiles (after the first dose of tacrolimus and at steady state).

For continuous variables, descriptive statistics included the number of transplant recipients, mean, SD, median, minimum, and maximum. In addition, for the PK parameters AUC_tau and C_max (and any other PK parameter determined, except t_max), the coefficient of variation and geometric mean were calculated. If C_max occurred at more than one time point, the first time it occurred was considered for t_max. Frequencies and percentages were displayed for categorical data.

Data were analyzed by type of organ transplant and overall. All data processing, summarization, and analyses were performed using SAS^® version 9.1.3 or higher on UNIX.

3.1 Patients

Trial enrollment commenced on June 9, 2011; 53 patients were screened, of whom 52 received transplants and treatment with tacrolimus granules (Figure 1). The study was completed by 46 transplant recipients (88.5%), and the last evaluation occurred on February 3, 2015. Six transplant recipients discontinued the study (three liver and three kidney transplant recipients). Of those undergoing liver transplantation, one discontinued owing to taking prohibited concomitant medication, one owing to intolerable TEAEs (vomiting after administration and toxicity to tacrolimus), and one owing to medication therapy. Of those undergoing kidney transplantation, two discontinued owing to withdrawal of consent, and one discontinued because they did not have an evaluable PK profile after the first dose of tacrolimus.

Baseline characteristics were generally consistent across each transplant group (Table 1). There were more male transplant recipients (35 [67.3%]) than female (17 [32.7%]), and 49 transplant recipients were white (94.2%; there was one Asian kidney transplant recipient and two liver transplant recipients whose ethnicities were recorded as “other”). A total of 36 transplant recipients (69.2%) were aged <5 years, and 17 transplant recipients (32.7%) were aged <2 years. The mean age distribution and weight of transplant recipients was lower in the liver transplant group than in the kidney and heart transplant groups (Table 1). All kidney transplant recipients were aged between 2 and 11 years, and no patients were multiorgan transplant recipients.

3.2 PK profile and exposure

Overall, 38 of 52 transplant recipients had two evaluable PK profiles and were included in the PKAS (14 [70.0%] liver transplant recipients, 12 [80.0%] kidney transplant recipients, and 12 [70.6%] heart transplant recipients). Within the PKAS, 66% of transplant recipients were aged <5 years.

Mean (±SD) whole blood concentration–time profiles after the first dose of tacrolimus and at steady state are shown in Figure 2. C_max was observed approximately 1 hour after drug dosing for all transplant groups after the first dose of tacrolimus and at steady state. In the PKAS, the mean initial dose of tacrolimus was 0.15 mg/kg for all transplant recipients; corresponding values at steady state were 0.18 mg/kg for liver, 0.16 mg/kg for kidney, and 0.14 mg/kg for heart transplant recipients.

After the first dose of tacrolimus, mean AUC_tau was approximately twofold higher in children who received a liver or heart transplant (211 and 224 hour*ng/mL, respectively) compared with those who received a kidney transplant (97 hour*ng/mL) (Figure 3). Overall, mean AUC_tau was 163 hour*ng/mL in children aged <5 years and 209 hour*ng/mL in those aged ≥5 years (Table 2). At steady state, mean AUC_tau was 195 hour*ng/mL in children who received a liver transplant, 208 hour*ng/mL in children who received a kidney transplant, and 165 hour*ng/mL in children who received a heart transplant (Figure 3). Mean AUC_tau at steady state was 185 hour*ng/mL in children aged <5 years and 199 hour*ng/mL in those aged ≥5 years (Table 3). A post hoc analysis found a low correlation (Pearson's coefficient: r = 0.11; P > 0.5) between age (range: 0.3-12.5 years) and AUC_tau at a fixed dose of tacrolimus 0.15 mg/kg (Figure 4).

Overall, there was a strong correlation between the C_trough of tacrolimus in whole blood and AUC after the first dose of tacrolimus and at steady state (Pearson's coefficient: r = 0.81 and r = 0.87, respectively; P < 0.01; Figure 5).

The mean (SD) C_trough level of tacrolimus over the 2-week study period was 11.7 (4.2) ng/mL (14.9 [4.5] ng/mL in liver, 9.6 [2.1] ng/mL in kidney, and 9.8 [2.9] ng/mL in heart transplant recipients). In the SAF, the mean (SD) C_trough level of tacrolimus was similar in both age subgroups (11.6 [3.9] ng/mL in transplant recipients aged <5 years and 11.9 [5.1] ng/mL in transplant recipients aged ≥5 years). The mean daily dose of tacrolimus was reduced from Day 2 in liver and heart transplant recipients to maintain required C_trough levels (Figure 6).

Secondary end-points are summarized in Table 4. Overall, five transplant recipients experienced acute rejection episodes, and no graft loss or deaths occurred. No unexpected clinically relevant differences in secondary end-points between the age categories were identified. Across all transplant groups, 34 transplant recipients (65.4%) reported at least one drug-related TEAE. The most commonly reported drug-related TEAE was hypertension (10 transplant recipients [19.2%]), followed by toxicity to various agents (six transplant recipients [11.5%]). The most commonly reported serious TEAEs were increased blood creatinine (three liver transplant recipients [5.8%]), and toxicity to various agents (three kidney transplant recipients [5.8%]) due to high exposure to tacrolimus after the starting dose. One liver transplant recipient reported two TEAEs (vomiting after administration and toxicity to tacrolimus) resulting in treatment discontinuation. The incidence of TEAEs was similar in transplant recipients aged <5 years compared with those aged ≥5 years (32 [88.9%] and 14 [87.5%], respectively).