Pharmacokinetic Profile of Prolonged-Release Tacrolimus When Administered via Nasogastric Tube in De Novo Liver Transplantation: A Sub-Study of the DIAMOND Trial

Background

The management of liver transplant recipients has been transformed over the past 2 decades by advances in immunosuppressive regimens [1]. During this time, the extensive therapeutic experience gained with tacrolimus in the clinical and trial settings [2–6] has demonstrated that absorption of tacrolimus early post-transplant is of particular importance. This is because tacrolimus has a narrow therapeutic index, such that small changes in systemic exposure can markedly affect pharmacodynamic response [7–9]. Tacrolimus is absorbed throughout the gastrointestinal tract, and is primarily metabolized by cytochrome P450-3A4 in the liver, as well as in the intestinal wall [10]. As pharmacokinetic (PK) studies demonstrated that oral bioavailability of tacrolimus is unaffected by the presence/absence of bile in the intestine [11–13], tacrolimus therapy is initiated by the oral route whenever possible. During the immediate post-liver transplant period, the established practice is to manage oral therapy by administering the contents of immediate-release tacrolimus capsules as a suspension via a nasogastric tube. In current clinical practice, this is also the case with the prolonged-release tacrolimus capsule formulation. It is, therefore, important to assess the PK profile of tacrolimus when the contents of prolonged-release capsules are administered via a nasogastric tube [14].

A previous Phase I study designed to assess the PK profile of tacrolimus administered to 20 healthy male volunteers found that when prolonged-release tacrolimus capsules were opened, and a suspension was prepared and administered via a nasogastric tube, there was a 28% increase in Cmax, a 75% faster Tmax, and a 17% lower AUC0–∞ of tacrolimus relative to intact capsules [14]. The study suggested that creating a suspension of prolonged-release tacrolimus may dissolve the more immediate-release component of the formulation before administration, potentially resulting in a more rapid absorption rate compared with intact capsules [14]. However, the PK profile of prolonged-release tacrolimus administered by nasogastric tube immediately post-liver transplant has not previously been reported.

Pharmacokinetics of tacrolimus following oral administration of intact prolonged-release capsules in the immediate post-liver transplant period have been assessed previously. In a Phase II study, prolonged-release tacrolimus capsules (0.1 mg/kg/day) resulted in an AUC0–24 of 146 ng·h/mL on Day 1 and 324 ng·h/mL on Day 14 [8]. In a Phase III study, prolonged-release tacrolimus capsules (0.2 mg/kg/day) resulted in an AUC0–24 of 320 ng·h/mL on Day 1 and 452 ng·h/mL on Day 3 [15].

Here, we present data from a PK sub-study of the DIAMOND trial, a Phase IIIb, randomized controlled trial of prolonged-release tacrolimus plus mycophenolate mofetil (MMF) (with and without basiliximab) and a single bolus of corticosteroid in de novo liver transplant recipients over 24 weeks of treatment [5]. This sub-study was designed to assess the absorption and PK profile of prolonged-release tacrolimus when administered by nasogastric tube immediately post-transplant.

Material and Methods

The materials and methods of the DIAMOND study (ClinicalTrials.gov number: NCT01011205) have been presented previously [5]. Patients undergoing liver transplantation were randomized to 1 of 3 study arms (1: 1: 1) to receive prolonged-release tacrolimus. In Arms 1 and 2, patients received prolonged-release tacrolimus at an initial dose of 0.2 mg/kg/day and 0.15–0.175 mg/kg/day on Day 1 post-transplant, respectively, while in Arm 3 tacrolimus initiation at a dose of 0.2 mg/kg/day was delayed until Day 5 post-transplant. All patients received MMF and 1 bolus of corticosteroid, and patients in Arms 2 and 3 also received basiliximab. In this sub-study, the PK profile of prolonged-release tacrolimus was evaluated only in patients randomized to Arms 1 and 2 who received prolonged-release tacrolimus via nasogastric tube immediately post-transplant.

To produce the tacrolimus suspension, prolonged-release tacrolimus capsules were opened and the contents emptied into a container and mixed with 50 mL of water. This suspension was drawn into a syringe and administered via the nasogastric tube. The container was then refilled with 50 mL of water and drawn into the same syringe to flush the nasogastric tube and the container. After administration, the nasogastric tube was clamped for 45–60 min. Polyvinyl chloride-containing material was avoided when administering tacrolimus capsule contents via a nasogastric tube.

In Arm 1, patients received prolonged-release tacrolimus (Advagraf™, Astellas Pharma Europe BV, Netherlands) at an initial dose of 0.2 mg/kg/day. In Arm 2, patients received prolonged-release tacrolimus at an initial dose of 0.15–0.175 mg/kg/day plus basiliximab (20 mg) on Days 0 and 4. In both groups, tacrolimus doses were adjusted to maintain target whole blood trough levels in the range of 5–15 ng/mL from Days 0 to 42. All patients enrolled in the DIAMOND study also received intravenous MMF (1 g) within 12 h of skin closure, and 1 g twice-daily until Day 14 (intravenous for Days 1–5, orally for Days 6–14). A bolus of intra-operative corticosteroid (≤1000 mg) was permitted according to center policy, but post-transplant maintenance steroids were not administered routinely.

PK analyses were performed on whole-blood samples collected on the morning of the first day of tacrolimus administration and on Day 3 post-transplantation, to provide 2 blood concentration – time profiles. On the first day of tacrolimus administration, PK profiles were assessed immediately after tacrolimus administration. On Day 3, the first blood sample was drawn in the morning no earlier than 5 min before administration of prolonged-release tacrolimus (Time 0 (pre-dose)). For each profile, blood samples were collected at Time 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, 12, 16, and 24 h post-dose. This resulted in samples from 11 time points for each assessment period.

Tacrolimus concentrations were determined using a validated high-performance liquid chromatography (HPLC) tandem mass-spectrometric (MS) (HPLC/MS/MS) assay (lower limit of quantification, 0.059 ng/mL). The assay was based on the method developed by Alak et al. [16]. Whole-blood calibrators, quality control samples, and study samples were thawed, and 1-mL aliquots taken. An analog internal standard of tacrolimus (FR900520; 20 mL, 50 ng/mL) was added and mixed briefly. 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 redissolved in a 50: 50 (volume: volume) mix of acetonitrile and water (mixed and centrifuged) before being submitted for HPLC/MS/MS. All procedures were performed in compliance with the principles of Good Laboratory Practice.

Analyses for the sub-study included area under the concentration–time curve from 0 to 24 h post-tacrolimus dose (AUC0–24), maximum observed concentration of tacrolimus (Cmax), time to Cmax (Tmax), minimum observed concentration of tacrolimus at 24-h post-dose (Cmin), and dose and body weight normalized AUC0–24, Cmax, and Cmin. Adjustments for dose and body weight were calculated by dividing the parameter by the dose per kg of body weight and are described in this publication as AUC24 (norm), Cmax (norm), and Cmin (norm). The arithmetic mean and standard deviation (SD) were calculated for dose and Cmin. Geometric mean and geometric coefficient of variation (CV) were calculated for all PK analyses except Tmax, for which the median (range) was reported. Analyses were undertaken on the PK population, defined as all randomized patients who received ≥1 dose of the study drug and who had evaluable PK data with complete profiles for both Days 1 and 3.

A total sample size ≥16 patients (8 evaluable patients in each of the 2 treatment arms in the DIAMOND sub-study) was considered necessary to evaluate the PK profile of prolonged-release tacrolimus administered via nasogastric tube. No separate analysis of safety or efficacy was performed for the PK sub-set.

Results

PATIENT AND DONOR DEMOGRAPHICS:

Due to early completion of the main DIAMOND clinical study, it was not possible to recruit 16 patients into the PK sub-study. While 11 patients from 3 centers were eligible for inclusion, 1 patient had an incomplete PK profile and was excluded from the analysis. The remaining 10 patients (5 per treatment arm) were included in the analyses. The mean (range) body weight for these patients was 76.6 kg (range 60–89 kg).

TREATMENT DOSE AND EXPOSURE:

Overall mean daily dose of prolonged-release tacrolimus was higher on Day 1 (0.179 mg/kg) compared with Day 3 (0.140 mg/kg). The arithmetic mean (SD) tacrolimus trough levels, measured by Cmin, were lower on Day 1 (8.16 (7.75) ng/mL) vs. Day 3 (10.7 (6.66) ng/mL). The PK profiles for Days 1 and 3 are presented in Figure 1.

PHARMACOKINETIC PROFILE:

For both treatment arms combined, the geometric mean of AUC0–24 for tacrolimus was lower on Day 1 compared with Day 3, while the interpatient variability in systemic exposure to tacrolimus, measured by CV, was higher on Day 1 vs. Day 3 (mean (CV) AUC0–24 Day 1: 193 (94.5) vs. Day 3: 301 (50.8) ng·h/mL) (Table 1). Cmax was lower on Day 1, and Tmax was shorter on Day 1 compared with Day 3 (mean (CV) Cmax: 15.1 (73.9) vs. 19.1 (47.9) ng/mL; median (range) Tmax: 2.0 (2.0–24.0) vs. 4.5 (0.5–24.0) h). The geometric mean (CV) of Cmin was lower on Day 1 compared with Day 3 (5.27 (141.0) vs. 8.77 (80.3) ng/mL, respectively).

When the data were normalized for dose and body weight, a similar pattern in the PK profile was observed (Table 1). AUC0–24 (norm) (CV) remained lower and more variable on Day 1 compared with Day 3 (1090 (97.5) vs. 2230 (54.2) mg/kg), and Cmax (norm) and Cmin (norm) were also lower on Day 1 compared with Day 3 (mean (CV) Cmax (norm): 85.2 (78.5) vs. 141 (55.6) mg/kg; mean (CV) Cmin (norm): 29.7 (145) vs. 64.9 (77.0)) (Table 1).

Discussion

Results from the DIAMOND PK sub-study indicate that, for patients who cannot swallow capsules in the immediate post-transplant period, prolonged-release tacrolimus capsules can be opened and administered as a suspension via nasogastric tube.

Overall systemic exposure to tacrolimus, as measured by AUC0–24 and Cmin, was higher on Day 3 vs. Day 1. This is consistent with data from earlier Phase II [8] and Phase III PK studies [15], in which intact prolonged-release tacrolimus capsules were administered. Considering the reasons for requiring nasogastric administration of tacrolimus and the gut motility of patients post-surgery, these findings are consistent with our understanding of liver transplant recipients in the immediate post-transplant period.

A previous Phase I study [14] compared systemic exposure of tacrolimus after administration of the contents of prolonged-release tacrolimus capsules via intact capsules, oral suspension, or nasogastric suspension in healthy volunteers. The data indicated that administration of prolonged-release tacrolimus suspension, orally or via nasogastric tube, resulted in a faster absorption profile (shorter Tmax and higher Cmax) compared with intact capsules. Mean exposure (estimated using AUC) was approximately 17% lower for nasogastric tube administration compared with intact capsules [14]. The authors speculated that incomplete tacrolimus absorption profiles were recorded for the participants who reached Cmax at the first blood-sampling time point, leading to an underestimation of the overall systemic exposure to tacrolimus.

When comparing the DIAMOND PK sub-study data for Day 1 with data from healthy volunteers [14], the median Tmax following nasogastric administration of prolonged-release tacrolimus on Day 1 in patients undergoing de novo liver transplantation was longer (2.5 h) vs. that in healthy volunteers (0.5 h). This suggests a more ‘normal’ absorption profile of prolonged-release tacrolimus when administered via nasogastric tube in liver transplant patients compared with healthy subjects. These differences could be due to the reduced gastrointestinal motility found in liver transplant patients immediately post-transplant, thereby limiting tacrolimus bioavailability.

The PK profile of tacrolimus, administered as a prolonged-release intact capsule and as an immediate-release intact capsule, have been studied previously in a Phase III trial [15]. The PK parameters of tacrolimus (AUC0–24, Cmax, Tmax, and Cmin) in the DIAMOND PK sub-study following once-daily nasogastric administration were broadly consistent with results from this study [15]. In addition, when comparing the DIAMOND PK sub-study data with those from a previously published Phase II study of de novo liver transplant recipients receiving intact capsules, the overall absorption and PK profile (Cmax, Tmax and Cmin) of tacrolimus were generally comparable when administered by nasogastric tube or intact capsules [8]. Taken together, these data indicate that once-daily nasogastric administration of prolonged-release tacrolimus early post-transplant does not substantially affect the absorption and disposition of tacrolimus when compared with de novo liver transplant patients receiving intact prolonged-release tacrolimus capsules.

The main limitations of the PK sub-study were that only 11 patients were eligible for inclusion in the study instead of the planned 16, and a full PK data set was only available for 10 of these patients. The lack of a PK comparator arm of patients who received intact prolonged-release tacrolimus capsules is also a limitation, and comparing data between trials should be undertaken with caution. Despite these limitations, the findings were broadly consistent with other PK studies of patients undergoing liver transplantation who received prolonged-release tacrolimus via intact capsules [8,15].

Conclusions

In contrast to the findings in healthy volunteers [14], data from this study suggest that once-daily nasogastric administration of prolonged-release tacrolimus does not have a substantial effect on the PK profile of tacrolimus compared with oral administration of prolonged-release tacrolimus capsules in de novo liver transplant recipients. Administration of prolonged-release tacrolimus via nasogastric tube is, therefore, a feasible option to ensure appropriate tacrolimus exposure in patients who are unable to swallow intact capsules in the first few days post-transplant.