Absorption of tacrolimus from the gastrointestinal tract after oral administration is incomplete and variable. The absolute bioavailability of tacrolimus was 17±10% in adult kidney transplant patients (N=26), 22±6% in adult liver transplant patients (N=17), 23±9% in adult heart transplant patients (N=11) and 18±5% in healthy volunteers (N=16).
A single dose trial conducted in 32 healthy volunteers established the bioequivalence of the 1 mg and 5 mg capsules. Another single dose trial in 32 healthy volunteers established the bioequivalence of the 0.5 mg and 1 mg capsules. Tacrolimus maximum blood concentrations (Cmax ) and area under the curve (AUC) appeared to increase in a dose proportional fashion in 18 fasted healthy volunteers receiving a single oral dose of 3, 7, and 10 mg.
In 18 kidney transplant patients, tacrolimus trough concentrations from 3 to 30 ng/mL measured at 10 — 12 hours post-dose (Cmin ) correlated well with the AUC (correlation coefficient 0.93). In 24 liver transplant patients over a concentration range of 10 to 60 ng/mL, the correlation coefficient was 0.94. In 25 heart transplant patients over a concentration range of 2 to 24 ng/mL, the correlation coefficient was 0.89 after an oral dose of 0.075 or 0.15 mg/kg/day at steady-state.
The rate and extent of tacrolimus absorption were greatest under fasted conditions. The presence and composition of food decreased both the rate and extent of tacrolimus absorption when administered to 15 healthy volunteers. The effect was most pronounced with a high-fat meal (848 kcal, 46% fat): mean AUC and Cmax were decreased 37% and 77%, respectively; Tmax was lengthened 5-fold. A high-carbohydrate meal (668 kcal, 85% carbohydrate) decreased mean AUC and mean Cmax by 28% and 65%, respectively.
In healthy volunteers (N=16), the time of the meal also affected tacrolimus bioavailability. When given immediately following the meal, mean Cmax was reduced 71%, and mean AUC was reduced 39%, relative to the fasted condition. When administered 1.5 hours following the meal, mean Cmax was reduced 63%, and mean AUC was reduced 39%, relative to the fasted condition.
In 11 liver transplant patients, tacrolimus administered 15 minutes after a high fat (400 kcal, 34% fat) breakfast, resulted in decreased AUC (27±18%) and Cmax (50±19%), as compared to a fasted state.
Tacrolimus capsules should be taken consistently every day either with or without food because the presence and composition of food decreases the bioavailability of tacrolimus [see Dosage and Administration (2.5)].
The plasma protein binding of tacrolimus is approximately 99% and is independent of concentration over a range of 5 to 50 ng/mL. Tacrolimus is bound mainly to albumin and alpha-1-acid glycoprotein, and has a high level of association with erythrocytes. The distribution of tacrolimus between whole blood and plasma depends on several factors, such as hematocrit, temperature at the time of plasma separation, drug concentration, and plasma protein concentration. In a U.S.trial, the ratio of whole blood concentration to plasma concentration averaged 35 (range 12 to 67).
Tacrolimus is extensively metabolized by the mixed-function oxidase system, primarily the cytochrome P-450 system (CYP3A). A metabolic pathway leading to the formation of 8 possible metabolites has been proposed. Demethylation and hydroxylation were identified as the primary mechanisms of biotransformation in vitro. The major metabolite identified in incubations with human liver microsomes is 13-demethyl tacrolimus. In in vitro studies, a 31-demethyl metabolite has been reported to have the same activity as tacrolimus.
The mean clearance following IV administration of tacrolimus is 0.040, 0.083, and 0.053, and 0.051 L/hr/kg in healthy volunteers, adult kidney transplant patients, adult liver transplant patients, and adult heart transplant patients, respectively. In man, less than 1% of the dose administered is excreted unchanged in urine.
In a mass balance study of IV administered radiolabeled tacrolimus to 6 healthy volunteers, the mean recovery of radiolabel was 77.8±12.7%. Fecal elimination accounted for 92.4±1.0% and the elimination half-life based on radioactivity was 48.1±15.9 hours whereas it was 43.5±11.6 hours based on tacrolimus concentrations. The mean clearance of radiolabel was 0.029±0.015 L/hr/kg and clearance of tacrolimus was 0.029±0.009 L/hr/kg. When administered PO, the mean recovery of the radiolabel was 94.9±30.7%. Fecal elimination accounted for 92.6±30.7%, urinary elimination accounted for 2.3±1.1% and the elimination half-life based on radioactivity was 31.9±10.5 hours whereas it was 48.4±12.3 hours based on tacrolimus concentrations. The mean clearance of radiolabel was 0.226±0.116 L/hr/kg and clearance of tacrolimus 0.172±0.088 L/hr/kg.
Pharmacokinetics of tacrolimus have been studied in liver transplantation patients, 0.7 to 13.2 years of age. Following IV administration of a 0.037 mg/kg/day dose to 12 pediatric patients, mean terminal half-life, volume of distribution and clearance were 11.5±3.8 hours, 2.6±2.1 L/kg and 0.138±0.071 L/hr/kg, respectively. Following oral administration to 9 patients, mean AUC and Cmax were 337±167 ng·hr/mL and 48.4±27.9 ng/mL, respectively. The absolute bioavailability was 31±24%.
Whole blood trough concentrations from 31 patients less than 12 years old showed that pediatric patients needed higher doses than adults to achieve similar tacrolimus trough concentrations [see Dosage and Administration (2.2)].
Pharmacokinetics of tacrolimus have also been studied in kidney transplantation patients, 8.2±2.4 years of age. Following IV infusion of a 0.06 (range 0.06 — 0.09) mg/kg/day to 12 pediatric patients (8 male and 4 female), mean terminal half-life and clearance were 10.2±5.0 (range 3.4 — 25) hours and 0.12±0.04 (range 0.06 — 0.17) L/hr/kg, respectively. Following oral administration to the same patients, mean AUC and Cmax were 181±65 (range 81 — 300) ng·hr/mL and 30±11 (range 14 — 49) ng/mL, respectively. The absolute bioavailability was 19±14 (range 5.2 — 56) %.
Renal and Hepatic Impairment
The mean pharmacokinetic parameters for tacrolimus following single administrations to patients with renal and hepatic impairment are given in Table 15.
|Population (No. of Patients)||Dose||AUC0-t (ng·hr/mL)||t1/2 (hr)||V (L/kg)||Cl (L/hr/kg)|
|Renal Impairment (n=12)||0.02 mg/kg/4hr IV||393 ± 123 (t=60 hr)||26.3 ± 9.2||1.07 ± 0.20||0.038 ± 0.014|
|Mild Hepatic Impairment (n=6)||0.02 mg/kg/4hr IV||367 ± 107 (t=72 hr)||60.6 ± 43.8 Range: 27.8 — 141||3.1 ± 1.6||0.042 ± 0.02|
|7.7 mg PO||488 ± 320 (t=72 hr)||66.1 ± 44.8 Range: 29.5 — 138||3.7 ± 4.7 *||0.034 ± 0.019 *|
|Severe Hepatic Impairment (n=6, IV)||0.02 mg/kg/4hr IV (n=2)||762 ± 204 (t=120 hr)||198 ± 158 Range:81 — 436||3.9 ± 1.0||0.017 ± 0.013|
|0.01 mg/kg/8hr IV (n=4)||289 ± 117 (t=144 hr)|
|(n=5, PO)*||8 mg PO (n=1)||658 (t=120 hr)||119±35 Range: 85 — 178||3.1±3.4*||0.016 ±0.011*|
|5 mg PO (n=4)||533±156 (t=144 hr)|
|4 mg PO (n=1)|
Renal Impairment: Tacrolimus pharmacokinetics following a single IV administration were determined in 12 patients (7 not on dialysis and 5 on dialysis, serum creatinine of 3.9±1.6 and 12.0±2.4 mg/dL, respectively) prior to their kidney transplant. The pharmacokinetic parameters obtained were similar for both groups. The mean clearance of tacrolimus in patients with renal dysfunction was similar to that in normal volunteers (Table15) [see Dosage and Administration (2.3) and Use in Specific Populations (8.6)].
Hepatic Impairment: Tacrolimus pharmacokinetics have been determined in six patients with mild hepatic dysfunction (mean Pugh score: 6.2) following single IV and oral administrations. The mean clearance of tacrolimus in patients with mild hepatic dysfunction was not substantially different from that in normal volunteers (see previous table). Tacrolimus pharmacokinetics were studied in 6 patients with severe hepatic dysfunction (mean Pugh score: >10). The mean clearance was substantially lower in patients with severe hepatic dysfunction, irrespective of the route of administration [see Dosage and Administration (2.4) and Use in Specific Populations (8.7)].
The pharmacokinetics of tacrolimus have been studied following single IV and oral administration of tacrolimus to 10 African-American, 12 Latino-American, and 12 Caucasian healthy volunteers. There were no significant pharmacokinetic differences among the three ethnic groups following a 4-hour IV infusion of 0.015 mg/kg. However, after single oral administration of 5 mg, mean (±SD) tacrolimus Cmax in African-Americans (23.6±12.1 ng/mL) was significantly lower than in Caucasians (40.2±12.6 ng/mL) and the Latino-Americans (36.2±15.8 ng/mL) (p<0.01). Mean AUC0-inf tended to be lower in African-Americans (203±115 ng·hr/mL) than Caucasians (344±186 ng·hr/mL) and Latino- Americans (274±150 ng·hr/mL). The mean (±SD) absolute oral bioavailability (F) in African-Americans (12±4.5%) and Latino-Americans (14±7.4%) was significantly lower than in Caucasians (19±5.8%, p=0.011). There was no significant difference in mean terminal T1/2 among the three ethnic groups (range from approximately 25 to 30 hours). A retrospective comparison of African-American and Caucasian kidney transplant patients indicated that African-American patients required higher tacrolimus doses to attain similar trough concentrations [see Dosage and Administration (2.1)].
A formal trial to evaluate the effect of gender on tacrolimus pharmacokinetics has not been conducted, however, there was no difference in dosing by gender in the kidney transplant trial. A retrospective comparison of pharmacokinetics in healthy volunteers, and in kidney, liver and heart transplant patients indicated no gender-based differences.
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