Nowadays, tacrolimus (Tc), the calcineurin inhibitor, is most commonly immunosuppressive drug used in kidney transplantation. The dose requirement to achieve tacrolimus target blood concentrations varies substantially between individual patients [
The substantial variability of oral drug absorption and liver metabolism in combination with its narrow therapeutic index result in the need for careful blood Tc concentration monitoring, and subsequent dose adjustment [
Early reports have shown that the first posttransplant Tc blood level > 15 ng/ml is more frequently observed in older and overweight kidney graft recipients [
The primary objective of the present study was to analyze the potential factors influencing the first posttransplant Tc blood level in a large single-center cohort of kidney transplant recipients. To set our research in the everyday clinical practice, we also included the corresponding blood cell count parameters, liver function tests, and all comedications that may alter Tc metabolism.
The Bioethics Committee of the Medical University of Silesia granted permission for this study. Informed consent was not deemed necessary; the majority of data were analyzed anonymously based on prospective center transplant database. Comedication data were retrieved from medical records.
Four hundred eighty-eight of 754 consecutive adult kidney graft recipients operated on in our center between 2000 and 2015, who were initially treated with immunosuppressive regimen containing tacrolimus BID, were studied (flow chart, Figure
Study flow chart.
After transplantation, most of the patients received triple immunosuppression therapy, which consisted of tacrolimus, mycophenolate or azathioprine or sirolimus, and steroids. The initial Tc dose (in general, 0.2 mg/kg/day) was already given orally prior to the transplantation procedure, and then twice a day, and was administered 2 hours after meal and 1 hour before the next meal. With this recommended dosing we have often observed supratherapeutic blood Tc levels, especially in obese or elderly patients; therefore, since 2011 we started to incidentally reduce the tacrolimus initial dose by up to 20% in such patients, based at the physician’s discretion. Besides, a total of 130 patients received basiliximab (Simulect®; Novartis, Basel, Switzerland) as an induction therapy (as those with polyclonal antibodies induction were excluded). Steroids were used in all patients, starting with 500 mg of methylprednisolone (intravenously) during the procedure, 125 mg at first posttransplant day, and then 20 mg of prednisone orally every morning.
In all analyzed patients, the first Tc blood level determination was performed on the morning between the first and fifth postoperative days, at least 24 hours after transplantation procedure. Blood samples for Tc trough level assessments were withdrawn 12 hours after the evening dose. Tc concentrations were assessed using the microparticle enzyme immunoassay (MEIA; Abbott Laboratories, Abbott Park, IL, USA). The upper limit was set at 30 ng/ml, and all values exceeding this result were encoded in the database as 30 ng/ml.
Nutritional status was scored according to World Health Organization criteria, based on anthropometric measurements performed immediately before the transplantation procedure (underweight: BMI < 18.5 kg/m2, normal weight: BMI 18.5–24.99 kg/m2, overweight: BMI 25–29.99 kg/m2, and obese: BMI ≥ 30 kg/m2).
Complete blood count examination was performed on the same day as the initial Tc level measurement; anemia was scored according to World Health Organization criteria. The rest of the biochemical parameters—liver function tests: aspartate aminotransferase (AST), alanine aminotransferase (ALT), and bilirubin—were determined simultaneously or a day later than the initial Tc level measurement.
Initial graft function was defined as immediate (IGF), slow (SGF), or delayed (DGF) graft function. IGF was defined as the serum creatinine concentration
The diagnosis of new onset diabetes after transplantation (NODAT) was based on WHO criteria, with fasting serum glucose ≥ 126 mg/dL, with or without drug therapy.
Among the medications, used concomitantly and potentially interfering with Tc metabolism, we have analyzed substances which may decrease Tc levels (nitrendipine, proton-pump inhibitors (PPIs), carbamazepine, and trimethoprim-sulfamethoxazole) and those increasing Tc levels (diltiazem, verapamil, H2 blockers (mostly ranitidine)). Other potentially interfering comedications (macrolides, HIV antiretroviral therapy, etc.) were not used in the analyzed cohort.
According to current recommendations [
Statistical analyses were performed using STATISTICA 10.0 PL for Windows software package (StatSoft Polska, Kraków, Poland) and MedCalc 12.3.0.0. (Mariakerke, Belgium). Values are presented as means and 95% confidence intervals (CI) or frequencies. The initial comparison was performed for subgroups defined by the first Tc trough level after transplant (≤15 or >15 ng/ml), as well as for the subjects excluded from the analysis. The subgroups were compared using the chi2 test (qualitative variables) and analysis of variance (ANOVA; quantitative variables). The univariate analyses included already defined and potential new variables for the risk of supratherapeutic first Tc levels. Correlations were calculated according to Pearson. Multivariate backward regression analysis of factors explaining the variability of first Tc trough blood level (model I) and multiple logistic regression analysis predicting the risk for first Tc trough blood level > 15 ng/ml (model II) in kidney transplant recipients were performed. Both models included age, gender, BMI, pretransplant diabetes, hemoglobin, the presence of anti-HCV antibodies, and Tc initial dose (in mg/kg body weight/day) as potential explanatory variables. Receiver operator curve (ROC) analysis was applied to determine the cut-off values for age, BMI, and hemoglobin level, associated with first Tc blood level > 15 ng/ml. Age and BMI values exceeding the cut-off values were considered risk factors for Tc blood level > 15 ng/ml, and the relative risk (RR) of first Tc blood level > 15 ng/ml was calculated for the subgroups of patients with one or two risk factors present, in relation to the subgroup without them. In addition, we analyzed the percentage of patients with inadequately low (<6 ng/ml) first Tc levels after transplantation and gave their clinical characteristics. In all statistical tests, the
The demographic and clinical characteristics of patients included and excluded from the analysis are shown in Table
Clinical characteristics and laboratory parameters in patients included into the analysis (stratified to the first posttransplant Tc trough level) with comparison to the excluded cohort.
Excluded |
Included |
ANOVA or chi2 | First Tc |
First Tc |
ANOVA |
|
---|---|---|---|---|---|---|
Age [years] | 43 (42–45) | 47 (46–49) | <0.001 | 45 (44–47) | 51 (49–53) | <0.001 |
Gender [M/F] | 137/129 | 323/165 | <0.001 | 187/112 | 136/53 | 0.04 |
BMI [kg/m2] | 23.4 (22.9–23.8) | 24.6 (24.2–24.9) | <0.001 | 23.6 (23.2–24.1) | 25.5 (25.0–26.0) | <0.001 |
Overweight/obese [%] | 22.6/2.3 | 37.1/6.1 | <0.001 | 28.4/5.4 | 50.8/7.4 | <0.001 |
Dialysis vintage [mo] | 46 (41–51) | 39 (36–42) | 0.17 | 39 (35–43) | 40 (36–45) | 0.66 |
Residual diuresis [ml] | 620 (519–722) | 626 (558–693) | 0.89 | 622 (536–709) | 612 (505–718) | 0.88 |
Hypertension [%] | 89.8 | 91.0 | 0.70 | 91.3 | 90.5 | 0.80 |
Diabetes [%] | 34.6 | 9.2 | <0.001 | 6.7 | 13.2 | 0.02 |
Anti-HCV positive [%] | 13.9 | 7.2 | 0.004 | 5.4 | 10.1 | 0.07 |
HBs antigen positive [%] | 3.4 | 3.3 | 0.89 | 2.7 | 4.2 | 0.50 |
CIT [h] | 16 (15–17) | 18 (17–19) | 0.008 | 18 (17–19) | 18 (17–19) | 0.97 |
First transplant [%] | 75.6 | 86.2 | <0.001 | 86.0 | 86.8 | 0.90 |
Induction [%] | 49.2 | 26.6 | <0.001 | 26.4 | 27.0 | 0.97 |
H2-blocker [%] | 15.0 | 31.1 | <0.001 | 34.8 | 25.4 | 0.04 |
PPIs [%] | 81.2 | 72.5 | 0.01 | 71.6 | 74.1 | 0.85 |
Tc initial dose [mg/kg] | 0.173 (0.168–0.179) | 0.184 (0.181–0.187) | <0.001 | 0.186 (0.182–0.189) | 0.182 (0.178–0.186) | 0.22 |
Tc first trough level [ng/ml] | 16.1 (15.1–17.1) | 14.7 (14.0–15.3) | 0.27 | 9.9 (9.6–10.2) | 22.3 (21.5–23.0) | <0.001 |
Day of first Tc assessment | 1.7 (1.5–1.9) | 3.3 (3.2–3.4) | <0.001 | 3.5 (3.4–3.6) | 3.0 (2.8–3.1) | <0.001 |
Serum creatinine | 493 (455–530) | 538 (510–565) | 0.15 | 520 (486–555) | 564 (519–610) | 0.12 |
Delayed graft function [%] | 27.8 | 26.8 | 0.84 | 25.1 | 29.6 | 0.32 |
Data shown as means ± 95% CI or frequencies.
The comedications that could potentially interfere with Tc metabolism included PPI (
For the entire group, 38.7% of the first measurements exceeded 15 ng/ml. The Tc initial dose was 0.184 mg/kg/day, similar in both study subgroups. The subgroup of patients with first Tc level > 15 ng/ml was significantly older and had higher BMI, greater percentage of pretransplant diabetes, and anti-HCV seropositive subjects. They were also less frequently treated with H2-blocker. Notably, the assessment of first Tc trough level was performed slightly earlier in the group with Tc > 15 ng/ml (Table
The subgroup of patients with first Tc level > 15 ng/ml was characterized by insignificantly higher occurrence of early NODAT (24.9 versus 18.7% in patients with first Tc level ≤ 15 ng/ml,
The systolic blood pressure values at postoperative day (POD) 7, POD 14, and at hospital discharge were similar in both groups (data not shown), whereas the diastolic blood pressure values at the same time-points differed between groups (POD 7: 84.6 versus 86.8 mmHg,
The first Tc trough blood level was measured on the third day at mean. Notably, the Tc trough blood level and the percentage of levels exceeding 15 ng/ml were not related to the day of assessment. There was also no association between an early graft function and the mean value of first Tc trough level (DGF:
Tc trough blood level variability was explained by age, gender, nutritional status, the occurrence of diabetes, anemia and anti-HCV antibodies, and the concurrent use of H2 blockers (Tables
The mean values of first tacrolimus blood trough level after kidney transplantation (left column) and the proportion of patients with first tacrolimus blood trough level exceeding 15 ng/ml (right column), presented in subgroups of patients with or without the presence of potential risk factor.
Tc first level [ng/ml] | Tc > 15 ng/ml |
|
---|---|---|
Gender | ||
Men ( |
|
|
Women ( |
13.4 (12.5–14.4) |
|
|
||
Nutritional status | ||
Underweight ( |
12.2 (9.5–14.8) |
|
Normal weight ( |
12.6 (11.8–13.4) |
|
Overweight ( |
|
|
Obesity ( |
|
|
|
||
Diabetes mellitus | ||
Yes ( |
|
|
No ( |
14.4 (13.7–15.1) |
|
|
||
Anti-HCV positive | ||
Yes ( |
|
|
No ( |
14.6 (14.0–15.3) |
|
|
||
HBs positive | ||
Yes ( |
15.7 (11.5–20.0) |
|
No ( |
14.8 (14.1–15.4) |
|
|
||
ALT > 40 IU/L | ||
Yes ( |
14.6 (12.6–16.5) |
|
No ( |
14.7 (14.1–15.4) |
|
|
||
AST > 40 IU/L | ||
Yes ( |
17.5 (13.3–21.7) |
|
No ( |
14.6 (13.9–15.2) |
|
|
||
AST/ALT > 1 | ||
Yes ( |
15.1 (14.0–16.2) |
|
No ( |
14.4 (13.6–15.3) |
|
|
||
Anemia | ||
Severe ( |
|
|
Mild ( |
|
|
No ( |
17.1 (16.0–18.2) |
|
|
||
Transplant No | ||
First ( |
14.7 (14.1–15.4) |
|
Next ( |
14.5 (12.7–16.3) |
|
|
||
Early graft function | ||
IGF ( |
14.1 (12.8–15.4) |
|
SGF ( |
15.0 (14.0–16.0) |
|
DGF ( |
15.1 (13.8–16.3) |
|
|
||
H2-blocker | ||
Yes ( |
|
|
No ( |
15.2 (14.4–16.0) |
|
|
||
PPI | ||
Yes ( |
14.9 (14.2–15.6) |
|
No ( |
14.0 (12.8–15.3) |
|
Data shown as means ± 95% CI or frequencies. BMI: body mass index, HCV: hepatitis C virus, HBs: hepatitis B surface antigen, IGF: immediate graft function, SGF: slow graft function, DGF: delayed graft function. Statistical significance:
The multivariate regression analysis (Table
Multivariate backward regression analysis of factors explaining variability of the first tacrolimus trough level (model I) and multiple logistic regression predicting the risk of first tacrolimus trough level > 15 ng/ml (model II) in kidney transplant recipients. Both models included age, gender, BMI, pretransplant diabetes, hemoglobin, the presence of anti-HCV antibodies, and tacrolimus initial dose in mg/kg of body weight/day.
Independent variable | Model I | Model II | ||
---|---|---|---|---|
|
|
OR (95% CI) |
| |
Age [per year] | 0.105 ± 0,022 | <0.001 | 1.02 (1.01–1.04) | 0.003 |
BMI [per unit] | 0.417 ± 0.082 | <0.001 | 1.10 (1.05–1.16) | <0.001 |
Hemoglobin [per 1 g/dL] | 0.607 ± 0.140 | <0.001 | 1.25 (1.12–1.40) | <0.001 |
Anti-HCV positive | 4.942 ± 1.024 | <0.001 | 3.22 (1.64–6.31) | <0.001 |
Tacrolimus dose [per 1 mg/kg/day] | 16.457 ± 9.321 | 0.08 | - |
SD: standard deviation, OR: odds ratio, BMI: body mass index, and HCV: hepatitis C virus. Statistics:
The ROC analysis for BMI revealed that values above 24.6 kg/m2 increase the risk for first Tc trough blood level > 15 ng/ml with 57% sensitivity and 66% specificity. For age, the cut-off value was 55 years, with 42% sensitivity and 74% specificity (Figure
The receiver operator curve analysis for recipient’s age which increases the risk for first tacrolimus blood trough level > 15 ng/ml.
We divided the patients into subgroups, based on the number of risk factors known prior to transplantation procedure. Among them, we included recipient’s age and BMI values exceeding the cut-off values from ROC analysis, and the presence of anti-HCV antibodies. There were 158 patients without, 194 with one, 111 with two, and only 1 patient with all three risk factors. Figure
The proportions of patients with first Tc blood trough level > 15 ng/ml in relation to the presence of one or more risk factors, including age > 55 years, BMI > 24.6 kg/m2, and presence of anti-HCV antibodies.
The analysis of early graft function revealed a significant increasing trend for the occurrence of DGF in study subgroups with zero, one, or two above risk factors present (20.3 versus 30.4 versus 31.3% respectively,
Notably, the occurrence of infectious complications in the early posttransplant period was significantly higher in patients with 1 or 2 risk factors as compared with no risk factors subgroup (
Reduced doses of tacrolimus (0.16–0.19 mg/kg/day) were received by 172 patients (35.2%). It resulted in decreased frequency of first Tc levels > 15 ng/ml in patients > 55 years (48.0 versus 56.4%), subjects with BMI > 24.6 kg/m2 (52.5 versus 55.0%), and patients with both those risk factors (62.9 versus 69.4%). However, these differences were not statistically significant.
Among patients with reduced Tc dosing (<0.19 mg/kg/day), only 3.4% presented first Tc level below 6 ng/ml (potentially subtherapeutic). Of note, the percentage of patients with first Tc level < 6 ng/ml among standard Tc dose recipients was 5.7%. The subgroup of patients with first Tc level < 6 ng/ml was significantly younger [38 (32–43) versus 48 (46–49),
The primary aim of our study was an in-depth analysis of a wide spectrum of potentially relevant demographic, laboratory, and clinical factors, which may supposedly influence the first postkidney transplant Tc trough level. Except for those previously proposed, we have also analyzed other potential confounders, such as residual diuresis, dialysis vintage, retransplant, presence of HBs antigen, and an early graft function. Additionally, we have analyzed blood cell counts (hemoglobin and hematocrit), as changes in these parameters were shown to influence the whole blood Tc concentration, and liver function tests (including AST/ALT ratio) for a more accurate interpretation of the hypothetical impact of hepatitis B virus and hepatitis C virus status on tacrolimus metabolism. We have also carefully analyzed the concomitant use of all medications, which were described by drug manufacturers as potentially modifying the drug trough concentrations.
In the present study, recipient’s age, BMI, hemoglobin level, and the presence of anti-HCV antibodies were shown to be independent risk factors for the potentially toxic first Tc whole blood trough level after kidney transplantation. Aside from blood cell count parameters, which are supposed to change during the perioperative period, the three other confounders are always known at the day of transplantation. Therefore, they should be taken into consideration when calculating the initial Tc dose. The presently obtained cut-off value for age (>55 years) is in line with the recent findings of Størset et al., wherein Tc bioavailability increases with age in both genders and remains relatively constant in patients aged > 55 years [
BMI, which generally increases with age, was shown to be independently related to increased Tc first level, when its value exceeded 24.6 kg/m2. It is probably partly due to the altered body fat mass in those patients, as it was shown that Tc dose monitoring based on bioimpedance-derived body composition may provide more adequate dosage that based on BMI [
In the whole analyzed group, there was only a small number of patients (10.5%) with positive HCV serology or presence of HBs antigen, and the vast majority had normal liver function test results. Despite this, the HCV(+) subgroup presented the second highest frequency of patients with first Tc blood level > 15 ng/ml, whereas there was no association between the first Tc level and liver enzymes activity at the time of Tc measurement. Notably, in the HBs (+) subgroup we have observed a similar proportion of patients with supratherapeutic Tc level (50% versus 54.3% in the HCV subgroup); however, the difference between HBs (+) and HBs (−) patients did not reach significance, owing to the probe size. To date, Trotter et al. have noted a lower Tc dose requirement in hepatitis C-infected versus noninfected patients after liver transplantation [
It is worth noting that the presence of above defined risk factors resulted not only in the increased percentage of first supratherapeutic Tc level, but also in the increased occurrence of potentially deleterious clinical complications after kidney transplantation, that is, DGF and infections during the hospital stay.
One of the main limitations of our study regardless of its retrospective character is the method of tacrolimus level assessment, MEIA. That is considered inferior to more specific liquid chromatography with mass spectrometric detection, which is used only by several transplant centers [
Nevertheless, our present study has several strengths. Except for the solely age-dependent differences study by Jacobson et al. [
In conclusion, initial Tc dose reduction should be considered in kidney transplant recipients aged 55 years or older, who are overweight or obese, and patients with the presence of anti-HCV antibodies. There is also a greater risk of Tc overdose in patients without anemia. Our analysis precludes detailed calculation of the dose reduction needed in patients with demonstrated risk factors. Further prospective studies are warranted with intentional Tc dose reduction in risk-loaded patients.
The authors declare that there are no conflicts of interest regarding the publication of this article.