The effect of graft function on FK506 plasma levels, dosages, and renal function, with particular reference to the liver

Topical Tacrolimus and Mycophenolic Acid Therapy Synergizes with Low Dose Systemic Immunosuppression to Sustain Vascularized Composite Allograft Survival

AIM

The goal of this study was to evaluate whether topical administration of tacrolimus (TAC) and mycophenolic acid (MPA) at the transplant site enables vascularized composite allograft (VCA) survival with significant minimization of the dose and adverse effects of systemic TAC (STAC) immunosuppression.

MATERIALS AND METHODS

Lewis (Lew) rats received orthotopic hind limb allotransplants from fully mismatched Brown Norway (BN) donors. Group 1 (Controls) received no treatment. Other groups were treated with STAC at a dose of 1 mg/kg/day for 7 days. On post-operative day (POD) 8, the STAC dose was dropped to 0.1 mg/kg/day for Group 2 and maintained at 1 mg/kg for Group 3. Group 4 received topical application of TAC and MPA on the transplanted (Tx) limb starting POD 8 without STAC. Group 5 received topical TAC and MPA on the contralateral non-Tx limb and Group 6 received topical TAC and MPA on the Tx limb starting POD 8 along with low dose STAC (0.1 mg/kg/day). Treatment was continued until the study end point was reached, defined as either grade 3 rejection or allograft survival exceeding 100 days. .We conducted sequential LC-MS/MS measurements to assess TAC and MPA concentrations in both blood/plasma and allograft tissues. Additionally, we evaluated markers indicative of organ toxicity associated with STAC immunosuppression.

RESULTS

Compared to controls, topical therapy with TAC+MPA significantly prolonged allograft survival beyond 100 daysat very low dose STAC (0.1 mg/kg/day) (Group 6). The histopathological assessment of the grafts was consistent with the clinical outcomes. .Drug levels in blood/plasma remained low or undetectable, while allograft tissues showed higher drug concentrations compared to contralateral limb tissues (P<0.05). . Urinary creatinine clearance remained within the normal range at 2.5 mL/min.

CONCLUSION

Combination therapy with topical TAC and MPA synergizes with a very low dose, corticosteroid- free-STAC regimen and facilitates rejection-free, prolonged VCA survival without morbidity.

Individualized dosing algorithms for tacrolimus in kidney transplant recipients: current status and unmet needs

INTRODUCTION

Tacrolimus is a potent immunosuppressive drug with many side effects including nephrotoxicity and post-transplant diabetes mellitus. To limit its toxicity, therapeutic drug monitoring (TDM) is performed. However, tacrolimus' pharmacokinetics are highly variable within and between individuals, which complicates their clinical management. Despite TDM, many kidney transplant recipients will experience under- or overexposure to tacrolimus. Therefore, dosing algorithms have been developed to limit the time a patient is exposed to off-target concentrations.

AREAS COVERED

Tacrolimus starting dose algorithms and models for follow-up doses developed and/or tested since 2015, encompassing both adult and pediatric populations. Literature was searched in different databases, i.e. Embase, PubMed, Web of Science, Cochrane Register, and Google Scholar, from inception to February 2023.

EXPERT OPINION

Many algorithms have been developed, but few have been prospectively evaluated. These performed better than bodyweight-based starting doses, regarding the time a patient is exposed to off-target tacrolimus concentrations. No benefit in reduced tacrolimus toxicity has yet been observed. Most algorithms were developed from small datasets, contained only a few tacrolimus concentrations per person, and were not externally validated. Moreover, other matrices should be considered which might better correlate with tacrolimus toxicity than the whole-blood concentration, e.g. unbound plasma or intra-lymphocytic tacrolimus concentrations.

Variability of Tacrolimus Trough Concentration in Liver Transplant Patients: Which Role of Inflammation?

Tacrolimus presents high intra and inter-individual variability in its blood trough concentration (Cmin). Knowledge of the factors that are involved in tacrolimus Cmin variability is thus clinically important to prevent or limit it. Inflammation can affect the pharmacokinetic properties of drugs. We evaluated the contribution of acute inflammation in the pharmacokinetic variability of tacrolimus blood Cmin in a large cohort of liver transplant patients. Demographic, biological, and clinical data from 248 liver transplant patients treated with tacrolimus from January 2010 to December 2016 were retrospectively collected from medical records. In total, 1573 Cmin/dose and concomitant C-reactive protein (CRP) measurements were analysed. In multivariate analysis, the log Cmin/dose of tacrolimus was significantly and positively associated with the hematocrit, ALAT, and CRP concentrations. CRP concentrations were higher (p = 0.003) for patients with tacrolimus overexposure (i.e., tacrolimus Cmin > 15 µg/L) (median CRP (10th–90th percentiles): 27 mg/L (3–149 mg/L), n = 91) than they were for patients with a tacrolimus Cmin ≤ 15 µg/L (13 mg/mL (3–95 mg/L), n = 1482)). CRP in the fourth quartile (49 to 334 mg/L) was associated with a 2.6-fold increased risk of tacrolimus Cmin overexposure. Our study provides evidence that inflammation contributes to tacrolimus Cmin variability and suggests that inflammation should be considered for the correct interpretation of tacrolimus blood concentration.

Role of Tacrolimus C/D Ratio in the First Year After Pediatric Liver Transplantation

Background: The calcineurin inhibitor (CNI) tacrolimus (TAC) is a cornerstone agent in immunosuppressive therapy in pediatric liver transplantation (LTX). Adverse effects limit the use of CNI. In adults, calculating the individual TAC metabolism rate allows to estimate the transplant recipient's risk for therapy-associated complications. Methods: A retrospective, descriptive data analysis was performed in children who had undergone LTX in 2009-2017 and had received TAC twice daily in the first year after LTX. A weight-adjusted concentration/dose ratio (C/D ratio) was calculated [TAC trough level/(daily TAC dose/body weight)] every 3 months after LTX to estimate the average individual TAC metabolism rate. Depending on the C/D ratio, all patients were divided into two groups: fast metabolizers (FM) and slow metabolizers (SM). Clinical and laboratory parameters were analyzed as risk factors in both groups. Results: A total of 78 children (w 34, m 44, median age at LTX 2.4; 0.4-17.0 years) were enrolled in the study. FM (SM) had a mean C/D ratio of <51.83 (≥51.83) ng/ml/(mg/kg). FM were younger at the time of LTX (median age 1.7; 0.4-15.8 years) than SM (5.1, 0.4-17.0), p = 0.008. FM were more likely to have biliary atresia (20/39, 51%) compared to SM (11/39, 28%), p = 0.038, whereas SM were more likely to have progressive familial intrahepatic cholestasis (9/39, 23%) vs. in FM (1/39, 3%), p = 0.014. Epstein-Barr virus (EBV) infection occurred more frequently in FM (27/39, 69%) than SM (13/39, 33%), p = 0.002. Three FM developed post-transplant lymphoproliferative disorder. The annual change of renal function did not differ in both groups (slope FM 1.2 ± 0.6; SM 1.4 ± 0.8 ml/min/1.73 m2 per year, and p = 0.841). Conclusions: Calculation of individual, weight-adjusted TAC C/D ratio is a simple, effective, and cost-efficient tool for physicians to estimate the risk of therapy-associated complications and to initiate individual preventive adjustments after pediatric LTX. Lower TAC levels are tolerable in FM, especially in the presence of EBV infection, reduced renal function, or when receiving a liver transplant in the first 2 years of life.

A Safety and Tolerability Study of Thin Film Freeze-Dried Tacrolimus for Local Pulmonary Drug Delivery in Human Subjects

Due to the low and erratic bioavailability of oral tacrolimus (TAC), the long-term survival rate following lung transplantation remained low compared to other solid organs. TAC was reformulated and developed as inhaled formulations by thin film freezing (TFF). Previous studies reported that inhaled TAC combined with 50% w/w lactose (LAC) was safe and effective for the treatment of lung transplant rejection in rodent models. In this study, we aimed to investigate the safety and tolerability of TFF TAC-LAC in human subjects. The formulation can be delivered to the lung as colloidal dispersions after reconstitution and as a dry powder. Healthy subjects inhaled TAC-LAC colloidal dispersions at 3 mg TAC/dose via a vibrating mesh nebulizer in the first stage of this study and TAC-LAC dry powder at 3 mg TAC/dose via a single dose dry powder inhaler in the second stage. Our results demonstrated that oral inhalation of TAC-LAC colloidal dispersions and dry powder exhibited low systemic absorption. Additionally, they were well-tolerated with no changes in CBC, liver, kidney, and lung functions. Only mild adverse side effects (e.g., cough, throat irritation, distaste) were observed. In summary, pulmonary delivery of TFF TAC-LAC would be a safe and promising therapy for lung transplant recipients.

Identifying the association between tacrolimus exposure and toxicity in heart and lung transplant recipients: A systematic review

AIMS

Tacrolimus is the cornerstone of immunosuppression management in heart and lung transplant recipients, improving overall survival. However, tacrolimus-associated toxicities, including nephrotoxicity, neurotoxicity, new-onset diabetes mellitus after transplant (NODAT), and gastrointestinal toxicity, are known contributors to increased post-transplant morbidity outcomes and reduced graft and recipient survival rates. The aim of this systematic review was to identify correlations between pharmacokinetic measures of tacrolimus exposure in heart and lung recipients and tacrolimus toxicities.

METHODS

MEDLINE, Embase, the Cochrane Library, CENTRAL and WHO Clinical Trial Registries were searched for published studies evaluating tacrolimus toxicities and their correlation to pharmacokinetic monitoring parameters in thoracic transplant recipients. Studies were reviewed by two authors, with data extracted for evaluation. Risk of bias was assessed using the PEDro scale for randomised control trials and the Newcastle Ottawa Scale for non-randomised cohort studies.

RESULTS

Eighteen studies were eligible; a randomised control trial, 11 observational cohort studies, and 6 case series or studies. Of these, 9 studies were in heart transplant recipients alone and 5 in lung transplant recipients alone, 2 studies were in heart and lung transplant recipients and 2 were heart, lung, liver or renal transplant recipients. Studies used variable criteria to define toxicities. Tacrolimus trough concentration (C₀) was the marker of tacrolimus exposure most commonly used. Ten studies reported on nephrotoxicity. Elevated tacrolimus C₀ was associated with acute kidney injury occurrence and severity in three observational studies. Increasing C₀ was a predictor of renal impairment in 6 studies. One study found that for each 5 ng/mL per year of tacrolimus exposure, defined by consecutive AUC, eGFR declined by 1.3 mL/min/1.73m² (p < 0.001). Comparatively, 2 studies failed to find a significant association between nephrotoxicity and tacrolimus exposure. Seven studies reported on neurotoxicity, including neuro-encephalopathies, polyneuropathies and symptomatic change in neurological status. Neurotoxicity occurred both with tacrolimus C₀ within therapeutic range and with supratherapeutic C₀. No significant association was found between NODAT and tacrolimus C₀ in two studies. One study reported on gastrointestinal toxicity, with supratherapeutic C₀ and elevated peak concentration in one lung transplant recipient three days prior to symptom development.

CONCLUSION

No clearly defined relationship between tacrolimus exposure and toxicities is described in the literature. Studies with clear toxicity criteria and pharmacokinetic markers of tacrolimus exposure are required to provide valuable information that may optimise tacrolimus therapy, helping to reduce toxicities in heart and lung transplant recipients.

The Effect of Weight and CYP3A5 Genotype on the Population Pharmacokinetics of Tacrolimus in Stable Paediatric Renal Transplant Recipients

BACKGROUND

The aim of this study was to develop a population pharmacokinetic model of tacrolimus in paediatric patients at least 1 year after renal transplantation and simulate individualised dosage regimens.

PATIENTS AND METHODS

We included 54 children with median age of 11.1 years (range 3.8-18.4 years) with 120 pharmacokinetic profiles performed over 2 to 4 h. The pharmacokinetic analysis was performed using the non-linear mixed-effects modelling software (NONMEM(®)). The impact of covariates including concomitant medications, age, the cytochrome P450 (CYP) CYP3A5*3 gene and the adenosine triphosphate binding cassette protein B1 (ABCB1) 3435 C→T gene polymorphism on tacrolimus pharmacokinetics was analysed. The final model was externally validated on an independent dataset and dosing regimens were simulated.

RESULTS

A two-compartment model adequately described tacrolimus pharmacokinetics. Apparent oral clearance (CL/F) was associated with weight (allometric scaling) but not age. Children with lower weight and CYP3A5 expressers required higher weight-normalised tacrolimus doses. CL/F was inversely associated with haematocrit (P < 0.05) and γ-glutamyl transpeptidase (γGT) (P < 0.001) and was increased by 45 % in carriers of the CYP3A5*1 allele (P < 0.001). CL/F was not associated with concomitant medications. Dose simulations show that a daily tacrolimus dose of 0.2 mg/kg generates a pre-dose concentration (C 0) ranging from 5 to 10 µg/L depending on the weight and CYP3A5 polymorphism. The median area under the plasma concentration-time curve (AUC) corresponding with a tacrolimus C 0 of 4-8 µg/L was 97 h·µg/L (interquartile range 80-120).

CONCLUSIONS

In patients beyond the first year after transplantation, there is a cumulative effect of CYP3A5*1 polymorphism and weight on the tacrolimus C 0. Children with lower weight and carriers of the CYP3A5*1 allele have higher weight-normalised tacrolimus dose requirements.

Clostridium difficile-Associated Colitis Post-Transplant Is Not Associated with Elevation of Tacrolimus Concentrations

BACKGROUND

Diarrhea is a common condition after solid organ transplant (SOT); Clostridium difficile-associated colitis (CDAC) is one of the most common infections after SOT. We documented previously that some types of enteritis are associated with an elevation of tacrolimus (TAC) trough concentrations by interfering with the drug's complex metabolism.

PATIENTS AND METHODS

Tacrolimus concentrations of 25 SOT recipients including 12 renal and 13 liver recipients before, during, and after CDAC were analyzed retrospectively.

RESULTS

Median age of the 25 patients was 54 y (range, 36-71), there were 15 males and 10 females. Clostridium difficile-associated colitis developed at a median of 55 d (range 2-4551) post-SOT. Median TAC concentrations prior to the outbreak of CDAC were 6.9 ng/mL (range, <1.5-17.2), 5.6 ng/mL (range, <1.5-13.2) during diarrhea, and 7.4 ng/mL (range, <1.5-24.3) after resolution of diarrhea (p > 0.05, NS). Treatment of CDAC consisted of metronidazole for 14 d in all cases. All patients recovered from CDAC but seven patients had CDAC relapse.

CONCLUSIONS

In contrast to other types of infectious diarrhea such as rotavirus enteritis and cryptosporidiosis, CDAC is not associated with an increase in TAC concentrations. This is because C. difficile causes primarily colitis as opposed to other organisms, which are associated with enteritis.

New strategy of tacrolimus administration in animal model based on tacrolimus-loaded microspheres

New strategies for tacrolimus administration that conserve its immunosuppressive effect but avoiding fluctuations in tacrolimus circulating levels are needed. The aim was to analyze if subcutaneous biodegradable tacrolimus-loaded microspheres injection promoted a significant immunosuppressive response in rats. Rats received two subcutaneous tacrolimus-loaded microspheres injections at different days, the first injection was done at day 0 and the second injection was done 12 days after. Plasma circulating levels of tacrolimus, interleukin-2 (IL-2) and calcineurin phosphatase (PP2B) activity in mononuclear cells were measured. Tacrolimus plasma levels were significantly increased from the day after tacrolimus-loaded microspheres injection and remained increased during 10days. Compared to control, plasma IL-2 levels and PP2B activity in mononuclear cells were significantly decreased during ten days. At day 12, a new subcutaneous injection of tacrolimus-loaded microspheres was performed and two days after injection, tacrolimus plasma levels were again increased and both IL-2 plasma levels and PP2B activity decreased. A single subcutaneous tacrolimus-loaded microspheres injection was enough to reduce tacrolimus-related immunosuppressive parameters. These results open the possibility of new therapeutic strategies to administrate calcineurin inhibitors reducing the variability of their circulating levels related to gastrointestinal drug absorption/metabolism modifications.

Determination of the most influential sources of variability in tacrolimus trough blood concentrations in adult liver transplant recipients: a bottom-up approach

Tacrolimus, an immunosuppressant drug, presents a narrow therapeutic window and a large pharmacokinetic variability with poor correlation between drug dosing regimen and blood concentration. The objective was to identify predictive factors influencing tacrolimus trough concentrations (C0) using a bottom-up approach. A physiologically based pharmacokinetic (PBPK) model of tacrolimus was proposed, taking into account the body weight, the proportion of fat (P(fat)), hematocrit, lipid fraction of organs, typical intrinsic clearance (CLi(typ)), CYP3A5 genotype of liver donor, plasma unbound fraction of tacrolimus (fu(p)), and concomitant drugs (CYP3A4 inhibitors). For the evaluation of the PBPK model, mean C0 and concentrations 2 h after oral dose of tacrolimus were compared with those from 66 liver transplant recipients included in a multicentric pharmacokinetic study and were found very close. Tacrolimus concentration profiles were simulated in a virtual population defined by a set of covariate values similar to those from the real population. The sensitivity of tacrolimus C0 with respect to each covariate has been tested to identify the most influential ones. With the range of covariate values tested, the impact of each covariate on tacrolimus C0 may be ranked as follows: fu(p), CLi(typ), bioavailability, body weight, hematocrit, CYP3A5 polymorphism, P(fat), and CYP3A4 inhibitory drug-drug interactions. Values for initial dosing regimen of tacrolimus in order to reach a C0 of 10 ng/ml at day 5 (assuming a constant dosing schedule) as a function of CYP3A5 donor genotype and patient's hematocrit and body weight are proposed.

A retrospective analysis of the safety and efficacy of low dose tacrolimus (FK506) for living donor liver transplant recipients

We sought to evaluate the efficacy and effects of low-dose tacrolimus (FK506) to recipients with living donor liver transplantation (LDLT). A total of 66 patients who underwent LDLT between 2001 and 2007 were enrolled in this study. According to different doses of tacrolimus, the recipients were randomly divided into two groups: the low-dose tacrolimus group (group A) and the normal-dose tacrolimus group (group B). The blood concentration of tacrolimus and its side effects including infection, hyperglycemia, hypertension, high blood creatinine and jaundice were monitored once a week at the perioperative period, and once a month thereafter. Besides, the survival rates of the recipients were analyzed at the 1- and 3-year time point after operation. Among these patients, no significant acute rejection was detected after LDLT. The incidences of infection, hyperglycemia, liver dysfunction and renal impairment in group A were markedly lower than those in group B. However, no significant differences were detected in the incidence of hypertension between the two groups. Moreover, the recipients in each group had a similar survival rate according to the results of 1- and 3-year follow-up. The incidence of side effects that associated with tacrolimus positively correlated with tacrolimus blood concentration. In conclusion, long-term and low-dose administration of tacrolimus is a safe and effective treatment for LDLT recipients.

Cryptosporidium enteritis in solid organ transplant recipients: multicenter retrospective evaluation of 10 cases reveals an association with elevated tacrolimus concentrations

BACKGROUND

Cryptosporidial enteritis, a diarrheal infection of the small intestine caused by the apicomplexan protozoa Cryptosporidium, is infrequently recognized in transplant recipients from developed countries.

METHODS

A retrospective review of all cases of cryptosporidiosis in solid organ transplant (SOT) recipients at 2 centers from January 2001 to October 2010 was performed and compared with transplant recipients with community-onset Clostridium difficile infection (CDI). A literature search was performed with regard to reported cases of cryptosporidiosis in SOT recipients.

RESULTS

Eight renal, 1 liver, and 1 lung transplant recipient were diagnosed with cryptosporidiosis at median 46.0 months (interquartile range [IQR] 25.2-62.8) following SOT. Symptoms existed for a median 14 days (IQR 10.5-14.8) before diagnosis. For the 9 patients receiving tacrolimus (TAC), mean TAC levels increased from 6.3 ± 1.1 to 21.3 ± 9.2 ng/mL (P = 0.0007) and median serum creatinine increased temporarily from 1.3 (IQR 1.1-1.7) to 2.4 (IQR 2.0-4.6) mg/dL (P = 0.008). By comparison, 8 SOT recipients (6 kidney, 2 liver) hospitalized with community-onset CDI had a mean TAC level of 10.8 ± 2.8 ng/dL during disease compared with 9.2 ± 2.3 ng/mL at baseline (P = 0.07) and had no change in median creatinine. All patients recovered from Cryptosporidium enteritis after receiving various chemotherapeutic regimens.

CONCLUSIONS

Cryptosporidiosis should be recognized as an important cause of diarrhea after SOT and is associated with elevated TAC levels and acute kidney injury. Increased TAC levels may reflect altered drug metabolism in the small intestine.

Evaluation of limited sampling methods for estimation of tacrolimus exposure in adult kidney transplant recipients

AIMS

To examine the predictive performance of limited sampling methods for estimation of tacrolimus exposure in adult kidney transplant recipients.

METHODS

Twenty full tacrolimus area under the concentration-time curve from 0 to 12 h post-dose (AUC(0-12)) profiles (AUCf) were collected from 20 subjects. Predicted tacrolimus AUC(0-12) (AUCp) was calculated using the following: (i) 42 multiple regression-derived limited sampling strategies (LSSs); (ii) five population pharmacokinetic (PK) models in the Bayesian forecasting program TCIWorks; and (iii) a Web-based consultancy service. Correlations (r(2)) between C(0) and AUCf and between AUCp and AUCf were examined. Median percentage prediction error (MPPE) and median absolute percentage prediction error (MAPE) were calculated.

RESULTS

Correlation between C(0) and AUCf was 0.53. Using the 42 LSS equations, correlation between AUCp and AUCf ranged from 0.54 to 0.99. The MPPE and MAPE were <15% for 29 of 42 equations (62%), including five of eight equations based on sampling taken ≤2 h post-dose. Using the PK models in TCIWorks, AUCp derived from only C(0) values showed poor correlation with AUCf (r(2)=0.27-0.54) and unacceptable imprecision (MAPE 17.5-31.6%). In most cases, correlation, bias and imprecision estimates progressively improved with inclusion of a greater number of concentration time points. When concentration measurements at 0, 1, 2 and 4 h post-dose were applied, correlation between AUCp and AUCf ranged from 0.75 to 0.93, and MPPE and MAPE were <15% for all models examined. Using the Web-based consultancy service, correlation between AUCp and AUCf was 0.74, and MPPE and MAPE were 6.6 and 9.6%, respectively.

CONCLUSIONS

Limited sampling methods better predict tacrolimus exposure compared with C(0) measurement. Several LSSs based on sampling taken 2 h or less post-dose predicted exposure with acceptable bias and imprecision. Generally, Bayesian forecasting methods required inclusion of a concentration measurement from >2 h post-dose to adequately predict exposure.

An improved validated ultra high pressure liquid chromatography method for separation of tacrolimus impurities and its tautomers

A selective, specific and sensitive ultra high pressure liquid chromatography (UHPLC) method was developed for determination of tacrolimus degradation products and tautomers in the preparation of pharmaceuticals. The chromatographic separation was performed on Waters ACQUITY UPLC system and BEH C₈ column using gradient elution of mobile phase A (90:10 v/v of 0.1% v/v triflouroacetic acid solution and Acetonitrile) and mobile phase B (90:10 v/v acetonitrile and water) at a flow rate of 0.6 mL min⁻¹. Ultraviolet detection was performed at 210 nm. Tacrolimus, tautomers and impurities were chromatographed with a total run time of 25 min. Calibration showed that the response of impurity was a linear function of concentration over the range 0.3-6 µg mL⁻¹ (r² ≥ 0.999) and the method was validated over this range for precision, intermediate precision, accuracy, linearity and specificity. For precision study, percentage relative standard deviation of each impurity was < 15% (n = 6). The method was found to be precise, accurate, linear and specific. The proposed method was successfully employed for estimation of tacrolimus impurities in pharmaceutical preparations.

Initial liver graft function is a reliable predictor of tacrolimus trough levels during the first post-transplant week

The narrow therapeutic range of tacrolimus requires careful management after liver transplantation (LT). The aim of this study was to investigate the influence of graft function on tacrolimus trough levels during the first post-transplant week. Ninety-three patients receiving deceased-donor LT were observed in a prospective observational study. Graft function was determined by the new LiMAx test (maximal liver function capacity). Significant correlations between LiMAx readouts and consecutive tacrolimus levels, up to r = -0.529 (p < 0.0001), were determined throughout the observed period of time. Patients with initially poor graft function revealed higher trough levels (n = 24; 20.1 ± 11.6ng/mL) in comparison with fair (n = 40; 13.7 ± 7.8 ng/mL) and good function (n = 29; 9.5 ± 4.4ng/mL; p < 0.0001) already at the second post-transplant day. Toxic levels could be predicted with an area under receiver operating characteristic analysis AUROC=0.751 (p = 0.001) with high sensitivity and specificity. Insufficient levels could be predicted with AUROC=0.800 (p = 0.003). In conclusion, initial graft function is a major factor influencing the pharmacokinetics of tacrolimus and can be validly determined by the LiMAx test. Thus, recipients with poor functioning grafts are prone of developing toxic levels within the first week after LT, whereas patients with good functioning grafts frequently develop insufficient levels with the current immunosuppressive protocols.

Acute renal failure after liver transplantation in MELD era

Model for End-Stage Liver Disease (MELD) score was used in our center from 2003 to assess the position of orthotopic liver transplantation (OLT) candidates on a waiting list. A key component of MELD score in the assessment of the degree of the illness is renal function. In this study, we measured the effects of this new scoring system on renal function and therapeutic strategies. We evaluated the incidence of acute renal function (ARF) after OLT requiring renal replacement therapy (hemofiltration or hemodialysis) in two patient groups: 240 transplanted before MELD era and 224 after the introduction of this parameter to select candidates. ARF occurred in 8.3% of patients in the pre-MELD group versus 13% in the MELD group, while the mortality rates were 40% and 27%, respectively. The creatinine level before OLT seemed to be a good predictor of ARF (P < .001), and blood transfusion rates (P < .05) as well as intraoperative diuresis (P < .05). In our analysis we did not observe a correlation between MELD score and postoperative ARF.

Liver transplantation in children

Liver transplantation (LT) is now a standard treatment for children with end-stage liver disease with excellent 1- and 5-year survival. This has been achieved through improvement of surgical techniques and anti-rejection treatment and management. The donor pool for children has been extended by the use of cut-down, split, living-related and, recently, non-heart-beating donor and isolated hepatocyte transplantation. Though the majority of transplanted children enjoy an excellent quality of life, there remain a high number of possible complications, including short-term primary non-function, vascular and biliary problems, bowel perforation, severe rejection, infection, hypertension and long-term renal impairment, chronic rejection, de novo autoimmunity, lymphoproliferative disease and cancer, most of which are related to anti-rejection drug toxicity. Hence, the focus of research for paediatric LT should be induction of tolerance, avoiding long-term immunosuppression and its toxicity.

Factors affecting the apparent clearance of tacrolimus in Korean adult liver transplant recipients

STUDY OBJECTIVE

To identify the factors affecting tacrolimus apparent total body clearance (Cl/F [F = bioavailability]) in adult liver transplant recipients.

DESIGN

Population pharmacokinetic analysis using data from a retrospective chart review.

SETTING

University-affiliated hospital in Seoul, South Korea.

PATIENTS

Fifty-one adult liver transplant recipients who had received tacrolimus after transplantation.

MEASUREMENTS AND MAIN RESULTS

Data on 35 adult liver transplant recipients for model building and 16 patients for model validation were obtained retrospectively. Population average parameter estimates of Cl/F and apparent volume of distribution (V/F) were sought by using the nonlinear mixed-effect model (NONMEM) program. A number of clinical covariates were screened for their influence on these pharmacokinetic parameters. The final optimal population model related Cl/F to total bilirubin, early (< or = 3 days) and late (> 35 days) postoperative days, international normalized ratio (INR), and graft:recipient weight ratio (GRWR). The NONMEM estimates indicated that the Cl/F of tacrolimus was decreased in patients with a small graft, hyperbilirubinemia, and a high INR. In addition, the Cl/F of tacrolimus almost doubled 4 days after transplantation, but decreased with an increase in duration of therapy after day 35. Mean prediction error and mean absolute prediction error were 0.26 and 3.78 ng/ml, respectively, for the validation sample. A final analysis in all 51 patients, which consisted of 1775 blood samples for concentration measurements, identified the following regression model: Cl/F (L/hr) = (0.36 + 2.01/POD * L) * TBIL(-0.23 (TBIL = 1 if TBIL level < or = 1.2 mg/dl, otherwise TBIL = TBIL level)) *49((if POD < or = 3 days)) * 0.75((if INR > 1.4)) * 0.86((if GRWR < or = 1.25%)) * WT, where L was 1 if postoperative day (POD) was greater than 35 days, otherwise L was 0; V/F was 568 L, TBIL was total bilirubin, and WT was body weight. The interindividual variabilities (coefficients of variation) in Cl/F and V/F were 35.35% and 68.12%, respectively. The residual variability was 3.14 ng/ml.

CONCLUSION

These findings could be useful to the health care provider for adjustment of tacrolimus dosage in adult liver transplant recipients with various clinical factors.

Treatment of acute tacrolimus whole-blood elevation with phenobarbital in the pediatric liver transplant recipient

The toxicities associated with the chronic use of tacrolimus are well described in the literature; however, little is known about the management during an acute overdose. Phenobarbital is a long-acting barbiturate metabolized in the liver by the cytochrome p450 3a4 system. It is known to enhance the rate of metabolism of itself and the clearance of drugs metabolized by p450 3a4. Because tacrolimus is a substrate of this particular isoenzyme, phenobarbital can be considered a potential option when rapid decreases in tacrolimus whole-blood levels are desired. We hereby report our experience using intravenous phenobarbital in the management of two infants with acute elevations in their tacrolimus whole-blood concentration following liver transplantation. Phenobarbital, through its up-regulation of hepatic cytochrome p450 system increases the elimination of whole-blood tacrolimus concentration in acute overdose situations.

Altered metabolism of tacrolimus in hepatic veno-occlusive disease

Tacrolimus is widely used for the prophylaxis and treatment of graft-versus-host disease after allogeneic hematopoietic stem cell transplantation (HSCT) and graft rejection in solid organ transplantation. The metabolism of tacrolimus has been reported to be impaired in association with liver dysfunction, mostly as documented in liver transplant recipients. Hepatic veno-occlusive disease (VOD) is one of the serious complications after allogeneic HSCT. It is characterized by jaundice, fluid retention, and painful hepatomegaly, caused by endothelial cell injury resulting from the toxicity of the conditioning regimen. The impaired metabolism of tacrolimus in hepatic VOD has not previously been reported in the literature. Here, we report the notable alteration in the metabolism of tacrolimus in two patients with hepatic VOD, in whom the half-lives of tacrolimus were markedly prolonged (288 and 146 h).

Renal function outcome in pediatric liver transplant recipients

The orthotopic liver transplantation (OLT) allows survival of children followed for severe hepatic injury, provided that the immunosuppressive treatment is prolonged. The nephrotoxicity of cyclosporine predicts the long-term outcome of the adult patients receiving a liver transplant. The aim of this study was to determine the long-term outcome of renal function in children receiving OLT. This study included 12 children, with a median for age of 7.1 yr (2-15 yr) at the time of OLT. The duration of follow-up was at least 4 yr, being 7 yr in 10 patients and more than 10 yr in seven. Renal function was evaluated with the serum level of creatinine, calculated glomerular filtration rate (cGFR), and measurement of glomerular filtration rate using chrome 51 ethylenediaminetetraacetate ((51)Cr EDTA) clearance performed at least once during follow-up. The doses and the serum concentrations (C(0)) of cyclosporine were reported at each study time. The cGFR decreased significantly 2 yr after the OLT [median (range): 106 mL/min/1.73 m(2) (71-150) at the time of OLT vs. 85 mL/min/1.73 m(2) (57-128) 2 yr after the OLT, p = 0.03], and decreased again between 7 and 10 yr after OLT [median (range): 99 mL/min/1.73 m(2) (76-125) 7 yr after OLT vs. 81 mL/min/1.73 m(2) (66-140) 10 yr after OLT, p = 0.04]. Six patients developed chronic renal failure (cGFR from 57 to 80 mL/min/1.73 m(2)) 2 yr after OLT associated with high doses of cyclosporine [median (range): 8.8 mg/kg/day (3.5-13)]. The cGFR overestimated renal function by 16% compared with the isotopic measurement of GFR (p = 0.03). Using the (51)Cr EDTA measurement, six of seven patients followed up more than 10 yr after OLT presented mild (n = 3) or moderate (n = 3) chronic renal failure. In our study, the majority of OLT recipients developed a chronic renal failure 10 yr after transplantation. Cyclosporine seems to be the most important factor responsible for the impairment of renal function. The use of the mycophenolate mofetil, a new immunosuppressive agent, allowing a reduction in the dose of cyclosporine, could minimize renal dysfunction. While awaiting the results of a prospective long-term study, close drug monitoring is advised.

Systemic toxicity of tacrolimus given by various routes and the response to dose reduction

PURPOSE

To evaluate the long-term systemic toxicity of tacrolimus (FK-506) administered by various routes, and to assess the effect of dose reduction on toxicity.

METHODS

The study animals were 120 experimentally naive adult female Wistar rats weighing 200-250 g each. The rats were randomly divided into 10 equal groups (n=12 in each) and treated with tacrolimus administered topically (in drops, 0.3%, q.i.d.), intravitreally (0.5 mg/kg bodyweight/week), intramuscularly (1 mg/kg bodyweight/week), low-dose intravenously (1 mg/kg bodyweight/week) and in high-dose intravenously (2 mg/kg bodyweight/week) for 3 months. The rats in the control groups (one for each different route of administration) were treated with 0.9% NaCl. The blood concentration of tacrolimus, complete blood count and biochemistry parameters were measured each month for the 3-month study period.

RESULTS

The rats in the control groups and experimental groups administered topical and intravitreal tacrolimus did not demonstrate any systemic toxic effects. The rats that developed certain toxic effects (hyperglycaemia, hyperkalaemia and nephrotoxicity) in the groups given low-dose or high-dose i.v. tacrolimus responded well to dose reduction. Following dose reduction, blood glucose concentrations decreased from 247.4 +/- 42.3 mg/dL to 189.6 +/- 37.9 mg/dL (P <0.05), and from 237.4 +/- 41.1 mg/dL to 182.3 +/- 22.7 mg/dL (P <0.05) in the low- and high-dose i.v. tacrolimus-treated rats, respectively. The rats that developed impaired hepatic function after high-dose tacrolimus did not respond to dose reduction. Baseline cholesterol concentrations for the intramuscular and low- and high-dose i.v. tacrolimus-treated groups, demonstrated decreases, respectively, from 87.4 +/- 14.0 mg/dL, 86.4 +/- 14.0 mg/dL and 90.4 +/- 14.3 mg/dL to 53.6 +/- 9.8 mg/dL, 52.1 +/- 12.5 mg/dL and 63.5 +/- 11.7 mg/dL by the end of the second month. The differences were found to be statistically significant (P <0.05 for each result).

CONCLUSION

Topical or intravitreal administration of tacrolimus seems to be systemically safe whereas parenteral administration can cause some systemic haematological changes such as dose-dependent decreased serum cholesterol concentrations. Dose reduction may prevent such adverse effects.

Changes in tacrolimus distribution in blood and plasma protein binding following liver transplantation

Therapeutic drug monitoring of tacrolimus is complicated by the conflicting evidence of a relationship between trough blood tacrolimus concentration and clinical outcome. This prospective study investigated the blood distribution and protein binding of tacrolimus in liver transplant recipients over the first 60 days after transplantation with a view to identifying possible predictors of clinical outcome. Blood samples were collected from 10 liver transplant recipients on days 1, 7, and 60 after the initiation of tacrolimus therapy, and the distribution of tacrolimus in blood and the plasma protein binding were investigated. The unbound concentration of tacrolimus in plasma was estimated. Graft status was assessed using liver function tests and liver biopsies. The association of tacrolimus with erythrocytes varied significantly (74.4 +/- 5.0% vs 80.4 +/- 3.4%; P = 0.034) from day 1 to day 60. In plasma, tacrolimus mainly associated with lipoprotein-deficient plasma (60.1 +/- 6.5%), followed by high-density lipoproteins (27.2 +/- 6.6%), low-density lipoproteins (10.0 +/- 4.2%), and very low-density lipoproteins (2.8 +/- 1.8%). The percentage of tacrolimus associated with leukocytes (1.10 +/- 0.40% vs 0.40 +/- 0.09%; P = 0.0003) and the unbound concentration of tacrolimus (0.70 +/- 0.19 vs 0.28 +/- 0.04 ng/L; P < 0.0001) were observed to be significantly lower during episodes of rejection. In patients experiencing tacrolimus-related side effects, only the unbound concentration of tacrolimus was found to be significantly higher (0.84 +/- 0.19 vs 0.53 +/- 0.19 ng/L; P < 0.0001), and blood concentrations were not different (9.2 +/- 2.2 vs 8.1 +/- 1.8 ng/mL; P = 0.1). Blood distribution and protein binding of tacrolimus vary significantly over the posttransplantation period, leading to changes in its unbound concentration. A prospective study in a larger cohort of patients is required to establish the role of blood distribution and protein binding of tacrolimus in its therapeutic drug monitoring.

Pharmacokinetic Considerations Relating to Tacrolimus Dosing in the Elderly

Relaxation of the upper age limits for solid organ transplantation coupled with improvements in post-transplant survival have resulted in greater numbers of elderly patients receiving immunosuppressant drugs such as tacrolimus. Tacrolimus is a potent agent with a narrow therapeutic window and large inter- and intraindividual pharmacokinetic variability. Numerous physiological changes occur with aging that could potentially affect the pharmacokinetics of tacrolimus and, hence, patient dosage requirements. Tacrolimus is primarily metabolised by cytochrome P450 (CYP) 3A enzymes in the gut wall and liver. It is also a substrate for P-glycoprotein, which counter-transports diffused tacrolimus out of intestinal cells and back into the gut lumen. Age-associated alterations in CYP 3A and P-glycoprotein expression and/or activity, along with liver mass and body composition changes, would be expected to affect the pharmacokinetics of tacrolimus in the elderly. However, interindividual variation in these processes may mask any changes caused by aging. More investigation is needed into the impact aging has on CYP and P-glycoprotein activity and expression. No single-dose, intense blood-sampling study has specifically compared the pharmacokinetics of tacrolimus across different patient age groups. However, five population pharmacokinetic studies, one in kidney, one in bone marrow and three in liver transplant recipients, have investigated age as a co-variate. None found a significant influence for age on tacrolimus bioavailability, volume of distribution or clearance. The number of elderly patients included in each study, however, was not documented and may have been only small. It is likely that inter- and intraindividual pharmacokinetic variability associated with tacrolimus increase in elderly populations. In addition to pharmacokinetic differences, donor organ viability, multiple co-morbidity, polypharmacy and immunological changes need to be considered when using tacrolimus in the elderly. Aging is associated with decreased immunoresponsiveness, a slower body repair process and increased drug adverse effects. Elderly liver and kidney transplant recipients are more likely to develop new-onset diabetes mellitus than younger patients. Elderly transplant recipients exhibit higher mortality from infectious and cardiovascular causes than younger patients but may be less likely to develop acute rejection. Elderly kidney recipients have a higher potential for chronic allograft nephropathy, and a single rejection episode can be more devastating. There is a paucity of information on optimal tacrolimus dosage and target trough concentration in the elderly. The therapeutic window for tacrolimus concentrations may be narrower. Further integrated pharmacokinetic-pharmacodynamic studies of tacrolimus are required. It would appear reasonable, based on current knowledge, to commence tacrolimus at similar doses as those used in younger patients. Maintenance dose requirements over the longer term may be lower in the elderly, but the increased variability in kinetics and the variety of factors that impact on dosage suggest that patient care needs to be based around more frequent monitoring in this age group.

Clinical pharmacokinetics and pharmacodynamics of tacrolimus in solid organ transplantation

The aim of this review is to analyse critically the recent literature on the clinical pharmacokinetics and pharmacodynamics of tacrolimus in solid organ transplant recipients. Dosage and target concentration recommendations for tacrolimus vary from centre to centre, and large pharmacokinetic variability makes it difficult to predict what concentration will be achieved with a particular dose or dosage change. Therapeutic ranges have not been based on statistical approaches. The majority of pharmacokinetic studies have involved intense blood sampling in small homogeneous groups in the immediate post-transplant period. Most have used nonspecific immunoassays and provide little information on pharmacokinetic variability. Demographic investigations seeking correlations between pharmacokinetic parameters and patient factors have generally looked at one covariate at a time and have involved small patient numbers. Factors reported to influence the pharmacokinetics of tacrolimus include the patient group studied, hepatic dysfunction, hepatitis C status, time after transplantation, patient age, donor liver characteristics, recipient race, haematocrit and albumin concentrations, diurnal rhythm, food administration, corticosteroid dosage, diarrhoea and cytochrome P450 (CYP) isoenzyme and P-glycoprotein expression. Population analyses are adding to our understanding of the pharmacokinetics of tacrolimus, but such investigations are still in their infancy. A significant proportion of model variability remains unexplained. Population modelling and Bayesian forecasting may be improved if CYP isoenzymes and/or P-glycoprotein expression could be considered as covariates. Reports have been conflicting as to whether low tacrolimus trough concentrations are related to rejection. Several studies have demonstrated a correlation between high trough concentrations and toxicity, particularly nephrotoxicity. The best predictor of pharmacological effect may be drug concentrations in the transplanted organ itself. Researchers have started to question current reliance on trough measurement during therapeutic drug monitoring, with instances of toxicity and rejection occurring when trough concentrations are within 'acceptable' ranges. The correlation between blood concentration and drug exposure can be improved by use of non-trough timepoints. However, controversy exists as to whether this will provide any great benefit, given the added complexity in monitoring. Investigators are now attempting to quantify the pharmacological effects of tacrolimus on immune cells through assays that measure in vivo calcineurin inhibition and markers of immunosuppression such as cytokine concentration. To date, no studies have correlated pharmacodynamic marker assay results with immunosuppressive efficacy, as determined by allograft outcome, or investigated the relationship between calcineurin inhibition and drug adverse effects. Little is known about the magnitude of the pharmacodynamic variability of tacrolimus.

Factors affecting variability in distribution of tacrolimus in liver transplant recipients

AIMS

Therapeutic drug monitoring (TDM) of tacrolimus is complicated by conflicting data on the correlation between tacrolimus trough blood concentrations and the incidence of rejection. The aim of this cross-sectional study was to investigate the blood distribution and protein binding of tacrolimus in liver transplant recipients to explore better predictors of clinical outcome.

METHODS

Blood and plasma distribution of 3H-dihydro-tacrolimus was investigated in 40 liver transplant recipients using Ficoll Paque and density gradient ultracentrifugation, respectively, and equilibrium dialysis to investigate plasma protein binding.

RESULTS

In blood tacrolimus was mainly associated with the erythrocyte fraction (83.2%, range 74.6-94.9%), followed by diluted plasma (16.1%, range 4.5-24.9%), and lymphocyte fraction (0.61%, range: 0.11-1.53%). In plasma, lipoprotein deficient serum fraction (54.2%, range 38.5-68.2%) was the main reservoir of tacrolimus. The unbound fraction of tacrolimus was found to be 0.47 +/- 0.18% (range 0.07-0.89%). The percentage of tacrolimus associated with the lymphocytes (0.8 +/- 0.4 vs 0.3 +/- 0.1%, P = 0.012) and estimated unbound concentration (0.42 +/- 0.21 ng l-1vs 0.24 +/- 0.08 ng l-1, P < 0.001) of tacrolimus were significantly different in stable transplant recipients and those experiencing rejection. Haematocrit and red blood cell count significantly influenced the percentage of tacrolimus associated with erythrocytes. The fraction unbound of tacrolimus was correlated with alpha1-acid glycoprotein and high density lipoprotein cholesterol concentrations.

CONCLUSIONS

Tacrolimus unbound concentration was observed to be lower in liver transplant recipients experiencing rejection and further study is required to evaluate its utility in the TDM of tacrolimus.

Effect of coadministered lopinavir and ritonavir (Kaletra) on tacrolimus blood concentration in liver transplantation patients

With the advent of highly active antiretroviral therapy (HAART), HIV positivity is no longer a contraindication for liver transplantation. Some of the antiretroviral agents, particularly protease inhibitors (e.g., ritonavir, indinavir, and nelfinavir) have been described as potent inhibitors of the metabolism of certain immunosuppressive drugs. In this article we describe a profound interaction between tacrolimus and Kaletra (Abbott Laboratories, Chicago, IL) (a combination of lopinavir and ritonavir) in 3 liver transplantation patients. Patient 1, who was maintained on a 5 mg twice daily dose of tacrolimus with a trough blood concentration around 10.6 ng/mL, required only 0.5 mg of tacrolimus per week after addition of Kaletra to achieve similar tacrolimus blood concentrations, with a half-life of 10.6 days. In patient 2, the area under the blood concentration versus time curve for tacrolimus increased from 31 ng/mL/h to 301 ng/mL/h after addition of Kaletra, with a corresponding half-life of 20 days. When the patient was subsequently switched to nelfinavir, the half-life decreased to 10.3 days. Patient 3, who was maintained with 4 to 8 mg/d of tacrolimus and a corresponding blood concentration of 10 ng/mL before Kaletra, required a tacrolimus dose of 1 mg/wk and tacrolimus concentrations of 5 ng/mL with Kaletra. In conclusion, a combination of lopinavir and ritonavir led to a much more profound increase in tacrolimus blood concentrations than use of single protease inhibitor, nelfinavir. A tacrolimus dose of less than 1 mg/wk may be sufficient to maintain adequate blood tacrolimus concentrations in patients on Kaletra. Patients may not need a further dose of tacrolimus for 3 to 5 weeks depending on liver function when therapy with Kaletra is initiated. Great caution is required in the management of tacrolimus dosage when Kaletra is introduced or withdrawn in HIV-positive patients after liver transplantation, particularly in the presence of hepatic dysfunction.

Bayesian forecasting and prediction of tacrolimus concentrations in pediatric liver and adult renal transplant recipients

AIM

To test the predictive capacity of two recently derived population pharmacokinetic models and the usefulness of Bayesian forecasting to predict tacrolimus blood concentrations in pediatric liver and adult kidney transplant recipients.

MATERIALS AND METHODS

New databases were added to the Abbottbase PKS (Bayesian dosage prediction) program to incorporate the population pharmacokinetic models developed for tacrolimus. Two independent populations of transplant recipients were used to predict tacrolimus trough concentrations. Pharmacokinetic, demographic, and covariate data were collected from patient records. Different time weighting factors were tested (1, 1.005, 1.01) and the influence of excluding data collected in the first 5 days post-transplant examined. Concentrations were predicted until the 10th tacrolimus measurement. Actual tacrolimus concentrations were compared with those predicted by the PKS program and bias and precision determined.

RESULTS

Tacrolimus concentrations predicted by the PKS program were, on average, unbiased for the pediatric liver population, but were over-predicted (9%) for the adult renal population. In both populations predictions were not precise (imprecision ranged from 39 to 50%).

CONCLUSIONS

Due to the imprecision seen in this study, these models could not be used in clinical practice in the immediate post-transplant period. Poor precision may be due to reliance on routine drug monitoring data alone, difficulties with expression of covariates in continuous modeling relationships in the PKS program, lack of accurate quantitative measures of liver function, or large, random intraindividual variability in the bioavailability of tacrolimus.

Toward better outcomes with tacrolimus therapy: population pharmacokinetics and individualized dosage prediction in adult liver transplantation

Patient outcomes in transplantation would improve if dosing of immunosuppressive agents was individualized. The aim of this study is to develop a population pharmacokinetic model of tacrolimus in adult liver transplant recipients and test this model in individualizing therapy. Population analysis was performed on data from 68 patients. Estimates were sought for apparent clearance (CL/F) and apparent volume of distribution (V/F) using the nonlinear mixed effects model program (NONMEM). Factors screened for influence on these parameters were weight, age, sex, transplant type, biliary reconstructive procedure, postoperative day, days of therapy, liver function test results, creatinine clearance, hematocrit, corticosteroid dose, and interacting drugs. The predictive performance of the developed model was evaluated through Bayesian forecasting in an independent cohort of 36 patients. No linear correlation existed between tacrolimus dosage and trough concentration (r(2) = 0.005). Mean individual Bayesian estimates for CL/F and V/F were 26.5 +/- 8.2 (SD) L/hr and 399 +/- 185 L, respectively. CL/F was greater in patients with normal liver function. V/F increased with patient weight. CL/F decreased with increasing hematocrit. Based on the derived model, a 70-kg patient with an aspartate aminotransferase (AST) level less than 70 U/L would require a tacrolimus dose of 4.7 mg twice daily to achieve a steady-state trough concentration of 10 ng/mL. A 50-kg patient with an AST level greater than 70 U/L would require a dose of 2.6 mg. Marked interindividual variability (43% to 93%) and residual random error (3.3 ng/mL) were observed. Predictions made using the final model were reasonably nonbiased (0.56 ng/mL), but imprecise (4.8 ng/mL). Pharmacokinetic information obtained will assist in tacrolimus dosing; however, further investigation into reasons for the pharmacokinetic variability of tacrolimus is required.

Mechanisms of clinically relevant drug interactions associated with tacrolimus

The clinical management of tacrolimus, a macrolide used as immunosuppressant after transplantation, is complicated by its narrow therapeutic index in combination with inter- and intraindividually variable pharmacokinetics. As a substrate of cytochrome P450 (CYP) 3A enzymes and P-glycoprotein, tacrolimus interacts with several other drugs used in transplantation medicine, which also are known CYP3A and/or P-glycoprotein inhibitors and/or inducers. In clinical studies, CYP3A/P-glycoprotein inhibitors and inducers primarily affect oral bioavailability of tacrolimus rather than its clearance, indicating a key role of intestinal P-glycoprotein and CYP3A. There is an almost complete overlap between the reported clinical drug interactions of tacrolimus and those of cyclosporin. However, in comparison with cyclosporin, only few controlled drug interaction studies have been carried out, but tacrolimus drug interactions have been extensively studied in vitro. These results are inconsistent and are of poor predictive value for clinical drug interactions because of false negative results. P-glycoprotein regulates distribution of tacrolimus through the blood-brain barrier into the brain as well as distribution into lymphocytes. Interaction of other drugs with P-glycoprotein may change tacrolimus tissue distribution and modify its toxicity and immunosuppressive activity. There is evidence that ethnic and gender differences exist for tacrolimus drug interactions. Therapeutic drug monitoring to guide dosage adjustments of tacrolimus is an efficient tool to manage drug interactions. In the near future, progress can be expected from studies evaluating potential pharmacokinetic interactions caused by herbal preparations and food components, the exact biochemical mechanism underlying tacrolimus toxicity, and the potential of inhibition of CYP3A and P-glycoprotein to improve oral bioavailability and to decrease intraindividual variability of tacrolimus pharmacokinetics.

A late episode of post-transplant diabetes mellitus during active hepatitis C infection in a renal allograft recipient using tacrolimus

BACKGROUND

An association between hepatitis C virus and (post-transplant) diabetes mellitus has been reported.

METHODS

We report a patient on tacrolimus-based immunosuppression who developed an episode of post-transplant diabetes mellitus (PTDM) 2 years after renal transplantation, after contracting a hepatitis C infection. Her glucose metabolism was evaluated regularly by intravenous glucose tolerance tests before and after the PTDM episode.

RESULTS

Before contracting hepatitis C, the patient's insulin resistance and insulin secretion were normal. After contracting hepatitis C, tacrolimus exposure increased, insulin resistance increased, and insulin secretion decreased markedly. Despite low tacrolimus exposure in the last 4 years, glucose metabolism did not recover completely. Although PTDM resolved and insulin resistance normalized, pancreatic beta cell secretion remained impaired by approximately 50% compared with the period before hepatitis C infection.

CONCLUSION

After an initial increase in insulin resistance, insulin secretion decreased markedly in a patient who contracted hepatitis C 12 to 22 months after renal transplantation. This change resulted in an episode of PTDM. Increased tacrolimus exposure secondary to reduced cytochrome P-450 metabolism as a result of impaired hepatocellular function at the time of the development of PTDM seems a likely explanation for the marked decrease in insulin secretion. Viral toxicity to the beta cell might be an additional explanation. The latter might be suspected from several reports about an association between diabetes mellitus and hepatitis C in patients who do not use drugs that interfere with glucose metabolism.

Correlation between optimal tacrolimus doses and the graft weight in living donor liver transplantation

The optimal doses of tacrolimus (FK) needed to reach and maintain a target blood level vary among cases of living donor liver transplantation (LDLT). One hundred and twenty four LDLTs in 122 patients were included in this study. Tacrolimus was administered by continuous intravenous infusion at a rate of 2.5 microg/kg/h just after the operation. The time needed to reach the target blood level and the dose needed to maintain this level for 1 week (17-18 ng/mL) were defined as the initial duration (ID) and secondary dose (SD), respectively. In the first 100 LDLTs, the correlations between ID or SD and some clinical factors were examined and equations for predicting ID or SD were derived. In the latest 24 LDLTs, FK was administered using these equations and the actual and calculated ID and SD values were compared. A multiple regression analysis revealed that only the graft weight/recipient standard liver volume (GW/SLV) ratio (%) correlated with ID or SD. Stepwise regression analysis led to the equations ID (h) = 0.4 x GW/SLV ratio + 0.2; SD (microg/kg/h) = 0.02 x GW/SLV ratio - 0.4. Simple regression analysis revealed a significant correlation between the actual and calculated ID and SD values (p < 0.0001). Initial duration and SD can be estimated from equations using the GW/SLV ratio.

Population pharmacokinetics of tacrolimus in children who receive cut-down or full liver transplants

BACKGROUND

The aim of this study was to investigate the population pharmacokinetics of tacrolimus in pediatric liver transplant recipients and to identify factors that may explain pharmacokinetic variability.

METHODS

Data were collected retrospectively from 35 children who received oral immunosuppressant therapy with tacrolimus. Maximum likelihood estimates were sought for the typical values of apparent clearance (CL/F) and apparent volume of distribution (V/F) with the program NONMEM. Factors screened for influence on the pharmacokinetic parameters were weight, age, gender, postoperative day, days since commencing tacrolimus therapy, transplant type (whole child liver or cut-down adult liver), liver function tests (bilirubin, alkaline phosphatase [ALP], aspartate aminotransferase [AST], gamma-glutamyl transferase [GGT], alanine aminotransferase [ALT]), creatinine clearance, hematocrit, corticosteroid dose, and concurrent therapy with metabolic inducers and inhibitors of tacrolimus.

RESULTS

No clear correlation existed between tacrolimus dosage and blood concentrations (r2=0.003). Transplant type, age, and liver function test values were the most important factors (P<0.01) that influenced the pharmacokinetics of tacrolimus. CL/F estimates were greater in whole liver recipients, decreased with increasing patient age and AST values, and increased with increasing GGT values. Average parameter estimates were CL/F=5.75 L/h (cut-down liver), CL/F=44 L/h (whole liver), and V/F=617 L. Marked intersubject variability (CV%=110% to 297%) and residual variability (CV%=42%) was observed.

CONCLUSIONS

Pharmacokinetic information obtained in this study may assist physicians in making individualized dosage decisions in regard to tacrolimus in pediatric liver transplant recipients. Children who received a whole child's liver appeared to retain "pediatric" clearance, whereas those who received a cut-down adult liver had "adult" clearances (on average 7-fold less).

Clinical utility of monitoring tacrolimus blood concentrations in liver transplant patients

The relationship between the dose of tacrolimus, trough tacrolimus blood concentration, and selected clinical endpoints (acute rejection, nephrotoxicity, and other toxicities) were examined in a prospective, multicenter clinical trial to validate the use of an enzyme-linked immunosorbent assay (ELISA) for monitoring whole-blood concentrations of tacrolimus in liver transplant patients. A total of 111 subjects from six transplant centers were evaluated over 12 weeks posttransplantation. In addition to trough tacrolimus blood concentrations, hematocrit, ALT, AST, GGTP, alkaline phosphatase, total bilirubin, serum creatinine, BUN, serum potassium, serum magnesium, blood glucose, and serum albumin were also measured. The relationship between trough tacrolimus blood concentrations and clinical endpoints was analyzed using both a logistic regression model and a Cox proportional hazard model. By logistic regression analysis, a statistically significant (p = 0.0465) relationship between increasing trough tacrolimus blood concentrations and decreasing risk of acute rejection was demonstrated over a 7-day time window. Nephrotoxicity and other toxicities also demonstrated statistically significant relationships with trough tacrolimus blood concentrations. The results of the Cox analysis were consistent with the logistic regression analysis. Using receiver operator characteristic curves, trough tacrolimus concentrations as measured by the ELISA method were able to differentiate the occurrence of nephrotoxicity and toxicity from nonevents. To minimize nephrotoxicity of tacrolimus, it is necessary to maintain trough blood concentrations below 15 ng/ml. This study demonstrates that the ELISA method used to measure tacrolimus blood concentrations in this study provides information of predictive value for managing the risk of nephrotoxicity, other toxicity, and rejection in liver transplant patients.

FK 506 rescue therapy for intractable liver allograft rejection

Intractable liver allograft rejection remains an important cause of graft loss. In this present study, we evaluated the role of oral FK 506 in 30 rejection episodes resistant to conventional cyclosporin-based triple immunosuppression in a series of 28 patients. Rejection was reversed in 11 (91.7%) of 12 patients for intractable acute rejection and in 10 (58.8%) of 17 patients for chronic rejection. A progressive decline in serum bilirubin was observed within 14 days in those successfully salvaged and a serum bilirubin of less than 200 micromol/l at the time of FK 506 conversion in the chronic rejection subgroup was found to be good predictor of response (specificity 100%, sensitivity 60%). New onset diabetes mellitus (29%) and reversible renal impairment (32%) were the commonest adverse events observed. Eleven (52%) of the responding patients successfully discontinued corticosteroid medication and are currently on FK 506 monotherapy. FK 506 therapy has a significant impact in the control of both intractable acute and chronic allograft rejection with an acceptable toxicity profile.

Optimal FK 506 dosage in patients under primary immunosuppression following liver transplantation

In a retrospective study, we analysed the FK 506 dosage used in primary liver graft recipients enrolled in the European FK 506 multicenter trial conducted from September 1990 to January 1992. In addition, a second cohort of patients treated more recently in a single centre was investigated. The impact of different dosing strategies on the clinical course of the patients was analysed with special emphasis on the incidence of rejection episodes and FK 506 side-effects. Among the patients enrolled in the European FK 506 multicenter trial, those patients enrolled during the "early" phase of the study received a higher oral FK 506 dose [mean oral dosage on day 7 = 0.19 mg/kg body weight (bw) per day, n = 134] compared to patients enrolled during the "late" period of the study (mean oral dosage on day 7 = 0.14 mg/kg bw per day, n = 133). This lower dosage was the result of several protocol amendments performed to reduce the incidence of FK 506 side-effects. Lowering of the FK 506 dosage was accompanied by a reduction in the long-term prevalence of side-effects such as diabetes (n. s.) or hypertension (P < 0.05), while patient survival and rejection frequency remained constant. Patients treated in centres with online FK 506 blood level monitoring experienced significantly less hypertension, less episodes of diabetes and less rejection episodes compared to patients treated in centres without. The clinical course of those patients enrolled in the multicentre trial was compared with the course of a cohort of liver-grafted patients treated with FK 506 more recently in a single centre. These patients had a further reduction in the FK 506 dosage (0.10 mg/kg bw per day p.o. or less according to whole blood levels, with no intravenous FK 506 administration). When compared to patients enrolled in the multicentre trial, these patients experienced less side-effects (nephrotoxicity, hypertension, serious early neurotoxicity) while adaequate immunosuppression was maintained.

Nephrotoxicity after orthotopic liver transplantation in cyclosporin A and FK 506-treated patients

Nephrotoxicity represents a serious side-effect of immunosuppression following orthotopic liver transplantation. In order to preserve the therapeutic potential of cyclosporin (CsA) and FK 506 in human liver transplantation and to differentiate the nephrotoxic action of either drug in a clinical setting, we evaluated the incidence of early and late nephrotoxicity in 121 patients, 60 randomly assigned to CsA- and 61 to FK 506-based immunosuppression. Early postoperative renal insufficiency (between POD0 and 30; SCr 1.5-3 mg/dl) was observed to a similar extent in patients treated with CsA (36.7%) and FK 506 (42.6%). Early postoperative acute renal failure (ARF; SCr > 3 mg/dl) occurred in 18.3%, regardless of the immunosuppressive management. Approximately 50% of patients with ARF required hemodialysis (CsA: 11.7%; and FK 506: 8.3%). Mean onset of hemodialysis in CsA-treated patients was POD1 and in FK 506-treated patients, POD6, which demonstrated a different time course of drug-specific nephrotoxicity of CsA and FK 506 in early ARF. All patients with early postoperative ARF requiring hemodialysis survived more than 1 year (100% survival). New onset of late ARF (between POD30 and 365), however, occurred in 6.5% under FK 506 and in 1.7% under CsA immunosuppression due to severe infections with the multiple organ failure syndrome. This observation was consistent with the assumption of over-immunosuppression rather than a primary nephrotoxic effect. Mortality of patients with late ARF requiring hemodialysis was 100%. Late renal insufficiency appeared in 23.3% of CsA- and in 29.4% of FK 506-treated patients, and represented a slowly progressing form of drug-specific nephrotoxicity. These preliminary results demonstrated a similar outcome in terms of early and late nephrotoxicity, but longer follow-up will delineate its overall efficacy and toxicity in humans.

Neurotoxicity after orthotopic liver transplantation in cyclosporin A- and FK 506-treated patients

Neurotoxicity is a serious complication following orthotopic liver transplantation leading to increased morbidity and mortality. Neurotoxicity may be evoked by various perioperative factors, or may be due to drug-specific toxicity of immunosuppression. In the present study we evaluated the incidence of central nervous system (CNS) toxicity occurring within the early postoperative period of 121 patients, 61 randomly assigned to FK 506- and 60 to CsA-based immunosuppression as part of a multicentre study. The incidence of moderate or severe CNS toxicity was higher in patients treated with FK 506 (21.3%) than in patients receiving CsA (11.7%). The duration of symptoms was also greater in patients treated with FK 506 than in patients receiving CsA. The incidence of moderate or severe neurotoxicity after retransplantation was markedly greater in patients treated with FK 506 (100% of the patients).

Conversion from cyclosporin A to tacrolimus in pediatric liver transplantation

The dosing regimen for conversion from cyclosporin A (CsA) to tacrolimus immunosuppression was studied in 12 pediatric liver allograft recipients. Patients were stratified according to their age. Tacrolimus was started orally at a dosage of 0.05 mg/kg b.i.d., 12 h after stopping CsA administration and increased thereafter if needed. Tacrolimus and CsA concentrations were assayed by immunoassay using, respectively, an IMx and a TDx autoanalyzer (Abbott-France). Mean CsA concentration was in the therapeutic range 12 h prior to and at the time of introduction of tacrolimus. After 72 h of tacrolimus therapy, CsA concentrations were undetectable whereas mean tacrolimus concentration was 10.4 ng/mL with a mean dose of 0.09 mg/ kg b.i.d. The decline of CsA concentration was clearly biphasic. A slower decline in CsA concentration was detected after initiation of tacrolimus therapy, suggesting an inhibition of CsA metabolism by tacrolimus. No nephrotoxicity was observed. This dosage regimen allowed effective immunosuppression while avoiding additive nephrotoxicity.

Regulation of glucose tolerance in patients after liver transplantation: impact of cyclosporin versus tacrolimus therapy

BACKGROUND

We investigated the factors regulating glucose homeostasis in 10 healthy (control) subjects, as well as in stable, long-term, liver-grafted patients receiving monotherapy in the form of either cyclosporin A (n=10) or tacrolimus (n=10).

METHODS

We measured insulin sensitivity, first- and second-phase insulin secretion, with a minimal modeling technique based on the analysis of glucose, insulin, and C-peptide profiles during frequently sampled intravenous glucose tolerance tests (FSIGTT). Proinsulin levels, as a marker of beta-cell dysfunction, were measured in the fasting state and during FSIGTT.

RESULTS

Glucose and insulin concentrations before and after glucose loading did not differ in liver transplant patients and in control subjects. Fasting C-peptide levels in both liver-grafted groups were higher than in healthy subjects and remained elevated during FSIGTT (P<0.05). Intravenous glucose tolerance [(K(G)), i.e. the slope of the regression of logarithm of the blood glucose concentrations vs. time], insulin sensitivity, and first-phase insulin secretion did not differ in liver-grafted groups and healthy subjects. Second-phase insulin secretion was about 56% higher in liver-grafted patients than in controls (P<0.05). Body mass index was the overall determinant of insulin sensitivity in all groups.

CONCLUSIONS

Long-term monotherapy with cyclosporin A or tacrolimus has no deleterious effects on insulin sensitivity, first-phase insulin secretion, and insulin synthesis in liver transplant patients. Normal insulin sensitivity (posthepatic insulin effect) and enhanced second-phase insulin secretion (prehepatic insulin) point to an accelerated hepatic insulin clearance rate in liver transplant patients. Increased hepatic insulin clearance is compensated by enhanced insulin secretion, indicating that insulin clearance is the major determinant of pancreatic function in liver-grafted patients.

Effects of liver disease on pharmacokinetics. An update

Liver disease can modify the kinetics of drugs biotransformed by the liver. This review updates recent developments in this field, with particular emphasis on cytochrome P450 (CYP). CYP is a rapidly expanding area in clinical pharmacology. The information currently available on specific isoforms involved in drug metabolism has increased tremendously over the latest years, but knowledge remains incomplete. Studies on the effects of liver disease on specific isoenzymes of CYP have shown that some isoforms are more susceptible than others to liver disease. A detailed knowledge of the particular isoenzyme involved in the metabolism of a drug and the impact of liver disease on that enzyme can provide a rational basis for dosage adjustment in patients with hepatic impairment. The capacity of the liver to metabolise drugs depends on hepatic blood flow and liver enzyme activity, both of which can be affected by liver disease. In addition, liver failure can influence the binding of a drug to plasma proteins. These changes can occur alone or in combination; when they coexist their effect on drug kinetics is synergistic, not simply additive. The kinetics of drugs with a low hepatic extraction are sensitive to hepatic failure rather than to liver blood flow changes, but drugs having a significant first-pass effect are sensitive to alterations in hepatic blood flow. The drugs examined in this review are: cardiovascular agents (angiotensin converting enzyme inhibitors, angiotensin II receptor antagonists, calcium antagonists, ketanserin, antiarrhythmics and hypolipidaemics), diuretics (torasemide), psychoactive and anticonvulsant agents (benzodiazepines, flumazenil, antidepressants and tiagabine), antiemetics (metoclopramide and serotonin antagonists), antiulcers (acid pump inhibitors), anti-infectives and antiretroviral agents (grepafloxacin, ornidazole, pefloxacin, stavudine and zidovudine), immunosuppressants (cyclosporin and tacrolimus), naltrexone, tolcapone and toremifene. According to the available data, the kinetics of many drugs are altered by liver disease to an extent that requires dosage adjustment; the problem is to quantify the required changes. Obviously, this requires the evaluation of the degree of hepatic impairment. At present there is no satisfactory test that gives a quantitative measure of liver function and its impairment. A critical evaluation of these methods is provided. Guidelines providing a rational basis for dosage adjustment are illustrated. Finally, it is important to consider that liver disease not only affects pharmacokinetics but also pharmacodynamics. This review also examines drugs with altered pharmacodynamics.

Newer immunosuppressive drugs: a review

In recent years, many new immunosuppressive drugs have been discovered and developed for clinical use in transplantation. This review focuses on those drugs (leflunomide, mycophenolate mofetil, sirolimus, tacrolimus) that have been shown to have immunosuppressive activity in patients. Different anti-interleukin-2 receptor antibodies are also reviewed as an example of a resurgence of development in the area of monoclonal antibodies. The price for reducing the incidence of allograft rejection by improved immunosuppression was thought to be a proportional increase in the incidence of infection and malignancy. Data from Phase III clinical trials of new immunosuppressants, however, show a statistically significant reduction in the incidence of acute rejection produced by these new drugs, which has not been accompanied by increases in infection and malignancy rates. The wide array of new drugs offers the opportunity to use combinations that block different pathways of immune activation while at the same time selecting drug combinations with nonoverlapping toxicity profiles so that doses of each single drug can be reduced below toxicity levels. The immunosuppressive therapy for patients can be tailored according to their individual needs.