Importance of cytochrome P-450IIIA activity in determining dosage and blood levels of FK 506 and cyclosporine in liver transplant recipients

Medication Barriers and Adherence: Experiences of Pediatric Transplant Recipients

This study examined associations between scores on the Adolescent Medication Barriers Scale (AMBS) and the Parent Medication Barriers Scale (PMBS), patient and family factors, and medication adherence outcomes. Patients and caregivers from a pediatric solid organ transplantation (SOT) program were recruited for participation. Pediatric SOT recipients ages 10 to 21 years were eligible for participation. Analyses included reliability analyses and regression modeling with posttransplant medication adherence measured by Medication Level Variability Index scores. Seventy-three patients and caregivers completed an AMBS or PMBS questionnaire. Patient-caregiver inter-rater reliability was poor to fair. Greater medication barriers were reported among younger and female patients and families with more children. AMBS scores predicted greater nonadherence, while the PMBS was not predictive of adherence. Results point to the difficulty of assessing barriers to medication adherence and the lack of agreement between adolescent patients and caregivers. AMBS scores were more closely aligned with medication nonadherence, whereas PMBS scores may have been more influenced by family social factors. Adolescent reports of medication barriers may offer multidisciplinary transplant teams greater clinical utility when addressing these challenges with patients. Transplant social workers and psychologists should engage adolescents and caregivers in efforts to address medication nonadherence.

ASP1126, a Novel Sphingosine-1-Phosphate-Selective Agonist With a Favorable Safety Profile, Prolongs Allograft Survival in Rats and Nonhuman Primates in Combination With Tacrolimus With a Broad Safety Margin for Bradycardia

Sphingosine-1-phosphate (S1P) is a biologically active sphingolipid that acts through the members of a family of 5 G protein-coupled receptors (S1P₁ to S1P₅). Among these, S1P₁ is a major regulator of lymphocyte trafficking. Fingolimod, whose active metabolite, fingolimod phosphate, acts as a nonselective S1P-receptor agonist, exerts its immunomodulatory effect, at least in part, by regulating lymphocyte trafficking via downregulation of S1P₁ expression on lymphocytes. Here, we describe the pharmacologic profile of a novel S1P₁ agonist, ASP1126. ASP1126 preferentially activated S1P₁ compared to S1P₃ in rat and human guanosine-5'-(γ-thio)-triphosphate (GTPγS) assays. Oral single administration of ASP1126 decreased the number of peripheral lymphocytes and repeated dosing showed a cumulative effect on lymphopenia in both rats and monkeys. ASP1126 prolonged allograft survival in a rat heterotopic heart transplantation model in combination with a subtherapeutic dose of tacrolimus that was independent of drug-drug interactions. In addition, in nonhuman primate (NHP) renal transplantation, pretreatment with ASP1126 reduced not only the number of naive T cells and central memory T cells but also effector memory T cells in the peripheral blood, all of which could contribute to acute graft rejection and prolonged allograft survival in combination with tacrolimus. Further, we confirmed that ASP1126 has a broad ranging safety margin with respect to its effect on lung weight in rats and bradycardia in NHPs, which were the adverse events found in clinical studies of fingolimod. ASP1126 with improved safety profile has the potential to be an adjunct therapy in combination with tacrolimus in clinical transplantation.

Voriconazole-Induced Periostitis & Enthesopathy in Solid Organ Transplant Patients: Case Reports

Background

Voriconazole is frequently used to treat fungal infections in solid organ transplant patients. Recently, there have been reports suggesting that prolonged voriconazole therapy may lead to periostitis.

Aim

Here we present two cases of voriconazole-induced periostitis in solid organ transplant patients.

Case Presentation

Voriconazole was given to two transplant patients-one with a liver transplant and the second with a heart transplant, to treat their fungal infections. Both developed voriconazole-induced toxicity. While undergoing voriconazole therapy, they had incapacitating bone pain. The liver transplant patient had to be taken off voriconazole, and the heart transplant patient succumbed to non-voriconazole related causes.

Conclusions

Voriconazole therapy in two solid organ transplant patients resulted in periostitis. We provide potential etiologies underlying voriconazole-induced periostitis, including fluoride toxicity, abnormalities in the pulmonary vascular bed leading to the production of downstream inflammatory mediators, and abnormal pharmacokinetics of hepatic drug metabolism. In addition to monitoring blood voriconazole trough levels, we suggest careful assessment for musculoskeletal pain in patients undergoing voriconazole treatment for two months or more, particularly if their daily dosages of voriconazole exceed 500 mg per day. Appropriate workup should include measurement of alkaline phosphatase, voriconazole trough and fluoride levels as well as a bone scan. Overall, early recognition of voriconazole-induced musculoskeletal toxicity is important for better morbidity outcomes.

Concise review: Interferon-free treatment of hepatitis C virus-associated cirrhosis and liver graft infection

Chronic hepatitis C is a major reason for development of cirrhosis and hepatocellular carcinoma and a leading cause for liver transplantation. The development of direct-acting antiviral agents lead to (pegylated) interferon-alfa free antiviral therapy regimens with a remarkable increase in sustained virologic response (SVR) rates and opened therapeutic options for patients with advanced cirrhosis and liver graft recipients. This concise review gives an overview about most current prospective trials and cohort analyses for treatment of patients with liver cirrhosis and liver graft recipients. In patients with compensated cirrhosis Child-Pugh-Turcotte (CTP) class A, all approved agents are safe and SVR rates do not significantly differ from patients without cirrhosis in general. In patients with decompensated cirrhosis CTP class B or C, daclastasvir, ledipasvir, velpatasvir, and sofosbuvir are approved, and SVR rates higher than 90% can be achieved. Especially for patients with a model of end stage liver disease score higher than 15 and therefore eligible for liver transplantation, data is scarce. Reported SVR rates in patients with cirrhosis CTP class C are lower compared to patients with a less severe liver disease. In liver transplant recipients with a maximum of CTP class A, SVR rates are comparable to patients without LT. Patients with decompensated graft cirrhosis should be treated on an individual basis.

Adherence in Adolescent and Young Adult Kidney Transplant Recipients

Poor adherence to immunosuppressive medications may be the most important barrier to long term graft survival. An understanding of medication adherence and its determinants is critical to addressing this important problem. In this paper, we will review the different ways in which adherence may be compromised, summarize the evidence that young people constitute a particularly high risk group, and consider the consequences and impact of poor adherence. We will also review the determinants of adherence, including characteristics of the patient and family, the treatment regimen, the healthcare team and its organization, and the healthcare system. We will highlight the most common barriers to adherence identified by young people, and consider different methods of measuring adherence, along with the advantages and limitations of each. Finally, we will consider possible intervention strategies to improve adherence in young people.

Strangers headed to a strange land? A pilot study of using a transition coordinator to improve transfer from pediatric to adult services

OBJECTIVE

To compare the impact of a transition coordinator on outcomes for pediatric liver transplant recipients vs a historical comparison group.

STUDY DESIGN

To examine the utility of a transition coordinator, medication adherence, as measured by SDs of tacrolimus blood levels (Tacrolimus SD), was compared between the "transition coordinator group" (20 transplant recipients transferred between 2007 and 2012) and comparison group for 1 year before and after transfer. Measures of health care management, quality of life, and acceptability were administered to the transition coordinator group as well.

RESULTS

A repeated measures ANOVA was used to compare adherence values between the transition coordinator group and the comparison group. During the year before transfer, for the transition coordinator group, Tacrolimus SD was 1.98 (SD = 1.05) vs 3.25 (SD = 1.19) for comparison patients, F(1,25) = 4.77, P = .04. After transfer, levels remained stable for the transition coordinator group, Tacrolimus SD = 1.88 (SD = 1.57), but increased for comparison patients, Tacrolimus SD = 4.36 (SD = 0.99), F(1,25) = 6.99, P = .01. Psychosocial outcomes remained stable during the transfer period and acceptability was high.

CONCLUSIONS

Our findings, although limited by a small sample size, suggest that a transition coordinator is a promising method to improve this process.

Adolescent transplant recipients as peer mentors: a program to improve self-management and health-related quality of life

The purpose of this study was to examine the safety, feasibility, acceptability, and preliminary efficacy of a cross-age peer mentoring program created to improve adherence and psychosocial outcomes for pediatric liver transplant recipients. Twenty-two participants were assigned to a "mentor now" or "mentor later" waitlist control group. Tacrolimus SD, a validated measure of adherence, was assessed for six months pre- and post-intervention for both groups. Self-report measures of self-management and HRQOL were completed at recruitment and three months after training. Participant report indicated the acceptability of the intervention. Clinically significant improvement in adherence was detected. No significant changes on the psychosocial outcome measures at follow-up were observed. This study demonstrated that an outpatient-based mentoring program is a safe, feasible, and acceptable option to incorporate within a pediatric liver transplant program with potential for promising application in other transplantation populations as well. These results also suggest that the program may have been associated with meaningful improvement in adherence, although further evaluation is warranted.

Breath tests to phenotype drug disposition in oncology

Breath tests (BTs) have been investigated as diagnostic tools to phenotype drug disposition in cancer patients in the pursuit to individualize drug treatment. The choice of the right phenotype probe is crucial and depends on the metabolic pathway of the anticancer agent of interest. BTs using orally or intravenously administered selective non-radioactive (13)C-labeled probes to non-invasively evaluate dihydropyrimidine dehydrogenase, cytochrome P450 (CYP) 3A4, and CYP2D6 enzyme activity have been published. Clinically, a (13)C-dextromethorphan BT to predict endoxifen levels in breast cancer patients and a (13)C-uracil BT to predict fluoropyrimidine toxicity in colorectal cancer patients are most promising. However, the clinical benefit and cost effectiveness of these phenotype BTs need to be determined in order to make the transition from an experimental setting to clinical practice as companion diagnostic tests.

CYP3A4 intron 6 C>T SNP (CYP3A4*22) encodes lower CYP3A4 activity in cancer patients, as measured with probes midazolam and erythromycin

AIM

The CYP3A4*22 allele was recently reported to be associated with reduced CYP3A4 activity. We investigated the impact of this allele on the metabolism of the CYP3A-phenotyping probes, midazolam (MDZ) and erythromycin.

PATIENTS & METHODS

Genomic DNA from 108 cancer patients receiving intravenous MDZ and 45 undergoing the erythromycin breath test was analyzed for CYP3A4*22 (rs35599367 C>T) and CYP3A5*3.

RESULTS

The MDZ metabolic ratio (1´-OH-MDZ:MDZ) was 20.7% (95% CI: -36.2 to -6.2) lower for CYP3A4*22 carriers compared with CYP3A4*1/*1 patients (p = 0.01). Combining CYP3A4*22 and CYP3A5*3 genotypes showed a 38.7% decrease (95% CI: -50.0 to -27.4; p < 0.001) in 1´-OH-MDZ:MDZ for poor (CYP3A4*22-CYP3A5*3/*3) and 28.0% (95% CI: -33.3 to -22.6; p < 0.001) for intermediate (CYP3A4*1/*1-CYP3A5*3/*3) metabolizers, compared with extensive (CYP3A4*1/*1-CYP3A5*1) CYP3A metabolizers. CYP3A4 erythromycin N-demethylation activity was 40% lower in CYP3A4*22 carriers compared with CYP3A4*1/*1 patients (p = 0.032).

CONCLUSION

The CYP3A4*22 allele is associated with decreased CYP3A4-mediated metabolism, as verified by CYP3A-phenotyping probes.

Liver involvement in hereditary hemorrhagic telangiectasia: can breath test unmask impaired hepatic first-pass effect?

Hepatic arteriovenous malformations (HAVMs) in hereditary hemorrhagic telangiectasia (HHT) have long been considered to have scarce clinical significance in most cases. Nevertheless, data are lacking regarding the influence of HAVMs on the liver first-pass effect on drugs in HHT patients. To gain insight into the effect of HAVMs on hepatic drug clearance by means of two specific (13)C-labeled probes, namely the (13)C-methacetin and (13)C-aminopyrine, 46 HHT patients and 44-matched healthy controls were enrolled. The liver first-pass effect was studied by the (13)C-based breath test using methacetin and aminopyrine. The methacetin breath test showed statistically significant reduced metabolism rates (p < 0.0001) in HHT when compared with controls, both in patients with and without CT-detectable HAVMs, and when expressed both as cumulative (13)C-percentage dose per hour and as (13)C-percentage peak after 15 min. In contrast, no significant difference was found between HHT and controls regarding aminopyrin metabolism rates. In HHT, (13)C%-methacetin breath test values are significantly lower than those found in normal subjects, probably due to the effect of hepatic shunts. A reduced perfusion and an impaired hepatic metabolism might affect hepatic drug clearance in HHT. Therefore, an appropriate dosage adjustments should be considered when high-hepatic-metabolism drugs are administered to HHT patients.

Impact of acute cellular rejection on coagulation and fibrinolysis biomarkers within the immediate post-operative period in pediatric liver transplantation

We studied restoration of the coagulation and fibrinolysis system in pediatric patients following liver transplantation and biomarkers of blood coagulation and fibrinolysis for suspecting the occurrence of acute cellular rejection. Coagulation activity recovered rapidly within two days following transplantation, but it took approximately 21-28 days for full recovery of the coagulation and fibrinolysis factors synthesized in the liver. PAI-1 levels were significantly higher in patients at the time of acute cellular rejection compared with levels after control of AR, and levels on days 14 and 28 in patients without AR. Plasma protein C and plasminogen levels at the time of rejection were significantly lower than those on day 14 in patients without AR. Statistical analysis suggested that an increase in plasma PAI-1 at a single time point in the post-operative period is a reliable marker among the coagulation and fibrinolysis factors for suspecting the occurrence of acute cellular rejection. These data suggested that appropriate anticoagulation may be required for 14 days after liver transplantation in order to avoid vascular complications and measurement of plasma PAI-1 levels may be useful for suspecting the occurrence of acute cellular rejection in pediatric patients following liver transplantation.

Challenges for drug studies in children: CYP3A phenotyping as example

A paucity of data exists on the disposition and effect of drugs in young children. This information gap can be reduced by elucidating developmental principles of absorption, distribution, metabolism and excretion (ADME) in vivo. Such knowledge might enable the prediction of the disposition of individual drugs in children over the whole pediatric age range. CYP3A, the most abundant human drug metabolizing enzyme, is involved in the metabolism of more than 50% of all marketed drugs. Hence, elucidating the developmental pattern of CYP3A in relation to genetic background, disease and comedications might greatly enhance our knowledge on drug disposition in children. Several methods have been used to determine in vivo CYP3A activity in human adults, while similar studies in children face several ethical, practical and scientific challenges. The aim of this review is to identify these challenges and offer feasible solutions for studying drugs in young children, with an emphasis on CYP3A phenotyping as an example.

CD25, CD28 and CD38 expression in peripheral blood lymphocytes as a tool to predict acute rejection after liver transplantation

BACKGROUND/AIM

The aim of this study was to determine whether the expression of CD25, CD28 and CD38 (which reflects the degree of T-cell activation) by peripheral blood mononuclear cells constitutes a useful means of measuring the immune status of liver transplant recipients.

METHODS

Fifty-two patients enrolled in a prospective randomized study comparing cyclosporine and tacrolimus as the principal immunosuppressive drugs were monitored prospectively. The expression of CD25, CD28 and CD38 was analyzed on CD3-, CD4- and CD8-positive cells from whole blood using flow cytometry. The prognostic value of baseline and day 14 measurements regarding acute rejection was examined using Kaplan-Meier estimates for univariate analyses and the Cox model for multivariate analyses.

RESULTS

The mean frequencies of CD28 and CD38-expressing T cells were significantly higher in patients with acute rejection (p = 0.01 and p = 0.001, respectively), whereas the frequency CD25-expressing T cells did not differ significantly. Under univariate analysis, baseline CD25 levels, the type of calcineurin inhibitor, as well as the CD28 and CD38 frequencies obtained at day 14 were associated with the subsequent development of acute rejection. Under multivariate analysis, only CD28 and CD38 frequencies obtained at day 14 were independently associated with acute rejection.

CONCLUSIONS

The evaluation of CD28 and CD38 expression in peripheral blood lymphocytes is a simple marker that could be used routinely in clinical practice to assess the level of immunosuppression.

[Therapeutic monitoring of immunosuppressive drugs: interest of calcineurin activity assessment in liver transplantation]

Therapeutic monitoring of calcineurin inhibitors (ciclosporin and tacrolimus) consists in pharmacokinetic monitoring. Pharmacodynamics based on calcineurin activity may be particularly interesting in liver transplantation due to the large intra- and interindividual variability of pharmacokinetics of ciclosporin and tacrolimus. A recent investigation on the pharmacokinetic-pharmacodynamic relationship of tacrolimus showed that monitoring of calcineurin activity in PBMC may be particularly relevant within the first three post-transplantation months. Thereafter, the monitoring of trough blood concentrations of tacrolimus remains adequate. Moreover, two clinical investigations carried out within the early and late post-transplantation periods reported a promising result which is a positive correlation between calcineurin activity and incidence of graft rejection, whatever graft type and calcineurin inhibitors. In each study, transplanted recipients with a graft rejection exhibited a greater trough calcineurin activity compared to patients without graft rejection. However, prospective investigations are required because of the small cohorts of patients enrolled in both studies. The aim of these investigations will be to confirm the interest of calcineurin activity monitoring as a marker of cellular immunity and its positive link with pharmacokinetic monitoring.

Adherence and health-related quality of life in adolescent liver transplant recipients

Adolescence is a particularly high-risk period for non-adherence with post-transplant medical regimens. There remains a lack of research investigating factors related to non-adherence in adolescent LT recipients. The present study empirically assessed the relationship between adherence and HRQOL in adolescent LT recipients. Participants included 25 adolescents (mean = 15.1 yr, range 12-17.9) and their parent/guardian(s). Adherence was assessed using multiple indices including clinician-conducted interviews, rate of clinic attendance, and s.d. of consecutive tacrolimus blood levels. HRQOL was examined using self-report and parent-proxy report on well-validated assessment measures. Results indicated that 76% of participants were non-adherent on at least one measure of adherence, and HRQOL was significantly lower than normative data for healthy children. Tacrolimus s.d. were significant related to poor HRQOL across domains of physical, school, and social functioning. Non-adherent adolescents reported poorer health perceptions, self-esteem, mental health, family cohesion, and more limitations in social and school activities related to physical, emotional, and behavioral problems. These results suggest that empirically based assessment of HRQOL may help identify those at highest risk for behavior, emotional and school difficulties, as well as non-adherence. The examination of tacrolimus s.d. may also help identify patients who may benefit from intervention to promote adherence and HRQOL. Prospective investigations are necessary to further identify the impact of HRQOL on adherence and long-term health outcomes to further guide clinical intervention.

Improving adherence to medications in pediatric liver transplant recipients

We describe results from a clinical program, which aimed at improving adherence to medications in children who had a liver transplant. We followed the medical outcomes of 23 children and adolescents who participated in a clinical adherence-improvement protocol during the years 2001-2002. The protocol included identification of non-adherent patients by examining tacrolimus blood levels and intervention by increasing the frequency of clinic visits for non-adherent patients. In the two-yr preintervention (1999-2000), there was no improvement in any of the outcomes. After the intervention, the number of patients with high alanine aminotransferase levels (100 and above) decreased significantly, from eight before the intervention to four afterwards. Other outcomes, including the number of rejection episodes (three before, none after) and the degree of adherence to tacrolimus, also improved, but the improvement did not reach statistical significance. Although non-adherent patients were called to clinic more often under the protocol, the intervention did not lead to increased outpatient costs. This adherence--improvement intervention appears to be promising in improving outcomes in pediatric liver transplant recipients. Larger, controlled studies are needed to establish the efficacy of this or other approaches.

Childhood abuse, nonadherence, and medical outcome in pediatric liver transplant recipients

OBJECTIVE

The study assessed the relationship between a history of child abuse, nonadherence to medications, and medical outcome in children who had a liver transplant.

METHOD

Abuse history for children and adolescents ages 8 to 21 who underwent a liver transplantation at Mount Sinai Medical Center in New York was obtained in interviews in 2002. Adherence to tacrolimus was assessed from January 1 to December 31, 2003 by computing the SD of a series of medication blood levels for each patient. Biopsy-proven rejection episodes, degree of fluctuation of alanine aminotransferase (ALT), and maximal ALT levels were recorded as indicators of medical outcome.

RESULTS

Of 72 eligible patients, 56 were evaluated. Five had documented abuse. Abused children were less adherent to their medication regimen (p = .02; 95% confidence interval [CI] -2.66 to -0.24), had poor disease control (higher maximal ALT, p <.01; 95% CI -613.72 to -249.55), had greater fluctuation in ALT levels (p <.01; 95% CI -151.19 to -65.91), and suffered more biopsy-proven rejection episodes (two episodes in the abused cohort versus none in the rest) in 2003.

CONCLUSIONS

A history of child abuse is a significant risk factor for poor outcome posttransplantation and should be evaluated routinely. Adherence to medications can be a target for intervention in patients with a history of abuse.

Adherence and medical outcomes in pediatric liver transplant recipients who transition to adult services

Non-adherence to medications is associated with poor medical outcomes in adolescent transplant recipients. It is unclear whether non-adherence is further compromised when transplant recipients transition to the adult health care system. The purpose of the present study was to examine whether adherence changes during transition. We reviewed the medical records of 14 recently transitioned patients and compared their adherence and corresponding medical outcomes before and after transition. These outcomes were also compared with two cohorts of patients receiving care solely in pediatric or adult services. Medication adherence, measured through the use of standard deviations of tacrolimus blood levels, was examined for all patients. We found that adherence to tacrolimus significantly decreased after transition. After transitioning, patients furthermore exhibited poorer adherence than patients in the other two cohorts did over time. This small retrospective study suggests that the period of transition from pediatric to adult transplant clinics is a vulnerable one. Larger, prospective investigations of the transition process are necessary before recommendations are made regarding interventions.

Optimization of conditions for clinical human hepatocyte infusion

Cytotoxicity and apoptosis are common problems in the isolation and storage of human hepatocytes. In vitro environments of hepatocytes during cell infusion may be critical to reducing cellular damage and enhancing cell viability. We examined the effects of donor liver histology (40-50% steatosis vs. normal), incubation time, temperature, and three solutions for infusion on banked primary human hepatocytes, by studying: trypan blue exclusion, AST release, LDH release, MTT assay, detection of DNA ladder, and a hepatocyte proliferation assay. In addition, the microstructure functions of the endoplasmic reticulum and mitochondria of the intact hepatocytes were determined by measuring correlates of UGT 1A1 and cytochrome P-450 3A (CYP3A4) activity. In general, hepatocyte viability decreased significantly within 60 min after thawing. Cells suspended in 5% dextrose lactated Ringers solution (D5LR) maintained greater cell viability. Hepatocytes from normal liver donors showed less AST and LDH enzyme leak in comparison with cells from fatty liver donors. Mild hypothermic temperature (32 degrees C) inhibited cellular damage that otherwise significantly increased at 60 min. Hepatocytes did not proliferate until 12 h from thaw, regardless of supernatant or conditions of suspension. CYP3A4 activity and a marker for UGT 1A1 activity in hepatocytes from normal donor livers were higher than those from steatotic donor livers. These findings suggest that hepatocytes suspended for infusion after isolation from normal liver donors have normal biological functions and less cellular damage/necrosis in contrast with those isolated from fatty liver donors. These damages are inhibited significantly by maintaining hepatocytes at a mild hypothermic temperature (32 degrees C). D5LR alone maintained the best cell viability for up to 60 min. Media of D5LR + adenosine and HMM were able to partially inhibit hepatocyte apoptosis in hepatocytes from steatotic livers.

Mechanism-based inhibition of cytochrome P450 3A4 by therapeutic drugs

Consistent with its highest abundance in humans, cytochrome P450 (CYP) 3A is responsible for the metabolism of about 60% of currently known drugs. However, this unusual low substrate specificity also makes CYP3A4 susceptible to reversible or irreversible inhibition by a variety of drugs. Mechanism-based inhibition of CYP3A4 is characterised by nicotinamide adenine dinucleotide phosphate hydrogen (NADPH)-, time- and concentration-dependent enzyme inactivation, occurring when some drugs are converted by CYP isoenzymes to reactive metabolites capable of irreversibly binding covalently to CYP3A4. Approaches using in vitro, in silico and in vivo models can be used to study CYP3A4 inactivation by drugs. Human liver microsomes are always used to estimate inactivation kinetic parameters including the concentration required for half-maximal inactivation (K(I)) and the maximal rate of inactivation at saturation (k(inact)). Clinically important mechanism-based CYP3A4 inhibitors include antibacterials (e.g. clarithromycin, erythromycin and isoniazid), anticancer agents (e.g. tamoxifen and irinotecan), anti-HIV agents (e.g. ritonavir and delavirdine), antihypertensives (e.g. dihydralazine, verapamil and diltiazem), sex steroids and their receptor modulators (e.g. gestodene and raloxifene), and several herbal constituents (e.g. bergamottin and glabridin). Drugs inactivating CYP3A4 often possess several common moieties such as a tertiary amine function, furan ring, and acetylene function. It appears that the chemical properties of a drug critical to CYP3A4 inactivation include formation of reactive metabolites by CYP isoenzymes, preponderance of CYP inducers and P-glycoprotein (P-gp) substrate, and occurrence of clinically significant pharmacokinetic interactions with coadministered drugs. Compared with reversible inhibition of CYP3A4, mechanism-based inhibition of CYP3A4 more frequently cause pharmacokinetic-pharmacodynamic drug-drug interactions, as the inactivated CYP3A4 has to be replaced by newly synthesised CYP3A4 protein. The resultant drug interactions may lead to adverse drug effects, including some fatal events. For example, when aforementioned CYP3A4 inhibitors are coadministered with terfenadine, cisapride or astemizole (all CYP3A4 substrates), torsades de pointes (a life-threatening ventricular arrhythmia associated with QT prolongation) may occur.However, predicting drug-drug interactions involving CYP3A4 inactivation is difficult, since the clinical outcomes depend on a number of factors that are associated with drugs and patients. The apparent pharmacokinetic effect of a mechanism-based inhibitor of CYP3A4 would be a function of its K(I), k(inact) and partition ratio and the zero-order synthesis rate of new or replacement enzyme. The inactivators for CYP3A4 can be inducers and P-gp substrates/inhibitors, confounding in vitro-in vivo extrapolation. The clinical significance of CYP3A inhibition for drug safety and efficacy warrants closer understanding of the mechanisms for each inhibitor. Furthermore, such inactivation may be exploited for therapeutic gain in certain circumstances.

Defective inhibition of peripheral CD8+ T cell IL-2 production by anti-calcineurin drugs during acute liver allograft rejection

BACKGROUND

The aim of this study was to evaluate calcineurin activity and interleukin-2 (IL-2) expression by peripheral blood cells as a means of assessing the immune status of liver transplant recipients.

METHODS

Twenty-one patients were studied in a randomized study comparing cyclosporine and tacrolimus as the main immunosuppressive drug. Calcineurin activity was determined after separation of phosphorylated and dephosphorylated products of a calcineurin specific peptide substrate by high performance liquid chromatography(HPLC). Intracellular IL-2 expression was measured by flow cytometry. In 34 additional patients, intracellular IL-2 expression was prospectively measured.

RESULTS

Calcineurin activity fell after transplantation. Values were marginally higher in patients with acute rejection (P=0.059). The percentage of IL-2-producing T cells fell after transplantation. This percentage did not differ between patients with and without rejection. In contrast, the proportion of IL-2-producing CD8+ T cells was higher in patients with acute rejection than in patients free of acute rejection (P=0.003). Moreover, pretransplantation IL-2 expression by CD8+ T cells was higher in patients who subsequently developed acute rejection, suggesting that IL-2 production may be constitutively higher in those patients. The results obtained in the 34 additional patients confirmed these results.

CONCLUSIONS

These data suggest that quantification of intracellular IL-2 in CD8+ T cells may be a useful index of immune status in liver transplant recipients. Preoperative IL-2 levels might serve to individually tailor the immunosuppressive regimen.

Clinical aspects of the MDR1 (ABCB1) gene polymorphism

Transporter proteins, in particular P-glycoprotein (Pgp), are important determinants in absorption, tissue targeting, and elimination of drugs. In addition to physiological and environmental factors, its expression and function are modified by genetic polymorphisms of the MDR1 gene. So far, several MDR1 SNPs have been identified, and mutations at positions 2677 and 3435 were associated with alteration of Pgp expression and/or function. In contrast to drug-metabolizing enzymes (eg, CYP2D6), for which loss of function mutations or gene amplification manifests as distinct phenotypes in the population, the impact of MDR1 polymorphisms on pharmacokinetics and pharmacodynamics of Pgp substrates is moderate. Clinical studies on the effects of the C3435T polymorphism and drug treatment with cardiac glycosides, the immunosuppressants cyclosporine and tacrolimus, HIV protease inhibitors, and tricyclic antidepressants are discussed.

Medication adherence in pediatric and adolescent liver transplant recipients

OBJECTIVE

Nonadherence to medications is a leading cause of morbidity in children and adolescents who have had a transplant, yet there are no published data about the use of different methods for detecting whether these children are taking their medications. There are also no published data about the age of transition at which a child assumes responsibility over taking the medications. This information is important if interventions to improve adherence are contemplated.

METHODS

We present an analysis of data obtained in the first year of the implementation of an adherence assessment protocol at a pediatric liver transplant clinic in a tertiary medical care center. Data were obtained for children and adolescents who had a liver transplant at least 1 year before the assessments took place. We used 5 adherence detection methods. The 4 subjective methods were self-reported, scaled questionnaires answered by nurses, physicians, caregivers, and patients. For the objective method, a standard deviation (SD) was calculated for tacrolimus blood levels obtained from each patient over time. A higher SD suggests increased variation among patients' blood levels and hence more erratic medication taking. We also asked the patients and caregivers who is responsible for taking the medications and what are the reasons for not taking them. The medical outcome measures were biopsy-proven rejection episodes, number of biopsies regardless of the results, number of hospital admissions, and number of in-patient days.

RESULTS

An analysis of 81 cases (258 assessments) revealed that the only method that predicted the medical outcome variables (biopsy-proven rejection and number of biopsies) was the SD of medication blood levels. Patients', clinicians', and caregivers' reports were not predictive. Clinicians' ratings of adherence were not correlated with patients' or caregivers'. The transition of responsibility for medication taking occurred approximately at the age of 12 years. Forgetfulness was cited as the most common reason for nonadherence by patients and caregivers; medication side effects were not frequently cited.

CONCLUSIONS

Our results indicate that clinical impression is not sufficient to determine whether children and adolescents are taking their medications after they have had a liver transplant. An objective assessment method should be used. Interventions targeting adherence should address the child's increasing role beginning in early adolescence. A clinical protocol incorporating objective assessments of adherence could potentially be implemented in other settings. It could form the basis for the evaluation of efficacy of interventions seeking to improve adherence to medications.

Treatment of Anxiety and Depression in Transplant Patients

Depressive and anxiety disorders appear during the transplant process due to psychological stressors, medications and physiological disturbances. Treatment is necessary to prevent impact on patient compliance, morbidity and mortality. Psychotropic medications provide an effective option, although most are only available as oral formulations. Because of this, they are more susceptible to alterations in pharmacokinetic behaviour arising from organ dysfunction in the pretransplant period. Kinetics are also an issue when considering potential drug-drug interactions before and after transplantation. Prior to transplant, organ dysfunction can change the pharmacokinetic behaviour of some psychotropic agents, requiring adjustment of dosage and schedules. Thoracic or abdominal organ failure may reduce drug absorption through disturbances in intestinal motility, perfusion and function. Cirrhotic patients experience increased drug bioavailability due to portosystemic shunting, and thus dosage is adjusted downward. In contrast, dosage needs to be raised when peripheral oedema expands the drug distribution volume for hydrophilic and protein-bound agents. Drug clearance for most psychotropic medications is dependent upon hepatic metabolism, which is often disrupted by endstage organ disease. Selection of drugs or their dosage may need to be adjusted to lower the risk of drug accumulation. Further adjustments in dosage may be called for when renal failure accompanies thoracic or abdominal organ failure, resulting in further impairment of clearance. Studies regarding the treatment of anxiety and depressive disorders in the medically ill are limited in number, but recommendations are possible by review of clinical and pharmacokinetic data. Selective serotonin reuptake inhibitors are well tolerated and efficacious for depression, panic disorder and post-traumatic stress disorder. Adjustments in dosage are required when renal or hepatic impairment is present. Among them, citalopram and escitalopram appear to have the least risk of drug-drug interactions. Paroxetine has demonstrated evidence supporting its use with generalised anxiety disorder. Venlafaxine is an alternative option, beneficial in depression, post-traumatic stress and generalised anxiety disorders. Nefazodone may also be considered, but there is some risk of hepatotoxicity and interactions with immunosuppressant drugs. Mirtazapine still needs to be studied further in anxiety disorders, but can be helpful for depression accompanied by anorexia and insomnia. Bupropion is effective in the treatment of depression, but data are sparse about its use in anxiety disorders. Psychostimulants are a unique approach if rapid onset of antidepressant action is desired. Acute or short-term anxiolysis is obtained with benzodiazepines, and selection of particular agents entails consideration of distribution rate, half-life and metabolic route.

The utility of the 13C-galactose breath test as a measure of liver function

BACKGROUND

The 13C-galactose breath test has been reported to be an accurate, non-invasive method for the assessment of liver function.

AIMS

To determine the optimal doses of labelled and unlabelled carrier galactose necessary to perform the 13C-galactose breath test, to assess the utility of the 13C-galactose breath test in distinguishing between normal subjects and those with liver cirrhosis and to determine whether the 13C-galactose breath test can stratify patients with cirrhosis based on their Child-Pugh score.

METHODS

Twenty-three control subjects and 30 patients with liver cirrhosis received fixed doses of unlabelled carrier galactose and labelled 13C-galactose. Breath samples were collected just before and at 30-min intervals up to 4 h after the ingestion of unlabelled carrier galactose and labelled 13C-galactose. Each sample was analysed for its 13CO2 content.

RESULTS

Doses of 25 g/m2 of unlabelled carrier galactose and 100 mg of 13C-galactose had the greatest sensitivity (93%; 95% confidence interval, 76-99%) and specificity (87%; 95% confidence interval, 65-97%) for distinguishing between normal subjects and cirrhotics when the test was performed 2 h after ingestion. The 13C-galactose breath test was also able to distinguish between class A and class B or C cirrhotics.

CONCLUSION

The 13C-galactose breath test is a useful non-invasive tool for distinguishing between healthy subjects and patients with liver cirrhosis and between cirrhotics with well-compensated liver disease and those with decompensated liver disease.

Relationship between postoperative erythromycin breath test and early morbidity in liver transplant recipients

BACKGROUND

Interindividual variability in dosage requirements of the calcineurin inhibitor immunosuppressive agents cyclosporine and tacrolimus after liver transplantation may result from differences in the CYP3A activity of the liver graft. Early postoperative erythromycin breath test (ERMBT) is an in vivo measure of graft CYP3A activity. This study evaluates the usefulness of an early postoperative ERMBT in predicting early morbidity in liver transplant recipients.

METHODS

In 26 liver transplant recipients, ERMBT was performed within 2 hr after transplantation. Main end points were the occurrence of cyclosporine and tacrolimus nephrotoxicity, episodes of early graft rejection, early graft function, and graft survival.

RESULTS

Cyclosporine and tacrolimus nephrotoxicity were associated with low postoperative ERMBT values (mean 0.63%+/-0.25% 14C/hr vs. 1.35%+/-0.84% 14C/hr, P=0.02). No significant association between early graft rejection and ERMBT values was demonstrated. There was a significant inverse correlation between postoperative ERMBT values and the time to normalization of international normalized ratio as a measure of early graft function (r=-0.78, P<0.001). Graft loss was associated with low postoperative ERMBT values (0.21%+/-0.15% 14C/hr vs. 1.09%+/-0.72% 14C/hr, P=0.002).

CONCLUSION

An early postoperative ERMBT may be useful in predicting the development of cyclosporine and tacrolimus nephrotoxicity, severe graft dysfunction, or even graft loss in liver transplant recipients when calcineurin inhibitors are administered according to protocols. Whether ERMBT results may be used to individualize dosage of calcineurin inhibitors needs to be explored.

Review article: breath testing for human liver function assessment

Carbon-labelled breath tests were proposed as tools for the evaluation of human liver function 30 years ago, but have never become part of clinical routine. One reason for this is the complex role of the liver in metabolic regulation, making it difficult to provide essential information for the management of patients with liver disease with a single test and to satisfy the hepatology community. As a result, a battery of breath tests have been developed. Depending on the test compound administered, different metabolic pathways (microsomal, cytosolic, mitochondrial) can be examined. Most available data come from microsomal function tests, whilst information about cytosolic and mitochondrial liver function is more limited. However, breath tests have shown promise in some studies, in particular to predict the outcome of patients with chronic liver disease or to monitor hepatic function after treatment. Whilst we await new substrates that can be used to measure liver function in a more valid manner, and large prospective studies to assess the usefulness of available test compounds, the aim of this review is to describe how far we have come in this controversial and unresolved issue.

Effect of influenza immunization on CYP3A4 activity

A number of clinical reports of drug interactions with influenza vaccine have been made. We hypothesized that CYP3A4 activity would decrease following influenza immunization. Fifteen healthy subjects had erythromycin breath tests (ERMBT) and influenza antibody titer hemagglutinin inhibition assay (HIA) before and after receiving influenza vaccine. The mean age of the subjects was 31.9 years (S.D. 10.2). The change in ERMBT following influenza immunization was not significant (mean -4%, S.D. 17%, P=0.25). Influenza immunization does not significantly change CYP3A4 activity. Changes in serum drug concentrations noted previously after influenza immunization are either due to very small changes in CYP3A4 activity or other pharmacokinetic interactions.

Race but not age affects erythromycin breath test results in older hypertensive men

Erythromycin breath tests (ERBT) were performed to determine age and racial effects on CYP3A4-mediated hepatic clearance in hypertensive men (n = 43) in the clinical setting. Older hypertensive African American men (n = 19: 71 +/- 8 years, mean +/- SD) had faster ERBT clearance compared with Caucasian (n = 20: 72 +/- 6 years) hypertensive men (at 20 minutes after dosing: 0.042 +/- 0.01 percent dose/min exhaled vs. 0.033 +/- 0.013; at 60 minutes after dosing: 0.030 +/- 0.05 vs. 0.023 +/- 0.007 percent dose/min exhaled; ANOVA, p = 0.007), while age, smoking, and reported alcohol intake did not affect ERBT. The data suggest faster hepatic CYP3A-mediated clearance in African American men compared with Caucasian men, and that race may significantly affect CYP3A-mediated hepatic clearance in patients treated for hypertension.

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.

Potential use of pharmacological markers to quantitatively assess liver function during liver transplantation surgery

Early functioning of the transplanted liver is of crucial importance to the recipient. This function may be assessed by measuring the disposition of substances that are mainly eliminated via the liver. None of the agents currently used is ideal for this purpose. Measurement of mono-ethyleneglycinexylidide (MEGX) formation from lignocaine is useful and has been widely used in liver transplantation to assess liver graft function. MEGX formation can be affected by the use of drugs that influence liver perfusion or interfere with the CYP450 enzyme system. Indocyanine green clearance is a convenient method but both blood flow and hepatocellular function affect the test results. Tests of caffeine clearance, galactose elimination capacity and antipyrine clearance all require time-consuming, technically cumbersome and expensive serial blood sampling. The aminopyrine breath test is non-invasive, but gastric emptying and the patient's physical state affect results. The potential hazard of exposure to radioactive compounds limits the wide clinical use of both aminopyrine and erythromycin breath tests. Monitoring the rate of recovery from neuromuscular blockade induced by vecuronium and rocuronium can provide valuable information on liver function.

Phenotyping of drug-metabolizing enzymes in adults: a review of in-vivo cytochrome P450 phenotyping probes

Cytochrome P450 phenotyping provides valuable information about real-time activity of these important drug-metabolizing enzymes through the use of specific probe drugs. Despite more than 20 years of research, few conclusions regarding optimal phenotyping methods have been reached. Caffeine offers many advantages for CYP1A2 phenotyping, but the widely used caffeine urinary metabolic ratios may not be the optimal method of measuring CYP1A2 activity. Several probes of CYP2C9 activity have been suggested, but little information exists regarding their use, largely due to the narrow therapeutic index of most CYP2C9 probes. Mephenytoin has long been considered the standard CYP2C19 phenotyping probe, but problems such as sample stability and adverse effects have prompted the investigation of potential alternatives, such as omeprazole. Several well-validated CYP2D6 probes are available, including dextromethorphan, debrisoquin and sparteine, but, in most cases, dextromethorphan may be preferred due to its wide safety margin and availability. Chlorzoxazone remains the only CYP2E1 probe that has received much study. However, questions concerning phenotyping method and involvement of other enzymes have impaired its acceptance as a suitable CYP2E1 phenotyping probe. CYP3A phenotyping has been the subject of numerous investigations, reviews and commentaries. Nevertheless, much controversy regarding the selection of an ideal CYP3A probe remains. Of all the proposed methods, midazolam plasma clearance and the erythromycin breath test have been the most rigorously studied and appear to be the most reliable of the available methods. Despite the limitations of many currently available probes, with continued research, phenotyping will become an even more valuable research and clinical resource.

A pilot study of posttraumatic stress and nonadherence in pediatric liver transplant recipients

BACKGROUND

Symptoms of posttraumatic stress disorder (PTSD) were described in survivors of life-threatening diseases, the trauma being the experiences associated with the disease or its treatment. Their prevalence in liver transplant recipients is unknown. Based on clinical observations, we hypothesize that a significant proportion of pediatric liver transplant recipients suffers from PTSD symptoms. We further hypothesize that nonadherence (noncompliance) to medical management may, in some cases, be associated with these symptoms. Traumatized patients, according to this hypothesis, will avoid taking their medications, because these serve as painful reminders of the disease.

OBJECTIVES

To determine the prevalence of PTSD symptoms in a sample of pediatric liver transplant recipients. To determine whether symptoms of PTSD are associated with nonadherence in these patients. To describe the clinical presentation of PTSD and the management of severe nonadherence in patients who suffer from this disorder.

METHODS

Nineteen pediatric liver transplant recipients and their caretakers were interviewed, using the UCLA Post Traumatic Stress Disorder Reaction Index (PTSRI). Data were obtained on a few demographic parameters and perception of disease threat. Adherence was evaluated by 2 methods: 1) a clinician panel (taking into account the clinical sequelae of severe nonadherence); and 2) computation of the standard deviations (SDs) of consecutive determinations of blood levels of Tacrolimus (a higher SD means higher variability between individual measures and is therefore an indicator of nonadherence). As an illustration of the general phenomenon, we describe 3 cases of liver transplant recipients who were nonadherent and who suffered from PTSD.

RESULTS

Six of 19 patients had positive scores on all 3 components of the PTSRI (PTSD patients). Three of these, and none of the others, were considered significantly nonadherent by the panel. Therefore, nonadherence was significantly associated with the existence of symptoms from all 3 domains of PTSD (Fisher's exact test) in our sample. In particular, a high avoidance score on the PTSRI was highly correlated with panel-determined nonadherence. Further, SD of medication levels were significantly higher in PTSD patients, compared with the rest of our sample. No significant differences were found in perception of disease threat or demographic variables between PTSD patients and the rest of our sample. The 3 cases that we describe became adherent to their medications when symptoms of PTSD subsided during the course of therapy.

CONCLUSIONS

Clinically significant nonadherence, determined by 2 different methods, was associated with the full spectrum of PTSD symptoms in this sample. It was especially associated with a high avoidance score, which suggests that avoidance of reminders of the disease (eg, medications) may be a mechanism of nonadherence. Screening for and management of these symptoms, therefore, may improve adherence. This novel concept may be applicable to other patient populations. However, more data are needed before any definite conclusions can be drawn.

Development of cytochrome P450 2D6-specific LKM-autoantibodies following liver transplantation for Wilson's disease -- possible association with a steroid-resistant transplant rejection episode

BACKGROUND/AIMS

Antibodies to cytochrome P450 2D6, also known as LKM1-autoantibodies, are characteristic for a subgroup of patients with autoimmune hepatitis, but can also occasionally be found in hepatitis C. We observed the occurrence of LKM1-autoantibodies 4 months after liver transplantation for Wilson's disease, in close association with a steroid-resistant rejection episode, in the absence of evidence for autoimmune hepatitis or hepatitis C.

METHODS

Sera from several time points prior to and following transplantation were tested for LKM-reactivity by immunofluorescence, ELISA and Western blotting. Antigen specificity was confirmed by Western blotting analysis on different cytochrome P450 isoenzymes. The absence of viral hepatitis C and hepatitis G virus infection was confirmed by polymerase chain reaction. The serum of the organ donor was also tested.

RESULTS

All the sera prior to transplantation and up to 4 months after transplantation were LKM-negative by all assay systems used. In the course of a steroid-resistant rejection episode at this time, the patient developed LKM antibodies at high titre (70% in inhibition ELISA) and has remained positive since (now more than 4 years). Reactivity was exclusively to the cytochrome isoenzyme 2D6. Hepatitis C infection never occurred, but hepatitis G was transiently present many years prior to transplantation. The donor serum was negative for all autoantibodies and for hepatitis C and G virus infection.

DISCUSSION

We here describe a patient developing LKM1-autoantibodies without evidence of autoimmune or viral hepatitis. The close temporal association with a transplant rejection episode suggests immunological mechanisms of rejection together with hepatocellular injury as a pathogenetic mechanism.

The lignocaine metabolite (MEGX) liver function test and P-450 induction in humans

AIMS

The N-deethylation of lignocaine to monoethylglycinexylidide (MEGX) is partially catalysed by the rifampicin inducible P-450 isoenzyme CYP3A4. This has led to the use of the MEGX test (MEGX plasma concentrations after i.v. lignocaine) as a marker of CYP3A4 activity. To test this hypothesis, we studied lignocaine and MEGX plasma pharmacokinetics.

METHODS

Ten healthy volunteers received rifampicin (600 mg day(-1)) for 6 days, resulting in a four- to sixfold increase in urinary 6beta-hydroxycortisol output. On days 1 and 7 (pretreatment), day 11 (treatment), and day 14 (48 h after rifampicin), 50 mg lignocaine i.v. was administered. MEGX concentrations at 30 min [MEGX30min] were assessed and normalised to MEGX test results after 1 mg kg(-1) lignocaine. On days 7 and 14 the lignocaine and MEGX plasma concentrations were measured over a 300 min period. MEGX test results and lignocaine and MEGX plasma pharmacokinetics before and after induction with rifampicin were compared.

RESULTS

The lignocaine plasma clearance increased from 7.5+/-1.2 ml min(-1) kg(-1) before to 8.6+/-2ml min(-1) kg(-1) (P=0.026) after induction. The normalised MEGX30min concentrations increased from 61+/-14 (day 7) to 82+/-34 microg l(-1) (day 14) by a mean of 21 microg l(-1) (95% confidence interval: -3 to 44 microg l(-1)) (P=0.055).

CONCLUSION

An insignificant increase of MEGX plasma concentrations was found in 10 volunteers after induction of CYP3A4 activity by rifampicin. Therefore, the MEGX test is not a sensitive marker of P-450 induction in healthy human liver.

Relationship between in vivo FK506 clearance and in vitro 13-demethylation activity in living-related liver transplantation

BACKGROUND

Although it is important to maintain an appropriate blood concentration of FK506 after liver transplantation, significant interindividual variability in the actual FK506 dosage has been observed, presumably due to the wide variability of cytochrome P450 3A4 activity in liver microsomes.

METHODS

A study was conducted in patients undergoing living-related liver transplantation and their donors to investigate the relationship between the in vitro FK506 demethylation activity in graft liver microsomes and the in vivo blood clearance of FK506. Liver biopsy tissue was obtained from 17 living donors to measure the in vitro formation rate of 13-demethyl derivative (M-I: the major metabolite of FK506). Erythromycin N-demethylation activity in vitro was also assessed in 11 cases. The FK506 blood clearance (CLss) was calculated from its constant infusion rate and steady-state blood concentration on day 4 after transplantation in 17 recipients.

RESULTS

The FK506 infusion rate varied 4.6-fold from 8.3 to 38.4 ng/min/kg. The mean CLss of FK506 was 22.1+/-10.8 ml/min (10.1-45.2 ml/min). The M-I formation rate showed a wide variability, ranging from 0.098 to 0.571 nmol/min/mg protein. A significant correlation was observed between the in vitro estimated total metabolic ability of the graft for FK506 (M-I formation rate x graft weight) and the in vivo CLss of FK506 (r=0.770, P<0.001). Erythromycin N-demethylation (0.066-0.443 nmol/min/mg protein) showed a strong correlation with the M-I formation rate (r=0.891, P<0.01).

CONCLUSIONS

The in vivo FK506 clearance can mainly reflect in vitro FK506 demethylation activity.

Serious interaction between mibefradil and tacrolimus

BACKGROUND/AIMS

Tacrolimus is metabolized by cytochrome P450 3A4 and 2D6 and has a narrow therapeutic range. We report a serious kinetic interaction between tacrolimus and mibefradil, a potent cytochrome P450 inhibitor.

CASE REPORT

A 62-year-old women who had undergone liver transplantation was treated with tacrolimus for immunosuppression. For control of blood pressure, the patient was treated with nifedipine. She developed ankle edema, and nifedipine was replaced by mibefradil. Four days later, she presented with mental confusion, renal failure, and hyperglycemia, compatible with tacrolimus toxicity. In agreement with this assumption, the tacrolimus blood concentration was 100 ng/ml. Mibefradil and tacrolimus were both stopped, and the patient recovered within 1 week. Eight days after stopping mibefradil, tacrolimus was restarted at the same dosage and the subsequent plasma concentrations remained in the therapeutic range.

CONCLUSIONS

Mibefradil increases the tacrolimus blood concentration by inhibiting its metabolism and should, therefore, not be used in patients treated with tacrolimus.

The use of the lidocaine-monoethylglycinexylidide test in the liver transplant recipient

The lidocaine-monoethylglycinexylidide (MEGX) test is used to monitor liver function in liver transplant recipients. Serial studies have been undertaken after 155 allografts. The initial MEGX concentration is significantly correlated with the donor MEGX concentration. It is also influenced by the recipient's pretransplant bilirubin concentration, being lowest among patients with very high bilirubin levels. Use of segmental grafts is also accompanied by low MEGX concentrations. The flow-dependent clearance of lidocaine makes it a sensitive indicator of disturbed liver blood flow, with decreased MEGX concentrations occurring in hepatic artery thrombosis and rejection and as a result of cardiac failure and pulmonary effusions. Significant hepatic ischemia resulting in delayed initial function or cholestasis also is associated with low MEGX concentrations. The initial median MEGX concentrations were lowest among patients who required retransplantation or who died within 2 months of allografting.

The use of lidocaine as a test of liver function in liver transplantation

The hepatic metabolism of lidocaine to monoethyl-glycinexylidide (MEGX) is the basis of a dynamic test of liver function. To understand its potential value in liver transplantation, the latter has been considered in the following three separate stages: pretransplantation assessment of potential candidates, potential liver donors, and the transplant recipient. In pretransplantation patients, data support its role in assessing risk of morbidity and mortality. In assessment of the liver transplant donor, there are differences concerning apparent usefulness, and these must be resolved. In the liver transplant recipient, serial measurements are useful to measure real-time hepatic metabolic activity. Low MEGX values reflect the clinical condition of the patient, and the importance of entirely assessing the patient, not just noting the test result, is paramount. This review has considered the role of the MEGX test in liver transplantation.

The erythromycin breath test predicts the clearance of midazolam

Midazolam, a commonly used sedative and amnestic medication, has recently been shown to be largely metabolized in the liver by a cytochrome P450, termed CYP3A4. There is at least a tenfold intersubject variability in the liver content and catalytic activity of CYP3A4, which may in part account for the known interpatient differences in the kinetics of midazolam. To test this hypothesis, we determined the intravenous midazolam kinetics of 20 medically stable, hospitalized patients, whose hepatic CYP3A4 activities were determined with use of the [14C-N-methyl]erythromycin breath test. During the kinetic study, we also performed psychometric testing designed to quantitate the level of sedation and amnesia. We found a significant positive correlation between the erythromycin breath test results and weight adjusted clearance (in milliliters per minute per kilogram) of both total midazolam (r = 0.52; p = 0.03) and unbound midazolam (r = 0.61; p < 0.01). The relatively low dose of midazolam used (0.0145 mg/kg) produced significant but transient sedation and memory impairment in some of the patients. We conclude that interpatient differences in liver CYP3A4 activity in part account for the variations in midazolam kinetics. Our observations account for reported drug interactions involving midazolam and suggest that patients with low CYP3A4 activity may be most susceptible to prolonged amnestic effects occasionally produced by this short-acting benzodiazepine.