Abrupt increase of tacrolimus blood levels during an episode of Shigella infection in a child after liver transplantation

Pharmacomicrobiomics: Immunosuppressive Drugs and Microbiome Interactions in Transplantation

The human microbiome is associated with human health and disease. Exogenous compounds, including pharmaceutical products, are also known to be affected by the microbiome, and this discovery has led to the field of pharmacomicobiomics. The microbiome can also alter drug pharmacokinetics and pharmacodynamics, possibly resulting in side effects, toxicities, and unanticipated disease response. Microbiome-mediated effects are referred to as drug-microbiome interactions (DMI). Rapid advances in the field of pharmacomicrobiomics have been driven by the availability of efficient bacterial genome sequencing methods and new computational and bioinformatics tools. The success of fecal microbiota transplantation for recurrent Clostridioides difficile has fueled enthusiasm and research in the field. This review focuses on the pharmacomicrobiome in transplantation. Alterations in the microbiome in transplant recipients are well documented, largely because of prophylactic antibiotic use, and the potential for DMI is high. There is evidence that the gut microbiome may alter the pharmacokinetic disposition of tacrolimus and result in microbiome-specific tacrolimus metabolites. The gut microbiome also impacts the enterohepatic recirculation of mycophenolate, resulting in substantial changes in pharmacokinetic disposition and systemic exposure. The mechanisms of these DMI and the specific bacteria or communities of bacteria are under investigation. There are little or no human DMI data for cyclosporine A, corticosteroids, and sirolimus. The available evidence in transplantation is limited and driven by small studies of heterogeneous designs. Larger clinical studies are needed, but the potential for future clinical application of the pharmacomicrobiome in avoiding poor outcomes is high.

Impact of Inflammation on Cytochromes P450 Activity in Pediatrics: A Systematic Review

Background and Objective

Cytochromes P450 (CYP) are the major enzymes involved in hepatic metabolism of drugs. Personalization of treatment in pediatrics is a major challenge, as it must not only take into account genetic, environmental, and physiological factors but also ontogeny. Published data in adults show that inflammation had an isoform-specific impact on CYP activities and we aimed to evaluate this impact in the pediatric population.

Methods

Articles listed in PubMed through 7 January, 2021 that studied the impact of inflammation on CYP activities in pediatrics were included in this systematic review. Sources of inflammation, victim drugs (CYP involved), effect of drug–disease interactions, number and age of subjects, and study design were extracted.

Results

Twenty-seven studies and case reports were included. The impact of inflammation on CYP activities appeared to be age dependent and isoform-specific, with some drug–disease interactions having significant pharmacokinetic and clinical impact. For example, midazolam clearance decreases by 70%, while immunosuppressant and theophylline concentrations increase three-fold and two-fold with intensive care unit admission and infection. Cytochrome P450 activity appears to return to baseline level when the disease is resolved.

Conclusions

Studies that have assessed the impact of inflammation on CYP activity are lacking in pediatrics, yet it is a major factor to consider to improve drug efficacy or safety. The scarce current data show that the impact of inflammation is isoform and age dependent. An effort must be made to improve the understanding of the impact of inflammation on CYP activities in children to better individualize treatment.

Intra-patient variability in tacrolimus exposure: causes, consequences for clinical management

Tacrolimus (Tac) is widely used for the prevention of rejection after solid organ transplantation. Finding the optimal balance between effective Tac concentrations and toxicity is a challenge and requires therapeutic drug monitoring. In addition to the well-known inter-patient variability, the clinical use of Tac is also complicated by considerable intra-patient variability (IPV) in Tac exposure. Tac IPV is defined as the amount of fluctuation of whole-blood concentrations over a certain period of time during which the Tac dose remains unchanged. A high IPV in Tac exposure has recently been recognized as a strong risk factor for acute rejection and poor long-term kidney transplantation outcome. In addition to non-adherence, several other factors determine the magnitude of the IPV in Tac exposure. Quantification of IPV is easy and can be easily incorporated into everyday clinical practice as a tool for optimizing transplantation outcomes.

Buccal vs. nasogastric tube administration of tacrolimus after pediatric liver transplantation

Tacrolimus is an important drug for immunosuppression after liver transplantation. Bioavailability of enterally administered tacrolimus is poor, and further reduced by gastric residuals or by enteral nutrition. Buccal administration might be an alternative route especially in children. Tacrolimus trough levels (TTLs) obtained after buccal administration of tacrolimus after liver transplantation have not been reported. The aim of this study was to determine whether buccal administration of tacrolimus is feasible and to compare TTLs after nasogastric tube (NGT) administration with buccal administration. TTLs after NGT or buccal administration during the first week after pediatric liver transplantation were analyzed from 28 cadaveric liver transplants in 23 pediatric recipients between June 2002 and March 2004. Each level was scored within, under or above the target range. Buccal administration was well tolerated in all patients. A total of 149 TTLs were obtained of which nine were excluded because of incomplete information on target levels. Overall 27% of TTLs was adequate. The percentage of levels under, within and above the target range were comparable in both groups (chi-square test; p = 0.64). Both groups had a decrease in percentages within the target range on day 3 and 4 after liver transplantation with a subsequent rise. Buccal tacrolimus administration is feasible. Similar TTLs are achieved compared with NGT tacrolimus administration during the first week after pediatric liver transplantation.

Elevated blood concentrations of calcineurin inhibitors during diarrheal episode in pediatric liver transplant recipients: involvement of the suppression of intestinal cytochrome P450 3A and P-glycoprotein

We encountered two cases of pediatric living-related liver transplant recipients who showed increases in blood concentration of cyclosporine or tacrolimus, a dual substrate for cytochrome P450 (CYP) 3A and P-glycoprotein (P-gp), during a diarrheal episode. To investigate the effect of intestinal inflammation on the metabolic and efflux pump activities, we conducted the experiments using the lipopolysaccharide (LPS)-induced intestinal damage model. Intestinal epithelial CYP3A activity was assessed by nifedipine oxidation using intestinal epithelial microsomes in rat. Drug efflux by P-gp was tested using digoxin flux with the excised intestine perfusion system in rats. Intraperitoneal injection of LPS (0.3 mg/kg) significantly reduced the intestinal epithelial CYP3A activity by 41% (p < 0.01). In the proximal jejunal segment of the rats treated with LPS, mucosal to serosal flux of digoxin was significantly enhanced compared to that of control (p < 0.05). Efflux of digoxin, which was taken up by intestinal epithelium, to mucosal perfusate was significantly blunted in the jejunum treated with LPS (p < 0.05), which indicates that the LPS treatment reduced the P-gp activity in rat small intestine. These findings suggest that the suppression of CYP3A and P-gp activities may be involved in the mechanism of elevated blood concentrations of cyclosporine and tacrolimus during enteritis-induced diarrhea. To prevent a drug-induced adverse effect, dose of a drug, which is a substrate of CYP3A or P-gp, should be reduced during such an episode.

Potential elevation of tacrolimus trough concentrations with concomitant metronidazole therapy

OBJECTIVE

To report the occurrence of a potential tacrolimus elevation in a renal transplant recipient after adding metronidazole to the medication regimen.

CASE SUMMARY

A 24-year-old white man status post living-related renal transplant who had been stabilized on tacrolimus 4 mg twice daily (trough concentrations 7-10 ng/mL) for 2 months and prednisone 20 mg daily presented to the clinic with severe diarrhea. Stool cultures were positive for Clostridium difficile, and therapy with metronidazole 500 mg 4 times daily was initiated. Between days 4 and 14 of metronidazole therapy, the patient's tacrolimus trough concentration and serum creatinine level increased to maximum levels of 26.3 ng/mL and 3.3 mg/dL (baseline 1.6-1.8 mg/dL), respectively. Tacrolimus was withheld for one dose and then decreased to 1 mg twice daily. Two days after metronidazole discontinuation, tacrolimus trough concentrations dropped to 9.4 ng/mL and serum creatinine to 2.3 mg/dL, warranting a tacrolimus dose increase to 3 mg daily.

DISCUSSION

As of April 15, 2005, one other case has been reported documenting an elevation in tacrolimus concentrations with the addition of metronidazole. The possible mechanism may be related to metronidazole's weak inhibition of CYP3A4 and, possibly, P-glycoprotein. According to the Naranjo probability scale, metronidazole was the probable cause of this adverse reaction.

CONCLUSIONS

Coadministration of tacrolimus with metronidazole may result in elevated tacrolimus concentrations, possibly leading to tacrolimus toxicity. Practitioners should be aware of this potential interaction and closely monitor tacrolimus concentrations and renal function.

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.

Increased tacrolimus trough levels in association with severe diarrhea, a case report

It is well known that during diarrhea episodes decreased cyclosporine and tacrolimus levels are often observed, usually requiring an increase in dose. An increase in tacrolimus trough levels is infrequently recognized as a potential cause of the adverse effect of severe diarrhea. Herein, we report the case of a renal transplant patient who displayed increased tacrolimus trough levels during an episode of gastroenteritis with severe diarrhea. The patient is 32-year-old male who received a renal transplant from his mother. Immunosuppression was initiated with tacrolimus in combination with mycophenolate mofetil and prednisone. The postoperative course was uneventful. The function of the transplanted kidney was normal. Eight months after transplantation he presented to our hospital with a history of high fever, abdominal pain, nausea and severe diarrhea. He was admitted with a diagnosis of enterocolitis of unknown etiology. The blood trough level of tacrolimus had increased from 6.7 ng/mL to 28.7 ng/mL after the onset of diarrhea. A therapeutic trough level of tacrolimus was reached 6 weeks after complete relief of diarrhea. Tacrolimus shows large variability in bioavailability after oral administration, both due to intestinal metabolism by cytochrome P450 (CYP3A4) and active secretion from enterocyte into intestinal lumen by P-glycoprotein. The epithelial cells of the intestine, may be destroyed abrogating P-glycoproteins during the course of enterocolitis, thereby increasing the levels of tacrolimus. It is recommended to monitor trough levels of tacrolimus during severe diarrhea of any nature to prevent tacrolimus-related complications.

Two- to three-fold increase in blood tacrolimus (FK506) levels during diarrhea in liver-transplanted children

BACKGROUND

The diagnosis and treatment of diarrhea in liver transplant recipients often pose a challenge owing to the variety of infectious and non-infectious causes. However, diagnosis is principally focused on ruling out an infectious etiology. Tacrolimus, an immunosuppressive agent generally used after liver transplantation, is absorbed mainly from the duodenum through the upper jejunum. It can be assumed that metabolism of the drug will be influenced by diarrhea.

METHODS

Four liver transplant recipients who developed an episode of acute gastroenteritis. Infectious etiology was confirmed; trough tacrolimus levels were measured before, during and after gastroenteritis.

RESULTS

All patients presented a two- to three-fold increase in blood tacrolimus levels after the onset of gastroenteritis.

CONCLUSIONS

Until the role played by the intestine in the metabolism of tacrolimus is fully understood, it is prudent to recommend early dose reduction of tacrolimus and careful monitoring of trough levels during diarrheal disorders of any nature in pediatric liver-transplanted patients.