The Magnitude and Time Course of Changes in Mycophenolic Acid 12-Hour Predose Levels During Antibiotic Therapy in Mycophenolate Mofetil-Based Renal 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.

Clinical Pharmacology in Sarcoidosis: How to Use and Monitor Sarcoidosis Medications

When sarcoidosis needs treatment, pharmacotherapy is usually required. Although glucocorticoids work reliably and relatively quickly for sarcoidosis, these drugs are associated with numerous significant side effects. Such side effects are common in sarcoidosis patients, as the disease frequently has a chronic course and glucocorticoid treatment courses are often prolonged. For these reasons, corticosteroid-sparing and corticosteroid-replacing therapies are often required for sarcoidosis. Unfortunately, many healthcare providers who care for sarcoidosis patients are not familiar with the use of these agents. In this manuscript, we provide a review of the pharmacotherapy of sarcoidosis. We discuss the mechanism of action, dosing, side-effect profile, approach to monitoring and patient counselling concerning glucocorticoids, and the common alternative drugs recommended for use in the recent European Respiratory Society (Lausanne, Switzerland) Sarcoidosis Treatment Guidelines. We also discuss the use of these agents in special situations including hepatic insufficiency, renal insufficiency, pregnancy, breastfeeding, vaccination, and drug-drug interactions. It is hoped that this manuscript will provide valuable practical guidance to clinicians who care for sarcoidosis patients.

Decrease in Mycophenolic Acid Plasma Level by Sacubitril/Valsartan in a Lupus Nephritis Patient: A Case Report

Introduction

Mycophenolate mofetil (MMF), an inactive prodrug of mycophenolic acid (MPA), is an immunosuppressive drug used widely in the treatment of lupus nephritis. In this case report, the area under the blood concentration time curve (AUC) of MPA was significantly decreased by the concomitant use of sacubitril/valsartan.

Case Presentation

The patient was a man in his 40s with a diagnosis of lupus nephritis class IVa/c+V. MMF dose was 1.5 g/day at admission, and AUC of MPA on day 14 was 25.1 μg⋅h/mL. Owing to poor blood pressure control, sacubitril/valsartan was initiated at 97/103 mg/day on day 29. On day 37, AUC of MPA was significantly decreased to 8.7 μg⋅h/mL, suggesting drug interaction with the newly initiated sacubitril/valsartan. Sacubitril/valsartan was decreased to 49/51 mg/day, and AUC of MPA on day 67 was 37.6 μg⋅h/mL, achieving the target range. The final MMF dose was set at 1.75 g/day. A possible mechanism of drug interaction between sacubitril/valsartan and MPA involves an organic anion transporting polypeptide (OATP). The inhibition of OATPs by sacubitril may have interrupted the enterohepatic circulation of MPA, resulting in a lower plasma concentration.

Conclusion

Since lupus nephritis is often associated with hypertension, the drug interaction observed in this report may also occur in other cases. However, it is impossible to conclude that the decrease in plasma MPA levels was due to the concomitant use of sacubitril/valsartan, and more cases and basic findings are needed.

Body Surface Area-Based Dosing of Mycophenolate Mofetil in Pediatric Hematopoietic Stem Cell Transplant Recipients: A Prospective Population Pharmacokinetic Study

Mycophenolate mofetil (MMF) is commonly used for acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (HSCT). However, limited population pharmacokinetic (PPK) data are available for pediatric HSCT patients. This study aimed to develop a PPK model and recommend optimal oral MMF dosage in pediatric HSCT patients. This prospective study involved pediatric HSCT patients at a tertiary academic institution. Patients received oral MMF 15-20 mg/kg twice daily for aGVHD prophylaxis and treatment. The PPK analysis was conducted using a nonlinear mixed-effects modeling method. Simulation was performed considering different body surface areas (BSAs) (0.5 m2, 1.0 m2, 1.5 m2) and dosing (400 mg/m2, 600 mg/m2, 900 mg/m2 twice daily). Based on the simulation, an optimal dosage of oral MMF was suggested. A total of 20 patients and 80 samples were included in the PPK model development. A one-compartment model with first-order absorption adequately described the pharmacokinetics of mycophenolic acid (MPA). BSA was a statistically significant covariate on Vd/F. Simulation suggested the optimal dosage of oral MMF as 900 mg/m2 twice daily, respectively. A reliable PPK model was developed with good predictive performance. This model-informed optimal MMF dosage in pediatric HSCT patients can provide valuable dosing guidance in real-world clinical practice.

Drug Interactions and Safe Prescription Writing for Liver Transplant Recipients

Immunosuppression optimization is central to graft function in liver transplant recipients. Post-transplantation patients develop new onset or worsening metabolic syndrome, are prone to atypical infections, and are at higher risk of developing cardiac and brain-related clinical events. In this context, liver transplant recipients are at risk of using multiple comedications alongside immunosuppressants. It is imperative for the transplant physician to understand the various drug-drug interactions that potentially reduce or promote toxicity of immunosuppression, as well as associated synergistic or antagonistic effects on extrahepatic organ systems. This comprehensive review discusses drug-drug interactions in liver transplant recipients and the impact and role of complementary and alternative medicines among individuals on immunosuppression.

Gut Microbiota-Mediated Pharmacokinetic Drug-Drug Interactions between Mycophenolic Acid and Trimethoprim-Sulfamethoxazole in Humans

Mycophenolic acid (MPA) and trimethoprim-sulfamethoxazole (TMP-SMX) are commonly prescribed together in certain groups of patients, including solid organ transplant recipients. However, little is known about the pharmacokinetic drug-drug interactions (DDIs) between these two medications. Therefore, the present study aimed to determine the effects of TMP-SMX on MPA pharmacokinetics in humans and to find out the relationship between MPA pharmacokinetics and gut microbiota alteration. This study enrolled 16 healthy volunteers to take a single oral dose of 1000 mg mycophenolate mofetil (MMF), a prodrug of MPA, administered without and with concurrent use of TMP-SMX (320/1600 mg/day) for five days. The pharmacokinetic parameters of MPA and its glucuronide (MPAG) were measured using high-performance liquid chromatography. The composition of gut microbiota in stool samples was profiled using a 16S rRNA metagenomic sequencing technique during pre- and post-TMP-SMX treatment. Relative abundance, bacterial co-occurrence networks, and correlations between bacterial abundance and pharmacokinetic parameters were investigated. The results showed a significant decrease in systemic MPA exposure when TMP-SMX was coadministered with MMF. Analysis of the gut microbiome revealed altered relative abundance of two enriched genera, namely the genus Bacteroides and Faecalibacterium, following TMP-SMX treatment. The relative abundance of the genera Bacteroides, [Eubacterium] coprostanoligenes group, [Eubacterium] eligens group, and Ruminococcus appeared to be significantly correlated with systemic MPA exposure. Coadministration of TMP-SMX with MMF resulted in a reduction in systemic MPA exposure. The pharmacokinetic DDIs between these two drugs were attributed to the effect of TMP-SMX, a broad-spectrum antibiotic, on gut microbiota-mediated MPA metabolism.

Influence of Calcineurin Inhibitors and Genetic Polymorphism of Transporters on Enterohepatic Circulation and Exposure of Mycophenolic Acid in Chinese Adult Renal Allograft Recipients

There is significant enterohepatic circulation (EHC) during the disposition of mycophenolic acid (MPA). The aim of this study was to elucidate factors influencing the EHC of MPA in Chinese adult renal allograft recipients. After 2 weeks of therapy with mycophenolate mofetil or enteric-coated mycophenolate sodium, blood samples were collected from 125 patients at 0 to 12 hours post-administration and MPA concentrations were determined. The influence of calcineurin inhibitors (CNIs) and genetic polymorphisms on MPA exposure and EHC was studied. The Shapley additive explanations method was used to estimate the impact of various factors on the area under the plasma drug concentration-time curve (AUC_0-12h ) for MPA. An extreme gradient boosting (XGboost) machine learning-based model was established to predict AUC_0-12h . Results showed that the dose-normalized AUC_6-12h (dn-AUC_6-12h ) of MPA was significantly lower in patients co-administered with cyclosporine (CsA) than in patients co-administered with tacrolimus (TAC) (P < .05). For patients co-administered with TAC, patients with ABCC2 C-24T CC or SLCO1B1 T521C TT genotypes had significantly higher values of dn-AUC_6-12h (P < .05). Patients with SLCO1B3 334T/699G alleles had significantly lower dn-AUC_6-12h values than homozygotes (P < .05). By introducing body weight, age, and EHC-related factors, including co-administered CNIs and genetic polymorphism of drug transporters, as covariates in the XGboost machine learning model, the prediction performance of AUC_0-12h for MPA in Chinese adult renal allograft recipients can be improved.

Review of Postoperative Care for Heart Transplant Recipients

The early postoperative management strategies after heart transplantation include optimizing the function of the denervated heart, correcting the causes of hemodynamic instability, and initiating and maintaining immunosuppressive therapy, allograft rejection surveillance, and prophylaxis against infections caused by immunosuppression. The course of postoperative support is influenced by the quality of allograft myocardial protection prior to implantation and reperfusion, donor-recipient heart size matching, surgical technique of orthotopic heart transplantation, and patient factors (eg, preoperative condition, immunologic compatibility, postoperative vasomotor tone, severity and reversibility of pulmonary vascular hypertension, pulmonary function, mediastinal blood loss, and end-organ perfusion). This review provides an overview of the early postoperative care of recipients and includes a brief description of the surgical techniques for orthotopic heart transplantation.

Sustained suppression of enterohepatic circulation of mycophenolic acid by antimicrobial-associated diarrhea in a kidney transplant recipient with Crohn's disease: A case report

Mycophenolic acid (MPA) undergoes enterohepatic circulation. A kidney transplant patient on mycophenolate mofetil was treated with tazobactam/piperacillin for pyelonephritis, and developed antimicrobial-associated diarrhea. Consequently, the MPA trough level decreased by approximately 90%. Furthermore, it took approximately a month for the MPA level to normalize even after diarrhea had resolved.

Reduced Enterohepatic Recirculation of Mycophenolate and Lower Blood Concentrations are Associated with the Stool Bacterial Microbiome After Hematopoietic Cell Transplantation

BACKGROUND

Mycophenolate mofetil (MMF) is an important immunosuppressant used after allogeneic hematopoietic cell transplant (HCT). MMF has a narrow therapeutic index and blood concentrations of mycophenolic acid (MPA), the active component of MMF, are highly variable. Low MPA concentrations are associated with risk of graft vs host disease (GvHD) while high concentrations are associated with toxicity. Reasons for variability are not well known and may be due, at least in part, to the presence of β-glucuronidase producing bacteria in the gastrointestinal tract which enhance MPA enterohepatic recirculation (EHR) by transforming MPA metabolites formed in the liver back to MPA.

OBJECTIVE

To determine if individuals with high MPA EHR have a greater abundance of β-glucuronidase producing bacteria in their stool and higher MPA concentrations relative to those with low EHR.

STUDY DESIGN

We conducted a pharmacomicrobiomics study in 20 adult HCT recipients receiving a myeloablative or reduced intensity preparative regimen. Participants received MMF 1g IV every 8 hours with tacrolimus. Intensive pharmacokinetic sampling of mycophenolate was conducted before hospital discharge. Total MPA, MPA glucuronide (MPAG) and acylMPAG were measured. EHR was defined as a ratio of MPA area under the concentration-versus-time curve (AUC)_4-8 to MPA AUC_0-8. Differences in stool microbiome diversity and composition, determined by shotgun metagenomic sequencing, were compared above and below the median EHR (22%, range 5-44%).

RESULTS

Median EHR was 12% and 29% in the low and high EHR groups, respectively. MPA troughs, MPA AUC_4-8 and acylMPAG AUC_4-8/AUC_0-8, were greater in the high EHR group vs low EHR group [1.53 vs 0.28 mcg/mL, p = 0.0001], [7.33 vs 1.79 hr*mcg/mL, p = 0.0003] and [0.33 vs 0.24 hr*mcg/mL, p = 0.0007], respectively. MPA AUC_0-8 was greater in the high EHR than the low EHR group and trended towards significance [22.8 vs. 15.3 hr*mcg/mL, p=0.06]. Bacteroides vulgatus, stercoris and thetaiotaomicron were 1.2-2.4 times more abundant (p=0.039, 0.024, 0.046, respectively) in the high EHR group. MPA EHR was positively correlated with B. vulgatus (⍴=0.58, p≤0.01) and B. thetaiotaomicron (⍴=0.46, p<0.05) and negatively correlated with Blautia hydrogenotrophica (⍴=-0.53, p<0.05). Therapeutic MPA troughs were achieved in 80% of patients in the high EHR group and 0% in the low EHR. There was a trend towards differences in MPA AUC_0-8 and MPA C_ss mcg/mL in high vs. low EHR groups (p=0.06).

CONCLUSION

MPA EHR was variable. Patients with high MPA EHR had greater abundance of Bacteroides species in stool and higher MPA exposure than patients with low MPA EHR. Bacteroides may therefore be protective from poor outcomes such as graft vs host disease but in others it may increase the risk of MPA adverse effects. These data need to be confirmed and studied after oral MMF.

Drug Interactions between Antimicrobial and Immunosuppressive Agents in Solid Organ Transplant Recipients

The number of allogeneic solid organ and bone marrow transplants is increasing all over the world. To prevent transplant rejection and treat acute rejection of transplant, immunosuppressant drugs are used. The outcomes of solid organ transplants have dramatically improved over last 30 years, due to availability of multiple immunosuppressive agents, with varied mechanisms of action. The use of intense immunosuppression makes the individual having undergone solid organ transplant at the risk of several serious infections, which may prove fatal. To prevent and treat these infections (when they occur), patients are often given antimicrobial prophylaxis and therapy. The use of antimicrobials can interfere with the metabolism of the immunosuppressants, and may put the patient at risk of developing severe adverse effects due to unwanted increase or decrease in the serum levels of immunosuppressive agents. Knowledge of these interactions is essential for successful management of solid organ transplant patients. We therefore decided to review the literature and present the interactions that commonly occur between these two life-saving groups of drugs.

How to cite this article: Bhagat V, Pandit RA, Ambapurkar S, Sengar M, Kulkarni AP. Drug Interactions between Antimicrobial and Immunosuppressive Agents in Solid Organ Transplant Recipients. Indian J Crit Care Med 2021;25(1):67–76.

Clinical Pharmacokinetics of Mycophenolic Acid in Hematopoietic Stem Cell Transplantation Recipients

Mycophenolate mofetil (MMF), an ester prodrug of mycophenolic acid (MPA), is widely used as a maintenance immunosuppressive regimen in solid organ transplant patients. It is increasingly used for the prophylaxis and treatment of graft-versus-host disease (GVHD) in hematopoietic stem cell transplantation (HSCT) patients. MPA displays extensive binding to serum albumin and glucuronidation to the inactive MPA-7-O-glucuronide (MPAG). Here, we review and discuss the pertinent information regarding the clinical pharmacokinetics of MPA in HSCT patients. The pharmacokinetics of MPA are altered in HSCT patients with lower oral bioavailability, shorter half-life and higher clearance than those in healthy volunteers and renal transplant recipients. Moreover, clearance may be increased in young pediatric patients. The optimal MMF dosing and preferred targets are still under investigation in HSCT patients due to the substantial intra- and inter-individual pharmacokinetic variability of MPA and broad range of transplants (malignant vs. nonmalignant, related vs. unrelated donor, and human leukocyte antigen mismatch). The complex pharmacokinetics of MPA have partly hampered the efficient use of MMF, and pharmacokinetic studies in HSCT patients have been limited in size and mostly inconclusive. Future research should be multi-institutional and focus on developing clinical decisions with adequate statistical power to improve clinical care of HSCT recipients.

Ciprofloxacin blocked enterohepatic circulation of diclofenac and alleviated NSAID-induced enteropathy in rats partly by inhibiting intestinal β-glucuronidase activity

AIM

Diclofenac is a non-steroidal anti-inflammatory drug (NSAID), which may cause serious intestinal adverse reactions (enteropathy). In this study we investigated whether co-administration of ciprofloxacin affected the pharmacokinetics of diclofenac and diclofenac-induced enteropathy in rats.

METHODS

The pharmacokinetics of diclofenac was assessed in rats after receiving diclofenac (10 mg/kg, ig, or 5 mg/kg, iv), with or without ciprofloxacin (20 mg/kg, ig) co-administered. After receiving 6 oral doses or 15 intravenous doses of diclofenac, the rats were sacrificed, and small intestine was removed to examine diclofenac-induced enteropathy. β-Glucuronidase activity in intestinal content, bovine liver and E coli was evaluated.

RESULTS

Following oral or intravenous administration, the pharmacokinetic profile of diclofenac displayed typical enterohepatic circulation, and co-administration of ciprofloxacin abolished the enterohepatic circulation, resulted in significant reduction in the plasma content of diclofenac. In control rats, β-glucuronidase activity in small intestinal content was region-dependent: proximal intestine<distal intestine<ileal valve. Administration of ciprofloxac caused significant reduction of β-glucuronidase activity in distal small intestine, and particularly in ileal valve. Furthermore, ciprofloxacin (10-2000 μmol/L) dose-dependently inhibited β-glucuronidase activity in distal small intestine content or E coli incubated in vitro, but did not affect that in proximal small intestine content or bovine liver incubated in vitro. After receiving 6 oral doses or 15 intravenous doses of diclofenac, typical enteropathy was developed with severe enteropathy occurred in distal small intestine. Co-administration of ciprofloxacin significantly alleviated diclofenac-induced enteropathy.

CONCLUSION

Co-administration of ciprofloxacin attenuated enterohepatic circulation of diclofenac and alleviated diclofenac-induced enteropathy in rats, partly via the inhibition of intestinal β-glucuronidase activity.

Effects of amoxicillin/clavulanic acid on the pharmacokinetics of valproic acid

Valproic acid (VPA) is mainly metabolized via glucuronide, which is hydrolyzed by β-glucuronidase and undergoes enterohepatic circulation. Amoxicillin/clavulanic acid (AMC) administration leads to decreased levels of β-glucuronidase-producing bacteria, suggesting that these antibiotics could interrupt enterohepatic circulation and thereby alter the pharmacokinetics of VPA. This study aimed to evaluate the effects of AMC on the pharmacokinetics of VPA. This was an open-label, two-treatment, one-sequence study in 16 healthy volunteers. Two treatments were evaluated; treatment VPA, in which a single dose of VPA 500 mg was administered, and treatment AMC + VPA, in which multiple doses of AMC 500/125 mg were administered three times daily for 7 days and then a single dose of VPA was administered. Blood samples were collected up to 48 hours. Pharmacokinetic parameters were calculated using noncompartmental methods. Fifteen subjects completed the study. Systemic exposures and peak concentrations of VPA were slightly lower with treatment AMC + VPA than with treatment VPA (AUC_last, 851.0 h·mg/L vs 889.6 h·mg/L; C_max, 52.1 mg/L vs 53.0 mg/L). There were no significant between-treatment effects on pharmacokinetics (95% confidence interval [CI]) of AUC_last and C_max (95.7 [85.9–106.5] and 98.3 [91.6–105.6], respectively). Multiple doses of AMC had no significant effects on the pharmacokinetics of VPA; thus, no dose adjustment is necessary.

Management of urinary tract infection in solid organ transplant recipients: Consensus statement of the Group for the Study of Infection in Transplant Recipients (GESITRA) of the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC) and the Spanish Network for Research in Infectious Diseases (REIPI)

BACKGROUND

Urinary tract infections (UTIs) are one of the most common infections in solid organ transplant (SOT) recipients.

METHODS

Experienced SOT researchers and clinicians have developed and implemented this consensus document in support of the optimal management of these patients. A systematic review was conducted, and evidence levels based on the available literature are given for each recommendation. This article was written in accordance with international recommendations on consensus statements and the recommendations of the Appraisal of Guidelines for Research and Evaluation II (AGREE II).

RESULTS

Recommendations are provided on the management of asymptomatic bacteriuria, and prophylaxis and treatment of UTI in SOT recipients. The diagnostic-therapeutic management of recurrent UTI and the role of infection in kidney graft rejection or dysfunction are reviewed. Finally, recommendations on antimicrobials and immunosuppressant interactions are also included.

CONCLUSIONS

The latest scientific information on UTI in SOT is incorporated in this consensus document.

Optimizing drug therapy in pediatric SCT: focus on pharmacokinetics

Given age-related differences in drug metabolism and indications for hematopoietic SCT (HSCT), personalized drug dosing of the conditioning regimen and post-transplant immunosuppression may reduce graft rejection, relapse rates and toxicity in pediatric HSCT recipients. This manuscript summarizes the pharmacokinetic/dynamic data of HSCT conditioning and post-grafting immunosuppression, presented at the First Annual Pediatric Bone Marrow Transplant Consortium (PBMTC) meeting in April 2013. Personalized dosing of BU to a target plasma exposure reduces graft rejection in children and improves relapse/toxicity rates in adults. Current weight-based dosing achieves the target BU exposure in only a minority (24.3%) of children. The initial BU dose should be based on the European Medicines Agency nomogram or population pharmacokinetic models to improve the numbers of children achieving the target exposure. There are limited pharmacokinetic data for treosulfan, CY, fludarabine and alemtuzumab as HSCT conditioning in children. For post-grafting immunosuppression, mycophenolic acid (MPA) clearance may be increased in younger children (<12 years). The preferred MPA pharmacokinetic monitoring parameters and target range are still evolving in HSCT recipients. Multi-institutional trials incorporating properly powered pharmacokinetic/dynamic studies are needed to assess the effect of variability in the plasma exposure of drugs/metabolites on clinical outcomes in pediatric HSCT recipients.

High prevalence of potential drug interactions affecting mycophenolic acid pharmacokinetics in nonmyeloablative hematopoietic stem cell transplant recipients

Objective: Mycophenolic acid (MPA) exposure is associated with clinical outcomes in hematopoietic cell transplant (HCT) recipients. Various drug interaction studies, predominantly in healthy volunteers or solid organ transplant recipients, have identified medications which impact MPA pharmacokinetics. Recipients of nonmyeloablative HCT, however, have an increased burden of comorbidities, potentially increasing the number of concomitant medications and potential drug interactions (PDI) affecting MPA exposure. Thus, we sought to be the first to characterize these PDI in nonmyeloablative HCT recipients. Materials and methods: We compiled PDI affecting MPA pharmacokinetics and characterized the prevalence of PDI in nonmyeloablative HCT recipients. A comprehensive literature evaluation of four databases and PubMed was conducted to identify medications with PDI affecting MPA pharmacokinetics. Subsequently, a retrospective medication review was conducted to characterize the cumulative PDI burden, defined as the number of PDI for an individual patient over the first 21 days after allogeneic graft infusion, in 84 nonmyeloablative HCT recipients. Results: Of the 187 concomitant medications, 11 (5.9%) had a PDI affecting MPA pharmacokinetics. 87% of 84 patients had one PDI, with a median cumulative PDI burden of 2 (range 0 – 4). The most common PDI, in descending order, were cyclosporine, omeprazole and pantoprazole. Conclusion: Only a minority of medications (5.9%) have a PDI affecting MPA pharmacokinetics. However, the majority of nonmyeloablative HCT recipients had a PDI, with cyclosporine and the proton pump inhibitors being the most common. A better understanding of PDI and their management should lead to safer medication regimens for nonmyeloablative HCT recipients.

Quinolone prophylaxis for the prevention of BK virus infection in kidney transplantation: study protocol for a randomized controlled trial

BACKGROUND

BK virus infection has emerged as a major complication in kidney transplantation leading to a significant reduction in graft survival. There are currently no proven strategies to prevent or treat BK virus infection. Quinolone antibiotics, such as levofloxacin, have demonstrated activity against BK virus. We hypothesize that administration of a quinolone antibiotic, when given early post-transplantation, will prevent the establishment of BK viral replication in the urine and thus prevent systemic BK virus infection.

METHODS/DESIGN

The aim of this pilot trial is to assess the efficacy, safety and feasibility of a 3-month course of levofloxacin in the kidney transplant population. This is a multicenter, randomized, double-blind, placebo-controlled trial with two parallel arms conducted in 11 Canadian kidney transplant centers. A total of 154 patients with end-stage renal disease undergoing kidney transplantation will be randomized to receive a 3-month course of levofloxacin or placebo starting in the early post-transplant period. Levofloxacin will be administered at 500 mg po daily with dose adjustments based on kidney function. The primary outcome will be the time to occurrence of BK viruria within the first year post-transplantation. Secondary outcomes include BK viremia, measures of safety (adverse events, resistant infections,Clostridium difficile-associated diarrhea), measures of feasibility (proportion of transplanted patients recruited into the trial), proportion of patients adherent to the protocol, patient drop-out and loss to follow-up,and use of quinolone antibiotics outside of the trial protocol.

DISCUSSION

Results from this pilot study will provide vital information to design and conduct a large, multicenter trial to determine if quinolone therapy decreases clinically meaningful outcomes in kidney transplantation. If levofloxacin significantly reduces BK viruria and urine viral loads in kidney transplantation, it will provide important justification to progress to the larger trial. If the full trial shows that levofloxacin significantly reduces BK infection and improves outcomes, its use in kidney transplantation will be strongly endorsed given the lack of proven therapies for this condition.

TRIAL REGISTRATION

This trial was funded by the Canadian Institutes of Health Research (grant number:222493) and is registered at ClinicalTrials.gov (NCT01353339).

Population pharmacokinetics and dose optimization of mycophenolic acid in HCT recipients receiving oral mycophenolate mofetil

We sought to create a population pharmacokinetic model for total mycophenolic acid (MPA), to study the effects of different covariates on MPA pharmacokinetics, to create a limited sampling schedule (LSS) to characterize MPA exposure (i.e., area under the curve or AUC) with maximum a posteriori Bayesian estimation, and to simulate an optimized dosing scheme for allogeneic hematopoietic cell transplantation (HCT) recipients. Four thousand four hundred ninety-six MPA concentration-time points from 408 HCT recipients were analyzed retrospectively using a nonlinear mixed effects modeling approach. MPA pharmacokinetics was characterized with a two-compartment model with first-order elimination and a time-lagged first-order absorption process. Concomitant cyclosporine and serum albumin were significant covariates. The median MPA clearance (CL) and volume of the central compartment were 24.2 L/hour and 36.4 L, respectively, for a 70 kg patient receiving tacrolimus with a serum albumin of 3.4 g/dL. Dosing simulations indicated that higher oral MMF doses are needed with concomitant cyclosporine, which increases MPA CL by 33.8%. The optimal LSS was immediately before and at 0.25 hours, 1.25 hours, 2 hours, and 4 hours after oral mycophenolate mofetil administration. MPA AUC in an individual HCT recipient can be accurately estimated using a five-sample LSS and maximum a posteriori Bayesian estimation.

Antimicrobial and immunosuppressive drug interactions in solid organ transplant recipients

Infections are frequent and can be severe in recipients of solid organ transplantation. Prevention and treatment are priority objectives of multidisciplinary transplant teams. Interactions between antimicrobials (indicated for prevention and therapy) and immunosuppressants (for preventing rejection) make treatment more complex than in the general population. Co-administration of immunosuppressants and antibiotics can cause harmful interactions, modifying the pharmacokinetic and pharmacodynamic characteristics of both groups of drugs. The loss of the transplanted organ due to reduced levels of immunosuppressants is a unique consequence of the often lethal interactions in this group of patients. By contrast, elevated levels of these drugs cause toxicity, and reduced concentrations of antimicrobial treatment fail to contain the infection. Azoles, rifabutin, protease inhibitors, non-nucleoside reverse transcriptase inhibitors and antimicrobial macrolides all interact with immunosuppressants. In this article, we review interactions between antibiotics and immunosuppressants in order to adopt the most appropriate clinical approach (dosage adjustments, close monitoring of plasma levels and organ function) and determine whether they can be used together with any measure of safety.

Omeprazole impairs the absorption of mycophenolate mofetil but not of enteric-coated mycophenolate sodium in healthy volunteers

In 2 crossover studies, 12 healthy volunteers (6 male/6 female) received a single oral dose of mycophenolate mofetil (MMF) 1000 mg or an equimolar dose of enteric-coated mycophenolate sodium (EC-MPS) 720 mg fasting with and without coadministered omeprazole 20 mg bid. The plasma concentrations of mycophenolic acid (MPA) and of the inactive metabolite mycophenolic acid glucuronide (MPA-G) were measured by high-performance liquid chromatography (HPLC). In addition, dissolution of MMF 500 mg or EC-MPS 360 mg tablets was determined using an USP paddle apparatus in aqueous buffer of pH 1 to 7. The bioavailability of MPA following administration of MMF or EC-MPS was similar except for the time to peak concentration, which was longer in the EC-MPS group. Concomitant treatment with omeprazole lowered significantly C(max) and AUC(12h) of MPA following administration of MMF. The pharmacokinetics of EC-MPS was not affected. Dissolution of MMF in aqueous buffer decreased dramatically at pH above 4.5. The EC-MPS tablet was stable up to pH 5. Above, EC-MPS was quantitatively disintegrated and MPS quantitatively dissolved. There is strong evidence that impaired absorption of MMF with concomitant proton pump inhibitors is due to incomplete dissolution of MMF in the stomach at elevated pH.

Mycophenolate monitoring in liver, thoracic, pancreas, and small bowel transplantation: a consensus report

Assessing the value of mycophenolic acid (MPA) monitoring outside renal transplantation is hindered by the absence of any trial comparing fixed-dose and concentration-controlled therapy. However, in liver and thoracic transplantation particularly, clinical trials, observational studies with comparison groups, and case series have described MPA efficacy, exposure/efficacy relationships, pharmacokinetic variability, and clinical outcomes relating to plasma MPA concentrations. On the basis of this evidence, this report identifies MPA as an immunosuppressant for which the combination of variable disposition, efficacy, and adverse effects contributes to interindividual differences seemingly in excess of those optimal for a fixed-dosage mycophenolate regimen. Combined with experiences of MPA monitoring in other transplant indications, the data have been rationalized to define circumstances in which measurement of MPA concentrations can contribute to improved management of mycophenolate therapy in nonrenal transplant recipients.

New insights into the pharmacokinetics and pharmacodynamics of the calcineurin inhibitors and mycophenolic acid: possible consequences for therapeutic drug monitoring in solid organ transplantation

Although therapeutic drug monitoring (TDM) of immunosuppressive drugs has been an integral part of routine clinical practice in solid organ transplantation for many years, ongoing research in the field of immunosuppressive drug metabolism, pharmacokinetics, pharmacogenetics, pharmacodynamics, and clinical TDM keeps yielding new insights that might have future clinical implications. In this review, the authors will highlight some of these new insights for the calcineurin inhibitors (CNIs) cyclosporine and tacrolimus and the antimetabolite mycophenolic acid (MPA) and will discuss the possible consequences. For CNIs, important relevant lessons for TDM can be learned from the results of 2 recently published large CNI minimization trials. Furthermore, because acute rejection and drug-related adverse events do occur despite routine application of CNI TDM, alternative approaches to better predict the dose-concentration-response relationship in the individual patient are being explored. Monitoring of CNI concentrations in lymphocytes and other tissues, determination of CNI metabolites, and CNI pharmacogenetics and pharmacodynamics are in their infancy but have the potential to become useful additions to conventional CNI TDM. Although MPA is usually administered at a fixed dose, there is a rationale for MPA TDM, and this is substantiated by the increasing knowledge of the many nongenetic and genetic factors contributing to the interindividual and intraindividual variability in MPA pharmacokinetics. However, recent, large, randomized clinical trials investigating the clinical utility of MPA TDM have reported conflicting data. Therefore, alternative pharmacokinetic (ie, MPA free fraction and metabolites) and pharmacodynamic approaches to better predict drug efficacy and toxicity are being explored. Finally, for MPA and tacrolimus, novel formulations have become available. For MPA, the differences in pharmacokinetic behavior between the old and the novel formulation will have implications for TDM, whereas for tacrolimus, this probably will not to be the case.