Interactions between anti-infective agents and immunosuppressants in solid organ transplantation

Evaluation of Published Population Pharmacokinetic Models to Inform Tacrolimus Therapy in Adult Lung Transplant Recipients

BACKGROUND

The applicability of currently available tacrolimus population pharmacokinetic models in guiding dosing for lung transplant recipients is unclear. In this study, the predictive performance of relevant tacrolimus population pharmacokinetic models was evaluated for adult lung transplant recipients.

METHODS

Data from 43 lung transplant recipients (1021 tacrolimus concentrations) administered an immediate-release oral formulation of tacrolimus were used to evaluate the predictive performance of 17 published population pharmacokinetic models for tacrolimus. Data were collected from immediately after transplantation up to 90 days after transplantation. Model performance was evaluated using (1) prediction-based assessments (bias and imprecision) of individual predicted tacrolimus concentrations at the fourth dosing based on 1 to 3 previous dosings and (2) simulation-based assessment (prediction-corrected visual predictive check; pcVPC). Both assessments were stratified based on concomitant azole antifungal use. Model performance was clinically acceptable if the bias was within ±20%, imprecision was ≤20%, and the 95% confidence interval of bias crossed zero.

RESULTS

In the presence of concomitant antifungal therapy, no model showed acceptable performance in predicting tacrolimus concentrations at the fourth dosing (n = 33), and pcVPC plots displayed poor model fit to the data set. However, this fit slightly improved in the absence of azole antifungal use, where 4 models showed acceptable performance in predicting tacrolimus concentrations at the fourth dosing (n = 33).

CONCLUSIONS

Although none of the evaluated models were appropriate in guiding tacrolimus dosing in lung transplant recipients receiving concomitant azole antifungal therapy, 4 of these models displayed potential applicability in guiding dosing in recipients not receiving concomitant azole antifungal therapy. However, further model refinement is required before the widespread implementation of such models in clinical practice.

Adaptation of a population pharmacokinetic model to inform tacrolimus therapy in heart transplant recipients

AIM

Existing tacrolimus population pharmacokinetic models are unsuitable for guiding tacrolimus dosing in heart transplant recipients. This study aimed to develop and evaluate a population pharmacokinetic model for tacrolimus in heart transplant recipients that considers the tacrolimus-azole antifungal interaction.

METHODS

Data from heart transplant recipients (n = 87) administered the oral immediate-release formulation of tacrolimus (Prograf®) were collected. Routine drug monitoring data, principally trough concentrations, were used for model building (n = 1099). A published tacrolimus model was used to inform the estimation of Ka , V2 /F, Q/F and V3 /F. The effect of concomitant azole antifungal use on tacrolimus CL/F was quantified. Fat-free mass was implemented as a covariate on CL/F, V2 /F, V3 /F and Q/F on an allometry scale. Subsequently, stepwise covariate modelling was performed. Significant covariates influencing tacrolimus CL/F were included in the final model. Robustness of the final model was confirmed using prediction-corrected visual predictive check (pcVPC). The final model was externally evaluated for prediction of tacrolimus concentrations of the fourth dosing occasion (n = 87) from one to three prior dosing occasions.

RESULTS

Concomitant azole antifungal therapy reduced tacrolimus CL/F by 80%. Haematocrit (∆OFV = -44, P < .001) was included in the final model. The pcVPC of the final model displayed good model adequacy. One recent drug concentration is sufficient for the model to guide tacrolimus dosing.

CONCLUSION

A population pharmacokinetic model that adequately describes tacrolimus pharmacokinetics in heart transplant recipients, considering the tacrolimus-azole antifungal interaction was developed. Prospective evaluation is required to assess its clinical utility to improve patient outcomes.

Pharmacokinetic and pharmacodynamic considerations of antibiotics and antifungals in liver transplantation recipients

The liver plays a major role in drug metabolism. Liver transplantation impacts the intrinsic metabolic capability and extrahepatic mechanisms of drug disposition and elimination. Different levels of inflammation and oxidative stress during transplantation, the process of liver regeneration, and the characteristics of the graft alter the amount of functional hepatocytes and activity of liver enzymes. Binding of drugs to plasma proteins is affected by the hyperbilirubinemia status and abnormal synthesis of albumin and alpha-1-acid glycoproteins. Postoperative intensive care complications such as biliary, circulatory, and cardiac also impact drug distribution. Renally eliminated antimicrobials commonly present reduced clearance due to hepatorenal syndrome and the use of nephrotoxic immunosuppressants. In addition, liver transplantation recipients are particularly susceptible to multidrug-resistant infections due to frequent manipulation, multiple hospitalizations, invasive devices, and frequent use of empiric broad-spectrum therapy. The selection of appropriate anti-infective therapy must consider the pathophysiological changes after transplantation that impact the pharmacokinetics and pharmacodynamics of antibiotics and antifungal drugs.

Flat Pattern Peaks of Tacrolimus Absorption and Associated Pharmacogenomic Variants in Kidney Transplantation Recipients

BACKGROUND

Tacrolimus is the most commonly used immunosuppressive drug in solid organ transplantation. After administering a conventional twice-daily dose of tacrolimus, peak levels were achieved within the first 1.5 to 2 hours. A group of patients showed different early absorption phase of tacrolimus after kidney transplantation.

METHODS

Trough(C₀) and 1.5-hour blood levels (C_1.5) of tacrolimus were measured in 95 kidney transplantation recipients. Patients with a C_1.5/C₀ < 1.5 and > 1.5 were defined as those having flat pattern peaks and as controls, respectively. Transplantation outcomes were compared between the groups. Whole exome sequencing was performed to investigate the genetic susceptibility to flat pattern peaks.

RESULTS

Twenty-eight patients showed flat pattern peaks. The mean C_1.5/C₀ values were 1.13 ± 0.22 and 3.78 ± 1.25 in the flat pattern peak and control groups, respectively. In multivariate analysis, flat pattern peak was an independent risk factor for biopsy-proven acute rejection (BPAR) and/or borderline change (P = 0.014). Patients having flat pattern peaks showed significantly lower post-transplant 36-month estimated glomerular filtration rate (P = 0.001). Two single nucleotide variants in ABCB1 genes, rs1922242 and rs2235035, were associated with flat pattern peaks (P = 0.019 and P = 0.027, respectively).

CONCLUSION

Both of C_1.5 and C₀ should be measured to distinguish the patients showing unique initial absorption. A C_1.5/C₀ ratio lower than 1.5 was associated with an increased risk of BPAR and/or borderline change. Single nucleotide variants s in ABCB1 gene might influence the flat pattern peaks of tacrolimus absorption.

Evaluation of published population pharmacokinetic models to inform tacrolimus dosing in adult heart transplant recipients

BACKGROUND AND AIM

Identification of the most appropriate population pharmacokinetic model-based Bayesian estimation is required prior to its implementation in routine clinical practice to inform tacrolimus dosing decisions. This study aimed to determine the predictive performances of relevant population pharmacokinetic models of tacrolimus developed from various solid organ transplant recipient populations in adult heart transplant recipients, stratified based on concomitant azole antifungal use. Concomitant azole antifungal therapy alters tacrolimus pharmacokinetics substantially, necessitating dose adjustments.

METHODS

Population pharmacokinetic models of tacrolimus were selected (n = 17) for evaluation from a recent systematic review. The models were transcribed and implemented in NONMEM version 7.4.3. Data from 85 heart transplant recipients (2387 tacrolimus concentrations) administered the oral immediate-release formulation of tacrolimus (Prograf) were obtained up to 391 days post-transplant. The performance of each model was evaluated using: (i) prediction-based assessment (bias and imprecision) of the individual predicted tacrolimus concentration of the fourth dosing occasion (MAXEVAL = 0, FOCE-I) from 1-3 prior dosing occasions; and (ii) simulation-based assessment (prediction-corrected visual predictive check). Both assessments were stratified based on concomitant azole antifungal use.

RESULTS

Regardless of the number of prior dosing occasions (1-3) and concomitant azole antifungal use, all models demonstrated unacceptable individual predicted tacrolimus concentration of the fourth dosing occasion (n = 152). The prediction-corrected visual predictive check graphics indicated that these models inadequately predicted observed tacrolimus concentrations.

CONCLUSION

All models evaluated were unable to adequately describe tacrolimus pharmacokinetics in adult heart transplant recipients included in this study. Further work is required to describe tacrolimus pharmacokinetics for our heart transplant recipient cohort.

The time is now: antimicrobial stewardship in solid organ transplantation

PURPOSE OF REVIEW

To provide a summary of complications of antimicrobials and opportunities for antimicrobial stewardship (AS) in solid organ transplant (SOT) patient care.

RECENT FINDINGS

Personalized, precision antimicrobial prescribing in SOT aiming to avoid negative consequences of antimicrobials is essential to improving patient outcomes. The positive impact AS efforts in transplant care has been recognized and bespoke activities tailored to special interests of transplant patients and providers are evolving. Strategies to optimize stewardship interventions targeting antibacterial, antiviral, and antifungal drug selection and dosing in the transplant population have been recently published though clinical integration using a 'handshake' stewardship model is an optimal starting point in transplant care. Other recent studies involving transplant recipients have identified opportunities to shorten duration or avoid antimicrobials for certain commonly encountered clinical syndromes. This literature, informing recent consensus clinical practice guidelines, may help support institutional practice guidelines and protocols. Proposals to track and report stewardship process and outcome measures as a routine facet of programmatic transplant quality reporting have been published. However, developing novel metrics accounting for nuances of transplant patients and programs is critical. Important studies are needed to evaluate organizational transplant prescribing cultures and optimal behavioral science-based interventions relevant to antimicrobial use in this population.

SUMMARY

Consequences of antimicrobial use, such as drug toxicities, and Clostridiodes difficile (CDI) and multidrug-resistant organisms colonization and infection disproportionately affect SOT recipients and are associated with poor allograft and patient outcomes. Stewardship programs encompassing transplant patients aim to personalize antimicrobial prescribing and optimize outcomes. Further studies are needed to better understand optimal intervention strategies in SOT.

Treatment optimization of maintenance immunosuppressive agents in pediatric renal transplant recipients

Introduction: Graft survival in pediatric kidney transplant patients has increased significantly within the last three decades, correlating with the discovery and utilization of new immunosuppressants as well as improvements in patient care. Despite these developments in graft survival for patients, there is still improvement needed, particularly in long-term care in pediatric patients receiving grafts from deceased donor patients. Maintenance immunosuppressive therapies have narrow therapeutic indices and are associated with high inter-individual and intra-individual variability.Areas covered: In this review, we examine the impact of pharmacokinetic variability on renal transplantation and its association with age, genetic polymorphisms, drug-drug interactions, drug-disease interactions, renal insufficiency, route of administration, and branded versus generic drug formulation. Pharmacodynamics are outlined in terms of the mechanism of action for each immunosuppressant, potential adverse effects, and the utility of pharmacodynamic biomarkers.Expert opinion: Acquiring abetter quantitative understanding of immunosuppressant pharmacokinetics and pharmacodynamic components should help clinicians implement treatment regimens to maintain the balance between therapeutic efficacy and drug-related toxicity.

Safe Use of Erythromycin For Refractory Gastroparesis After Small Bowel Transplantation

Current therapeutic options with prokinetic agents for posttransplant gastroparesis are limited. Erythromycin is associated with adverse reactions, including corrected QT interval prolongation and cytochrome P450 3A4 isoenzyme inhibition. The use of erythromycin has been avoided in patients undergoing treatment with cyclosporine or tacrolimus because of significant fluctuations in therapeutic immunosuppression levels. We report herein the successful use of erythromycin after visceral transplant to treat delayed gastric emptying. Two patients were managed with oral erythromycin (initial dose of 750 mg/d divided into 3 doses) for gastroparesis after visceral transplant. Patient 1 was a woman aged 42 years with a history of chronic intestinal pseudo-obstruction syndrome who underwent isolated small bowel transplant with dual (gastric and duodenal) proximal allograft anastomosis. Posttransplant gastroparesis was initially managed with oral metoclopramide. The patient also required high doses of tacrolimus (36 mg/d) to maintain adequate immunosuppression levels. The decision was made to change metoclopramide to erythromycin, which significantly decreased the daily tacrolimus dose requirement (from 36 to 9 mg/d), with resolution of nausea and intermittent bloating symptoms. Patient 2 was a woman aged 35 years with ultra-short gut syndrome after extensive enterectomy due to intestinal volvulus who underwent uneventful combined intestinal and colon transplant. Conventional pharmacologic therapy for gastroparesis was initiated after surgery without success. Erythromycin was started 15 days posttransplant, with significant improvement in her symptoms, and discontinued 47 days post-transplant. To maintain therapeutic levels (8-10 mg/dL), daily tacrolimus dose was decreased 75.8% and 36.5% for patients 1 and 2, respectively. No significant side effects associated with erythromycin use were observed in either patient. Our findings here suggest that erythromycin may be safely used for gastroparesis after small bowel transplant. Close monitoring of immunosuppressive drug levels and dose adjustments of other medications affected by inhibition of cytochrome P450 3A4 are advised.

Painless rash in a transplant patient

Dermatophytes are common keratinophilic fungi responsible for superficial skin infections. Deep dermatophytosis is a rare form of invasive skin infection described in immunocompromised patients. We report the case of a 65-year-old man with a history of an orthotopic liver transplant for hepatocarcinoma 6 months earlier, who presented with small painless erythematous papules in lower limbs, some of which were umbilicated. Skin biopsy showed an intense non-necrotizing granulomatous reaction in the dermis around fungal structures. Trichophyton rubrum was identified as the causal agent through culture and internal transcribed spacer sequencing.

Comparative analysis of the drug-drug interaction between immunosuppressants, safety and efficacy of rifabutin from rifampicin-based Anti-TB treatment in living donor liver transplant recipients with active tuberculosis

Background

The Interaction between anti-tuberculous and immunosuppressive drugs which may increase the risk of graft rejections is a major challenge in managing transplant recipients with tuberculosis (TB). Instead of rifampicin (RFM), most guidelines recommended the use of rifabutin (RFB) because of its reduced capacity to induce immunosuppressant metabolism while maintaining the same efficacy as RFM against TB. However, there has been no available data directly comparing the outcome of RFB from RFM-based anti-TB regimens in liver transplant patients with TB. This study aimed to compare the effects of RFB from RFM-based treatment in terms of the drug interaction with immunosuppressants, as well as the safety, efficacy and clinical outcomes of living donor liver transplant (LDLT) recipients with active TB.

Methods

A retrospective study was conducted on all adult LDLT recipients diagnosed with active TB from June 1994 to May 2016 that had concurrently and continuously received either RFB or RFM-based treatment and immunosuppressants.

Results

Twenty-two patients were included. Twelve (55%) patients were in the RFM group. Ten (45%) patients were in the RFB group. RFB group showed a lesser rate of immunosuppressant trough level reduction (20% vs 50%, p = 0.009) during TB treatment. There was no TB recurrence and no significant change in platelet or leukocyte count in either group. Acute cellular rejection (ACR), rate of TB-treatment completion and overall survival, rates were excellent and statistically similar in both groups.

Conclusion

The use of RFB in LDLT recipients with active TB, had a lesser drug interaction than when RFM was used. However, RFB did not significantly reduced the rate of ACR. RFB and RFM are both effective and safe to use in LDLT recipients with active TB.

COVID-19 and kidney transplantation: an Italian Survey and Consensus

Italy was the first Western country to face the COVID-19 pandemic. Here we report the results of a national survey on kidney transplantation activity in February and March 2020, and the results of a three-round Delphi consensus promoted by four scientific societies: the Italian Society of Organ Transplantation, the Italian Society of Nephrology, the Italian Society of Anesthesia and Intensive Care, and the Italian Group on Antimicrobial Stewardship. All 41 Italian transplant centers were invited to express their opinion in the Delphi rounds along with a group of seven experts. The survey revealed that, starting from March 2020, there was a decline in kidney transplantation activity in Italy, especially for living-related transplants. Overall, 60 recipients tested positive for SARS-CoV2 infection, 57 required hospitalization, 17 were admitted to the ICU, and 11 died. The online consensus had high response rates at each round (95.8%, 95.8%, and 89.5%, respectively). Eventually, 27 of 31 proposed statements were approved (87.1%), 12 at the first or second round (38.7%), and 3 at the third (9.7%). Based on the Italian experience, we discuss the reasons for the changes in kidney transplantation activity during the COVID-19 pandemic in Western countries. We also provide working recommendations for the organization and management of kidney transplantation under these conditions.

Drug interactions between tacrolimus and clotrimazole troche: a data mining approach followed by a pharmacokinetic study

PURPOSE

This study investigated the effects of clotrimazole troche on the risk of transplant rejection and the pharmacokinetics of tacrolimus.

METHODS

The data mining approach was used to investigate whether the use of clotrimazole increased the risk of transplant rejection in patients receiving tacrolimus therapy. Patient data were acquired from the US Food and Drug Administration's Adverse Event Reporting System (FAERS) from the first quarter of 2004 to the end of 2017. Next, we retrospectively investigated the effect of clotrimazole troche on tacrolimus pharmacokinetics in seven patients who underwent heart transplantation between March and December 2017.

RESULTS

The FAERS subset data indicated a significant association between transplant rejection and tacrolimus with clotrimazole [reporting odds ratio 1.92, 95% two-sided confidence interval (95% CI) 1.43-2.58, information component 0.81, 95% CI 0.40-1.23]. The pharmacokinetic study demonstrated a significant correlation between trough concentration (C₀) and area under the concentration-time curve of tacrolimus after discontinuation of clotrimazole (R² = 0.60, P < 0.05) but not before its discontinuation. Furthermore, the median clearance/bioavailability of tacrolimus after discontinuation of clotrimazole was 2.2-fold greater than that before its discontinuation (0.27 vs. 0.59 L/h/kg, P < 0.05). The median C₀ decreased from 10.7 ng/mL on the day after discontinuation of clotrimazole to 6.5 ng/mL at 1 day and 5.3 ng/mL at 2 days after its discontinuation.

CONCLUSION

Immediate dose adjustments of tacrolimus may be beneficial to avoid transplant rejection when clotrimazole troche is added or discontinued.

Determining the conversion ratios for oral versus sublingual administration of tacrolimus in solid organ transplant recipients

Tacrolimus is utilized as maintenance immunosuppression in solid organ transplant (SOT). Current literature has reported conflicting conversion ratios when transitioning between oral and sublingual tacrolimus, and the exact conversion ratio has not been fully established in SOT. The purpose of this study was to determine the conversion ratios between oral and sublingual tacrolimus needed to achieve equivalent whole blood concentrations in heart, kidney, liver, and lung transplant recipients. A retrospective, single-center analysis was conducted at Mayo Clinic in Florida. One hundred and eighteen hospitalized SOT recipients who received oral and sublingual tacrolimus during the same inpatient admission from June 1, 2012, through June 1, 2017, were reviewed. The median conversion ratio of sublingual to oral tacrolimus was 1.34 (IQR: 1.03-1.93) in all SOT, 1.25 (IQR: 1.08-1.64) in heart transplant, 1.23 (IQR: 1.1-2.06) in kidney transplant, 1.64 (IQR: 1.27-2.29) in liver transplant, and 1.34 (IQR: 0.94-1.93) in lung transplant. A slightly higher dose of oral tacrolimus is needed in the majority of solid organ recipients in our population when converting between sublingual to oral tacrolimus administration.

Diagnostic and therapeutic approach to infectious diseases in solid organ transplant recipients

Purpose

Prognosis of solid organ transplant (SOT) recipients has improved, mainly because of better prevention of rejection by immunosuppressive therapies. However, SOT recipients are highly susceptible to conventional and opportunistic infections, which represent a major cause of morbidity, graft dysfunction and mortality.

Methods

Narrative review.

Results

We cover the current epidemiology and main aspects of infections in SOT recipients including risk factors such as postoperative risks and specific risks for different transplant recipients, key points on anti-infective prophylaxis as well as diagnostic and therapeutic approaches. We provide an up-to-date guide for management of the main syndromes that can be encountered in SOT recipients including acute respiratory failure, sepsis or septic shock, and central nervous system infections as well as bacterial infections with multidrug-resistant strains, invasive fungal diseases, viral infections and less common pathogens that may impact this patient population.

Conclusion

We provide state-of the art review of available knowledge of critically ill SOT patients with infections.

Management of Mycobacterium Other than Tuberculosis in Solid Organ Transplantation

Mycobacteria other than tuberculosis are important pathogens to consider in solid organ transplant recipients. Delay in recognition and treatment may incur significant morbidity and mortality. Management of mycobacteria other than tuberculosis requires a knowledge of treatment specific for each species and drug-drug interactions between antimicrobial and immunosuppressive drugs. Therapy in solid organ transplant can be prolonged and may require a reduction in immunosuppression to improve outcomes.

Clinical Outcomes of Tuberculosis in Recipients After Living Donor Liver Transplantation

Background

This study aimed to determine clinical outcomes using various drugs during tuberculosis (TB) treatment among living donor liver transplant (LDLT) recipients with TB and to assess the impact of performing LDLT in patients with active TB at the time of LDLT.

Material/Methods

Out of 1313 LDLT performed from June 1994 to May 2016, 26 (2%) adult patients diagnosed with active TB were included in this study. Active TB was diagnosed using either TB culture, PCR, and/or tissue biopsy.

Results

The median age was 56 years and the male/female ratio was 1.6: 1. Most patients had pulmonary TB (69.2%), followed by extrapulmonary and disseminated TB (15.4% each). Fourteen (53.8%) patients underwent LDLT even with the presence of active TB. All patients concurrently received anti-TB [Rifampicin-based: 13 (50%); Rifabutin-based: 12 (46.2%); INH-based: 1 (3.8%)] and immunosuppressive drugs [Tacrolimus-based: 6 (23%); Sirolimus/Everolimus-based: 20 (77%)]. During treatment, adverse drug reactions (ADR) occurred in 34.6% of patients: acute rejection in 6 (23.1%), hepatotoxicity in 2 (7.7%), and blurred vision in 1 (3.8%). Twenty-three (88%) patients completed their TB treatment. Neither TB recurrence nor TB-specific mortality were observed. Three (11.5%) patients died of non-TB-related causes. The overall 5-year survival rate was 86.2%. Patients with ADRs had a higher incidence of incomplete TB treatment (log-rank: p=0.012). Furthermore, patients with incomplete treatment were significantly associated with decreased overall survival (log-rank: p<0.001). Immunosuppressive and anti-TB drugs used during TB treatment and performing LDLT in patients with active TB at the time of LDLT were not associated with ADRs and overall survival.

Conclusions

Outcomes are generally favorable with intensive peri-operative evaluation and surveillance. ADRs and incomplete TB treatment may result in poor prognosis and increased mortality rates.

Individualizing immunosuppression in lung transplantation

Immunosuppression management after lung transplantation continues to evolve, with an increasing number of agents available for use in various combinations allowing for more choice and individualization of immunosuppressive therapy. Therapeutic developments have led to improved outcomes including lower acute rejection rates and improved survival. However, a one size fits all approach for any immunosuppressive strategy may not be best suited to the individual patient and ultimately patient specific factors must be considered when designing the immunosuppressive regimen. Recipient factors including age, race, co-morbidities, immunologic risk, genetic polymorphisms, concomitant and previous pharmacotherapy, and overall immunosuppression burden should be considered. There are several significant drug-drug interactions with select immunosuppressive agents utilized in lung transplant pharmacotherapy that must be considered when choosing and devising a dosing strategy for an individual immunosuppressive agent. Herein, considerations for immunosuppression management in the individual patient will be reviewed.

Using known drug interactions to manage supratherapeutic calcineurin inhibitor concentrations

OBJECTIVES

To summarize the available body of evidence guiding the management of supratherapeutic concentrations of calcineurin inhibitors (CNI) using cytochrome P450 (CYP450) enzyme inducers.

METHODS

A nondate restricted literature search within MEDLINE, Embase, and Scopus was performed using the terms "cyclosporine," "tacrolimus," "calcineurin inhibitor," "toxicity," "pharmacokinetics," "carbamazepine," "rifampin," "phenytoin," and "phenobarbital." Additional references were identified from a review of all included citations. All English-language reports that describe the management of supratherapeutic CNI concentrations with interventions targeting metabolic induction using CYP450 enzyme inducers were evaluated.

RESULTS

A total of 10 publications were identified in which a CYP450 enzyme inducer was utilized intentionally to enhance CNI clearance in the setting of supratherapeutic concentrations; 7 case reports describe the use of phenytoin and 3 case reports describe the use of phenobarbital. Patient demographics, dosing strategies employed, and reported efficacy across this series of publications are heterogeneous; however, both agents appear to be well-tolerated when used in this setting.

CONCLUSIONS

There is a paucity of published data on the use of CYP450 enzyme inducers for the management of supratherapeutic CNI concentrations. While routine use of this approach cannot be recommended, thorough risk-benefit analyses should be performed in the management of each such clinical scenario.

Valganciclovir Dosing for Cytomegalovirus Prophylaxis in Pediatric Solid-organ Transplant Recipients: A Prospective Pharmacokinetic Study

BACKGROUND

Valganciclovir is extensively used for prophylaxis and treatment of cytomegalovirus (CMV) infection in solid-organ transplant recipients. However, pharmacokinetic data in children are scarce, and the pediatric dosing regimen is uncertain. This study sought to prospectively evaluate the pharmacokinetic profile, the clinical efficacy and safety of oral valganciclovir in pediatric transplant recipients and compare different dosing regimens.

METHODS

The cohort included solid-organ transplant recipients treated with valganciclovir for CMV prophylaxis in 2014-2015 at a tertiary pediatric medical center. All received a weight-based once-daily oral dose of 17 mg/kg. Ganciclovir concentrations were measured and the area under the curve (AUC0-24) was calculated.

RESULTS

Thirteen children of median age 7.3 years (interquartile range, 2.2-11.6) were included. Median ganciclovir AUC0-24 was 21.0 mcg·h/mL (interquartile range, 17.1-39.8); 10 patients (77%) attained AUC0-24 <40 mcg·h/mL. Exposure to ganciclovir was about 2-fold lower in young children (<9 years old; P = 0.01) and children with low body surface area (BSA; <0.7 m; P = 0.006) than in their counterparts. Significantly lower doses were recommended with our weight-based protocol than with the manufacturer-recommended BSA- and glomerular filtration rate-based protocol (P = 0.002), reaching a 3-fold difference in infants. No evidence of CMV viremia or disease was observed while prophylaxis was given.

CONCLUSIONS

The weight-based regimen of 17 mg/kg/dose oral valganciclovir results in relatively low ganciclovir exposure, especially in young children with low BSA, yet showed satisfactory clinical efficacy for CMV prophylaxis. The manufacturer's dosing recommendation appears to result in supratherapeutic ganciclovir concentrations. Further studies are needed to establish target AUCs and valganciclovir dosing for CMV prophylaxis in pediatric transplant recipients.

New facets of antifungal therapy

Invasive fungal infections remain a major cause of morbidity and mortality in immunocompromised patients, and such infections are a substantial burden to healthcare systems around the world. However, the clinically available armamentarium for invasive fungal diseases is limited to 3 main classes (i.e., polyenes, triazoles, and echinocandins), and each has defined limitations related to spectrum of activity, development of resistance, and toxicity. Further, current antifungal therapies are hampered by limited clinical efficacy, high rates of toxicity, and significant variability in pharmacokinetic properties. New antifungal agents, new formulations, and novel combination regimens may improve the care of patients in the future by providing improved strategies to combat challenges associated with currently available antifungal agents. Likewise, therapeutic drug monitoring may be helpful, but its present use remains controversial due to the lack of available data. This article discusses new facets of antifungal therapy with a focus on new antifungal formulations and the synergistic effects between drugs used in combination therapy.

Cryptosporidium infection in solid organ transplantation

Diarrhea is a common complication in solid organ transplant (SOT) recipients and may be attributed to immunosuppressive drugs or infectious organisms such as bacteria, viruses or parasites. Cryptosporidium usually causes self-limited diarrhea in immunocompetent hosts. Although it is estimated that cryptosporidium is involved in about 12% of cases of infectious diarrhea in developing countries and causes approximately 748000 cases each year in the United States, it is still an under recognized and important cause of infectious diarrhea in SOT recipients. It may run a protracted course with severe diarrhea, fluid and electrolyte depletion and potential for organ failure. Although diagnostic methodologies have improved significantly, allowing for fast and accurate identification of the parasite, treatment of the disease is difficult because antiparasitic drugs have modest activity at best. Current management includes fluid and electrolyte replacement, reduction of immunosuppression and single therapy with Nitazoxanide or combination therapy with Nitazoxanide and other drugs. Future drug and vaccine development may add to the currently poor armamentarium to manage the disease. The current review highlights key epidemiological, diagnostic and management issues in the SOT population.

The role of the pharmacist in the management of kidney transplant recipients

Pharmacists may play a key role on the multidisciplinary transplant team. This article describes the development and current status of pharmacists in the management of transplant recipients in the United States. Traditionally, pharmacists played an important support role in transplant medicine. This role has been expanded to include direct patient care for the avoidance, detection, and/or treatment of side effects from the polypharmacy necessary in the management of these complex patients. Pharmacists provide pre- and post-transplant education to transplant recipients to enhance adherence to complicated medical regimens and thereby reduce readmission to hospital and unscheduled, costly visits to urgent care centers and/or hospital emergency departments.

The Critically Ill Kidney Transplant Recipient: A Narrative Review

Kidney transplantation is the most common solid organ transplantation performed worldwide. Up to 6% of kidney transplant recipients experience a life-threatening complication that requires ICU admission, chiefly in the late posttransplantation period (≥ 6 months). Acute respiratory failure and septic shock are the main reasons for ICU admission. Cardiac pulmonary edema, bacterial pneumonia, acute graft pyelonephritis, and bloodstream infections account for the vast majority of diagnoses in the ICU. Pneumocystis jirovecii pneumonia is the most common opportunistic infection, and one-half of the patients so infected require mechanical ventilation. The incidence of cytomegalovirus visceral infections in the era of preemptive therapy has dramatically decreased. Drug-related neutropenia, sirolimus-related pneumonitis, and posterior reversible encephalopathy syndrome are among the most common immunosuppression-associated toxic effects. Importantly, the impact of critical illness on graft function is worrisome. Throughout the ICU stay, acute kidney injury is common, and about 40% of the recipients require renal replacement therapy. One-half of the patients are discharged alive and free from dialysis. Hospital mortality can reach 30% and correlates with acute illness severity and reason for ICU admission. Transplant characteristics are not predictors of short-term survival. Graft survival depends on pre-ICU graft function, disease severity, and renal toxicity of ICU investigations and treatments.

Value of solid organ transplant-trained pharmacists in transplant infectious diseases

Advances in organ transplantation have led to improved graft and patient survival. Transplant pharmacist's education and training uniquely position them to contribute knowledge and skills to the management of these highly complex patients. In 2004, the United Network for Organ Sharing bylaws added requirements that all transplant programs identify one or more pharmacists with experience in transplant pharmacotherapy to be responsible for providing pharmaceutical care to solid organ transplant recipients. These bylaws also delineated the transplant pharmacist's roles and responsibilities. To further support these efforts, in 2007 the Centers for Medicare and Medicaid Services accreditation standards for transplant centers also mandated that a center have a designated, qualified expert in transplant pharmacology as a multidisciplinary team member. The transplant pharmacist is a consistent member of the transplant team that can add value to the multidisciplinary approach of prevention and treatment of transplant infectious diseases through all phases of transplant care.

Clinical pharmacokinetics and pharmacodynamics of ganciclovir and valganciclovir in children with cytomegalovirus infection

INTRODUCTION

Among infants and immunocompromised children cytomegalovirus (CMV) is associated with significant morbidity and mortality.

AREAS COVERED

This review describes the clinical pharmacokinetics and pharmacodynamics of ganciclovir and valganciclovir for the treatment and prevention of CMV infection in children.

EXPERT OPINION

A 24-h ganciclovir area under the concentration versus time curve (AUC₀₋₂₄) of 40 - 60 μg h/ml decreased the risk of CMV infection for adults undergoing CMV prophylaxis. For adults undergoing treatment for active CMV disease, a target AUC₀₋₁₂ of 40 - 60 μg h/ml has been suggested. The applicability of these targets to children remains uncertain; however, with the most sophisticated dosing regimens developed to date only 21% of patients are predicted to reach these targets. Moving forward, identification of optimal pediatric ganciclovir and valganciclovir dosing regimens may involve the use of an externally validated pediatric population pharmacokinetic model for empirical dosing, an optimal sampling strategy for collecting a minimal number of blood samples for each patient and Bayesian updating of the dosing regimen based on an individual patient's pharmacokinetic profile.