Factors Influencing the Magnitude and Clinical Significance of Drug Interactions Between Azole Antifungals and Select Immunosuppressants

Ranolazine-Tacrolimus Interaction

Objective:

To report the case of a kidney allograft recipient on a stable regimen of tacrolimus who exhibited increased tacrolimus concentrations within 24 hours of initiating ranolazine.

Case Summary:

A 64-year-old kidney allograft recipient on a stable dose of tacrolimus (10 mg twice daily) was admitted for recent worsening of her chronic anginal pain. The patient was initiated on ranolazine 500 mg twice daily on hospital day 2. Tacrolimus concentrations rose from 7.0-10.1 ng/mL preadmission to 17.8 ng/mL within 24 hours of ranolazine initiation. Ranolazine therapy was continued due to the patient's beneficial response; therefore, the tacrolimus dose was eventually decreased by 70% to 3 mg twice daily to maintain steady-state trough concentrations between 6.6 and 7.9 ng/mL with ranolazine therapy. Ranolazine dechallenge on a subsequent admission produced subtherapeutic tacrolimus concentrations requiring dosage increases.

Discussion:

Ranolazine, an antianginal agent, is both a substrate and a weak inhibitor of CYP3A as well as a substrate and moderate inhibitor of the P-glycoprotein (P-GP) efflux transport system. Tacrolimus, an immunosuppressant, is also a substrate of CYP3A and P-GP. Through possible inhibition of both P-GP– and CYP3A-mediated first-pass metabolism and CYP3A systemic metabolism, ranolazine may have significantly increased serum concentrations of tacrolimus necessitating an eventual 70% decrease in the tacrolimus dose. Based on the Horn Drug Interaction Probability Scale, this interaction is possible.

Conclusions:

We suggest that the eventual 70% decrease in tacrolimus dose after ranolazine initiation may indicate that ranolazine decreases the metabolism and clearance of tacrolimus, causing an elevation in tacrolimus concentrations and the potential for tacrolimus toxicity. Clinicians should be aware of this possible interaction when initiating ranolazine in patients on tacrolimus.

Humoral Rejection after Pediatric Heart Transplantation: A Case Report

Humoral rejection was observed 2 years after heart transplantation in a 10-year-old African American girl with sickle cell disease. Hemodynamic compromise developed, and the patient started treatment with extracorporeal membrane oxygenation within 24 hours of admission. With cellular rejection initially believed to be the cause, administration of thymoglobulin and high-dose steroids was initiated. Human leukocyte antigen antibody analysis revealed high titers of donor-specific class I and II antibodies. Aggressive treatment for antibody-mediated rejection was started with plasmapheresis and administration of intravenous immune globulin and ritux-imab. The patient displayed clinical signs of infection and was treated with antimicrobial, antiviral, and antifungal agents. Computed tomography of the chest suggested asperigillous infection. The patient underwent a left upper lobectomy. The patient recovered and has done well, now 4 years after having received the heart transplant. Antibody-mediated rejection should be considered early in heart transplant patients presenting with hemodynamic compromise and may respond to aggressive antibody and B cell–directed therapy. Vigilance for secondary infections, especially during treatment for rejection, is crucial.

Common drug interactions leading to adverse drug events in the intensive care unit: management and pharmacokinetic considerations

Critically ill patients are predisposed to drug interactions because of the complexity of the drug regimens they receive in the intensive care setting. Drugs may affect the absorption, distribution, metabolism, and/or elimination of an object drug and consequently alter the intended pharmacologic response and potentially lead to an adverse event. Certain disease states that afflict critically ill patients may also amplify an intended pharmacologic response and potentially result in an unintended effect. A team approach is important to identify, prevent, and address drug interactions in the intensive care setting and optimize patient outcomes.

Pharmacokinetics of voriconazole after oral administration of single and multiple doses in Hispaniolan Amazon parrots (Amazona ventralis)

OBJECTIVE

To determine the pharmacokinetics and safety of voriconazole administered orally in single and multiple doses in Hispaniolan Amazon parrots (Amazona ventralis).

ANIMALS

15 clinically normal adult Hispaniolan Amazon parrots.

PROCEDURES

Single doses of voriconazole (12 or 24 mg/kg) were administered orally to 15 and 12 birds, respectively; plasma voriconazole concentrations were determined at intervals via high-pressure liquid chromatography. In a multiple-dose trial, voriconazole (18 mg/kg) or water was administered orally to 6 and 4 birds, respectively, every 8 hours for 11 days (beginning day 0); trough plasma voriconazole concentrations were evaluated on 3 days. Birds were monitored daily, and clinicopathologic variables were evaluated before and after the trial.

RESULTS

Voriconazole elimination half-life was short (0.70 to 1.25 hours). In the single-dose experiments, higher drug doses yielded proportional increases in the maximum plasma voriconazole concentration (C(max)) and area under the curve (AUC). In the multiple-dose trial, C(max), AUC, and plasma concentrations at 2 and 4 hours were decreased on day 10, compared with day 0 values; however, there was relatively little change in terminal half-life. With the exception of 1 voriconazole-treated parrot that developed polyuria, adverse effects were not evident.

CONCLUSIONS AND CLINICAL RELEVANCE

In Hispaniolan Amazon parrots, oral administration of voriconazole was associated with proportional kinetics following administration of single doses and a decrease in plasma concentration following administration of multiple doses. Oral administration of 18 mg of voriconazole/kg every 8 hours would require adjustment to maintain therapeutic concentrations during long-term treatment. Safety and efficacy of voriconazole treatment in this species require further investigation.

Emergent toxicities associated with the use of mTOR inhibitors in patients with advanced renal carcinoma

The inhibitors of the mammalian target of rapamycin (mTOR) improve outcomes in patients with advanced renal cell carcinoma. These agents are associated with unusual class-adverse events that represent a challenge to the clinician, making it critical to recognize and treat them appropriately. This study aims to highlight the clinical management of these toxicities by presenting evidence from the literature and suggesting treatment recommendations. A critical review of the literature is performed and a summary of the most relevant emergent toxicities and their management is presented. Treatment recommendations of metabolic disturbances induced by mTOR inhibitors, such as hypophosphatemia, hyperglycemia, and hyperlipidemia along with the management of drug-induced pneumonitis and possible pharmacological interactions are presented. Most of these toxicities, if recognized and treated accordingly, should resolve with minimal impact on patients' quality of life and in the efficacy of this anticancer therapy. Oncologists should be familiar with the recognition and appropriate medical management of these clinical scenarios.

Clinical safety and tolerability issues in use of triazole derivatives in management of fungal infections

There has been an increase in the number of patients susceptible to invasive fungal infections (IFIs) leading to a greater need for effective, well tolerated, and easily administered antifungal agents. The advent of triazoles has revolutionized the care of patients requiring treatment or prophylaxis for IFIs. However, triazoles have been associated with a number of adverse events and significant drug–drug interactions. While commonly used, physicians and patients should be aware of the distinct properties of these agents in order to ensure that patients are optimally treated with the least amount of toxicity possible. Clinicians should have a full understanding of the basic pharmacokinetics, absorption, and bioavailability of triazoles. Moreover, knowledge of the drug–drug interactions and potential toxicities of each agent is critical prior to administering a triazole. Careful history taking, thorough review of the patient’s medication list, and detailed discussion with the patients and their families about the efficacy, safety, and tolerability of these agents should be performed. Clinicians treating patients with triazoles should closely follow them, monitor pertinent laboratory tests, and consider measuring drug levels as needed. This article will review the basic pharmacokinetic properties and most frequently encountered adverse events and pitfalls associated with triazoles in clinical practice.

Primary antifungal prophylaxis in adult hematopoietic stem cell transplant recipients: current therapeutic concepts

In recipients of hematopoietic stem cell transplants (HSCTs), the mortality associated with invasive fungal infections (IFIs) remains high, despite the introduction of broad-spectrum antifungal agents over the past 2 decades. Preventing exposure to fungal pathogens in this population is impossible; therefore, clinicians have focused on prophylactic use of antifungal agents to prevent IFIs in high-risk HSCT recipients. It is important to target antifungal prophylaxis by type of HSCT (autologous or allogeneic), local epidemiology, and risk factors for IFIs so that patients can receive the most appropriate agent while balancing costs and the risks of toxicity, and minimizing the development of resistance. To assist clinicians in weighing the pros and cons of currently available antifungal agents when choosing a suitable prophylactic regimen, we provide a review of several key prospective randomized trials that evaluated various antifungal agents for primary prophylaxis in adult HSCT recipients. In addition, we describe the epidemiology of and risk factors for IFIs in HSCT recipients, the difficulties in diagnosing IFIs, antifungal agents used for prophylaxis, and the goals of primary prophylaxis. Fluconazole remains the gold standard for primary prophylaxis in autologous HSCT recipients. For allogeneic HSCT recipients, the agent chosen for prophylaxis must be based on the patient's risk factors for IFIs. In low-risk patients, fluconazole is an appropriate agent to use for primary prophylaxis immediately after transplantation. However, in allogeneic HSCT recipients who develop complications, such as graft failure, graft-versus-host disease, or cytomegalovirus infection, prophylaxis with a mould-active agent should be used.

Pretransplant cryptococcosis and outcome after liver transplantation

The posttransplant outcomes and optimal management of patients with end-stage liver disease who develop cryptococcosis prior to transplantation have not been defined. We discuss these issues in the context of successful liver transplantation and pretransplant cryptococcal disease. Our report suggests that liver transplantation may be cautiously considered under the umbrella of fluconazole therapy in patients with end-stage liver disease and pretransplant cryptococcosis, provided that disease control is achieved with adequate treatment before transplantation.

Effects of voriconazole on tacrolimus metabolism in a kidney transplant recipient

Infection occurs frequently in the organ transplant recipients during the post-transplant period because of immunosuppression. Therefore, prophylactic antimicrobial agents are often used. The azole antifungals, widely prescribed prophylactically, are known to have many drug-drug interactions. This report presents a case of drug-drug interaction between voriconazole and tacrolimus in a kidney transplant recipient. Voriconazole treatment led to a dramatic increase in tacrolimus concentration that required its discontinuation in spite of the manufacturer's guidelines that recommend a reduction of tacrolimus dosage by one-third. The present drug-drug interaction can be attributed to a strong inhibitory effect on cytochrome P450-3A4 activity by voriconazole. When voriconazole and tacrolimus are coadministered, close monitoring of tacrolimus blood levels is recommended as the rule-of-thumb reduction of tacrolimus dose by one-third may not be satisfactory.

Effect of itraconazole on the pharmacokinetics of everolimus administered by different routes in rats

The effect of itraconazole on the pharmacokinetics of everolimus was investigated in rats. Ten minutes after an intravenous or intraintestinal administration of itraconazole, everolimus was delivered intravenously (0.2 mg/kg) or intraintestinally (0.5 mg/kg). Blood concentrations of everolimus were measured up to 240 min, and pharmacokinetic parameters were calculated. Intraintestinally administered itraconazole (20 mg/kg) significantly increased the area under the concentration-time curve (AUC) of intraintestinally administered everolimus about 4.5-fold, but even at 50 mg/kg did not affect the AUC of intravenously administered everolimus. However, intravenously administered itraconazole (50 mg/kg) increased the AUC of both intraintestinally and intravenously administered everolimus approximately 2-fold. Using a value for hepatic blood flow from the literature (50 ml/min/kg), the apparent intestinal and hepatic extraction of everolimus without itraconazole was calculated as about 80% and 13%, respectively. Intraintestinally administered itraconazole (20 mg/kg) changed the apparent intestinal extraction by 0.26-fold from 0.829 to 0.215, but the hepatic availability of everolimus was almost unchanged after the intravenous or intraintestinal administration of itraconazole even at a dose of 50 mg/kg from 0.871 to 0.923 or 0.867, respectively. In conclusion, intraintestinally administered itraconazole dramatically increased the AUC of everolimus delivered intraintestinally by inhibiting the intestinal first-pass extraction of this drug.

Safety of triazole antifungal drugs in patients with cancer

Triazole drugs are widely used in cancer patients for prophylaxis and treatment of life-threatening invasive fungal infections. Fluconazole, available for over two decades, is safe and effective in patients with cancer; however, the excellent safety profile of fluconazole may not be applicable to the newer triazoles. Itraconazole, voriconazole and posaconazole are associated with adverse events, and drug interactions frequently occur, particularly in cancer patients, since the triazoles and many drugs used in cancer chemotherapy are metabolized via a common metabolic pathway, the hepatic cytochrome P450 system. Close monitoring for drug interactions is needed when triazoles are used with anti-neoplastic drugs and dosage modification of the triazole or its discontinuation may be required. Monitoring of triazole serum concentrations is becoming an important aspect of management to minimize toxicity and ensure efficacy.

Drug interactions and adverse events associated with antimycotic drugs used for invasive aspergillosis in hematopoietic SCT

The aim of this study was to assess the frequency of potential drug-drug interactions (pDDIs) and adverse drug events (ADEs) associated with antimycotics in hospitalized patients with hematopoietic SCT (HSCT). Of the 120 HSCT recipients evaluated, 36 received antimycotics. A total of 124 ADEs were recorded in 32 of the 36 patients treated, with 54 ADEs being possibly and 9 probably related to antimycotics. Of the treatments with amphotericin B, 93% were associated with one or more possible and 36% with probable ADEs. The corresponding figures for lipid-based amphotericin B were 100% and 7%, for voriconazole 68% and 11% and for caspofungin 70% and 0%. A total of 57 potentially severe DDIs associated with antimycotics were detected in 31 of the 36 patients. Of these, 14 DDIs were a possible cause of an ADE and 5 (4 times a combination of voriconazole with CYA and once a combination of CYA with conventional amphotericin B) were probably related. Although the prevalence of pDDIs and ADEs is high in HSCT patients, ADEs related with a high probability to treatment with antimycotics are rare. Regarding the high prevalence of pDDIs, our findings underscore the importance of close monitoring of laboratory and clinical parameters, as well as dose adjustment for critical drugs, in patients with HSCT.

Drug interactions in transplant patients: what everyone should know

PURPOSE OF REVIEW

Adverse events due to drug-drug interactions remain a challenge in the postsurgical care of transplant recipients. A combination of potent and selective immunosuppressive drugs, which have a narrow therapeutic index, with medications for the treatment of comorbidities such as dyslipidemia, infection, psychiatric conditions, and hypertension, can lead to life-threatening drug-drug interactions.

RECENT FINDINGS

There are a number of important drug-drug interactions which are important for physicians to consider. It is critical to understand the pharmacodynamics and pharmacokinetics of drug-drug interactions, their potential impact on patient care, and the management strategies.

SUMMARY

Close therapeutic drug monitoring and evaluation of drug-specific side effects continue to be an important key to minimize adverse events due to drug-drug interactions.

Immunotherapy in elderly transplant recipients: a guide to clinically significant drug interactions

Currently, >50% of candidates for solid organ transplantation in Europe and the US are aged >50 years while approximately 15% of potential recipients are aged >or=65 years. Elderly transplant candidates are characterized by specific co-morbidity profiles that compromise graft and patient outcome after transplantation. The presence of coronary artery or peripheral vascular disease, cerebrovascular disease, history of malignancy, chronic obstructive lung disease or diabetes mellitus further increases the early post-transplant mortality risk in elderly recipients, with infections and cardiovascular complications as the leading causes of death. Not only are elderly patients more prone to developing drug-related adverse effects, but they are also more susceptible to pharmacokinetic and pharmacodynamic drug interactions because of polypharmacy. The majority of currently used immunosuppressant drugs in organ transplantation are metabolized by cytochrome P450 (CYP) or uridine diphosphate-glucuronosyltransferases and are substrates of the multidrug resistance (MDR)-1 transporter P-glycoprotein, the MDR-associated protein 2 or the canalicular multispecific organic anion transporter, which predisposes these immunosuppressant compounds to specific interactions with commonly prescribed drugs. In addition, important drug interactions between immunosuppressant drugs have been identified and require attention when choosing an appropriate immunosuppressant drug regimen for the frail elderly organ recipient. An age-related 34% decrease in total body clearance of the calcineurin inhibitor ciclosporin was observed in elderly renal recipients (aged >65 years) compared with younger patients, while older recipients also had 44% higher intracellular lymphocyte ciclosporin concentrations. Similarly, using a Bayesian approach, an inverse relationship was noted between sirolimus clearance and age in stable kidney recipients. Ciclosporin and tacrolimus have distinct pharmacokinetics, but both are metabolized by intestinal and hepatic CYP3A4/3A5 and transported across the cell membrane by P-glycoprotein. The most common drug interactions with ciclosporin are therefore also observed with tacrolimus, but the two drugs do not interact identically when administered with CYP3A inhibitors or inducers. The strongest effects on calcineurin-inhibitor disposition are observed with azole antifungals, macrolide antibacterials, rifampicin, calcium channel antagonists, grapefruit juice, St John's wort and protease inhibitors. Drug interactions with mycophenolic acids occur mainly through inhibition of their enterohepatic recirculation, either by interference with the intestinal flora (antibacterials) or by limiting drug absorption (resins and binders). Rifampicin causes a reduction in mycophenolic acid exposure probably through induction of uridine diphosphate-glucuronosyltransferases. Proliferation signal inhibitors (PSIs) such as sirolimus and everolimus are substrates of CYP3A4 and P-glycoprotein and have a macrolide structure very similar to tacrolimus, which explains why common drug interactions with PSIs are comparable to those with calcineurin inhibitors. Ciclosporin, in contrast to tacrolimus, inhibits the enterohepatic recirculation of mycophenolic acids, resulting in significantly lower concentrations and hence risk of underexposure. Therefore, when switching from tacrolimus to ciclosporin and vice versa or when reducing or withdrawing ciclosporin, this interaction needs to be taken into account. The combination of ciclosporin with PSIs requires dose reductions of both drugs because of a synergistic interaction that causes nephrotoxicity when left uncorrected. Conversely, when switching between calcineurin inhibitors, intensified monitoring of PSI concentrations is mandatory. Increasing age is associated with structural and functional changes in body compartments and tissues that alter absorptive capacity, volume of distribution, hepatic metabolic function and renal function and ultimately drug disposition. While these age-related changes are well-known, few specific effects of the latter on immunosuppressant drug metabolism have been reported. Therefore, more clinical data from elderly organ recipients are urgently required.

Evolving role of early antifungals in the adult intensive care unit

BACKGROUND

Invasive candidiasis (IC) is associated with significant morbidity and mortality in critically ill patients. This, in conjunction with difficulties in diagnosis, underscores the need for novel treatment strategies based on the identification of significant risk factors for IC.

OBJECTIVE

To review the evidence surrounding the use of early antifungals in critically ill adult patients and to present concise and specific recommendations for different early treatment strategies for IC.

DATA SOURCES AND DATA EXTRACTION

Pubmed search from 1966 to July 2008 using the search terms "antifungals, critical care, prophylaxis, preemptive therapy, and empiric therapy." Examined all relevant peer-reviewed original articles, meta-analyses, guidelines, consensus statements, and review articles.

CONCLUSION

The use of early antifungal therapy should be reserved for patients with a high risk (10% to 15%) of developing IC. Despite a large number of articles published on this topic, there is no single predictive rule that can adequately forecast IC in critically ill patients. Until further prospective validation of existing data is completed, clinicians should assess patients on a case-by-case basis and determine the need for early antifungal treatment strategies based on frequent evaluations of risk factors and clinical status.

Effects of oral posaconazole on the pharmacokinetics of sirolimus

OBJECTIVES

Azole antifungal agents are often coadministered with immunosuppressants to recipients of solid organ and hematopoietic stem cell transplants. Posaconazole, an extended-spectrum triazole, is an inhibitor of the cytochrome P450 (CYP) isoenzyme CYP3A4, and sirolimus, an immunosuppressant, is a substrate of the enzyme. We evaluated the effects of posaconazole on sirolimus pharmacokinetics in an open-label, multiperiod, drug-interaction study.

METHODS

Twelve healthy subjects received one dose of sirolimus 2 mg on day 1. After a 28-day washout period, subjects received posaconazole 400 mg bid for 16 days (to day 45). On day 36, sirolimus 2 mg and posaconazole 400 mg were coadministered. Blood samples to determine sirolimus plasma concentrations were collected up to 216 hours post dose on days 1 and 36 and plasma pharmacokinetic parameters were calculated. Drug interactions were evaluated using one-way analysis of variance. Mean (% coefficient of variation) maximum plasma concentration (C(max)) and area under the curve (AUC) of sirolimus at day 1 were 4.9 ng/mL (38) and 145 h x ng/mL (45), respectively.

RESULTS

Coadministration with posaconazole increased sirolimus C(max) and AUC by 6.7- and 8.9-fold, respectively. These increases are consistent with CYP3A4 inhibition by posaconazole. Adverse events were reported by five subjects (42%) receiving posaconazole and sirolimus and by three (25%) and eight (67%) subjects receiving posaconazole only on days 30 to 35 (presirolimus) and days 37 to 45 (postsirolimus), respectively.

CONCLUSION

Because posaconazole has a clinically relevant effect on sirolimus exposure, the agents should probably not be coadministered. Although this was a descriptive study, one potential limitation was the small sample size. The conclusion could have been made stronger if the number of people enrolled in the study had been greater.

Azoles and antidepressants: a mini-review of the tolerability of co-administration

Depression is a common condition in chronically ill immunosuppressed patients on long-term antifungal therapy with azoles. As both azoles and more recent antifungals are metabolised by the P450 enzymatic system in the liver, here we review the potential of clinically meaningful interactions between antidepressants and azoles. Selective serotonin reuptake inhibitors are safer compared to tricycle antidepressants when co-administered with azoles. More pharmacovigilance is needed.

Mini-series: II. clinical aspects. clinically relevant CYP450-mediated drug interactions in the ICU

BACKGROUND

In the critically ill, multiple drug therapies for acute and chronic conditions are often used at the same time and adverse drug events occur frequently. Many pharmacological and disease-related factors, e.g. altered renal and hepatic function, catecholamine-related circulatory changes, altered drug volume of distribution, enteral versus parenteral feeding and morbid obesity, along with concomitant multiple drug regimens may account for the wide inter-individual variability in drug exposure and response in critically ill patients and for the high risk for drug-drug interactions to occur. The practicing intensivist must remain aware of the major mechanisms for drug-drug interactions, among which the drug-metabolizing enzyme inhibitory or induction potential of associated chemical entities are paramount. Metabolism-based drug-drug interactions are largely due to changes in levels of drug-metabolizing enzymes caused by one drug, leading to changes in the systemic exposure clearance of another. Among the numerous drug-metabolizing enzymes identified to date, the activity of cytochrome P450s (CYP450) is a critical determinant of drug clearance and appears to be involved in the mechanism of numerous clinically relevant drug-drug interactions observed in critically ill patients.

DISCUSSION

This manuscript will cover a practical overview of clinically relevant CYP450-mediated drug-drug interactions. Medications frequently used in the intensive care unit such as benzodiazepines, immunosuppressive agents, opioid analgesics, certain anticonvulsants, the azoles and macrolides have the potential to interact with CYP450-mediated metabolism and may lead to toxicity or therapeutic failure.

Exophiala spinifera as a cause of cutaneous phaeohyphomycosis: case study and review of the literature

Exophiala spinifera has been reported as an agent of cutaneous disease 18 times in the literature. Clinical presentations of cutaneous lesions vary widely, including erythematous papules, verrucous plaques, and deep subcutaneous abscesses. The clinical distribution and course of disease are also variable, depending on the age and immune competency of the patient. Histologic appearance occurs in one of two patterns--phaeohyphomycosis or chromoblastomycosis. While E. spinifera appears to be susceptible to multiple antimicrobial agents in vitro, clinical experience with treatment modalities has been variable. Prior to the availability of sequencing methods, species identification was based on the histopathologic presentation in tissue and morphologic features of the fungus in culture. It is likely that E. spinifera cutaneous infections have been underreported due to its incorrect identification based on earlier methods. We report an additional case of E. spinifera phaeohyphomycosis, the first to be definitively identified by sequencing. In addition, we summarize the variable clinical, histopathologic, and morphologic features, as well as treatment responses described in previously reported cutaneous infections caused by E. spinifera.

Therapeutic drug monitoring of voriconazole

Voriconazole is a triazole antifungal developed for the treatment of life-threatening fungal infections in immunocompromised patients. The drug, which is available for both oral and intravenous administration, has broad-spectrum activity against pathogenic yeasts, dimorphic fungi, and opportunistic molds. Voriconazole has a nonlinear pharmacokinetic profile with a wide inter- and intraindividual variety. This variability is caused by many factors such as gender, age, genotypic variation, liver dysfunction, the presence of food, and so on. Another important factor influencing voriconazole's pharmacokinetic profile is drug-drug interactions with CYP450 inhibitors as well as inducers. Variability in plasma concentrations, as a result of the previously mentioned aspects, may lead to variability in efficacy or toxicity. Determination of plasma concentrations is indicated in situations to guide dosing and to individualize and improve the treatment options resulting in better therapeutic outcome or fewer side effects. In this article, we review factors influencing voriconazole pharmacokinetic profile, the data supporting exposure-effect and exposure-toxicity relationships, review the gaps in current knowledge, which make broad recommendations for therapeutic drug monitoring difficult for voriconazole, provide the indications in which therapeutic drug monitoring is reasonable based on currently available data (eg, children), and outline the ways in which this problem could be solved. We provide a summary of the problem so that further research can be conducted to address this are of clinical need.

Clinical relevance of pharmacokinetics and pharmacodynamics in cardiac critical care patients

Pharmacokinetics is a discipline aimed at predicting the best dosage and dosing regimen for each single drug in order to ensure and maintain therapeutically effective concentrations at the action sites. In cardiac critical care patients, various pathophysiological conditions may significantly alter the pharmacokinetic behaviour of drugs. Gastrointestinal drug absorption may be erratic and unpredictable in the early postoperative period, and so patients may be unresponsive to oral therapy; thus the intravenous route should be preferred for life-saving drugs whenever feasible. Variations in the extracellular fluid content as a response to the trauma of surgery and the fluid load or significant drug loss through thoracic drainages may significantly lower plasma concentrations of extracellularly distributed hydrophilic antimicrobials (beta-lactams, aminoglycosides and glycopeptides). Drug metabolism may be altered by the systemic inflammatory response and/or multiple organ failure and/or drug-drug pharmacokinetic interactions that can potentially occur during polytherapy, especially in immunosuppressed cardiac transplant patients. Instability of renal function may promote significant changes in body fluid concentrations of renally eliminated drugs, even in a brief period of hours. Finally, the application of extracorporeal circulation by means of cardiopulmonary bypass may significantly alter the disposition of several drugs during the operation because of acute haemodilution, hypoalbuminaemia, hypothermia and/or adsorption to the bypass equipment. Accordingly, to avoid either overexposure and the consequent increased risk of toxicity or underexposure and the consequent risk of therapeutic failure in critically ill cardiac patients, the dosing regimens of several drugs are expected to be significantly different from those suggested for clinically stable patients. Additionally, therapeutic drug monitoring may be helpful in the management of drug therapy and should be routinely used to guide individualized dose adjustments for (i) immunosuppressants whenever cytochrome P450 3A4 isoenzyme inhibitors (e.g. macrolide antibacterials, azole antifungals) or inducers (e.g. rifampicin [rifampin]) are added to or withdrawn from the regimen; and (ii) glycopeptide and aminoglycoside antibacterials whenever haemodynamically active agents (such as dopamine, dobutamine and furosemide [frusemide]) are added to or withdrawn from the regimen, and also whenever significant changes of haemodynamics and/or of renal function occur.

Pharmacokinetic Interaction Between Everolimus and Antifungal Triazoles in a Liver Transplant Patient

Objective:

TO describe the management of a pharmacokinetic interaction between azole antifungals (fluconazole and voriconazole) and everolimus in a patient who underwent an orthotopic liver transplant.

Case Summary:

A 65-year-old male who received an orthotopic liver transplant experienced an iatrogenic retroperitoneal duodenal perforation on postoperative day 55. His condition was subsequently complicated by severe sepsis and acute renal failure. Intravenous fluconazole 400 mg, followed by 100 mg every 24 hours according to impaired renal function, was immediately started; to avoid further nephrotoxicity, immunosuppressant therapy was switched from cyclosporine plus mycophenolate mofetil to oral everolimus 0.75 mg every 12 hours. Satisfactory steady-state minimum concentration (Cmin) of everolimus was achieved (∼5 ng/mL). On day 72 posttransplant, because of invasive aspergillosis, antifungal therapy was switched to intravenous voriconazole 400 mg every 12 hours on the first day, followed by 200 mg every 12 hours; to prevent drug toxicity, the everolimus dosage was promptly lowered to 0.25 mg every 24 hours. At that time, the everolimus Cmin averaged approximately 3 ng/mL. The concentration/dose ratio of everolimus (ie, Cmin reached at steady-state for each milligram per kilogram of drug administered) was markedly lower during fluconazole versus voriconazole cotreatment (mean ± SD, 3.49 ± 0.29 vs 11.05 ± 0.81 ng/mL per mg/kg/daily; p < 0.001). Despite intensive care, the patient's condition continued to deteriorate and he died on day 84 posttransplant

Discussion:

Both azole antifungals were considered probable causative agents of an interaction with everolimus according to the Drug Interaction Probability Scale. The Interaction is due to the inhibition of CYP3A4–mediated everolimus clearance. Of note, prompt reduction of the everolimus dosage since the first azole coadministration, coupled with intensive therapeutic drug monitoring, represented a useful strategy to prevent drug overexposure.

Conclusions:

Our data suggest that during everolimus-azole cotreatment, a dose reduction of everolimus is needed to avoid overexposure. According to the different inhibitory potency of CYP3A4 activity, the reduction should be lower during fluconazole than during voriconazole cotreatment.