Pharmacological management of invasive mold infections in solid organ transplant recipients

INTRODUCTION

Solid organ transplant (SOT) recipients face an increased susceptibility to invasive fungal infection (IFI) due to filamentous fungi. Post-transplant invasive aspergillosis (IA) and mucormycosis are related to exceedingly high mortality rates and graft loss risk, and its management involve a unique range of clinical challenges.

AREAS COVERED

First, the current treatment recommendations for IA and mucormycosis among SOT recipients are critically reviewed, including the supporting evidence. Next, we discussed particular concerns in this patient population, such as drug-drug interactions (DDIs) between triazoles and post-transplant immunosuppression or treatment-related toxicity. The role for immunomodulatory and host-targeted therapies is also considered, as well as the theoretical impact of the intrinsic antifungal activity of calcineurin inhibitors. Finally, a personal opinion is made on future directions in the pharmacological approach to post-transplant IFI.

EXPERT OPINION

Despite relevant advances in the treatment of mold IFIs in the SOT setting, such as the incorporation of isavuconazole (with lower incidence of DDIs and better tolerability than voriconazole), there remains a large room for improvement in areas such as the position of combination therapy or the optimal strategy for the reduction of baseline immunosuppression. Importantly, future studies should define the specific contribution of newer antifungal agents and classes.

Difference in immunosuppressant dose requirement when transitioning to isavuconazole from other azoles in thoracic transplant recipients

The triazole antifungal isavuconazole (ISAVU) is used for prevention and treatment of fungal infections in solid organ transplant (SOT). SOT recipients commonly need to transition from one azole to another due to breakthrough infection, toxicity, or other reasons. The purpose of our study was to evaluate the effect of ISAVU on immunosuppressant concentrations in thoracic transplant recipients when ISAVU was started de novo or transitioned from another azole. We conducted a single-center retrospective cohort study including 68 patients (51 lung, 14 heart, and 3 heart/lung transplant). Concentration to dosage ratios (C/D) of immunosuppressants were assessed at baseline, day 3, and weekly for 9 weeks. When starting ISAVU de novo, we observed a temporary doubling of tacrolimus exposure. Cyclosporine and sirolimus required dose decreases. Tacrolimus C/D increased by 110% at day 3 in patients started on ISAVU de novo then returned to baseline C/D ± 17% weeks 2-9 (n = 8). One cyclosporine patient started on ISAVU de novo had variable C/D, and C/D increased by 219% ± 72% in 2 sirolimus patients. When transitioning from other azoles, tacrolimus and cyclosporine required about twice the initial dose. After week 1, tacrolimus C/D decreased by 53% ± 6% in patients transitioned from posaconazole (n = 33), voriconazole (n = 14), or fluconazole (n = 2). Cyclosporine C/D decreased by 45% ± 16% in patients transitioning from other azoles (posaconazole [n = 2], voriconazole [n = 2], fluconazole [n = 1]). Sirolimus C/D decreased by 73% ± 13% in patients transitioned from posaconazole (n = 7). Aside from the initial loading phase, ISAVU had a lesser degree of interaction with immunosuppressants than other azoles in loading phase, ISAVU had a lesser degree of interaction with immunosuppressants than other azoles in adjustments for the 4-week period after initiating antifungal therapy with ISAVU or switching from another agent.

Isavuconazole-tacrolimus drug-drug interactions in HSCT patients

OBJECTIVES

Because tacrolimus has a narrow therapeutic window and exhibits both intraindividual and interindividual variability, we attempted to establish the percentage of calcineurin inhibitor (CNI) dose reduction to prevent toxicity and ensure stem cell engraftment when using this immunosuppressant with the antifungal isavuconazole (ISA). By calculating the tacrolimus concentration/dose (C/D) ratio, we expected to demonstrate the magnitude of change in the C/D ratio from baseline after ISA administration.

METHODS

We evaluated the interaction between ISA, a new triazole antifungal used in prophylaxis for invasive fungal infections, and the CNI class of immunosuppressive drugs, specifically tacrolimus, in 11 blood samples from HSCT recipients.

RESULTS

The mean tacrolimus C/D ratio increased 1.44-fold from baseline 48 h after ISA administration (P = 0.001).

CONCLUSIONS

Although further investigation is needed, the results of this study suggest that a reduction of 18% in tacrolimus may be recommended.

Invasive aspergillosis in liver transplant recipients

BACKGROUND

Liver transplantation is increasing worldwide with underlying pathologies dominated by metabolic and alcoholic diseases in developed countries.

METHODS

We provide a narrative review of invasive aspergillosis (IA) in liver transplant (LT) recipients. We searched PubMed and Google Scholar for references without language and time restrictions.

RESULTS

The incidence of IA in LT recipients is low (1.8%), while mortality is high (∼50%). It occurs mainly early (<3 months) after LT. Some risk factors have been identified before (corticosteroid, renal, and liver failure), during (massive transfusion and duration of surgical procedure), and after transplantation (intensive care unit stay, re-transplantation, re-operation). Diagnosis can be difficult and therefore requires full radiological and clinicobiological collaboration. Accurate identification of Aspergillus species is recommended due to the cryptic species, and susceptibility testing is crucial given the increasing resistance of Aspergillus fumigatus to azoles. It is recommended to reduce the dose of tacrolimus (50%) and to closely monitor the trough level when introducing voriconazole, isavuconazole, and posaconazole. Surgery should be discussed on a case-by-case basis. Antifungal prophylaxis is recommended in high-risk patients. Environmental preventative measures should be implemented to prevent outbreaks of nosocomial aspergillosis in LT recipient units.

CONCLUSION

IA remains a very serious disease in LT patients and should be promptly sought and, if possible, prevented by clinicians when risk factors are identified.

Effect of Isavuconazonium Sulfate and Posaconazole Delayed Release Tablets on Tacrolimus Dose-to-Concentration Ratios

INTRODUCTION

Limited evidence exists on the effect of isavuconazonium sulfate and posaconazole delayed release tablets on tacrolimus dose-to-concentration ratios in lung transplant recipients.

PROJECT AIMS

The purpose of this evaluation was to assess the impact of novel triazoles on tacrolimus dose-to-concentration ratios.

DESIGN

This retrospective review included lung transplant recipient ≥18 years of age from January 1, 2017 to October 1, 2020 who received either posaconazole delayed release tablets or isavuconazonium sulfate for. A paired analysis evaluated outcomes pre-triazole and post-triazole initiation.

RESULTS

Forty-one patients met evaluation criteria for inclusion. A total of 34 of 41 patients received posaconazole delayed release tablets. Of these patients, 22 of 34 were transitioned from previous triazole to posaconazole delayed release tablets and experienced a 47% reduction in tacrolimus dose-to-concentration ratio. Twelve patients were newly initiated on posaconazole delayed release tablets and experienced a 50% reduction in tacrolimus dose-to-concentration ratios. Although not statistically significant, a 30% reduction in tacrolimus dose-to-concentration ratio was observed when transitioning to isavuconazonium sulfate from previous triazole therapy.

CONCLUSION

Limited data exists to provide guidance on tacrolimus dose adjustments with initiation and conversion of novel triazoles, however, this evaluation provides more knowledge on the drug interaction with novel triazoles and tacrolimus.

The Overview on the Pharmacokinetic and Pharmacodynamic Interactions of Triazoles

Second generation triazoles are widely used as first-line drugs for the treatment of invasive fungal infections, including aspergillosis and candidiasis. This class, along with itraconazole, voriconazole, posaconazole, and isavuconazole, is characterized by a broad range of activity, however, individual drugs vary considerably in safety, tolerability, pharmacokinetics profiles, and interactions with concomitant medications. The interaction may be encountered on the absorption, distribution, metabolism, and elimination (ADME) step. All triazoles as inhibitors or substrates of CYP isoenzymes can often interact with many drugs, which may result in the change of the activity of the drug and cause serious side effects. Drugs of this class should be used with caution with other agents, and an understanding of their pharmacokinetic profile, safety, and drug-drug interaction profiles is important to provide effective antifungal therapy. The manuscript reviews significant drug interactions of azoles with other medications, as well as with food. The PubMed and Google Scholar bases were searched to collect the literature data. The interactions with anticonvulsants, antibiotics, statins, kinase inhibitors, proton pump inhibitors, non-nucleoside reverse transcriptase inhibitors, opioid analgesics, benzodiazepines, cardiac glycosides, nonsteroidal anti-inflammatory drugs, immunosuppressants, antipsychotics, corticosteroids, biguanides, and anticoagulants are presented. We also paid attention to possible interactions with drugs during experimental therapies for the treatment of COVID-19.

Comparative effects of fluconazole, posaconazole, and isavuconazole upon tacrolimus and cyclosporine serum concentrations

INTRODUCTION

Calcineurin inhibitors are commonly used in hematopoietic stem cell transplant (HSCT) patients to prevent graft versus host disease, but as CYP3A4 substrates they are frequently involved in drug-drug interactions. The purpose of this study is to characterize the effects of isavuconazole, fluconazole, and posaconazole on tacrolimus and cyclosporine serum concentrations and dose adjustments in allogeneic HSCT patients.

METHODS

This retrospective study included patients admitted to Oregon Health and Science University between April 2008 and December 2018 who underwent hematopoietic stem cell transplantation and received concomitant tacrolimus or cyclosporine and fluconazole, isavuconazole or posaconazole therapy. Data on patient characteristics, drug dosing, and serum drug concentrations were collected through chart review, and descriptive statistics were used to summarize the results.

RESULTS

A total of 139 patients were included in this study. We found fluconazole initiation leads to a 25% reduction in both tacrolimus and cyclosporine doses in order to maintain goal serum concentrations. Posaconazole and isavuconazole initiation requires tacrolimus dose reductions by 53% and 21%, respectively.

CONCLUSIONS

Based on our experience, FLC, POS, and ISA initiation may require CNI dose reductions and close monitoring of CNI levels to ensure levels remain within goal serum concentrations. Larger studies are needed to fully quantify the percentage in CNI dose reductions and characterize differences among these antifungals.

Successful Treatment of Severe Aspergillosis with Isavuconazole Therapy after Allogeneic Stem Cell Transplantation

Invasive fungal infections are one of the main infectious complications in allogeneic stem cell transplantation (SCT). Triazoles (voriconazole, posaconazole) are the main prophylactic and therapeutic options for the treatment of invasive aspergillosis. However, pharmacological interactions and hepatotoxicity limit its use. Isavuconazole (ISV) is a recently approved azole with a promising interaction and safety profile. We present a case with invasive aspergillosis in the post-allogeneic SCT setting in a critically ill patient with severe multiorgan failure due to veno-occlusive disease. The patient was treated with ISV and B amphotericin during severe kidney and liver failure and multiple immunosuppressants, without significant drug-related toxicity and with favorable outcome. The interaction and safety profile of ISV is discussed along the reported experience. ISV can be an effective salvage therapy even in complex clinical situations with multiple potential interactions.

Effect of isavuconazole on tacrolimus and sirolimus serum concentrations in allogeneic hematopoietic stem cell transplant patients: A drug-drug interaction study

INTRODUCTION

Isavuconazole, a triazole antifungal, is an inhibitor of cytochrome P450 3A4, which also metabolizes tacrolimus and sirolimus. In previous studies, isavuconazole administration increased tacrolimus and sirolimus area under the curve values by 2.3-fold and 1.8-fold, respectively, in healthy adults and tacrolimus concentration/dose (C/D) ratio by 1.3-fold in solid organ transplant patients. We aimed to determine the magnitude of effect of isavuconazole administration on tacrolimus and sirolimus C/D ratios in allogeneic hematopoietic stem cell transplant (alloHSCT) patients.

METHODS

A retrospective, single-center, single-arm study in adult alloHSCT patients who received at least 10 days of combination therapy with isavuconazole and tacrolimus and/or sirolimus as inpatients or outpatients was conducted. Tacrolimus and sirolimus trough serum concentrations were measured up to twice weekly for up to 4 weeks.

RESULTS

Twenty-two patients receiving tacrolimus and twenty patients receiving sirolimus met the inclusion criteria. The mean C/D ratio increased from baseline by 1.42-fold for tacrolimus during week 1 (P = 0.002) and up to 1.56-fold for sirolimus during week 2 (P = 0.02). For the remaining timepoints, tacrolimus and sirolimus C/D ratios were not statistically significantly different from baseline.

CONCLUSION

In alloHSCT patients, modest increases in tacrolimus and sirolimus C/D ratios from baseline were observed within the first 2 weeks after initiation of isavuconazole.