The Fragile Patient: Considerations in the Management of Invasive Mould Infections (IMIs) in India

Invasive mould infections (IMIs), which are mostly caused by Aspergillus spp. and Mucormycetes, are opportunistic infections that impose a substantial threat to patients who are considered to be ‘fragile’. There is no fixed definition for fragile patients; however, patients with cancer or acquired immunodeficiency syndrome (AIDS), patients who have undergone organ transplants, and patients being treated in the intensive care units (ICUs) were considered fragile. Management of IMIs in fragile patients is challenging, owing to their compromised immune status. The diagnostic challenges associated with IMIs due to insufficient sensitivity and specificity of the current diagnostic tests lead to delayed treatment. A widening demographic of at-risk patients and a broadening spectrum of pathogenic fungi have added to the challenges to ascertain a definite diagnosis. A recent surge of mucormycosis associated with SARS-CoV-2 infections and the resultant steroid usage has been reported. Liposomal amphotericin B (L-AmB) is the mainstay for treating mucormycosis while voriconazole has displaced amphotericin B as the mainstay for treating Aspergillus infection due to its better response, improved survival, and fewer severe side effects. The selection of antifungal treatment has to be subjected to more scrutiny in fragile patients owing to their comorbidities, organ impairment, and multiple ongoing treatment modalities. Isavuconazole has been documented to have a better safety profile, stable pharmacokinetics, fewer drug-drug interactions, and a broad spectrum of coverage. Isavuconazole has thus found its place in the recommendations and can be considered a suitable option for treating fragile patients with IMIs. In this review, the authors have critically appraised the challenges in ascertaining an accurate diagnosis and current management considerations and suggested an evidence-based approach to managing IMIs in fragile patients.


Introduction And Background
Invasive fungal infections (IFIs) increase morbidity and mortality in the vulnerable population and impose a substantial burden on critical care units. Invasive mould infections (IMIs) are mostly caused by Aspergillus spp. and Mucormycetes. Each of these two infections requires a different diagnostic and management approach [1,2]. Early diagnosis and newer antifungal drugs have managed to curb mortality in immunocompromised patients with IMIs [3]. The challenges currently associated with antifungal pharmacotherapy include a surge in resistance to antifungals, breakthrough fungal infections with inherently resistant fungi, potentially life-threatening adverse effects, and drug-drug interactions, especially with extended therapy [3]. The demographics of cancer patients, patients with acquired immunodeficiency syndrome (AIDS), patients who have undergone organ transplants, and patients being treated in the intensive care units (ICUs) can be considered to be 'fragile' patients [4]. The risk of getting an invasive mycological infection is higher in fragile patients. The antifungal options are limited due to the obvious demand for higher safety [4]. Although there is no fixed definition, these patients can be considered to be fragile because of their compromised immunity owing to the primary diagnosis, potential drug-drug interactions due to multiple ongoing pharmacotherapies, adverse drug reactions from the pharmacotherapy of the primary disease, existing organ dysfunction (e.g., hepatic and renal), and added toxicity of antimicrobials.
Thus, there is a distinct challenge in treating fragile patients. In this review, the authors have critically appraised the changes in the epidemiology of fungal infections, the challenges in ascertaining an accurate diagnosis, and current management considerations, and suggested an evidence-based approach to managing IMIs in fragile patients.
Globally, each year about 250,000 cases of invasive aspergillosis (IA) and about 10,000 cases of mucormycosis are reported. There is limited information on the global incidence of these infections due to the absence of national surveillance systems. Additionally, there is no compulsion to report fungal diseases, and the clinicians might miss the signs and diagnostic tests may not be conclusive [5]. Considering these clinical challenges, there is a possibility of under-reporting of IFIs [5,6].
The prevalence of mucormycosis in Asia is considerably higher as compared to Europe (i.e., 14 per 100,000 people vs. <0.6 per 100,000 people) and has been increasing over the recent decades [5,7,8]. There has been a recent surge of mucormycosis associated with SARS-CoV-2 infections and the resultant steroid usage [9]. There is a paucity of prevalence data specifically for IA from India. The available epidemiological data from India are summarised in Table 1

Diagnostic challenges
Imaging using computed tomography (CT), microbiological tools, and histopathology are the pillars of the diagnostic workup of IMI. Cultures of secretions retrieved from the lower respiratory tract using bronchoscopy or bronchoalveolar lavage fluid (BAL) and galactomannan and (1,3)-β-D-glucan are key diagnostic tools to identify pulmonary fungal infections and aspergillosis, respectively. However, establishing a diagnosis of IMI is difficult due to the insufficient sensitivity and specificity of the current diagnostic tests. A widening in the spectrum of pathogens causing IMI and in the demographics of immunocompromised patients has added to the challenges of a proper diagnosis. Although advances in polymerase chain reaction (PCR) techniques have eased the diagnostic challenges for IA and invasive mucormycosis (IM) to a certain degree, it is not available at all medical facilities [18]. Since the currently available diagnostic tests provide insufficient sensitivity and specificity, the optimal approach is to combine multiple diagnostic strategies, including imaging, fungal biomarkers (galactomannan and (1,3)-β-D-glucan), and molecular tools [18,19].

The Challenge of Differentiating Invasive Aspergillosis From Mucormycosis
Mucormycosis and IA have common clinical and radiological signs. Lesions (such as halo sign, reverse halo sign (RHS), nodules, cavities, wedge-shaped effusions, and pleural effusions), which are observed with pulmonary mucormycosis, are also observed with Aspergillus spp. and Pseudomonas aeruginosa infections [20]. Hence, a high index of suspicion along with host factors and the presence of clinical signs are required to make early identification of mucormycosis [20,21]. Mucormycosis should be considered when there is a history of prior voriconazole use or an RHS (in lung parenchyma) on high-resolution computed tomography [20,22]. Multiple (≥10) nodules along with pleural effusion picked up on a radiograph indicate pulmonary mucormycosis [23]. Rhinocerebral mucormycosis can be diagnosed in diabetic patients using an algorithm enlisting the 'red flags' such as diplopia, periorbital swelling, cranial nerve palsy, sinus pain, orbital apex syndrome, proptosis, and palate ulcers [24]. Another helpful investigative approach for ascertaining a diagnosis is fine needle aspiration, guided by endobronchial ultrasound [21].

Management considerations
The modern antifungals for the treatment of mould infections consist of three chief classes: triazoles, echinocandins, and amphotericin B (AmB). These three classes are individually limited by their spectrum [3].
The general treatment principles in the management of IMIs in immunocompromised patients, which can be considered while developing an effective personalised treatment strategy, are as follows: knowing the spectrum of activity of commonly used antifungals; understanding epidemiology of IMIs; knowing the pathogenesis as well as natural history of the mould infection to enable effective use of therapy in high-risk patients; knowledge of pharmacokinetics and pharmacodynamics of the antifungals; understanding the adverse effects associated with antifungals; knowing importance of early diagnosis to warrant sufficient treatment response; understanding that prognosis is severely dependent on the degree and course of immunosuppression in the patient; understanding that acute versus chronic states of treatment can influence selection of antifungal agent; implementation of multidisciplinary approach; and acknowledging that evidence-based guidelines provide a starting point and not a road-map for managing patients [3].
The approved treatment modalities along with their approved indications have been summarised in Table 2.

Immunocompromised Patients
Aspergillus spp. and Mucorales are opportunistic fungi that frequently cause menace for immunocompromised patients, including organ transplant patients, haemato-oncological patients, and immunodeficiency syndrome patients [46].
Voriconazole has displaced AmB as the mainstay for treating Aspergillus infection in immunocompromised patients [46]. Liposomal amphotericin B (L-AmB) is recommended as the first-line agent for treating mucormycosis by the European Conference on Infections in Leukaemia (ECIL, 2017) and the European Confederation of Medical Mycology (ECMM, 2019) [46,47]. The ECMM 2019 guidelines strongly recommend high-dose L-AmB as the first-line treatment for mucormycosis in the general population. Isavuconazole and posaconazole (intravenous or delayed-release tablets) have moderate strength of recommendation as the first-line treatment [48].

Solid Organ Transplantation
IFIs increase mortality and morbidity in patients undergoing solid organ transplants (SOTs). SOT is imperative for patients with end-stage organ failure. Hence, the prevention and treatment of fungal infections are crucial. Voriconazole is the suggested first-line therapy for IA in SOT patients. Other agents for IA include L-AmB, AmB lipid complex, isavuconazole, caspofungin, and micafungin. Echinocandins have only static activity against aspergillosis as they act against the growing fungal hyphae. A combination of voriconazole and echinocandin is advised to be reserved as salvage therapy [49]. Mucormycosis infection is rare in SOT patients but with a fatality rate of up to 60%. Managing mucormycosis often involves surgical excision or debridement of the necrotic area along with intravenous antifungals. L-AmB is recommended as induction therapy and isavuconazole as the first-line agent. Posaconazole can be given as salvage therapy to patients not unresponsive to AmB. Isavuconazole is recommended for maintenance and also as salvage therapy in SOT patients [49].

Haematologic Malignancy
IFI adds to the morbidity and mortality in patients with haematologic malignancies and patients going through haematopoietic cell transplant (HCT) [50]. Clinicians might need to consider the possibility of IA in such patients with a fever of more than three to four days. It is advised to start empiric antifungals after 96 hours of fever that persists even after empirical antibiotic treatment [51]. Posaconazole is recommended for prophylactic use in cases with prolonged neutropenia due to chemotherapy for acute myeloid leukaemia (AML) or myelodysplastic syndrome (MDS) and in HCT recipients requiring augmented immunosuppression for graft vs. host disease (GVHD) [50]. The initial treatment of invasive pulmonary aspergillosis (IPA) can be done with voriconazole or isavuconazole, except in cases where it is a breakthrough infection due to azole prophylaxis. IA sinusitis should be treated with surgical debridement combined with systemic antifungals. Initial treatment with triazole may reduce the six-week mortality rate [51]. IA of the central nervous system (CNS) is mitigated with surgical procedures and voriconazole [51]. ECIL-6 strongly recommend voriconazole and isavuconazole for treating IA in leukaemia patients and patients undergoing haematopoietic stem cell transplant [52].
For treating mucormycosis in stem cell transplant recipients and haematologic malignancy patients, L-AmB is the preferred antifungal that can be combined with an echinocandin [51]. Isavuconazole is advised in patients who cannot endure AmB. Voriconazole, however, is ineffective [51]. ECIL-6 recommends a multidisciplinary approach, including antifungal, surgery, and controlling underlying conditions in leukaemia patients and patients undergoing haematopoietic stem cell transplant [52].

Critically Ill Patients in ICU
Opportunistic fungi often take advantage of the immunocompromised state of critically ill patients admitted to the ICU. In response to sepsis, a biphasic immunological pattern is observed. It consists of an early hyperinflammatory phase trailed by an anti-inflammatory response, causing a hypo-inflammatory state. This is known as compensatory anti-inflammatory response syndrome (CARS or immunoparalysis) [53]. Treatment of IA with first-line therapy (voriconazole or isavuconazole), at an early stage when the infection is suspected, improves outcomes and mortality. For managing infection with Mucorales, a combination of correcting the underlying conditions where feasible, surgical resection when possible, and antifungal therapy is required [1].

Diabetic Patients
Mucormycosis is becoming a progressively prevalent infection in diabetes mellitus patients whose blood glucose levels are not well managed. Hyperglycaemia impairs acquired and innate immunity and increases the chances of getting IA [1]. Diabetes mellitus is the chief risk factor for mucormycosis in India. The prevalence of mucormycosis in India is hence much higher (14 per 100,000 population). The prevalence rate in the United States and Europe ranges from 0.01 to 0.2 per 100,000 population, which is lower compared to Indian estimates [54,55]. In patients with uncontrolled diabetes and suspected mucormycosis, rapid correction of metabolic aberrations is obligatory along with pharmacotherapy with antifungal agents [55]. L-AmB has a broad spectrum and is efficacious for most fungal infections. It remains the first-line agent for treating mucormycosis. However, the formulation contains about 900 mg of sucrose per vial, which may prove detrimental in hyperglycaemic patients. Isavuconazole is the recommended second-line agent along with posaconazole in patients who cannot tolerate L-AmB [47,56].

COVID-19-Associated Fungal Infections
The ongoing SARS-CoV-2 or coronavirus disease 2019 (COVID-19) pandemic has given rise to secondary infections known as COVID-19-associated pulmonary aspergillosis (CAPA) and COVID-19-associated mucormycosis (CAM) [57,58]. India has reported a significant burden of IM as a fatal complication of COVID-19 [59]. Diagnosis of CAPA and CAM is especially difficult considering the fragile state of the patients [57]. For diagnosing CAPA, the conventionally used procedures for IA are at a disadvantage because they either are unsuitable for testing the lower respiratory tract (e.g., testing sputum, non-bronchoscopic lavage, and tracheal aspirate) or they risk contamination (e.g., bronchoscopy with BAL) by SARS-CoV-2. BAL testing is preferable for diagnosing IPA in COVID-19 patients [58]. For ascertaining mucormycosis, diagnostic procedures employed are biopsy or mycological examination with potassium hydroxide (KOH) mount and calcofluor stain. A biopsy is the mainstay of diagnosis and the benefits of performing the test outweigh the risk, even in a 'difficult to access' location or in the presence of coagulopathy [59].
The 2020 ECMM/International Society for Human and Animal Mycology (ISHAM) consensus criteria for research and clinical guidance recommends voriconazole or isavuconazole as first-line agents for the management of CAPA. For azole-resistant variants, voriconazole or isavuconazole plus echinocandin is recommended for suspected CAPA and L-AmB for suspected or proven CAPA [60]. AmB is the preferred antifungal for treating CAM. Due to possible renal impairment, isavuconazole and posaconazole may be advised. Adjuvant therapy with caspofungin, statins, aspirin, and hyperbaric oxygen may be considered on a need basis [59].

COVID-19-Associated Mucormycosis in India
A multicentre study was conducted in India from September to December 2020, across 16 healthcare centres. Among them, seven centres reported 112 cases of mucormycosis in 2019 and 231 cases in 2020, of which 139 (60.2%) were CAM. A surge in CAM cases is thus evident. From the 16 centres, during the study period, 287 cases of mucormycosis were reported, of which 187 (65.2%) had CAM. The overall prevalence of CAM is estimated to be 0.27%. A higher proportion of cases of CAM have been observed in the older population (mean age of the study population: 56.9 years) and the male gender (80.2%). Uncontrolled diabetes was found to be the common underlying issue for both CAM and non-CAM patients. Interestingly, newly detected diabetes mellitus was more frequently noted in CAM patients as compared to non-CAM (20.9% vs. 10%). As compared to non-CAM patients (84%), the use of L-AmB was lower in CAM patients (72.7%). CAM patients were more frequently treated with isavuconazole and posaconazole. The mortality rate among the two groups was found to be similar, i.e., 38.3% at six weeks. Hypoxemia due to COVID-19 and inappropriate glucocorticoid use were determined to be the causative factors for late CAM [10]. A case-control study conducted across 25 hospitals in India during January-June 2021 reported 1,733 cases of CAM with a mortality rate of 32.2%. The study concluded that the unmonitored use of medications like glucocorticoids and zinc supplements in addition to host factors (renal transplantation, diabetes mellitus, and elevated Creactive protein) was associated with CAM [61]. Another retrospective, observational study of patients with COVID-19-associated rhino-orbital-cerebral mucormycosis (ROCM) including 2,826 patients ascertained the use of corticosteroids and diabetes mellitus as predisposing factors. The authors also suggested that treatment with antifungals can be initiated empirically upon suspicion due to clinical or clinical-radiological correlation in a symptomatic patient with COVID-19 [62].

Hepatic and Renal Dysfunction
The therapeutic decisions for treating mould infections should be done in consideration of the impairment of hepatic and/or renal function and the potential drug-drug interactions [63]. A summary of the required dose adjustments for various antifungals is present in

Drug-Drug Interactions
Voriconazole has a high risk of drug-drug interactions, especially in the Asian population due to the substantial proportion of slow metabolizers. Its concomitant use with immunosuppressants, including sirolimus, tacrolimus (nephrotoxic drug), and cyclosporine, is advised to be monitored and dose adjustments should be done as required since voriconazole causes a significant increase in their plasma concentrations. Proton pump inhibitors are competitive inhibitors of voriconazole metabolism and hence can increase voriconazole plasma concentrations, leading to concentrations outside the therapeutic range, which can be associated with either impaired treatment of IA or increased toxicity for the patient [62,65,66].
Posaconazole is a potent inhibitor of CYP3A4 and can cause significant drug-drug interactions with other medications metabolized by this enzyme [67]. Co-administration with terfenadine, astemizole, cisapride, pimozide, halofantrine, and quinidine may increase plasma concentrations of these medical products [35]. This can lead to QTc prolongation, which has been linked with cardiovascular events such as torsades de pointes [68]. Posaconazole's increased risk of drug-drug interactions, coupled with its non-linear pharmacokinetics, which leads to a large inter-and intra-individual variation in bioavailability, results in the need for therapeutic drug monitoring (TDM) when using oral suspension [69][70][71]. Azole levels decrease significantly with rifampicin [26,38,45,72].
Isavuconazole is a moderate CYP3A4 inhibitor and does not inhibit either CYP2C9 or CYP2C19. The current US and European Union prescribing information does not recommend dose adjustment with concomitant administration of isavuconazole and ciclosporin, tacrolimus, or sirolimus. However, monitoring the drug concentrations of the immunosuppressive agents with dose adjustments is advised as required [73]. Triazoles are associated with QTc prolongation. Isavuconazole, unlike other triazoles, causes a dosedependent QTc interval shortening, whose clinical significance is unknown. The safety profile of isavuconazole is more favourable as compared to other azoles [74]. The SECURE trial reported less drugassociated hepatotoxicity with isavuconazole when compared to voriconazole [75].

Therapeutic Drug Monitoring Considerations
TDM is a useful tool to monitor the safety and efficacy of antifungals with a narrow therapeutic window and unpredictable pharmacokinetics with a well-defined exposure activity relationship. Considering that the patients at risk of systemic fungal infections include fragile and immunocompromised patients dealing with a myriad of other health concerns, TDM helps optimise the management approach [71,76]. The antifungal agents that are recommended for a routine TDM are itraconazole, voriconazole, posaconazole, and flucytosine. Flucytosine is under the TDM scanner due to its toxic potential and interpatient variability concerning kidney function. Voriconazole displays significant interpatient variability in pharmacokinetics. Hence, TDM helps in ensuring therapeutic concentration is achieved in these patients. Posaconazole's TDM is dependent on the type of formulation in question. The delayed-release tablets and intravenous formulations have a relatively stable pharmacokinetic profile. TDM is critical when the suspension is used to monitor therapeutic levels. TDM is also needed when potential drug-drug interactions are identified [76].
Isavuconazole has a dose-dependent pharmacokinetic profile with minimal variability. The intra-subject variability is also minimal. Hence, TDM is not recommended for isavuconazole [74]. Although TDM could be beneficial in monitoring and clinical evaluation of isavuconazole-treated individuals for situations like unforeseen toxicity, treatment failure, and pharmacokinetic drug-drug interactions. TDM will also prove useful if pathogens with elevated minimum inhibitory concentration (MIC) or infections at sanctuary sites (e.g., CNS) are being treated with isavuconazole. A plasma trough of 2-3 mg/L range (mean concentration range from phase II/III clinical studies) after day five (including loading doses) indicates an acceptable drug exposure, in case precise therapeutic targets are missing [77].

Pharmacodynamic considerations
Aspergillus fumigatus is the most common causative agent for IA globally. But, in Asian, African, and Middle Eastern regions, Aspergillus flavus is known to be the predominant causative agent. Approximately 10% of global bronchopulmonary aspergillosis cases are due to A. flavus [14]. It is known to be inherently resistant to polyenes while triazole resistance is occasionally observed in A. fumigatus. A. flavus is resistant to AmB probably due to higher ergosterol levels and a rise in enzymatic activity of the peroxidase and superoxide dismutase, with decreased lipid peroxidation. The definite mechanism for the resistance is undetermined. The MIC of AmB for A. flavus is high. Voriconazole and isavuconazole are recommended drugs of choice to treat IA. Echinocandins may be added to make a combination therapy if the situation demands. AmB preparations are advised to be avoided [14]. Isavuconazole has been reported to have favourable in vitro antifungal activity against clinically significant Aspergillus and Mucorales isolates. Its MIC range against Mucor spp. is <0.015 to >8 µg/mL and its minimum fungicidal concentration (MFC) range is 2 to >16 µg/mL [78]. The European Committee on Antimicrobial Susceptibility Testing (EUCAST)-issued clinical MIC breakpoints for isavuconazole for A. fumigatus are ≤1 µg/mL for susceptible and ≤1 µg/mL for resistant isolates [78].

Evidence-based approach in managing IMI in the fragile patient
Various guidelines have been developed to provide recommendations for the treatment of IMIs in different populations. These guidelines use graded strength of evidence and different levels of quality of evidence to make the recommendations [48,52,77,79].
The ECIL guidelines published in 2017 are formulated by the European Hematology Association for patients with haematologic malignancies or haematopoietic stem cell transplantation recipients. They comprise recommendations for diagnosis, prophylaxis, and preventive or targeted therapy for various types of fungal infections in such patients ( Table 4) [52].  Considering the current challenges faced by the medical fraternity due to COVID-19 and associated fungal infections, the ECMM and the ISHAM have published updated recommendations for the diagnosis and treatment of patients with CAPA (summarised in Table 4) [60].

SoR QoE Comments
Isavuconazole has been given the same recommendation level and strength as voriconazole. But it is well noted that it is highlighted to be better tolerated as compared to voriconazole, which is tagged for TDM. Isavuconazole also has a better recommendation profile as compared to AmB preparations.

Guidelines on Invasive Mucormycosis
The 2019 global guidelines for the diagnosis and management of mucormycosis were published based on an initiative of the ECMM in cooperation with the Mycoses Study Group Education and Research Consortium (MSG-ERC) [48]. The management recommendations when all the treatment options are available are illustrated in Figure 1. The ECMM-MSG-ERC guidelines have strongly recommended the use of isavuconazole for the treatment of mucormycosis in renally compromised patients, patients with progressive disease, and patients experiencing toxicity. Isavuconazole is tagged with moderate strength as the first-line treatment of mucormycosis.

Conclusions
The fragile patient with comorbidities and organ impairment has special requirements when it comes to antifungal usage. Although the general principles of treatment of fungal infections remain similar, there are differences in which antifungals can be safely used in this situation.
The addition of isavuconazole in the armamentarium of Indian physicians is a step towards addressing this special need. Although voriconazole and L-AmB remain the treatments of choice in Aspergillus and mucormycosis, respectively, isavuconazole provides an effective alternative for the treatment of IMIs. The SECURE trial has proven it to be non-inferior to voriconazole with better safety outcomes. It is proven to have a better safety and tolerability profile as compared to other azoles. The option of oral preparation also gives isavuconazole an advantage. It has a broad-spectrum antifungal activity covering clinically significant isolates of Aspergillus spp., especially A. flavus (inherently resistant to AmB preparations possibly due to higher ergosterol levels and increased enzymatic activity of the peroxidase and superoxide dismutase, with lower lipid peroxidation) and Mucorales. The pharmacokinetic profile of isavuconazole does not warrant routine TDM and has comparatively fewer drug-drug interactions. It is hence not surprising to see isavuconazole favourably climb the recommendation ladder in the globally recognized guidelines and being accepted as a frontrunner in the management of invasive aspergillosis and mucormycosis.

Conflicts of interest:
In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: Neha Gupta declare(s) personal fees from Pfizer Ltd. Nitin Sood declare(s) personal fees from Pfizer Ltd. Prithwijit Kundu declare(s) employment from Pfizer Ltd. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.