Combatting antifungal resistance: Paradigm shift in the diagnosis and management of onychomycosis and dermatomycosis

Mapping the Global Spread of T. indotineae: An Update on Antifungal Resistance, Mutations, and Strategies for Effective Management

INTRODUCTION

The global spread of Trichophyton indotineae presents a pressing challenge in dermatophytosis management. This systematic review explores the current landscape of T. indotineae infections, emphasizing resistance patterns, susceptibility testing, mutational analysis, and management strategies.

METHODS

A literature search was conducted in November 2023 using Embase, PubMed, Scopus, and Web of Science databases. Inclusion criteria covered clinical trials, observational studies, case series, or case reports with T. indotineae diagnosis through molecular methods. Reports on resistance mechanisms, antifungal susceptibility testing, and management were used for data extraction.

RESULTS AND DISCUSSION

A total of 1148 articles were identified through the systematic search process, with 45 meeting the inclusion criteria. The global spread of T. indotineae is evident, with cases reported in numerous new countries in 2023. Tentative epidemiological cut-off values (ECOFFs) suggested by several groups provide insights into the likelihood of clinical resistance. The presence of specific mutations, particularly Phe397Leu, correlate with higher minimum inhibitory concentrations (MICs), indicating potential clinical resistance. Azole resistance has also been reported and investigated in T. indotineae, and is a growing concern. Nevertheless, itraconazole continues to be an alternative therapy. Recommendations for management include oral or combination therapies and individualized approaches based on mutational analysis and susceptibility testing.

CONCLUSION

Trichophyton indotineae poses a complex clinical scenario, necessitating enhanced surveillance, improved diagnostics, and cautious antifungal use. The absence of established clinical breakpoints for dermatophytes underscores the need for further research in this challenging field.

An update on antifungal resistance in dermatophytosis

INTRODUCTION

The reports of resistance to antifungal agents used for treating onychomycosis and other superficial fungal infections are increasing. This rise in antifungal resistance poses a public health challenge that requires attention.

AREAS COVERED

This review explores the prevalence of dermatophytes and the current relationship between dermatophyte species, their minimum inhibitory concentrations (MICs) for terbinafine (an allylamine) and itraconazole (an azole), and various mutations prevalent in these species. The most frequently isolated dermatophyte associated with resistance in patients with onychomycosis and dermatophytosis was T. mentagrophytes. However, T. indotineae emerged as the most prevalent isolate with mutations in the SQLE gene, exhibiting the highest MIC of 8 µg/ml for terbinafine and MICs of 8 µg/ml and ≥ 32 µg/ml for itraconazole.Overall, the most prevalent SQLE mutations were Phe397Leu, Leu393Phe, Ala448Thr, Phe397Leu/Ala448Thr, and Lys276Asn/Leu415Phe (relatively recent).

EXPERT OPINION

Managing dermatophyte infections requires a personalized approach. A detailed history should be obtained including details of travel, home and occupational exposure, and clinical examination of the skin, nails and other body systems. Relevant testing includes mycological examination (traditional and molecular). Additional testing, where available, includes MIC evaluation and detection of SQLE mutations. In case of suspected terbinafine resistance, itraconazole or voriconazole (less commonly) should be considered.

Navigating fungal infections and antifungal stewardship: drug resistance, susceptibility testing, therapeutic drug monitoring and future directions

Antifungal stewardship refers to the rational use of antifungal agents. Historically, in some instances, the misuse or overuse of antifungal agents has predisposed patients to an elevated risk of systemic side-effects and treatment resistance, as well as increased healthcare costs. Superficial mycoses, such as onychomycosis, are sometimes treated without any diagnostic testing and is associated with a high likelihood of self-diagnosis and self-treatment, potentially leading to the emergence of resistance against commonly used antifungals like terbinafine. Practitioners need to ensure that a proper clinical diagnosis is backed up by appropriate testing. This may include the traditional light microscopy and culture; additionally, molecular techniques (such as polymerase chain reaction, terbinafine gene mutational analysis) and antifungal susceptibility testing are considerations as appropriate. The choice of antifungal agent should be guided by what is the standard of care in the location where the clinician practices as well as more broadly state and national prescription patterns. Recently, reports of treatment resistance concerning both superficial and deep fungal infections have added another layer of difficulty to clinical practice. This review aims to explore the phenomenon of antifungal drug resistance, and highlights the importance of adopting antifungal stewardship programs. We provide an overview of treatment resistance and mechanisms of resistance reported thus far in dermatophytes. Challenges of performing antifungal susceptibility testing and therapeutic drug monitoring are discussed, as well as principles, recommendations and future directions of antifungal stewardship programs.

------Topical Antifungal Prescribing for Medicare Part D Beneficiaries - United States, 2021

Incorrect use of topical antifungals and antifungal-corticosteroid combinations is likely contributing to the global emergence and spread of severe antimicrobial-resistant superficial fungal infections, which have recently been detected in the United States. Understanding prescribing patterns is an initial step in establishing and promoting recommended use of these medications. Using 2021 Medicare Part D data, CDC examined prescription volumes, rates, and costs for topical antifungals (including topical combination antifungal-corticosteroid medications). Total prescription volumes were compared between higher-volume prescribers (top 10% of topical antifungal prescribers by volume) and lower-volume prescribers. During 2021, approximately 6.5 million topical antifungal prescriptions were filled (134 prescriptions per 1,000 beneficiaries), at a total cost of $231 million. Among 1,017,417 unique prescribers, 130,637 (12.8%) prescribed topical antifungals. Primary care physicians wrote the highest percentage of prescriptions (40.0%), followed by nurse practitioners or physician assistants (21.4%), dermatologists (17.6%), and podiatrists (14.1%). Higher-volume prescribers wrote 44.2% (2.9 million) of all prescriptions. This study found that enough topical antifungal prescriptions were written for approximately one of every eight Medicare Part D beneficiaries in 2021, and 10% of antifungal prescribers prescribed nearly one half of these medications. In the setting of emerging antimicrobial resistance, these findings highlight the importance of expanding efforts to understand current prescribing practices while encouraging judicious prescribing by clinicians and providing patient education about proper use.

Treatment of onychomycosis in an era of antifungal resistance: Role for antifungal stewardship and topical antifungal agents

A growing body of literature has marked the emergence and spread of antifungal resistance among species of Trichophyton, the most prevalent cause of toenail and fingernail onychomycosis in the United States and Europe. We review published data on rates of oral antifungal resistance among Trichophyton species; causes of antifungal resistance and methods to counteract it; and in vitro data on the role of topical antifungals in the treatment of onychomycosis. Antifungal resistance among species of Trichophyton against terbinafine and itraconazole-the two most common oral treatments for onychomycosis and other superficial fungal infections caused by dermatophytes-has been detected around the globe. Fungal adaptations, patient characteristics (e.g., immunocompromised status; drug-drug interactions), and empirical diagnostic and treatment patterns may contribute to reduced antifungal efficacy and the development of antifungal resistance. Antifungal stewardship efforts aim to ensure proper antifungal use to limit antifungal resistance and improve clinical outcomes. In the treatment of onychomycosis, critical aspects of antifungal stewardship include proper identification of the fungal infection prior to initiation of treatment and improvements in physician and patient education. Topical ciclopirox, efinaconazole and tavaborole, delivered either alone or in combination with oral antifungals, have demonstrated efficacy in vitro against susceptible and/or resistant isolates of Trichophyton species, with low potential for development of antifungal resistance. Additional real-world long-term data are needed to monitor global rates of antifungal resistance and assess the efficacy of oral and topical antifungals, alone or in combination, in counteracting antifungal resistance in the treatment of onychomycosis.

The safety of oral antifungals for the treatment of onychomycosis

INTRODUCTION

Oral antifungals are used for the treatment of moderate-severe onychomycosis. Terbinafine and itraconazole are approved for onychomycosis treatment in North America; additionally, fluconazole is indicated for onychomycosis in Europe. Other oral antifungals such as ketoconazole and griseofulvin are no longer used for the treatment of onychomycosis due to safety concerns and relatively lower efficacy.

SEARCH STRATEGY

On 7 March 2023, we conducted a comprehensive search in PubMed and Google Scholar, while also manually examining selected article bibliographies and package inserts.

AREAS COVERED

Terbinafine, itraconazole, and fluconazole have several interactions with cytochrome-p450, and either alone, or when co-administered with other drugs these interactions can facilitate a multitude of adverse events. This article identifies possible hepatic, renal, cutaneous, cardiovascular, neurological, hemopoietic, and obstetric adverse events. We have also compared the rates of hepatotoxicity, clinically apparent liver injury, and alanine transaminase elevations between oral antifungals, and recommendations for hepatic monitoring.

EXPERT OPINION

We recommend laboratory testing of liver function tests prior to the administration of any oral antifungals, especially when clinically indicated. In the event of a first treatment failure, the diagnosis of onychomycosis must be confirmed, and consideration given to antifungal susceptibility testing. Antifungal stewardship will help reduce the incidence of antifungal resistance.