Effectiveness and safety of oral terbinafine for dermatophyte distal subungual onychomycosis

INTRODUCTION

Terbinafine has been a cornerstone in dermatophyte infection treatment. Despite its global efficacy, the emergence of terbinafine resistance raises concerns, requiring ongoing vigilance.

AREAS COVERED

This paper focuses on evaluating the efficacy and safety of terbinafine in treating dermatophyte toenail infections. Continuous and pulse therapies, with a 24-week continuous regimen and a higher dosage of 500 mg/day have demonstrated superior efficacy to the FDA approved regimen of 250 mg/day x 12 weeks. Pulse therapies, though showing comparable effectiveness, present debates with regards to their efficacy as conflicting findings have been reported. Safety concerns encompass hepatotoxicity, gastrointestinal, cutaneous, neurologic, hematologic and immune adverse-effects, and possible drug interactions, suggesting the need for ongoing monitoring.

EXPERT OPINION

Terbinafine efficacy depends on dosage, duration, and resistance patterns. Continuous therapy for 24 weeks and a dosage of 500 mg/day may enhance outcomes, but safety considerations and resistance necessitate individualized approaches. Alternatives, including topical agents and alternative antifungals, are to be considered for resistant cases. Understanding the interplay between treatment parameters, adverse effects, and resistance mechanisms is critical for optimizing therapeutic efficacy while mitigating resistance risks. Patient education and adherence are vital for early detection and management of adverse effects and resistance, contributing to tailored and effective treatments.

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.

Onychomycosis: Rapid Evidence Review

Onychomycosis is a chronic fungal infection of the fingernail or toenail bed leading to brittle, discolored, and thickened nails. Onychomycosis is not just a cosmetic problem. Untreated onychomycosis can cause pain, discomfort, and physical impairment, negatively impacting quality of life. Onychomycosis should be suspected in patients with discolored nails, nail plate thickening, nail separation, and foul-smelling nails. Accurate diagnosis is important before initiating treatment because therapy is lengthy and can cause adverse effects. A potassium hydroxide preparation with confirmatory fungal culture, periodic acid-Schiff stain, or polymerase chain reaction is the preferred diagnostic approach if confirmative testing is cost prohibitive or not available. Treatment decisions should be based on severity, comorbidities, and patient preference. Oral terbinafine is preferred over topical therapy because of better effectiveness and shorter treatment duration. Patients taking terbinafine in combination with tricyclic antidepressants, selective serotonin reuptake inhibitors, atypical antipsychotics, beta blockers, or tamoxifen should be monitored for drug-drug interactions. Topical therapy, including ciclopirox 8%, efinaconazole 10%, and tavaborole 5%, is less effective than oral agents but can be used to treat mild to moderate onychomycosis, with fewer adverse effects and drug-drug interactions. Nail trimming and debridement used concurrently with pharmacologic therapy improve treatment response. Although photodynamic and plasma therapies are newer treatment options that have been explored for the treatment of onychomycosis, larger randomized trials are needed. Preventive measures such as avoiding walking barefoot in public places and disinfecting shoes and socks are thought to reduce the 25% relapse rate.

Subacute cutaneous lupus erythematosus in a patient with Sjögren's syndrome taking terbinafine for onychomycosis

We report the case of a 40-year old woman followed at our Rheumatology department for a 14-year history of a relatively well controlled Sjögren's syndrome who developed, for the first time in life, lesions suggestive of subacute cutaneous lupus erythematosus, nine weeks after taking oral terbinafine prescribed for onychomycosis. She denied additional symptoms, namely systemics, and no other clinical finding besides cutaneous lesions were detected. No laboratory findings were in favour of a flare of her connective tissue disease. Here we explore the possibility of terbinafine-induced subacute cutaneous lupus erythematosus in the context of previous autoimmunity. This clinical case highlights the importance of avoiding the prescription of terbinafine in this kind of patients.

Terbinafine-induced lichenoid drug eruption: case report and review of terbinafine-associated cutaneous adverse events

Terbinafine is an antifungal agent used in the treatment of hair, nail, and skin dermatophyte infections. Skin side effects to terbinafine are not common. Lichenoid drug eruption is a medication-related adverse cutaneous event; the lesion morphology and pathology mimic lichen planus. A woman with onychomycosis developed a lichenoid drug eruption one week after starting terbinafine. The features of her dermatosis and the characteristics of two additional men who also experienced terbinafine-induced lichenoid drug eruption are discussed. They were receiving a daily terbinafine dosage of either 125mg or 250mg to treat onychomycosis or tinea cruris. The lichenoid drug eruption presented as diffuse or symmetric lesions within one to two weeks after starting terbinafine treatment. The extremities, chest, abdomen, and/or trunk were common sites. Less frequent locations were the lips, nails, palms, soles, and suprapubic region; lesions did not occur on the oral or genital mucosa. The eruption resolved after discontinuation of the medication (with or without treatment using topical corticosteroids, systemic corticosteroids, or both). In addition, more frequently occurring terbinafine-associated cutaneous adverse events (such as urticaria, erythematous eruptions, pruritus, acute generalized exanthematous pustulosis, subacute cutaneous lupus erythematosus, and papulosquamous conditions) are reviewed.

An Implementation and Visualization of the Tree-Based Scan Statistic for Safety Event Monitoring in Longitudinal Electronic Health Data

INTRODUCTION

Longitudinal electronic healthcare data hold great potential for drug safety surveillance. The tree-based scan statistic (TBSS), as implemented by the TreeScan^® software, allows for hypothesis-free signal detection in longitudinal data by grouping safety events according to branching, hierarchical data coding systems, and then identifying signals of disproportionate recording (SDRs) among the singular events or event groups.

OBJECTIVE

The objective of this analysis was to identify and visualize SDRs with the TBSS in historical data from patients using two antifungal drugs, itraconazole or terbinafine. By examining patients who used either itraconazole or terbinafine, we provide a conceptual replication of a previous TBSS analyses by varying methodological choices and using a data source that had not been previously used with the TBSS, i.e., the Optum Clinformatics™ claims database. With this analysis, we aimed to test a parsimonious design that could be the basis of a broadly applicable method for multiple drug and safety event pairs.

METHODS

The TBSS analysis was used to examine incident events and any itraconazole or terbinafine use among US-based patients from 2002 through 2007. Event frequencies before and after the first day of drug exposure were compared over 14- and 56-day periods of observation in a Bernoulli model with a self-controlled design. Safety events were classified into a hierarchical tree structure using the Clinical Classifications Software (CCS) which mapped International Classification of Diseases, 9th Revision (ICD-9) codes to 879 diagnostic groups. Using the TBSS, the log likelihood ratio of observed versus expected events in all groups along the CCS hierarchy were compared, and groups of events that occurred at disproportionally high frequencies were identified as potential SDRs; p-values for the potential SDRs were estimated with Monte-Carlo permutation based methods. Output from TreeScan^® was visualized and plotted as a network which followed the CCS tree structure.

RESULTS

Terbinafine use (n = 223,968) was associated with SDRs for diseases of the circulatory system (14- and 56-day p = 0.001) and heart (14-day p = 0.026 and 56-day p = 0.001) as well as coronary atherosclerosis and other heart disease (14-day p = 0.003 and 56-day p = 0.004). For itraconazole use (n = 36,025), the TBSS identified SDRs for coronary atherosclerosis and other heart disease (p = 0.002) and complications of an implanted or grafted device (14-day p = 0.001 and 56-day p < 0.05). Use of both drugs was associated with SDRs for diseases of the digestive system at 14 days (p < 0.05) and this SDR had been observed among terbinafine users in a previous TBSS analysis with a different data source. The TreeScan^® visualization facilitated the identification of the atherosclerosis and other heart disease SDRs as well as highlighting the consistency of the SDR for diseases of the digestive system across drugs and data sources.

CONCLUSION

With the TBSS, we identified potential SDRs related to the circulatory system that may reflect the cardiac risk that was described in the itraconazole product label. SDRs for diseases of the digestive system among terbinafine users were also reported in a previous signal detection analysis, although other SDRs from the previous publications were not replicated. The TBSS visualizations aided in the understanding and interpretation of the TBSS output, including the comparisons to the previous publications. In this conceptual replication, differences in the results observed in our analysis and the previous analyses could be attributable to variation in modeling and design choices as well as factors that were intrinsic to the underlying data sources. The broad consistency, but far from perfect concordance, of our results with the known safety profile of these antifungals including the risks from the itraconazole product label supports the rationale for continued investigations of signal detection methods across differing data sources and populations.