When to start oral antifungal therapy for onychomycosis (fungal infection of the nail)?

From the Guidelines

Oral antifungal therapy for onychomycosis should be initiated after confirming the diagnosis with laboratory testing such as KOH preparation, fungal culture, or nail clipping histopathology, as recommended by the British Association of Dermatologists' guidelines for the management of onychomycosis 2014 1.

Key Considerations

• The diagnosis of onychomycosis should be confirmed before starting treatment, as stated in the guidelines for treatment of onychomycosis 1.
• First-line oral treatments include terbinafine 250mg daily for 6 weeks (fingernails) or 12 weeks (toenails), itraconazole 200mg twice daily for 1 week per month for 2 months (fingernails) or 3 months (toenails), or fluconazole 150-300mg once weekly for 3-6 months (fingernails) or 6-12 months (toenails) 1.
• Before starting treatment, obtain baseline liver function tests since these medications can cause hepatotoxicity, as noted in the summary of drug therapies in adults 1.

Indications for Oral Therapy

• Oral therapy is indicated when infection involves the nail matrix or more than 50% of the nail plate.
• Topical treatments have failed, or in patients with multiple affected nails or significant discomfort.
• Patients with diabetes or immunocompromised status may benefit from earlier oral therapy to prevent complications.

Mechanism of Action

• Oral antifungals work by inhibiting ergosterol synthesis in the fungal cell membrane, effectively killing the fungus throughout the nail unit, which is why they're more effective than topical treatments for moderate to severe infections.

Treatment Options

• Terbinafine is generally preferred over itraconazole due to its higher efficacy and tolerability, as demonstrated in a multicentre, randomized trial involving 508 subjects 1.
• Itraconazole may be considered as an alternative, especially in cases of Candida onychomycosis, where it has shown higher efficacy rates compared to terbinafine 1.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Determining the Start of Oral Antifungal Treatment for Onychomycosis

• The decision to start oral antifungal treatment for onychomycosis depends on various factors, including the severity of the infection, the patient's medical history, and the presence of any comorbidities 2, 3.
• According to a study published in 2022, terbinafine and itraconazole are the most commonly used oral antifungals to treat onychomycosis, with terbinafine showing higher efficacy rates 4.
• Another study from 2003 found that oral terbinafine 250 mg/day for 12 or 16 weeks was more efficacious than itraconazole, fluconazole, and griseofulvin in treating dermatophyte onychomycosis of the toenails 5.
• A 2005 study noted that terbinafine has a low potential for drug-drug interactions, making it a preferred choice for treating onychomycosis in patients with comorbidities 6.
• When to start oral antifungal treatment is not explicitly stated in the provided studies, but it is generally recommended to start treatment when the diagnosis of onychomycosis is confirmed, and the patient's medical history and current medications have been assessed 2, 3.
• The safety and efficacy of oral antifungal agents, including terbinafine and itraconazole, have been established in various studies, but it is essential to monitor patients for potential adverse events and drug interactions 2, 6.