What is the recommended treatment for onychomycosis (fungal infection of the nail) of a single nail?

Treatment of Onychomycosis of a Single Nail

Oral terbinafine 250 mg daily is the recommended first-line treatment for onychomycosis of a single nail, administered for 6 weeks for fingernail infections and 12 weeks for toenail infections. 1

Diagnostic Confirmation

Before initiating treatment, proper diagnosis is essential:

• Obtain appropriate nail specimens for laboratory testing (KOH preparation, fungal culture, or nail biopsy) to confirm the diagnosis 2
• Identify the causative organism (dermatophytes, Candida, or non-dermatophyte molds) to guide treatment decisions 1

Treatment Algorithm

First-line Treatment:

• Oral terbinafine 250 mg daily:
  • 6 weeks for fingernail infections
  • 12 weeks for toenail infections
  • Expected cure rates: 80-90% for fingernails and 70-80% for toenails 1
  • Terbinafine has a fungicidal mechanism of action against dermatophytes with superior efficacy compared to other antifungals 1

Second-line Treatment:

• Itraconazole:
  • Continuous therapy: 200 mg daily for 12 weeks
  • Pulse therapy: 400 mg daily for 1 week per month (2 pulses for fingernails, 3 pulses for toenails) 1

Third-line Treatment:

• Fluconazole:
  • 150-450 mg once weekly for 3 months (fingernails) or 6 months (toenails) 1

Topical Therapy Options:

• Recommended for superficial white onychomycosis or early distal lateral subungual onychomycosis with <80% nail involvement:
  • Ciclopirox 8% nail lacquer applied once daily for up to 48 weeks 1, 3
  • Amorolfine 5% lacquer
  • Tioconazole 28% solution 1

Special Patient Populations

• Diabetic patients: Terbinafine preferred over itraconazole due to lower risk of drug interactions and no contraindication in cardiac disease 1
• Immunosuppressed patients: Terbinafine or fluconazole preferred over itraconazole due to fewer interactions with antiretrovirals 1

Monitoring and Follow-up

• Baseline liver function tests and complete blood count before starting terbinafine, especially in patients with:

  • History of hepatotoxicity
  • Hematological abnormalities
  • Concomitant use of hepatotoxic drugs 1

• Follow-up for at least 48 weeks (preferably 72 weeks) from treatment start

• Re-evaluate 3-6 months after treatment initiation

• Provide additional treatment if disease persists 1

Adjunctive Measures

To improve outcomes:

• Keep nails short
• Disinfect footwear
• Treat concomitant tinea pedis
• Treat infected family members 1

Treatment Failure Considerations

Treatment failure may occur due to:

• Poor compliance
• Poor drug absorption
• Immunosuppression
• Dermatophyte resistance
• Subungual dermatophytoma preventing drug penetration 1

If treatment fails, consider:

• Partial nail removal
• Alternative drug therapy
• Complete nail removal in combination with further antifungal therapy 1

Evidence Strength

Recent evidence strongly supports continuous terbinafine over pulse therapy, with one 2023 study showing 76.67% efficacy for continuous dosing versus only 26.67% for pulse dosing 4. This aligns with the British Journal of Dermatology guidelines recommending continuous therapy as first-line treatment 1.

Earlier studies demonstrated that 12 weeks of terbinafine treatment is optimal for toenail infections, with cure rates of 71-82% 5, 6, while 6 weeks is generally sufficient for fingernail infections 6.