What is the recommended treatment for a patient with onychomycosis (fingernail fungus)?

Treatment of Fingernail Onychomycosis

First-Line Treatment Recommendation

Terbinafine 250 mg once daily for 6 weeks is the definitive first-line treatment for fingernail onychomycosis caused by dermatophytes. 1, 2, 3

This recommendation is based on:

• Superior efficacy: Complete cure rate of 55% versus 26% for itraconazole at 72 weeks 2
• Fungicidal activity against dermatophytes with very low minimum inhibitory concentrations (approximately 0.004 μg/mL) 1
• Minimal drug interactions compared to azole antifungals, making it safer for patients on multiple medications 1, 2
• Strength of recommendation A with level of evidence 1+ from the British Association of Dermatologists 1

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Pre-Treatment Requirements

Mandatory Diagnostic Confirmation

• Obtain mycological confirmation before initiating therapy through KOH preparation, fungal culture, or nail biopsy to confirm dermatophyte infection 2, 3
• This step is critical because treatment selection differs based on the causative organism (dermatophyte versus Candida) 2

Required Baseline Laboratory Tests

• Liver function tests (ALT and AST) are mandatory before starting terbinafine 1, 2
• Complete blood count is required before treatment initiation 1, 2
• These tests are particularly important in patients with history of hepatitis, heavy alcohol use, or hematological abnormalities 1

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Treatment Protocol

Standard Dosing

• Terbinafine 250 mg once daily for 6 weeks for fingernail infections 1, 2, 3
• Can be taken with or without food, as absorption is not affected by food intake 1

Pharmacokinetic Advantage

• Terbinafine persists in the nail for 6 months after treatment completion due to its long half-life (24-156 days) and lipophilic properties, allowing for continued fungicidal activity 1, 4
• The optimal clinical effect is seen months after mycological cure and cessation of treatment, related to the period required for outgrowth of healthy nail 3

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Absolute Contraindications

• Active or chronic liver disease 1, 3
• Lupus erythematosus 1
• History of allergic reaction to oral terbinafine due to risk of anaphylaxis 3

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Critical Safety Warnings

Hepatotoxicity

• Cases of liver failure, some leading to liver transplant or death, have occurred with terbinafine use 3
• Patients must be warned to report immediately: persistent nausea, anorexia, fatigue, vomiting, right upper abdominal pain, jaundice, dark urine, or pale stools 3
• Discontinue terbinafine immediately if biochemical or clinical evidence of liver injury develops 3

Sensory Disturbances

• Taste disturbance, including taste loss, can be severe enough to result in decreased food intake, weight loss, and depressive symptoms 3
• May be prolonged (greater than one year) or permanent 3
• Smell disturbance, including loss of smell, may also be prolonged or permanent 3
• Discontinue terbinafine if symptoms of taste or smell disturbance occur 3

Other Serious Adverse Effects

• Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported 1
• Depressive symptoms have occurred during postmarketing use 3

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Follow-Up and Monitoring

Re-evaluation Timeline

• Re-evaluate patients 3-6 months after treatment initiation 1, 2
• Assessment should include both clinical improvement and mycological cure (negative microscopy and culture) 2
• Follow-up period of at least 48 weeks from start of treatment is ideal to identify potential relapse 2

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Management of Treatment Failure

If First Course Fails

• Confirm the infection is due to dermatophytes (not Candida) 2
• Repeat pre-treatment checks (liver function tests and complete blood count) 2
• Resume terbinafine 250 mg daily for another 6 weeks 2

If Second Course Fails

• Switch to itraconazole as second-line alternative 2
• Dosing options: 200 mg daily for 12 weeks continuously, or pulse therapy at 400 mg daily for 1 week per month for 2 pulses 2, 5

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Special Consideration: Candida Onychomycosis

If mycological testing confirms Candida species, itraconazole becomes the first-line treatment, with a superior cure rate of 92% versus 40% for terbinafine in Candida infections 2

This is a critical distinction because terbinafine is significantly less effective against Candida species 2

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Adjunctive and Alternative Therapies

Topical Therapy

• Appropriate for mild, superficial, or distal onychomycosis involving less than 50% of the nail plate without matrix involvement 2
• FDA-approved topical agents: efinaconazole 10% solution and tavaborole 5% solution, with mycological cure rates approaching 50% and complete cure in 15% 2
• Can be combined with systemic therapy for enhanced efficacy 5

Prevention of Recurrence

• Decontaminate or replace contaminated footwear 2, 5
• Apply antifungal powders inside shoes regularly 2, 5
• Consider periodic spraying of terbinafine solution into shoes 2, 5

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Common Pitfalls to Avoid

• Do not skip mycological confirmation before treatment—this is the most common error leading to treatment failure 2
• Do not use terbinafine for Candida onychomycosis—it has poor efficacy against Candida species 2
• Do not ignore baseline liver function tests—hepatotoxicity can occur even in patients without pre-existing liver disease 3
• Do not expect immediate clinical improvement—healthy nail outgrowth takes months after mycological cure 3