What are the treatment guidelines for dermatophyte infections?

Treatment Guidelines for Dermatophyte Infections

Confirm Diagnosis Before Treatment

Always obtain mycological confirmation through KOH preparation, fungal culture, or nail biopsy before initiating systemic therapy, as incorrect diagnosis is the most common cause of treatment failure. 1, 2

• Collect subungual debris from the most proximal part of the infection using a dental scraper for best results 1
• Submit as much material as possible to the laboratory due to the relative paucity of fungal elements 1
• Culture on Sabouraud's glucose agar and incubate at 28°C for at least 3 weeks before declaring negative 1
• Identifying the causative organism is crucial, as treatment varies based on pathogen type 3

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Treatment by Site and Organism

Onychomycosis (Nail Infections) - Dermatophytes

Terbinafine 250 mg daily is first-line therapy due to superior efficacy and tolerability compared to all other antifungals. 1, 4, 3

Dosing Regimens:

• Fingernail infections: 250 mg daily for 6 weeks 2
• Toenail infections: 250 mg daily for 12-16 weeks 4, 3, 2

Expected Outcomes:

• Mycological cure rates: 70-80% for toenail infections 3
• Success rates approach 100% when partial nail removal is combined with oral therapy 3
• Optimal clinical effect occurs months after mycological cure due to the period required for healthy nail outgrowth 2
• Complete nail regrowth may take up to 18 months 3

Monitoring Requirements:

• Obtain baseline liver function tests (LFTs) before starting treatment 4, 2
• Re-evaluate patients 3-6 months after treatment initiation 4
• Continue treatment if disease persists 4
• More vigilant LFT monitoring is required in patients with pre-existing liver disease, concomitant hepatotoxic medications, continuous therapy >1 month, or heavy alcohol consumption 4

Alternative for Dermatophyte Onychomycosis:

• Itraconazole: 400 mg daily for 1 week per month, repeated for 3 pulses (toenails) or 2 pulses (fingernails) 1
• Itraconazole is less effective than terbinafine for dermatophyte infections 1, 4

Griseofulvin (No Longer Recommended):

• Poor cure rates and long treatment duration make it no longer the treatment of choice for dermatophyte onychomycosis 1
• Cost-effectiveness ratio is poor despite low drug cost due to frequent treatment failures 1

Onychomycosis - Candida Species

Itraconazole 400 mg daily for 1 week per month, repeated for 3-4 pulses for toenail infections. 3

• Alternative: Fluconazole 150-450 mg weekly for at least 6 months 3

Tinea Capitis (Scalp Infections)

Species-specific systemic therapy is required; topical therapy alone is inadequate. 1, 5

For Trichophyton Species:

• First-line: Terbinafine 5
• Alternatives: Itraconazole or fluconazole 5

For Microsporum Species:

• First-line: Griseofulvin 6, 5
• Alternatives: Itraconazole or fluconazole 5
• Terbinafine is less effective for Microsporum infections 5

Additional Measures:

• Screen all family members, as >50% may be affected with occult disease 1
• Treat all positive family members simultaneously to prevent recurrence 1, 3
• Children may return to school once appropriate systemic and adjuvant topical therapy is commenced 1
• Cleanse hairbrushes and combs with bleach or 2% aqueous sodium hypochlorite solution 1
• Follow-up with repeat mycology sampling monthly until mycological clearance is documented 1

Tinea Corporis, Tinea Pedis, Tinea Cruris (Skin Infections)

Topical antifungal therapy is first-line for localized infections. 7, 5

• Topical allylamines (e.g., terbinafine) have higher cure rates and shorter treatment courses than azoles 7
• Oral therapy is reserved for extensive or recalcitrant disease 7, 8

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Contraindications and Safety Warnings

Terbinafine Contraindications:

• History of allergic reaction to oral terbinafine (risk of anaphylaxis) 2
• Active or chronic liver disease 4, 2
• Lupus erythematosus 4

Critical Safety Warnings for Terbinafine:

• Hepatotoxicity: Cases of liver failure leading to transplant or death have occurred 2

• Discontinue immediately if biochemical or clinical evidence of liver injury develops 2

• Warn patients to report persistent nausea, anorexia, fatigue, vomiting, right upper abdominal pain, jaundice, dark urine, or pale stools 2

• Taste disturbance: Can be severe, prolonged (>1 year), or permanent 2

• Smell disturbance: May be prolonged or permanent 2

• Depressive symptoms: Monitor and instruct patients to report 2

Drug Interactions:

• Terbinafine has minimal drug interactions compared to azoles 4
• Main concern is with drugs metabolized by cytochrome P450 2D6 4
• Itraconazole has significant interactions with warfarin, antihistamines, antipsychotics, anxiolytics, digoxin, cisapride, cyclosporine, and simvastatin 1

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Common Pitfalls and Treatment Failures

Treatment failure occurs in 20-30% of cases. 3

Common Causes:

• Poor compliance 3
• Poor drug absorption 3
• Immunosuppression 3
• Dermatophyte resistance 3
• Presence of dermatophytoma (dense white lesions under nail requiring nail removal) 3
• Clinical diagnosis without mycological confirmation 1

Prevention of Recurrence:

• Keep nails short 3
• Wear protective footwear in public bathing facilities 3
• Apply antifungal powders to shoes and feet 3
• Wear cotton, absorbent socks 3
• Discard heavily contaminated footwear or treat with antifungal solutions 3
• Treat all infected family members simultaneously 3

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Important Clinical Considerations

• Mycological cure rates are approximately 30% better than clinical cure rates 1
• Nail appearance may not return to completely normal if there was pre-existing dystrophy 1, 3
• Dermatophyte onychomycosis should not be considered trivial; it can cause cellulitis and compromise limbs in patients with diabetes or peripheral vascular disease 1
• The disease is relentlessly progressive without treatment 1