What is the next step in managing a patient with tinea corporis that has failed topical nystatin and topical ketoconazole therapy?

Oral Antifungal Therapy for Topical-Resistant Tinea Corporis

When tinea corporis fails topical nystatin and ketoconazole, switch to oral antifungal therapy—specifically terbinafine 250 mg daily for 1-2 weeks or itraconazole 100 mg daily for 15 days. 1, 2

Why Topical Treatment Failed

• Nystatin is ineffective against dermatophytes—it only treats Candida species, not the fungi causing tinea corporis (Trichophyton, Microsporum, Epidermophyton). This was the wrong drug from the start. 3, 4
• Topical ketoconazole failure indicates either extensive disease, deep infection, or treatment non-adherence requiring systemic therapy. 1, 5

First-Line Oral Treatment Options

Terbinafine (Preferred for Most Cases)

• Dose: 250 mg daily for 1-2 weeks 1, 2
• Particularly effective against Trichophyton tonsurans (the most common cause of tinea corporis in many regions) 1, 2
• Shorter treatment duration improves compliance 2
• Check baseline liver function tests before starting 1, 2

Itraconazole (Alternative First-Line)

• Dose: 100 mg daily for 15 days 1, 2, 6
• 87% mycological cure rate in clinical trials 1, 6
• Effective against both Trichophyton and Microsporum species when the organism is unknown 2
• Critical drug interactions: Avoid with warfarin, certain antihistamines (terfenadine, astemizole), antipsychotics, midazolam, digoxin, cisapride, simvastatin 2, 7
• Contraindicated in heart failure 2

Treatment Selection Algorithm

If you know the causative organism (from KOH prep or culture):

• Trichophyton species → Terbinafine 250 mg daily for 1-2 weeks 1, 2
• Microsporum species → Itraconazole 100 mg daily for 15 days 2

If organism unknown (most common scenario):

• Start terbinafine 250 mg daily for 1-2 weeks as empiric first-line 1, 2
• Switch to itraconazole if no clinical improvement after 2 weeks 2

Essential Diagnostic Step Before Treatment

• Obtain KOH preparation or fungal culture now to confirm dermatophyte infection and identify the species 1, 2, 3
• Scrape the active border of the lesion with a scalpel for best yield 1, 2
• This confirms you're treating the right organism and guides therapy if first-line treatment fails 1, 5

Monitoring and Treatment Endpoints

• Mycological cure (negative microscopy and culture) is the definitive endpoint, not just clinical improvement 1, 2
• Repeat mycology sampling at the end of treatment and monthly until clearance is documented 1, 2
• If clinical improvement occurs but mycology remains positive, continue therapy for an additional 2-4 weeks 2
• If no initial clinical improvement, switch to second-line therapy 2

Prevention of Recurrence

• Screen and treat family members, especially for anthropophilic species like T. tonsurans (over 50% of family members may be affected) 1, 2
• Clean all fomites (towels, clothing, bedding) with disinfectant or 2% sodium hypochlorite solution 1, 2
• Avoid skin-to-skin contact with infected individuals and do not share personal items 1, 2
• Cover lesions during treatment to prevent spread 1

Common Pitfalls to Avoid

• Never use nystatin for tinea corporis—it has zero activity against dermatophytes 3, 4
• Do not stop treatment based on clinical appearance alone; wait for mycological clearance 1, 2
• Do not use terbinafine empirically if Microsporum is suspected or confirmed—it has poor efficacy against this organism 8
• Do not ignore concurrent infections (tinea pedis, onychomycosis) as they serve as reservoirs for reinfection 2

When to Consider Griseofulvin

• Griseofulvin is not recommended as first-line due to longer treatment duration (2-4 weeks), lower efficacy than terbinafine, and lower cure rates 1, 9
• Reserve for Microsporum infections when itraconazole is contraindicated 2
• Dose: 500 mg daily for adults (or 10 mg/kg/day for children) for 2-4 weeks 9