What is the most likely diagnosis and recommended treatment for a fungal skin infection of the foot (tinea pedis)?

Fungal Skin Infection on Foot (Tinea Pedis)

For uncomplicated tinea pedis, apply topical terbinafine 1% cream twice daily for 1 week—this short course is more effective than longer regimens with other antifungals and should be your first-line treatment. 1

Diagnosis and Clinical Presentation

Tinea pedis presents in three main forms that guide treatment decisions:

• Interdigital type: Fine scaly eruptions between toes, often itchy—the most common presentation 2
• Hyperkeratotic (moccasin) type: Diffuse scaling on soles, heels, and sides of foot 3
• Vesiculobullous (inflammatory) type: Vesicles and pustules, typically more severe 3

Clinical diagnosis alone is unreliable—perform a KOH wet-mount examination of skin scrapings from the active border before starting treatment to confirm dermatophyte infection. 3 The causative organisms are predominantly Trichophyton rubrum and T. mentagrophytes. 1

First-Line Topical Treatment

Topical terbinafine 1% cream applied twice daily for 1 week achieves superior cure rates (66% effective cure) compared to 4 weeks of other topical agents. 1, 2 This fungicidal agent allows dramatically shorter treatment duration than fungistatic alternatives. 4

Alternative Topical Options (if terbinafine unavailable):

• Ciclopirox olamine 0.77% cream/gel twice daily for 4 weeks: achieves 60% cure at end of treatment and 85% cure two weeks post-treatment, superior to clotrimazole 1, 2
• Clotrimazole 1% cream twice daily for 4 weeks: less effective but widely available over-the-counter 1
• Econazole nitrate 1% cream once daily for one month per FDA labeling 5

When to Use Oral Therapy

Reserve oral antifungals for severe disease, failed topical therapy, concomitant onychomycosis (nail infection acts as reinfection reservoir), or immunocompromised/diabetic patients. 1, 3

Oral Treatment Regimens:

• Terbinafine 250 mg once daily for 1-2 weeks: First-line oral option with fungicidal action and >70% oral absorption unaffected by food 1, 6
• Itraconazole 100 mg daily for 2 weeks: Similar efficacy to oral terbinafine but slightly higher relapse rates; offers broader spectrum against Candida and non-dermatophyte molds 1, 6
• Fluconazole: Less effective than terbinafine or itraconazole for dermatophytes, but useful when other agents contraindicated due to fewer drug interactions 1

For diabetic patients specifically, choose terbinafine over itraconazole due to lower risk of drug interactions and hypoglycemia—up to one-third of diabetics have onychomycosis which significantly predicts foot ulcer development. 1

Critical Prevention Measures to Prevent Recurrence

Failure to address these factors leads to treatment failure and reinfection:

• Examine for concomitant onychomycosis (nail infection)—this requires 12-16 weeks of oral terbinafine and serves as a persistent reservoir for reinfection 1
• Treat all infected family members simultaneously—transmission amongst family members is the most common route 1, 3
• Decontaminate footwear: Shoes harbor large numbers of viable fungal spores. Either discard old footwear or seal with naphthalene mothballs in plastic bag for minimum 3 days, then air out. Alternatively, spray terbinafine solution inside shoes periodically. 1
• Apply antifungal foot powder after bathing: reduces infection rates from 8.5% to 2.1% 1
• Thoroughly dry between toes after showering and change to cotton, absorbent socks daily 1, 2
• Cover active foot lesions with socks before wearing underwear to prevent spread to groin area 1

Safety Monitoring for Oral Terbinafine

Monitor for rare but serious adverse events including isolated neutropenia and hepatic failure, particularly in patients with pre-existing liver disease. 1 Consider baseline liver function tests and complete blood count before initiating therapy in at-risk patients. 1 Common adverse effects include headache, taste disturbance, and gastrointestinal upset. 1

Common Pitfalls to Avoid

• Failing to examine and treat onychomycosis concurrently—nail infection requires extended therapy and perpetuates foot infection 1
• Neglecting footwear decontamination—this is a major source of recurrence 1
• Treating only the index patient without addressing subclinical infections in household contacts 1
• Stopping treatment when symptoms improve—mycological cure (not just clinical response) should be the endpoint to prevent relapse 2

Special Populations

Athletes require minimum 72 hours of antifungal therapy before return to contact sports, with lesions covered by gas-permeable dressing, underwrap, and stretch tape. Exclude from swimming pools and discourage barefoot walking in locker rooms until treatment initiated. 1

Risk factors for tinea pedis include: swimming, running, warm humid environments, male gender, obesity, and diabetes. 1, 2