What is the next step for treating a fungal infection on the soles of both feet that has not improved with over-the-counter (OTC) antifungal medications?

Management of Fungal Infection on Soles of Bilateral Feet After Failed OTC Treatment

For patients with bilateral tinea pedis (athlete's foot) that has not responded to over-the-counter antifungal medications, the next step should be oral terbinafine therapy at 250 mg once daily for 2-4 weeks.

Diagnosis Confirmation

• Before initiating prescription therapy, confirm the diagnosis through mycological examination (direct microscopy and culture) to identify the causative organism 1
• Failure to confirm diagnosis is the most common cause of treatment failure 1

Treatment Algorithm

First-line Therapy

• Oral terbinafine 250 mg once daily for 1-4 weeks is the recommended first-line treatment for dermatophyte infections of the feet that have failed topical therapy 2, 1
• Terbinafine offers advantages of:
  • Once-daily dosing 2
  • Shorter treatment duration than topical treatments 2
  • Higher cure rates compared to other oral antifungals for dermatophyte infections 2

Alternative Treatments

• Itraconazole 100-200 mg daily is an effective alternative, particularly if Candida infection is suspected or confirmed 2, 1
• Fluconazole 150-300 mg weekly can be considered if terbinafine or itraconazole are contraindicated 2

Special Considerations

For Candida Infections

• If mycology confirms Candida as the causative organism, itraconazole should be preferred over terbinafine 2
• Itraconazole can be given at 200 mg daily or as pulse therapy (400 mg daily for 1 week per month) 2

For Resistant Cases

• For infections that fail to respond to first-line oral therapy, consider:
  • Longer duration of treatment 2
  • Combination of oral and topical therapy 1
  • Alternative diagnosis or secondary bacterial infection 3

Adjunctive Measures

• Careful and thorough drying between toes after bathing 2
• Daily changes of socks 2
• Periodic cleaning of footwear 2
• Use of foot powder after bathing (has been associated with decline in tinea pedis rates) 2

Monitoring and Follow-up

• Monitor for potential adverse effects:
  • With terbinafine: rare isolated neutropenia and liver failure (especially in those with preexisting liver disease) 2
  • With azoles: hepatotoxicity, hormone-related effects, and drug interactions 4
• Follow-up after completion of treatment course to confirm clinical and mycological cure 1

Prevention of Recurrence

• Onychomycosis and tinea pedis have high recurrence rates (40-70%) 1
• Continue preventive measures even after clinical cure 2
• Consider treating footwear with antifungal powders 2

Remember that treatment failure with OTC medications may be due to incorrect diagnosis, insufficient treatment duration, or resistant organisms, making proper diagnosis confirmation essential before initiating prescription therapy 1, 3.