Treatment of Onychomycosis (Fungal Toenail Infection)
Oral terbinafine 250 mg daily is the first-line treatment for onychomycosis: 12 weeks for toenails and 6 weeks for fingernails. 1, 2, 3
Understanding the Causative Organisms
The term "mold in toenails" refers to onychomycosis, which can be caused by three categories of fungi:
- Dermatophytes (90-95% of cases): Trichophyton rubrum is the most common causative organism 4, 5
- Yeasts: Primarily Candida albicans 4, 5
- Nondermatophyte molds: Including Scopulariopsis, Aspergillus, Fusarium, and Acremonium 6
Treatment Algorithm Based on Pathogen
For Dermatophyte Infections (Most Common)
- Dosage: 250 mg daily for 12 weeks (toenails) or 6 weeks (fingernails) 1, 2
- Mechanism: Inhibits squalene epoxidase, directly fungicidal against dermatophytes 1, 2
- Evidence level: Strength A, Level 1+ 2
- Superior efficacy compared to all other oral agents 1, 2
Alternative: Itraconazole 1, 2
- Dosage: 200 mg twice daily for 1 week per month (pulse therapy) 1, 2
- Duration: 2 pulses for fingernails, 3 pulses for toenails 6, 1
- Take with food for better absorption 1
For Candida Infections
First-line: Itraconazole 6
- Dosage: 200 mg daily or 400 mg daily pulse therapy (1 week per month) 6
- Duration: Minimum 4 weeks for fingernails, 12 weeks for toenails 6
- Cure rates: 92% with pulse itraconazole versus 40% with pulse terbinafine 6
Alternative: Fluconazole 6
For Nondermatophyte Molds (Difficult to Treat)
Preferred: Itraconazole 6
- Broader antimicrobial coverage than terbinafine for molds 6
- Aspergillus: Excellent susceptibility to itraconazole 6
- Scopulariopsis: High cure rates (88%) with itraconazole 6
- Standard regimen: 200-400 mg daily for 1 week per month for 3 months 6
Important caveat: Terbinafine demonstrates the lowest activity against most nondermatophyte molds despite being superior for dermatophytes 6
Topical Therapy (Limited Role)
Topical treatments should only be used in these specific scenarios 1, 7:
- Superficial white onychomycosis
- Very early distal infection (<80% nail involvement, no lunula involvement)
- When oral therapy is contraindicated 1, 7
Topical options (if appropriate):
- Amorolfine 5% nail lacquer: ~50% effectiveness when infection limited to distal nail 1, 7, 2
- Ciclopirox 8% nail lacquer: 34% mycological cure versus 10% placebo 7, 2, 8
- Efinaconazole 10% solution: FDA-approved, enhanced nail penetration 9
Special Populations
Diabetic Patients
Strongly prefer terbinafine over itraconazole 1, 7, 2
- Lower risk of drug interactions and hypoglycemia 1, 7
- Onychomycosis is a significant predictor for foot ulcers in diabetics 1, 2
Immunosuppressed Patients
Prefer terbinafine or fluconazole 1, 7
Pediatric Patients
Pulse itraconazole therapy 6, 1
- Dosage: 5 mg/kg/day for 1 week every month 6, 1
- Duration: 2 months for fingernails, 3 months for toenails 6, 1
Alternative: Terbinafine daily 6, 1
- <20 kg: 62.5 mg/day 1
- 20-40 kg: 125 mg/day 1
40 kg: 250 mg/day 1
- Pediatric cure rates are higher (88-100%) than adults 6
Critical Pitfalls to Avoid
Always confirm diagnosis before treatment 7, 3
- Use KOH preparation, fungal culture, or nail biopsy 3
- Most common cause of treatment failure is incorrect diagnosis made on clinical grounds alone 7
Do not use topical therapy for extensive disease 7
- Predictable failure when used inappropriately 7
Monitor for drug interactions 7, 4
- Itraconazole: Potent CYP3A4 inhibitor 4
- Terbinafine: Inhibits CYP2D6, monitor with SSRIs, beta blockers, tamoxifen 4, 10
- Fluconazole: Inhibits CYP3A4, CYP2C9, CYP2C19 4
Expect treatment failures and recurrences 7, 2
Prevention of Recurrence
Implement these strategies to reduce the 40-70% recurrence rate 1, 2:
- Wear protective footwear in public facilities 1, 2
- Use absorbent and antifungal powders in shoes 1, 2
- Keep nails short 1, 2
- Avoid sharing nail clippers 1, 2
- Consider discarding contaminated footwear or treating with naphthalene mothballs 2
Second-Line Options (Avoid if Possible)
Griseofulvin: Only use when other agents unavailable or contraindicated 1, 2