This is a multicenter, randomized, double-blind, parallel-group, placebo-controlled study of HTU-520 in subjects with clinically diagnosed onychomycosis of the great toenail.

A Randomized, Double-Blind, Parallel-Group, Multicenter, Placebo-Controlled Study of the Safety & Efficacy of HTU-520 in the Treatment of Mild to Moderate Distal Subungual Onychomycosis of the Toenail

Inclusion Criteria:

1. Clinical diagnosis of DSO for at least one great toenail
2. Direct microscopy of subungual debris positive for hyphal elements (KOH test)
3. Culture confirmation of the growth of a dermatophyte
4. Good general health
5. Willing to refrain from using any lotions, creams, liquids, or polish on treated toenails
6. Willing to refrain from receiving pedicures for the duration of the study
7. If female, using an acceptable form of birth control

Exclusion Criteria:

1. Unable to apply test product onto toenails by him/herself
2. Use of topical antifungal agents on the nail within 1 month
3. Uncontrolled diabetes
4. Onychomycosis of the fingernails
5. Confirmed non-dermatophyte infection of the target toenail
6. Structural deformities of the target toenail, open wounds, lesions, sores, surgery on the feet or toenails
7. History of severe or chronic immunosuppression, an immunocompromised condition
8. Any systemic or dermatologic disorder, such as severe eczema, or severe atopic dermatitis
9. Psoriasis of the toenails
10. Hypersensitivity or allergy to topical preparations (including terbinafine) or adhesive dressings