Efinaconazole

FDA-Approved Indications:

• Onychomycosis of the Toenails:
• Treatment of mild to moderate distal subungual onychomycosis caused by Trichophyton rubrum and Trichophyton mentagrophytes in immunocompetent adults.

Off-label/Clinically Accepted Uses:

• Onychomycosis of the Fingernails (off-label):
• Sometimes used for mild to moderate fingernail onychomycosis based on clinical discretion, though not officially approved.
• Recurrent Dermatophytic Nail Infections:
• Used in select cases of recurrent tinea unguium as part of long-term topical antifungal maintenance therapy.

Adults:

• Recommended Dose:
• Apply one drop of 10% topical solution to the affected toenail once daily for 48 weeks.
• For the big toenail, apply a second drop at the end of the nail to ensure coverage of the nail folds and hyponychium.

Pediatrics:

• Safety and efficacy in pediatric patients have not been established; not routinely recommended in children.

Elderly:

• No specific dose adjustment is required. Use as in adults.

Renal/Hepatic Impairment:

• Since systemic absorption is negligible, no dosage adjustment is necessary.

Administration Route:

• Topical only. Not for oral, ophthalmic, or intravaginal use.

Duration of Therapy:

• Full treatment course is 48 weeks. Visible clinical improvement may take several months due to slow nail growth.

Efinaconazole is a triazole antifungal that inhibits fungal lanosterol 14α-demethylase, a key enzyme in the ergosterol biosynthesis pathway. By blocking ergosterol production, the drug disrupts the integrity of the fungal cell membrane, leading to increased permeability and eventual fungal cell death. Its low surface tension formulation allows deep penetration into the nail unit and surrounding tissue, enhancing its effectiveness against nail-invading dermatophytes.

• Absorption:
• Minimal systemic absorption (<2%) after topical administration.
• Higher absorption may occur if applied to damaged or broken skin.
• Distribution:
• Primarily acts locally within the nail bed and plate.
• Negligible systemic distribution.
• Metabolism:
• Minor hepatic metabolism via CYP3A4, CYP2C8, and CYP2C9 when absorbed systemically, though clinically insignificant due to low plasma levels.
• Elimination:
• Minimal systemic excretion; primarily through skin desquamation and local metabolism.
• Half-life:
• Not clinically relevant for topical use due to low systemic absorption.

• Pregnancy:
• Not assigned an FDA pregnancy category.
• Animal studies did not demonstrate teratogenic effects; however, use in pregnant women should be considered only if clearly needed.
• Lactation:
• Unknown whether efinaconazole is excreted in human milk.
• Due to negligible systemic absorption, the risk to a nursing infant is expected to be low.
• Avoid application to breast area.
• General:
• Caution advised due to limited human data.

• Primary Class: Topical Antifungal
• Subclass: Triazole derivative (azole antifungal)

• Known hypersensitivity to efinaconazole or any component of the formulation.
• Use in mucosal or ophthalmic infections is contraindicated.

• Hypersensitivity Reactions:
• Rare cases of allergic contact dermatitis have been reported. Discontinue if hypersensitivity occurs.
• Use on Intact Skin Only:
• Do not apply to broken or inflamed skin.
• Limited Use in Non-Dermatophyte Infections:
• Effectiveness in non-dermatophyte molds or yeast nail infections (e.g., Candida) is not well established.
• Avoid Occlusive Dressings:
• Occlusion may increase absorption and risk of local irritation.
• Treatment Duration Compliance:
• Counsel patients that visible nail clearing may take time and adherence is critical.

Local (Dermatologic) Side Effects:

• Common (≥1%):
• Ingrown toenail
• Application site dermatitis
• Application site vesicles or blistering
• Erythema, pain, or pruritus at the site of application
• Less Common (<1%):
• Nail discoloration
• Nail detachment (onycholysis)
• Paronychia

Systemic Side Effects:

• Extremely rare due to negligible systemic absorption.

• Drug-Drug Interactions:
• No significant systemic interactions expected due to low absorption.
• Systemic interaction via CYP enzymes is minimal but theoretically possible in rare high-exposure scenarios.
• Drug-Food and Drug-Alcohol Interactions:
• Not applicable for topical use.
• Enzyme Systems Involved:
• Minor metabolism via CYP3A4, CYP2C8, CYP2C9 (not clinically significant).

• Guideline Endorsements:
• Recommended by dermatology and infectious disease guidelines (e.g., AAD, IDSA) as a first-line topical therapy for mild to moderate distal subungual onychomycosis.
• Regulatory Updates:
• No major changes in recent years to indications or formulation.
• Continued support for its once-daily regimen and favorable safety profile.
• Research Direction:
• Studies ongoing to assess its efficacy in fingernail onychomycosis and in combination with laser or systemic therapy for improved outcomes.

• Storage Temperature:
• Store at 20°C to 25°C (68°F to 77°F)
• Excursions permitted between 15°C and 30°C (59°F to 86°F)
• Light and Humidity Protection:
• Store in original container. Protect from direct light and excessive moisture.
• Handling Precautions:
• For topical use only. Avoid contact with eyes, mouth, or mucous membranes.
• Keep out of reach of children.
• No refrigeration or reconstitution required.