Terbinafine

What is Terbinafine?

Terbinafine is an antifungal medication that belongs to the allylamine class of antifungal drugs. It is used to treat fungal infections of the skin, hair, and nails, working by disrupting the cell membranes of fungi. The medication is available in both oral tablets for systemic infections and topical formulations for localized skin conditions.

Uses

Onychomycosis (nail fungal infections): Terbinafine is commonly prescribed to treat fungal infections of the fingernails and toenails, particularly those caused by dermatophytes.

Tinea pedis (athlete’s foot): Both topical and oral forms are effective against fungal infections of the feet, especially persistent or severe cases.

Tinea corporis (ringworm): The medication treats fungal skin infections that appear as circular, scaly patches on the body.

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Tinea cruris (jock itch): Terbinafine effectively treats fungal infections in the groin area and inner thighs.

Tinea capitis (scalp ringworm): Oral terbinafine is used to treat fungal infections of the scalp and hair follicles, particularly in children.

How it works

Terbinafine works by inhibiting an enzyme called squalene epoxidase, which is essential for fungal cell membrane formation. This action prevents fungi from producing ergosterol, a crucial component of their cell walls, leading to cell membrane damage and ultimately fungal cell death. The medication is fungicidal, meaning it actively kills fungi rather than just preventing their growth.

Side effects

Common side effects:

• Gastrointestinal upset (nausea, diarrhea, stomach pain)
• Headache
• Skin rash or itching
• Altered taste or loss of taste
• Dizziness
• Fatigue
• Local irritation (with topical use)
• Joint or muscle pain

Serious side effects requiring immediate medical attention:

• Severe liver problems (yellowing of skin or eyes, dark urine, persistent nausea)
• Severe skin reactions (blistering, peeling, severe rash)
• Signs of serious allergic reaction (difficulty breathing, swelling of face or throat)
• Persistent or severe changes in taste or smell
• Unusual bleeding or bruising

Warnings and precautions

Liver function monitoring: Regular liver function tests are recommended during oral treatment, as terbinafine can cause serious liver damage in rare cases. Patients with pre-existing liver disease should use this medication with extreme caution.

Pregnancy and breastfeeding: Terbinafine is classified as pregnancy category B, but oral treatment is generally postponed until after pregnancy and breastfeeding unless the infection is severe and treatment cannot be delayed.

Kidney impairment: Patients with kidney problems may need dosage adjustments, as the medication and its metabolites are eliminated through the kidneys.

Autoimmune conditions: Terbinafine may worsen symptoms in patients with lupus or other autoimmune disorders.

Taste changes: Some patients experience persistent taste disturbances that may last weeks to months after discontinuing treatment.

Interactions

Warfarin and blood thinners: Terbinafine may increase the effects of warfarin, potentially leading to increased bleeding risk and requiring more frequent monitoring of blood clotting times.

Tricyclic antidepressants: The medication can increase blood levels of drugs like amitriptyline and nortriptyline, potentially causing increased side effects.

Beta-blockers: Terbinafine may increase levels of certain beta-blockers such as metoprolol, potentially affecting heart rate and blood pressure control.

Caffeine: The medication can slow caffeine metabolism, leading to increased caffeine effects and potential jitteriness or sleep disturbances.

Cyclosporine: Terbinafine may decrease cyclosporine levels, potentially reducing its effectiveness in transplant patients or those with autoimmune conditions.

Rifampin: This antibiotic can significantly reduce terbinafine blood levels, potentially making the antifungal treatment less effective.

Cimetidine: This acid reducer can increase terbinafine levels in the blood, potentially increasing the risk of side effects.

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Dosage

Oral tablets: For nail infections, the typical adult dose is 250 mg once daily for 6 weeks (fingernail infections) or 12 weeks (toenail infections). For skin infections, 250 mg daily for 2-6 weeks depending on the condition and severity.

Topical cream: Applied to affected areas once or twice daily for 1-4 weeks, depending on the type and location of infection. Treatment should continue for several days after symptoms resolve.

Dosage should always be determined by a healthcare provider based on the specific infection type, severity, patient factors, and response to treatment. Regular monitoring may be required during extended oral treatment courses.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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