Terbinafine

Fungal Nail Infections

Oral terbinafine is primarily used to treat fungal infections of the fingernails and toenails, a condition known as onychomycosis. It works by stopping the growth of the fungus that causes the infection, allowing a new, healthy nail to grow in over time.

Fungal Skin Infections

Topical forms of terbinafine, including creams, gels, and sprays, are used to treat several types of fungal skin infections. These conditions include:

• Athlete's foot (tinea pedis): A fungal infection that typically starts between the toes.
• Jock itch (tinea cruris): A fungal infection that causes an itchy or burning rash in the groin or inner thigh area.
• Ringworm (tinea corporis): A fungal infection that appears as a red, circular, itchy rash on the body.
• Tinea versicolor: A fungal infection that results in small, discolored patches of skin.

In some instances, oral terbinafine may be prescribed for fungal skin infections if they are severe, widespread, or do not respond to topical treatments.

Mechanism of Action

Terbinafine belongs to a group of medicines called antifungals. It works by preventing fungi from growing and spreading. Specifically, it interferes with the fungus's ability to produce ergosterol, which is a vital component of the fungal cell membrane.

When the production of ergosterol is blocked, the following happens:

• The fungal cell membrane becomes weak and develops holes.
• The fungus is unable to maintain its structure or reproduce.
• The infection eventually clears as the fungi die off or stop multiplying.

This medication is effective against various types of fungi, including those that cause athlete's foot, ringworm, jock itch, and fungal infections of the fingernails or toenails.

Common Side Effects

Common side effects of oral terbinafine may include:

• Diarrhea, nausea, or stomach pain
• Gas or bloating
• Headache
• Changes in the sense of taste or smell, which may persist after stopping the medication
• Mild skin rash or itching

Common side effects of topical terbinafine (creams, gels, or sprays) include:

• Burning or stinging
• Itching
• Redness or irritation at the application site

Serious Side Effects

Contact a healthcare provider immediately if you experience any of the following serious side effects:

• Signs of liver problems, such as yellowing of the eyes or skin (jaundice), dark urine, pale stools, or persistent nausea and vomiting
• Severe skin reactions, including blistering, peeling, or a red or purple rash
• Signs of a new or worsening autoimmune condition, such as joint pain or a butterfly-shaped rash on the cheeks
• Changes in vision
• Depression or unusual mood changes
• Severe swelling, hives, or difficulty breathing

Liver Safety

Oral terbinafine is associated with a risk of serious liver injury, including liver failure that may require a transplant or result in death. This risk applies to individuals with or without a history of liver problems. Treatment is generally not recommended for those with active or chronic liver disease. Healthcare providers typically conduct liver function tests before starting the medication and may monitor liver health during treatment.

Serious Skin Reactions

Severe skin reactions, such as Stevens-Johnson syndrome and toxic epidermal necrolysis, have occurred. If a progressive skin rash or signs of a hypersensitivity reaction develop, the medication is usually discontinued immediately.

Changes in Taste and Smell

Use of oral terbinafine may lead to a partial or complete loss of taste (ageusia) or smell (anosmia). While these changes often resolve after the medication is stopped, they can persist for a long time or become permanent in some cases.

Additional Considerations

• Immune System: Terbinafine may trigger or worsen systemic lupus erythematosus.
• Blood Disorders: Low white blood cell counts (neutropenia) and other blood-related issues have been reported. Monitoring of complete blood counts may be necessary for some patients.
• Mental Health: Some individuals may experience depressive symptoms while taking this drug.
• Topical Application: Topical terbinafine is for skin use only. It should not be applied to the eyes, mouth, or inside the vagina.

Pregnancy

There are no adequate and well-controlled studies of terbinafine use in pregnant women. While animal reproduction studies have not shown evidence of harm to the fetus, human data is limited. Because the treatment of fungal nail infections is often considered elective and can be postponed, healthcare providers typically recommend that oral terbinafine treatment not be started during pregnancy.

Breastfeeding

Oral terbinafine passes into breast milk. Because of the potential for adverse effects in nursing infants, breastfeeding is not recommended while taking terbinafine tablets. For topical forms of terbinafine, it is not known if the medication passes into breast milk or if it could harm a nursing baby. Individuals should consult with a healthcare provider to discuss the potential risks and benefits of using this medication while nursing.

Oral Forms

Terbinafine is available in the following oral preparations:

• Tablets
• Oral granules

Topical Forms

Terbinafine is available in various topical preparations for application to the skin:

• Cream
• Gel
• Spray solution
• Powder

FDA Approval and Indications

Terbinafine was first approved by the U.S. Food and Drug Administration (FDA) for the treatment of fungal infections. The oral tablet form is specifically indicated for the treatment of onychomycosis (fungal infection of the nails) caused by susceptible fungi.

Topical formulations, including creams, gels, and sprays, are approved for the treatment of various skin infections, such as:

• Athlete's foot (tinea pedis)
• Jock itch (tinea cruris)
• Ringworm (tinea corporis)

Regulatory History and Safety Monitoring

The FDA monitors the safety of terbinafine through the Adverse Event Reporting System (FAERS). In 2016, the FDA identified a potential signal of a serious risk known as Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) associated with terbinafine use. Following an evaluation, the FDA determined that no regulatory action was needed at that time, but safety monitoring continues.

While terbinafine does not carry a boxed warning, the FDA-approved labeling for oral terbinafine includes strong warnings regarding the risk of liver injury. Healthcare providers are advised to assess liver function before and during treatment with the oral form.

Types of Infections Treated

Terbinafine is effective against several types of fungal infections, depending on whether it is used as an oral tablet or a topical treatment:

• Nail Infections (Onychomycosis): Oral terbinafine is primarily used to treat fungal infections of the fingernails and toenails. Because nails grow slowly, treatment usually lasts several weeks or months to allow a healthy nail to replace the infected one.
• Athlete's Foot (Tinea Pedis): Topical forms are used for fungal infections on the feet, especially between the toes or on the soles.
• Jock Itch (Tinea Cruris): This medication treats fungal infections in the groin or inner thigh area.
• Ringworm (Tinea Corporis): It is used for fungal skin infections that appear as itchy, red, circular rashes on the body.
• Tinea Versicolor: Certain topical formulations are used to treat this condition, which causes small, discolored patches of skin.

How It Works

Terbinafine belongs to a class of drugs known as antifungals. It works by interfering with the ability of fungi to produce ergosterol, which is a vital component of their cell membranes. When the cell membrane is disrupted, the fungal cells cannot grow or survive, eventually clearing the infection.

For skin infections, topical terbinafine is applied directly to the affected area to kill the fungus on the surface. For nail infections, the medication must be taken orally so it can reach the nail bed through the bloodstream and become part of the new nail as it grows.