Terbinafine: Uses, Side Effects & Dosage Guide

Terbinafine is an antifungal drug available in various forms including spray or gel, tablets or capsule, and creams. Terbinafine is widely used to treat various kinds of fungal infections including ringworm, pityriasis Versicolor, athlete’s foot and jock itch. Terbinafine has various drug interactions and some adverse reactions; therefore, it is available on a doctor’s prescription only. 

Terbinafine can be taken by mouth or used as a cream to apply on the affected area, but this depends on the type and severity of the fungal infection because creams or gel are not as effective as oral terbinafine for nail fungal infection.

Terbinafine is one of the essential medicines of the world health organization (WHO) and was first discovered in 1991. Terbinafine is one of the most prescribed medicines in the United States Of America. It is estimated that in 2017 there were more than 1 million prescriptions of terbinafine in the USA.

Terbinafine works by inhibiting the synthesis of ergosterol in fungi by inhibiting the enzyme called squalene epoxidase. Squalene to lanosterol conversion is carried out by the enzyme called squalene epoxidase, and this is a significant reaction in the synthesis of ergosterol. In human beings, lanosterol converts to cholesterol whereas in fungi it converts to ergosterol. Terbinafine specifically inhibits the fungal squalene epoxidase and hence causes to inhibit the fungal ergosterol synthesis, not human cholesterol production. It is thought that terbinafine causes the death of fungi by changing the permeability of cell membranes of fungus by inhibiting ergosterol synthesis.

Because of the lipophilic nature of terbinafine, it accumulates in the skin, nails, hair, and fatty tissue. Many mild to moderate fungal infections get better after terbinafine therapy of 7 days, but some infections can take more than two months to get better like fungal nail infection.

Skin irritation is the most common adverse effect of terbinafine when used as a cream or gel on the other hand loss of appetite, muscles and joint pain, and an upset stomach is the most common adverse reaction when taking terbinafine in tablet form.

Usually, it will take approximately two weeks for terbinafine creams or gel to work; on the other hand, terbinafine tablets take more than two months to work.

Terbinafine comes under the brand name of Lamisil. 

Indications

The antifungal medicine terbinafine is used to treat the fungal infection of skin and nail which includes

• Athlete’s foot
• Onychomycosis (Fungal nail infection. fingernail or toenail)
• Ringworm
• Jock itch ( also known as a dhobi itch, an infection of groin area)
• Pityriasis Versicolor ( this is small patches of scaly and discoloured skin on back, chest, arm, neck and abdominal skin)
• For the treatment of fungal infection of hair follicles in children who are less than four years old

Contraindications

Terbinafine is contraindicated in the following conditions

• Chronic or active liver disease
• History of an allergic reaction

Side effects

There are many patients reported with the adverse reactions of terbinafine in the clinics. This is because the antifungal treatment usually needed a considerable duration of more than two months. Side effects of terbinafine include:

• Headache
• Gastrointestinal symptoms
• Diarrhoea
• Dyspepsia
• Abdominal pain
• Nausea
• Flatulence
• Dermatological symptoms
• Pruritus
• Urticaria
• Rash
• Steven Johnson disease
• Toxic epidermal necrosis
• Erythema multiforme
• Exfoliative dermatitis
• Bullous dermatitis
• Ear and labyrinth disorders
• Hearing impairment
• Vertigo
• Tinnitus
• Liver enzymes abnormalities
• Nervous system disorders
• Taste disturbance
• Taste loss
• Decrease food intake
• Weight loss anxiety
• Depressive symptoms
• Paresthesia
• Hypoesthesia
• Eye disorders
• Visual field defects
• Reduced visual acuity
• Musculoskeletal and connective tissue disorders
• Rhabdomyolysis
• Arthralgia
• Myalgia
• Immune system disorders
• Severe hypersensitivity reactions ( angioedema and allergic reactions)
• Precipitation and exacerbation of cutaneous lupus erythematosus
• Precipitation and exacerbation of systemic lupus erythematosus
• Blood and lymphatic disorders
• Pancytopenia
• Agranulocytosis
• Severe neutropenia
• Thrombocytopenia
• Anaemia
• Thrombotic microangiopathy
• Thrombotic thrombocytopenic purpura
• Hemolytic uremic syndrome

Terbinafine can cause adverse reactions in patients with MTHFR C677T genetic enzyme mutation. Terbinafine can cause headache, fatigue and dizziness in these patients.

Warnings

• Do not use terbinafine if someone has the previous history of allergic reactions to this drug and if your doctor recommends terbinafine, then tell him that you are allergic to this drug.
• If someone has any history of, previous or present, Lupus, kidney disease, immune system problem, and liver disease, then consult with your doctor before taking this medication.
• Terbinafine may interact with the alcohol; therefore, you should not use this drug if you are alcoholic because this can increase the chance of adverse reactions.
• The regular use of the terbinafine can cause your skin to become more sensitive to the ultraviolet light of the sun. Therefore if you are on antifungal therapy, then you should avoid to go in the sunlight or use sunblocks before going out in the sunlight because this medication can cause sunburn and skin blisters.
• In pregnant females, this drug should only be used if indicated. Otherwise, pregnant mothers should wait for the delivery of the baby or consult with your doctor.
• Terbinafine is used with precautions in patients with liver disease ( chronic or active) and patients with pre-existing allergies.

Many drugs can interact with the terbinafine and can hinder the clearance of the terbinafine by the liver in the body; therefore, these drugs should be avoided when taking terbinafine therapy. These drugs are:

• Warfarin
• Amiodarone
• Cimetidine
• Rifampin
• fluconazole/ketoconazole
• Antidepressants
• SSRI antidepressants
• beta-blockers
• Dextromethorphan
• Thioridazine
• monoamine oxidase inhibitors
• rasagiline

High-risk groups

High-risk groups for terbinafine are patients with pre-existing illnesses like chronic liver disease and pregnant mothers.