Terbinafine: Effects, Uses & Risks

The active ingredient terbinafine is used to treat fungal diseases. The agent can be used both topically and systemically.

What is terbinafine?

The antifungal agent is mainly used for the treatment of athlete’s foot (tinea pedis) and nail fungus (onychomycosis). Terbinafine is an allylamine derivative, which is one of the antifungal agents. The antifungal agent is mainly used for the treatment of athlete’s foot (tinea pedis) and nail fungus (onychomycosis). It is suitable for local (topical) treatment in the form of creams, but can also be used systemically with tablets. Due to its chemical structure, Terbinafine belongs to the group of allylamines. Terbinafine was developed by the Swiss pharmaceutical company Novartis. The antimycotic was launched in Europe in 1991. The USA followed in 1996. In Germany, several generic drugs containing terbinafine can now also be administered.

Pharmacologic action

Fungi that can cause disease in humans are composed of individual cells. A cell forms the smallest independent unit in all life forms. For the specific treatment of fungal diseases, medicine uses the differences between the various life forms to effectively combat fungal cells in this way. However, since the cell differences from humans are not always very pronounced, numerous antifungal drugs are directed against the cell membrane. This has a different structure in fungi and humans. The membrane of humans and animals is mainly composed of lipids such as cholesterol. Cholesterol gives the cell membrane of humans flexibility, which enables it to withstand environmental influences. In fungi, this function is performed by ergosterol, a substance that has a chemical similarity to cholesterol. Nevertheless, there are some crucial differences in its structure. The effect of ergosterol can be slowed down by terbinafine. The drug inhibits the important enzyme squalene epoxidase, thereby counteracting the build-up of the fungal cell wall. In addition, the precursor squalene accumulates within the fungal tissue. As a result, most fungi die. Terbinafine’s fungicidal effect is already seen in low concentrations on molds, skin fungi and some dimorphic fungi. The antifungal agent also inhibits the growth of yeasts or kills them, depending on the type of yeast. The duration of action of terbinafine is considered long-lasting. Absorption of the substance in the intestine is considered to be good. However, a rapid degradation of parts of the active substance takes place in the liver. As a result, only 50 percent of the dose enters the bloodstream. Terbinafine reaches its highest level there after about 90 minutes. Due to its fat solubility, the antifungal agent can easily reach the skin and nails. About 30 hours after its ingestion, approximately 50 percent of the terbinafine has left the organism. Excretion of the degradation products takes place via urine and stool.

Medical use and application

The most important areas of application of terbinafine are fungal skin infections caused by dermatophytes such as athlete’s foot or nail fungus. Furthermore, the antifungal agent can be administered against candidiasis (yeast infections), Kleienpilzflechten as well as against the fungus Microsporum canis. This fungus is frequently found in animals. It is not uncommon for it to be transmitted from cats to children. In addition to its external administration, Terbinafine is used internally in the form of tablets in the case of onychomycosis (fungal infections of toenails and fingernails). External administration of terbinafine is through gels, sprays or one-percent creams. These are applied once or twice a day to the areas of the body to be treated. Depending on the type of fungal infection, the duration of therapy is one to two weeks. Internal administration by tablets containing 250 milligrams of terbinafine takes place when the patient suffers from severe nail or skin fungal infections. The tablets are taken once a day, independently of meals, with a glass of water. It is recommended to take the tablets always at the same time of the day. The duration of Terbinafine application depends on the severity of the disease. While it usually takes four to six weeks for fungal skin infections, it can last up to three months for nail fungus.

Risks and side effects

About ten percent of all patients suffer adverse side effects during therapy with terbinafine. The nature of the side effects depends on the form of dosing. For example, local application may cause allergic reactions in the treated skin areas (redness, itching, or burning). In individual cases, the allergy spreads over the affected regions and leads to scatter reactions. When used internally, side effects such as loss of appetite, bloating, nausea, vomiting, diarrhea, mild abdominal pain, joint pain, muscle pain, rashes on the skin, hives, headache, and taste disorders are possible. If allergic reactions or irritation of the skin occur during terbinafine therapy, stop treatment. If a sore throat or high fever occurs, a doctor must be consulted immediately. Terbinafine must not be administered either internally or externally if the patient suffers from hypersensitivity to the drug. In the case of acute or chronic liver disease or alcohol addiction, terbinafine cannot be administered in tablet form. The same applies in the case of significant limitations of kidney function. Only limited data are available for use during pregnancy. For this reason, the antifungal agent should be administered only after medical advice. Because terbinafine passes into breast milk, its internal and external use should be avoided during lactation.