How Terbinafine works
Like animals and humans, fungi also consist of individual cells, which are also individually viable under certain conditions. The cell is thus the smallest, independent structural unit of all life forms. In order to damage only the fungal cells in a targeted and selective manner when infected with a fungus, the differences between the life forms are exploited. These differences are not very great at the cellular level (for example, humans and molds are more closely related than some bacterial species are to each other). Therefore, many antifungal drugs target the cell membrane, which has a different structure in fungi and humans.
In humans and many animals, the membrane that separates the cell from the outside and enables many metabolic pathways consists mainly of special lipids such as cholesterol. Cholesterol gives the cell membrane the flexibility it needs to withstand environmental influences. In fungi, this task is performed by the substance ergosterol, which is chemically similar to cholesterol but has a different structure in some respects.
The active ingredient terbinafine inhibits the production of ergosterol in the fungal cells. The resulting lack of ergosterol in the membrane inhibits the growth of the fungal cells or even causes them to die.
Uptake, degradation and excretion of terbinafine
After ingestion, the active ingredient terbinafine is well absorbed in the intestine. However, part of it is rapidly broken down in the liver, so that only about half of the administered dose reaches the large bloodstream, where the highest levels can be measured after one and a half hours. Since the active ingredient is highly fat-soluble, it passes well into the skin and nails. After about 30 hours, half of the active ingredient is excreted.
Terbinafine can be broken down by many different subforms of the cytochrome P450 enzyme, which is necessary to make it more water-soluble. The degradation products are excreted via the kidney in the urine or via the intestine in the stool.
When is terbinafine used?
The antifungal drug terbinafine is used for the treatment of skin and nail fungal diseases. In the case of fungal skin disease, it is usually applied locally (for example, as a terbinafine cream). In addition, there is water-soluble nail polish with terbinafine for the treatment of mild to moderate nail fungus. In the case of a severe skin fungus or nail fungus infection, therapy is systemic (in the form of terbinafine tablets).
The application is usually only a few weeks for skin fungus, but for nail fungus, it may be several months.
How Terbinafine is used
In the treatment of fungal skin diseases, terbinafine is used as a one-percent cream, gel or spray. It should be applied to the affected and adjacent areas once or twice a day. It is applied for one to two weeks, depending on the type of infection.
A water-soluble nail polish is available for mild to moderate nail fungus infestation. It is applied to the entire affected nail plate, the surrounding skin and below the front edge of the nail. After six hours, the lacquer residues can be removed with water.
In the case of severe skin fungal infections or nail fungal diseases, therapy takes the form of terbinafine tablets, each containing 250 milligrams of active ingredient. The tablets are taken once a day with a glass of water, independently of meals. Terbinafine should always be taken at the same time of day. Depending on the severity of the disease, Terbinafine is usually taken for four to six weeks (in the case of fungal skin infections) or for a period of up to three months (in the case of fungal nail infections).
What are the side effects of terbinafine?
While taking terbinafine, more than ten percent of those treated experience headache, decreased appetite, gastrointestinal symptoms (such as nausea, abdominal pain, diarrhea), skin reactions (such as rash and itching), muscle and joint pain.
One in ten to one hundred patients report terbinafine side effects such as depression, taste disturbance, loss of taste, and fatigue.
The side effects presented here occur mainly when Terbinafine is taken. When applied to the skin, the side effects occur at most very attenuated. Terbinafine nail polish occasionally causes redness and skin irritation.
What should be considered when using terbinafine?
Since terbinafine is broken down by enzymes in the liver that also break down many other drugs and substances foreign to the body, simultaneous use can affect the active ingredient levels of each individual substance – both increasing and decreasing them:
In particular, active substances metabolized via the cytochrome P450 2D6 enzyme are broken down more slowly in combination with terbinafine and can thus accumulate in the body. These include, for example, agents against depression (tricyclic antidepressants, selective serotonin reuptake inhibitors, MAO inhibitors), agents that stabilize the heart rhythm (antiarrhythmics of classes 1A, 1B and 1C) and beta-blockers (cardiovascular agents).
Since only very limited data are available on the use of terbinafine in pregnant women, the active substance should not be used during pregnancy to be on the safe side. The same applies to breastfeeding. The use of terbinafine is also not recommended in children.
Elderly patients (over 65 years of age) may take terbinafine, but liver and kidney function should be checked beforehand. Patients with liver or kidney dysfunction must not take Terbinafine.
How to get medicines with terbinafine
Preparations for application to the skin containing no more than one percent of the active ingredient are available without prescription from pharmacies. The same applies to terbinafine nail varnish. Terbinafine tablets for oral use require a prescription.
How long has terbinafine been known?
Terbinafine was launched by the pharmaceutical company Novartis in Europe in 1991 and in the USA in 1996. The patent expired in 2007, after which an extension patent was filed for the treatment of children in the USA. However, numerous generics containing the active ingredient terbinafine are already available in Germany.
