Terfenadine is an anti-allergic drug and is used to treat allergic reactions. Because it competes for the receptor site for histamine in the human body, the body’s own hormone histamine can no longer dock. Histamine is responsible for allergic symptoms such as itching and redness. Terfenadine is administered in tablet form. It has been withdrawn from the market in some countries because it has caused cardiac arrhythmias in some patients. Other side effects of the drug also occur.
What is terfenadine?
Terfenadine is an antihistamine. It is used to treat allergies. It was first manufactured in the 1970s and came on the market in 1982. The active ingredient was available over the counter for a very long time. Terfenadine is sold in Germany under the drug names Hisfedin, Terfemundin and Terfedura. Terfenadine is a so-called racemate. A racemate is an active ingredient that is composed of two molecules in a ratio of one to one and exhibits pharmacological activity. The active ingredient is present as a crystalline white powder and is very poorly soluble in water. Terfenadine is a prodrug. Prodrugs are active ingredients that initially have no pharmacological effect. They develop their effect only through a conversion step in the human body. The pharmacologically active conversion form is called fexofenadine. This substance belongs to the second generation of antihistamines. Terfenadine has been withdrawn from the market in many countries due to its potential life-threatening side effects. Fexofenadine by itself is approved as a possible alternative for the treatment of allergic symptoms.
Pharmacologic action
Terfenadine has antiallergic and antihistamine activity. Accordingly, the drug is used in human medicine to treat allergic reactions. Antihistamines are active substances that inhibit the body’s own hormone histamine. They have an anti-inflammatory and antipruritic effect. In addition, these drugs can have a sedative and sleep-inducing effect. Terfenadine competes for the binding receptor for histamine in the bronchial muscles, uterus and digestive tract. This docking site for the endogenous neurotransmitter is also called the H1 receptor. Terfenadine prevents the histamine from binding to the receptor and from exerting its effect. This reduces the symptoms of allergy caused by histamine. Itching, redness and edema decrease.
Medical use and application
In Germany, the active ingredient terfenadine is approved for the treatment of allergic conjunctivitis and allergic rhinitis. Allergic rhinitis is also known as hay fever. Conjunctivitis is an inflammation of the conjunctiva of the eye. In addition, allergic reactions of the skin, such as hives, can be treated with the drug. Terfenadine should not be administered in cases of previous heart disease, impaired liver function, anorexia, vomiting, diarrhea, and magnesium or potassium balance disorders. Treatment with concurrent therapy with other drugs such as antibiotics or antifungals is also a contraindication for this agent. If the patient is taking drugs for the treatment of cardiac arrhythmias, terfenadine must not be prescribed. In addition, pregnant women and children must not take the active substance. People weighing less than 50 kilograms should not be treated with the substance. Terfenadine should be taken according to the doctor’s instructions. Usually, one to two tablets per day are prescribed, depending on the degree of discomfort. The tablets should be administered with plenty of liquid and unchewed. Terfenadine should not be taken with grapefruit juice. This drink can immensely delay the breakdown of the substance in the body. The drug should be stored out of the reach of children.
Risks and side effects
In general, the drug is well tolerated. However, side effects such as insomnia, fatigue, dizziness, lightheadedness, gastrointestinal symptoms, depression, or muscle tremors may occur. In many countries, such as Switzerland, terfenadine has been withdrawn from the market because in some cases severe cardiac arrhythmias have occurred after taking it. These can cause ventricular fibrillation and ultimately be fatal.Symptoms such as loss of consciousness, convulsions, dizziness, low blood pressure or palpable heartbeats may indicate these cardiac arrhythmias. Because of this fact, special caution should be exercised when taking the drug.
