Definition
Antihistamines are substances that block the effects of histamine in the body, reducing the intensity of allergic reactions..
Description
Histamine occurs naturally in the body and is responsible for tissue growth and repair, and the control of gastric secretions. It is stored in cells called mast cells, which are found in the nose, lungs and gastrointestinal tract. When the mast cells are damaged, through chemicals, drugs, heat or trauma, abnormally large amounts of histamine are released. This is what we call an allergic reaction. Histamine release can cause reactions ranging from barely noticeable, to severe anaphylactic shock.
Antihistamines used for treating allergies are called H-1 Antihistamines. Another group, called H-2 Antihistamines, are used for reducing stomach acid secretion. H-1 Antihistamines come from several different chemical groups. Therefore, if one type gives undesirable side effects, another from a different group may be more suitable. Many Antihistamines are present with other ingredients in cough relief preparations. Always ask your Pharmacist for advice when choosing a cough remedy, especially for children and babies.
Side effects
Side effects may include:
- Drowsiness
- Dry mouth
- Rapid heart rate
- Dizziness and low blood pressure
- Loss of appetite
- Skin sensitivity to sunlight
- Tremors
Although Antihistamines are often present in cough syrups, they should not be used if a moist cough is present, as the drying effect can thicken the mucus in the lungs and make symptoms worse. Antihistamines can become addictive when used for sedation, so short-term use (2-3 days only) is recommended.
Antihistamines must not be taken with alcohol or other sedatives. People taking Antihistamines should avoid operating machinery and driving a car or any kind of vehicle. Fatalities have occurred due to people engaging in such activities when under the influence of Antihistamines.
Children and babies are more susceptible to side effects from Antihistamines. Never give your child an Antihistamine unless your Doctor or Pharmacist has advised it. Some Antihistamines are not recommended for use in pregnant or breastfeeding women. Again, consult your Doctor or Pharmacist for advice.
Medical use
Antihistamines may come as tablets, capsules, creams, eye drops, nasal sprays, syrups or injections. They have several effects on the body. They cause the blood vessels to constrict, which reduces swelling and itching. They dry up oral, nasal and gastric secretions and can suppress coughing. They may also reduce nausea and vomiting. Antihistamines are used for treatment of various conditions including:
- Bites and stings
- Hives, chickenpox and other itchy skin rashes
- Hay fever (allergic rhinitis) with runny nose and sneezing
- Sinusitis
- Conjunctivitis
- Motion sickness and other causes of nausea and vomiting
- Cough suppression (dry cough only)
- Short term sedation
Notes
Antihistamines can interact with many other medications, particularly blood pressure and depression medications. Always consult your Doctor or Pharmacist before using an Antihistamine and be sure to inform them of all other medications you or your child is taking.