How Do Antihistamines Work?
Antihistamines are a type of medication people with various types of allergies use. This type of medication is defined as "an agent that counteracts the action of histamine."
Histamine is a physiologically active depressor amine produced by decarboxylation of histidine that causes capillary dilation, an increase in capillary permeability, more gastric acid secretion, a higher heart rate, lower blood pressure and the tightening of smooth muscles.
More About Histamines
In plain English, histamine is a compound found in cells. It's created when the essential amino acid, histidine, breaks down. It causes a variety of allergic inflammatory reactions including coughing, sneezing, stomach upset, headaches and watery eyes.
Histamines are broken down into three cellular receptors: H1, H2 and H3.
H1 receptors cause capillary dilation and smooth muscle contraction. H2 receptors increase the secretion of gastric acid which causes upset stomach. It also increases the heart rate. H3 receptors are partially responsible for the release of histamine and neurotransmitters.
Everybody produces histamine. Too much histamine causes allergic reactions. Antihistamines work by blocking the H1 and H2 receptors.
What Do Antihistamines Do?
Histamine is stored in cells in the body called mast cells. Mast cells are in almost all tissues of the body. The substance is released when the body reacts to what it considers a foreign substance.
The histamine causes a chain reaction. Often blood flow increases to the area. The histamine can cause the release of other body chemicals which can cause additional allergic responses like itching.
Antihistamines prevent histamine receptors from causing the chain reaction in your body that produces some of the unpleasant symptoms of an allergy. They do this by coating the receptors so that they can't bind together.
To be effective, antihistamines need to be taken at least two to five hours before exposure to an allergen. Or they need to be taken on a near daily regular basis to prevent symptoms.
Histamine works so quickly once it's released that by the time your symptoms appear, the allergic reaction is well established and the histamine is firmly attached to the cell receptors.
Antihistamines vary in effectiveness depending on your personal reaction to them, the type and the kind of symptoms you have. Many reach their peak effectiveness two hours after you've taken them. Some people experience some symptom relief within 30 minutes of taking the medication.
Understanding the Different Types
There are two types of antihistamines: the kind that will make you drowsy and the kind that will let you remain alert. The sedating antihistamines are an older type and technology has advanced to allow you to experience allergy symptom relief without being forced to walk around in a drowsy stupor.
Sometimes it's beneficial to take the sedating kind. They tend to be more effective at itch treatment. Often itching feels worse at night so a sedating antihistamine can help you sleep and relief the itch. Examples of sedating antihistamines include Phenergan (promethazine), Vallergan (alimemazine) or Atarax (hydroxyzine). Examples of non-sedating antihistamines are loratadine or cetirizine.
Antihistamines can be available in tablet form to take orally or they're available in creams. Topical creams can sometimes cause additional allergic reactions in the skin and are not always the best choice. They tend to not help with the itch of eczema, for example.
Side Effects
Like many medications, there are side effects to using antihistamines. Medical experts say the antihistamine side effects are more common among the elderly and children. Regardless of whom you are or what age you are, you should be aware of the possible side effects.
· Confusion, often also associated with the drowsiness
· Dizziness
· Headache
· Constipation
· Difficulty urinating
· Blurred vision
· Dry mouth
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