Anti-Allergic Drugs: Antihistamines

Antihistamines are drugs (as name suggests) which blocks activity of produced histamines.

Histamines

Histamines are very important protein (neuro-transmitters) produced by immune system, a system that defends body against unknown substances. Our body produces histamines to react to substances (dust particles, pollens) which are not potent to cause serious health condition. Allergic reaction is, therefore, caused when such substances attaches itself to lymphocytes. Histamines, when released by immune system, widen blood vessels at the affected site. Widened vessels causes greater blood flow to that particular area which results in swelling, mucous production, red eye watering, running nose and itching etc.

How Antihistamine Drugs Work?

Antihistamine drugs work by attaching itself to histamine-receptors-cells. Thus antihistamine drugs blocks attachment of histamines to its receptive receptors which eventually stops blood vessels widening and provides relief from allergic symptoms.

Types of Antihistamine / Histamine Antagonists Drugs

There are two types of antihistamine drugs.

H1 Blockers

Type one histamine antagonists, known as H1 blockers, are those that act on H1 receptors. Drugs such as Benadryl (diphenhydramine) and Cloropiril (chlorpheniramine) and allegra (Fexofenadine) are of this type. H1 receptors, by blocking effects of histamine, prevents widening of capillaries, bronchial (passage that provide air to lungs) and gastrointestinal smooth muscle. They are used for relief of allergic and gastrointestinal disorders.

H2 Blockers

H2-blockers drugs are indicated to treat gastrointestinal ulceration. Drugs of this class block the mechanism that leads gastric acid secretion.

How H2 Blockers or H2-receptor antagonists Work?

Histamine2, a neurotransmitter, stimulates parietal cell of stomach to make acid. H2 Blockers reduces the excess of acid formation in stomach by not allowing H2 to trigger acid secretion process. Drugs of this class are indicated to treat gastroesophageal acid reflux disease a condition in which the stomach produces excess acid. H2 blockers are also being prescribed to treat peptic ulcer symptoms.

LTRA (leukotriene receptor antagonist)

Singulair (a brand name with Montelukast as active ingredient) belong to class of leukotriene receptor antagonist. Leukotrienes, a fatty molecule, are produced by immune system to react to allergens such as tiny fibers, dust and pollens. These allergens are received in body by their receptors known as leukotriene receptors. Production of leukotrienes usually accompanies by formation of histamines (a type of protein). These chemicals are responsible to make bronchial congested and inflamed.

Montelukaste acts by blocking leukotrienes to attach to its receptors and thereby inhibiting production chemical that make airway passage to lungs inflamed.

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