Antihistamines

When your immune system overreacts to an allergy such as pollen or pet dander, symptoms such as coughing, sneezing, and watery eyes can occur. Histamine is a substance produced by your immune system that can trigger these symptoms. Antihistamines are drugs that can treat allergies and stomach problems, colds, anxiety, and other conditions.

The best antihistamines are a class of medications that are often used to ease the symptoms of allergies and other respiratory conditions. These medications aid in treating illnesses caused by an excess of histamine, a substance produced by your body’s immune system. Individuals who suffer from dust and other allergens are the most popular target for the best antihistamines. As well as stomach troubles, colds, nervousness, and other diseases, they are also used to treat a range of other conditions.

Allergies

Your body defends you against numerous dangers. Your ribs protect your heart and lungs. Your skin shields you from harmful external factors such as the sun, wind, and germs that can bring disease and infection. Your eyelashes protect your eyes from foreign objects. And your body’s defence system — your immune system fights foreign toxins that enter your body.

When your immune system responds to a “foreign” substance, an allergy ensues. When you have an allergy, elements that are usually safe and cause no discomfort to some individuals, such as dust or animal dander, cause you discomfort! Your body perceives these compounds as “foreign,” eliciting an overreaction from your body’s defensive system, including the release of histamine. Allergens are the compounds that cause the hypersensitivity reaction. The resulting symptoms are referred to as an allergic response. Allergies are one of the most prevalent chronic diseases worldwide.

Histamine

Histamine is a critical molecule that plays a part in various biological activities. It boosts stomach acid secretion, contributes to inflammation, dilates blood vessels, changes intestinal and pulmonary muscle contractions, and influences your heart rate. Additionally, it aids in transmitting information between nerve cells and the passage of fluids through blood vessel walls. Histamine is also released when your body detects an allergen as a threat. Histamine causes vessels to dilate and swell, which results in allergic symptoms.

Antihistamines

Antihistamines are prescription or over-the-counter medications that work by inhibiting some of the effects of histamine. Because the term “anti” means “against,” antihistamines are medications that act against or inhibit histamine.

Antihistamines: Classification

Antihistamines are classified into two broad categories. The first subclass is referred to as H-1 antagonists or H-1 blockers. Antihistamines of this class are used to treat allergy symptoms. The second subclass is referred to as H-2 antagonists or H-2 blockers. They are used to treat gastroesophageal reflux disease [GERD] (also known as acid reflux), peptic ulcers, gastritis, motion sickness, nausea, and vomiting. Doctors and scientists use the naming structure (H-1 and H-2) to determine the cell type and location of the histamine receptor that the antihistamine medicine blocks.

The H-1 blocker subclass is classified into two categories: first-generation and second-generation antihistamines.

Mechanism of Action of Antihistamines

Histamine is a substance created naturally by various cells in your body. It serves a range of purposes. Histamine is produced in large numbers by cells called mast cells in areas of the body that come into touch with the external environment. In the nose, throat, lungs, and skin, for example. Mast cells and histamine are components of your immunological defence system in this area. (In contrast, histamine produced by the stomach’s lining cells aids in producing acid necessary for food digestion.)

Your immune system cells constantly scan your blood and mucosae for anything not produced by your body (for example, pathogens such as bacteria or viruses). (Mucosae are the membranes that line the cavities of the body, such as the mouth, nose, and digestive tract.) Histamine is released from mast cells when your skin is wounded or your immune system senses a foreign material. Histamine binds to unique locations (receptors) on other cells called H1 receptors. This initiates a chain reaction that results in the area’s blood vessels being slightly leaky. Specialised cells and molecules that help your body defend itself can now enter the site. While this is a beneficial response, it also results in swelling, redness, and itching.

Allergic reactions such as hay fever are triggered by an immune system hypersensitivity or hyper response to a specific allergen. An allergen is a foreign material to the body and can trigger an allergic reaction in susceptible individuals—for instance, pollen, dander, mould, and some bacteria. The immunological response to these foreign chemicals is usually normal and appropriate in most persons. However, it is considerable in allergic individuals. For example, contact with pollen in persons with hay fever activates the mast cells in the nose, throat, and eyes to release far more histamine than usual. This increased histamine release results in the accompanying symptoms of itching, puffiness, and runny eyes.

Antihistamines function by physically inhibiting histamine’s ability to reach its target. This reduces your body’s reactivity to allergens, assisting in reducing allergy-related symptoms.

Antihistamines are also used to relieve nausea and vomiting (vomiting). However, the precise mechanism by which they alleviate these symptoms is unknown. The brain contains multiple critical areas that regulate vomiting. Antihistamines are thought to block H1 receptors in the part of the brain responsible for nausea caused by substances in the body.

Certain antihistamines may also have an antimuscarinic effect. This suggests that the medication can also inhibit another receptor found on the surface of specific cells. If these receptors are impacted, you may suffer some antihistamine-associated adverse effects. For instance, dry mouth, impaired eyesight, and urinary retention. These effects are primarily due to the older first-generation antihistamines discussed in greater detail below.

Antihistamines must not be confused with H2 blockers, which decrease stomach acid production. While both types of medication inhibit histamine’s activity, they act on distinct receptors in different body systems.

Conclusion

Histamine is a substance produced by your immune system that can trigger these symptoms. Antihistamines are drugs that can treat allergies and stomach problems, colds, anxiety, and other conditions. Allergens are the compounds that cause the hypersensitivity reaction. The resulting symptoms are referred to as an allergic response. Allergies are one of the most prevalent chronic diseases worldwide. Histamine is a critical molecule that plays a part in various biological activities. 

It boosts stomach acid secretion, contributes to inflammation, dilates blood vessels, changes intestinal and pulmonary muscle contractions, and influences your heart rate. Antihistamines are classified into two broad categories. The first subclass is referred to as H-1 antagonists or H-1 blockers. Antihistamines of this class are used to treat allergy symptoms. The second subclass is referred to as H-2 antagonists or H-2 blockers.