Different Antihistamines and Their Uses

Today we're going to talk about different antihistamines and their uses. For example, they treat allergies and can help prevent vomiting.
Different Antihistamines and Their Uses

Last update: 20 April, 2021

Antihistamines are medications that are used to reduce or eliminate the effects of allergies. To do this, they block the receptors that histamine binds to during allergic reactions. In today’s article, we’ll tell you about different antihistamines and their uses.

Histamine, as you’ll see later, is a substance that the body releases when it’s experiencing an allergic reaction.

Since the discovery of antihistamines (pyrilamine and diphenhydramine) in the 1930s and 1940s, scientists have developed hundreds of molecules with antihistamine properties. In addition, this medication has become very popular in recent years.

Also, scientists have introduced second and third generation antihistamines, which is a great advancement for the field of medicine. These drugs are similar in efficacy to first-generation antihistamines, but they have far more moderate adverse side effects.

In addition to treating allergies, there are certain antihistamines that can help prevent vomiting, vertigo or inducing sleep in patients with insomnia. 

Histamine and its receptors

Medication vials.

Histamine is a chemical that participates in and is involved in many processes that occur in cells. Among these processes, its role in allergic reactions, inflammation, the secretion of stomach acid and the transmission of nerve impulses stands out. 

When playing a role in these processes, it binds to a series of receptors that are distributed throughout the body.

Then, when histamine binds to one of these structures, the body activates mechanisms and releases substances that will activate and bind to other structures. This triggers a physiological reaction. 

The reactions that it triggers will depend on what it binds to. These are some of the receptors that histamine binds to:

  • Histamine 1 receptors: These structures are in the bronchi, in the smooth muscle of the digestive system, and in the brain. When these receptors are activated, both the smooth muscle of the bronchi and the blood vessels get constructed.
  • Histamine 2 receptors: H2 receptors are distributed in the lining of the stomach, uterus and brain. When something triggers them, the permeability of the blood vessels increases and it stimulates the secretion of gastric acid.
  • Histamine H3 receptors: These are located in the brain and in the bronchi. They’re responsible for cerebral vasodilation and could be involved in a feedback system or negative feedback. In this system, the histamine inhibits its own synthesis and ability to release from nerve endings.

Different antihistamines and their uses

Classical or first-generation H1 antihistamines

These types of antihistamines are able to easily cross the blood-brain barrier of the brain. That barrier is a kind of membrane that protects the brain. As a result of crossing it, and managing to bind to the receptors in that organ, the antihistamine triggers quite intense sedative effects. 

In addition, they also have other properties such as antiemetics and anti-kinetosides. The sedative and anticholinergic effects of these drugs cause these actions.

Some drugs that are in this group of medications are:

  • Ethanolamines: Most notably, the drug diphenhydramine. Its derivative, dimenhydrinate, has anti-kinetoside properties and you can use it to prevent motion sickness. In addition, there are studies that show this active principle is effective for treating vertigo and in the prophylaxis of vomiting after an operation.
  • Ethylenediamines
  • Alkylamines
  • Piperazines
  • Phenothiazines
  • Piperidines

Second-generation H1 antihistamines

A Skin test.

Second-generation H1 antihistamines are recommended for H1 receptors that aren’t found in the brain. This is because scientists eliminated the parts of its chemical structure that allows it to cross this barrier with ease. Therefore, they’re not capable of crossing the blood-brain barrier.

As a result, they trigger fewer adverse side effects. For example, they cause less sedation and less anticholinergic effects. Some examples of these medications are:

  • Loratadine: This is an antiallergic drug that has almost zero sedative and anticholinergic effects.
  • Ebastine: Doesn’t have anticholinergic or sedative properties, but can cause weight gain. Also, it’s useful for treating seasonal allergies.
  • Desloratadine: This medication helps treat acute cases of allergies.

Commonly used medications

As you can see, doctors usually prescribe antihistamines to treat allergies. However, they can also help prevent vomiting or to induce sleep in patients with insomnia.

Now that you’ve read about the different antihistamines and their uses, you should talk to your doctor. They will be able to tell you which antihistamine is best for your personal situation. After that, it’s important to always follow the instructions they give you.

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  • Petriz, N., & Parisi, C. (2013). Uso de antihistamínicos en pediatría. Conexion Pediatrica.
  • Presa, I. J. (1999). Antihistamínicos H1: revisión. Alergol Inmunol Clin, Octubre.