They may also be used to help reducenausea and vomiting , in addition to the emergency treatment of anaphylaxis or in the event of a severe allergic reaction .

The side effects of using these drugs are usually mild.


What are antihistamines?

Antihistamines are a class of drugs used in the treatment of allergic diseases.

They include:

  • Clemastine Acid Fumarate (Agasten)
  • Tripelenamine Hydrochloride and Mepyramine Maleate (Alergitrat)
  • Cetotifeno (Asdron, Asmalergin, Asmax)
  • Azatadine Maleate and Pseudoephedrine Sulfate (Cedrin)
  • Phenylephrine and Bromofeniramine (Bialerge)
  • Cetirizine (Cetrizin)
  • Astemizole (Hisnot)
  • Loratadina micronizada (Claritin)
  • Pseudoephedrine sulfate (Claritin-d)
  • Loratadina (Clistin)

They may be taken in the form of tablets, syrups, nasal sprays and eye drops. 
Antihistamines are commonly used:

  • To relieve the symptoms of allergic rhinitis  which may include:
    1. Rhinitis and conjunctivitis (inflammation, respectively, of the nose and conjunctiva of the eyes),
    2. Sneezing,
    3. Itchy eyes, nose, throat,
    4. Rhinorrhea ( runny nose ).
  • To reduce the severity of the itching  associated with rashes such as urticaria.
  • To prevent nausea and other causes of nausea .
  • In the care of the terminally ill , by the sedative and antiemetic effect.
  • In the emergency treatment of severe allergic reactions .


How do antihistamines work?

Histamine is a chemical naturally produced by various cells in the body. Some cells called mast cells produce large amounts of histamine, are found mainly in areas more exposed to possible tissue lesions:

  • Nose,
  • Boca,
  • Foot.

If the skin is injured and the immune system detects a foreign substance, the mast cells release histamine that binds to receptors on other cells. 
This causes a chain reaction that causes an increase in the permeability of the blood vessels in the area. 
In this way, the specialized cells and the chemicals that serve to defend the organism can access that area.

This response causes:

Allergic reactions, such as allergic rhinitis, are caused by hypersensitivity or an overreaction of the immune system to a particular allergen. 
An allergen is a substance foreign to the body that can cause an allergic reaction. 
Allergens can be of various types:

  • Foods,
  • Insect poisons,
  • Inhaled or absorbed substances,
  • Drugs

In most people, the immune reaction to these foreign substances is normal while in allergic people the response is excessive. 
For example, in people suffering from hay fever, when they are in contact with pollen at the nose, throat and eyes level they have a much higher than normal release of histamine from the mast cells, producing symptoms such as:

  • Itch,
  • Swelling,
  • Nasal discharge.

Antihistamines work by blocking the histamine receptors . 
This decreases the body’s reaction to foreign substances (allergens) and thus helps reduce the unpleasant symptoms associated with allergy. 
Antihistamines are also used in the treatment of nausea and vomiting . 
The exact way in which these symptoms are alleviated is not fully understood. 
They are believed to block histamine receptors in the brain (called the “vomit center”) that cause nausea in response to certain chemicals in the body.

Some antihistamines are poorly specific and characterized by low selectivity for histamine receptors. 
However, they have a significant antimuscarinic action (ie, blocking the muscarinic acetylcholine receptor, another important neurotransmitter) at the level of the central nervous system, causing some side effects such as:

These effects are primarily caused by the first-generation antihistamines described below. 
Note: Antihistamines should not be confused with H2 blockers, which reduce acid production in the stomach. 
Both types of drugs block the action of histamine, working on different receptors in different systems of the body.


Are there different types of antihistamines?

Generally, antihistamines were classified into two groups:

1) First generation histamines  – which can cause marked drowsiness:

  • Due to the low selectivity for the H1 receptor,
  • By the ability to pass the blood-brain barrier.

These include:

  • Fenergan ® is indicated for the symptomatic treatment of all disorders included in the group of anaphylactic and allergic reactions
  • Zyrtec®  is indicated for the treatment of allergic rhinitis, allergic conjunctivitis, urticaria and other allergic conditions
  • Difenidrin® is a first-generation antihistamine with anticholinergic activity, used to ameliorate allergic reactions
  • Flufenan®.

These drugs may be used for sedative purposes or when sleep is disturbed by itching.

2) Second-generation antihistamines – which have greater selectivity and cause less drowsiness. 
However, those taking these medicines should be aware of the particular sedative effect in combination with alcohol. 
Second-generation antihistamines include:

  • cetirizine,
  • Desloratadine,
  • Loratadina,
  • Rupatadina,
  • Mizolastina.


What is the best antihistamine?

All antihistamines work well enough to reduce allergy symptoms . 
Your doctor or pharmacist may recommend or prescribe a specific antihistamine depending on the exact cause of the allergy . 
However, second-generation antihistamines tend to be more used because they cause less drowsiness. 
Cetirizine and loratadine are often prescribed for urticaria. 
Desloratadine may be more useful in reducing the symptom of a stuffy nose , a symptom not controlled by the use of antihistamines. 
A sedative antihistamine may be particularly useful for children at bedtime if they have allergy symptoms.


How to take antihistamines?

These drugs are sold in several forms:

  • Tablets,
  • Syrups,
  • Sprays,
  • Eye drops.

Your doctor or pharmacist can advise you how to take them. 
An antihistamine tablet usually starts working within 30 minutes. 
The peak effectiveness is typically within 1-2 hours.

Antihistamines are most effective when taken daily , rather than as needed. 
This is especially true for people who suffer from allergic rhinitis. During the spring, the concentration of pollen is generally higher and you can often contact the allergen. 
Taking regular medication helps keep your symptoms under control. 
Efficacy also depends on the dose taken and the dosage form.


How Long Do You Need To Take The Treatment?

This can vary depending on the type of allergy for example if you suffer from allergic rhinitis you can take the medication for the entire period that the pollens are in the air. 
Sometimes the prescription for antihistamines may be long-term, the basic therapy accompanies the daily life of the allergic patient, sometimes in place of cortisone . 
There are no dangers in taking antihistamines for a long time, perhaps a sudden interruption is more risky .

It is not that they are addictive, but the detox of antihistamines should be done gradually to prevent the allergy from manifesting again and with greater intensity. 
It should be followed by your doctor, it is possible to:

  • Reduce daily doses,
  • Alternate one day and another not.


Who can not take antihistamines?

Most people can safely take antihistamines. 
Antihistamines should not be used or should only be used under strict medical supervision in case of:


Side effects

Most people taking antihistamines do not have serious side effects. If they occur, they are usually mild. 
The most common are:



Some medications interact with antihistamines, such as some antidepressants and anti-fungals. 
Therefore, if you are taking other medicines, it is advisable to talk to your doctor before taking an antihistamine. 
If you are taking an antihistamine you should avoid alcohol as this may aggravate drowsiness.

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