What is Antihistamine?
Antihistamines are a class of drugs that are used to cure the allergies triggered by the physiological action of the histamines. Histamines are the organic compounds that are involved in the local immune responses and act as a neurotransmitter. Histamines take part in the inflammatory response and act as a mediator of pruritus. Basophils produce histamines, and they are found in the connected nearby tissues. Histamines increase the permeability of the white blood cells, and this makes the pathogens to get more engaged with the infected tissues. Antihistamine examples are ranitidine, loratadine, meclizine, cetirizine, etc.
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The Action of Antihistamines on the Human Body, How do they Suppress Antihistamines?
Our immune system might start to mistake a harmless substance as a dangerous material or pathogen, this shows the start of the development of an allergy. These harmless foreign substances that are considered dangerous by the immune system, are named as the allergen. One of the most common allergens are pollen and milk (Lactose intolerance).
When the body comes in contact with any of the allergen, the immune system responds harshly in order to suppress the upcoming foreign substance named allergen. To deal with the allergens the immune system releases various chemicals and antibodies. One such chemical is named histamine, the histamine is the chemical which transports the information regarding the allergen to the brain and thus causing the major symptoms of the allergies. These symptoms can be nasal swelling, runny eyes, and, in some cases, mouth itching.
Antihistamines, as the name suggests (Anti-histamine), are the chemical that stalls and suppresses the action of the histamines. Thus protecting them from the various symptoms of the allergies. Antihistamine fights for a space in the neural receptors or the binding site of neural receptors with the histamine and thus stopping them from sending the information regarding the allergy to the brain.
However, Antihistamine has a limited range of applications and can not be used to treat many types of symptoms like for the symptoms of nasal congestion and swelling, the doctors do recommend the use of decongestant rather than Antihistamine. In many conditions, Antihistamine and decongestant are prescribed together along with some other types of medication depending on the patients.
Antihistamine Drugs Classification
Antihistamines drugs can be classified into two types according to the H receptor-targeted: -
H1: They are generally used to treat allergic reactions as well as mast cell-mediated disorders. This category can be further divided into two classes: first-generation H1 antihistamines, which have a central effect and are used as sedatives; and second-generation H1 antihistamine which have a lesser central effect and are used as antiallergic drugs.
H2: They are used for gastric reflux disease as they help in reducing the production of stomach acid by reversibly blocking the H2 histamines receptors in the parietal cells of the gastric mucosa.
Example of Drugs and Antihistamine Uses According to Antihistamine Classification
H1 First-Generation: Meclizine, Clemastine, Hydroxyzine, Brompheniramine, Dimetindene, Doxylamine, etc. that are used as sedative agents, antiallergic agents, to cure motion sickness, and an antiemetic agent. These drugs have strong sedative action and anticholinergic side effects.
H1 Second-Generation: Loratadine, Cetirizine, levocetirizine, azelastine, fexofenadine, etc. that are used as antiallergic agents, or adjuvant treatment for anaphylactic shock. These drugs are non-sedative or mildly sedative.
H2: Ranitidine, Cimetidine, Famotidine, etc. that are used to reduce the production of stomach acid and are generally used as a second-line treatment or in combination with proton pump inhibitors (PPIs).
Antihistamine Side-Effects
The severity and the frequency of the adverse effects of histamines vary according to the type of antihistamine. The H1 first-generation antihistamines are considered to be more harmful, and they usually cause drowsiness. H1 antihistamines cause anticholinergic effects like dry mouth and eyes, dizziness, urinary retention, mydriasis tinnitus, and tachycardia along with headaches. Benadryl and Chlor-Trimeton are examples of such drugs. The side effects of H2 antihistamines include confusion, dizziness, headaches. For example, Allegra, Clarinex, and Zyrtec. Cimetidine can lead to erectile dysfunction and gynecomastia because of its antiandrogenic effect. Cimetidine and ranitidine decrease the renal excretion of creatinine.
Solved Questions
Question 1. What is the difference between Claritin and Clarinex?
Answer: Claritin is loratadine that is metabolized in the liver to produce Clarinex that is desloratadine.
Question 2. How do antihistamines protect against allergies?
Answer: Antihistamines block the action of the histamines that gets triggered when our body comes in contact with components like pollen, dust mites, etc. These components make the histamines come in action to cause allergies like swelling of the nose, running nose and eyes, etc. Antihistamines block the course of action of histamines and protect us from allergies.
Question 3. Can antihistamines be used to cure skin allergies?
Answer: Yes, antihistamines can be used to take care of insect bites and skin allergies. Zyrtec and Claritin are both best antihistamines to help you with your skin allergies.
Question 4. What is an allergy?
Answer: An allergy is an immunological hypersensitivity that is mediated by immunoglobulin E antibody (IgE). An allergy is not related to any disease or infections.
Question 5. What causes an allergy?
Answer: Allergies generally occur when your immune system reacts to a foreign substance like pollens, bee venom etc. Allergies are basically the reactions of your body coming into contact with foreign substances.
FAQs on Antihistamine
1. Who must not consume antihistamines?
Though antihistamines can be safely consumed by the majority of people of all age groups, there are a few exceptions that must not consume antihistamines.
Women who are pregnant or are breastfeeding.
People with underlying health issues like epilepsy, high blood pressure, liver disease, kidney disease, overactive thyroid, diabetes or asthma.
Always check the label before giving an antihistamine to children as not all antihistamines are suitable for children.
Any medication must be taken only after the prescription given by the doctor.
2. Can you develop an allergy for an antihistamine itself?
Yes, one can develop an allergy to any kind of medication, including antihistamines as each person’s body reacts in a different way to each kind of medication. You must always consult a doctor before starting with any medication and should always adhere to the dose prescribed by the doctor. If you find that a drug does not work well for you, then instead of increasing its dose on your own, you must consult the doctor to try another drug rather than changing the dose without a prescription. Consuming antihistamines in an overdose can cause serious side effects like tightness, respiratory depression, a burning sensation in the nose, or even death in the worst cases.
3. What are the reasons or causes for a person to get allergies?
Allergy begins when the immune system of the body starts to misjudge a harmless substance as a harmful or dangerous invader. The immune system starts to produce anti- bodies for that harmless substance but gets identified as a harmful one. These newly produced anti- bodies remain at an alert for such foreign substances. These foreign substances are called the allergen and when any of such allergen gets in contact with the body, the antibodies present will start producing certain chemicals to suppress these allergen molecules, one of these chemical produced are the histamine, which is the reason for various allergic reactions.
Common substances which might be considered as an allergen are:-
1. Airborne Allergen:- Pollen grains, dust mites and molds. The biggest allergen in human species is the pollen grains.
2. Certain Foods:- mainly include the peanuts, soy, egg and milk etc.
3. Medication such as penicillin and penicillin-based antibiotics can also become allergens.
4. How do antihistamine keep allergies at check?
When the human body comes in contact with the harmless foriegn substances that are considered very harmful by the immune system, which are collectively called allergens. Then the immune system in order to counter these allergens release the many specific immunity chemicals such as histamines, which are responsible to transfer the information about the entering of the allergen and thus get the body to cause all those symptoms of allergies. The antihistamine goes and hurts the functioning of these histamines; it is also why they are named as Anti- histamine. Thus controlling the allergies to some extent by suppressing the symptoms of the allegeries.
5. Which one is the most effective Antihistamine to use and do they have anti inflammatory properties?
There exists a very little amount of evidence to prove if one Antihistamine is better than the others. Some types of Antihistamine works for a group of people but is not necessary to work for all people as the body of every person is different.
Claritin and Zyrt are two widely used Antihistamine in the country. Doctors considered them as the safest and most effective Antihistamine or allergy treatment. Both of these two Antihistamine (Claritin and Zyrt) are both the types of second generation antihistamines. Second generation antihistamines induces a lower level of sedative effect than first generation antihistamines.
Some studies have now shown that most of the antihistamines have anti inflammatory effects to the human body, according to the new research that this drug is reducing the expression of the cell adhesion molecules too, and simply inhibiting histamine receptors.