Antihistamines are a class of drugs used primarily to treat hypersensitive reactions, such as seasonal allergic rhinitis (hay fever), urticaria (hives), and itching after insect bites.
They can also be used to reduce nausea and vomiting. as well as for emergency treatment of anaphylaxis, i.e. a severe allergic reaction.
The side effects that may occur after using these drugs are usually minor.
What are antihistamines?
Antihistamines are a class of drugs used for allergic ailments.
- Cetirizine (Zyrtec)
- Desloratadine (Aerius)
- Fexofenadine (Telfast)
- Levocetirizine (Xusal)
- Loratadine (Clarityn)
- Mizolastine (Mizollen)
- Chlorphenamine (Grippostad C)
- Cyproheptadine (Peritol)
- Hydroxyzine (Atarax)
- Ketotifen (Zadites)
They can be used as a tablet, syrup, nasal spray and eye drops.
Antihistamines are usually used in the following cases:
– to relieve symptoms of hay fever, which may include rhinitis and conjunctivitis (inflammation of the nose and eyes), such as sneezing, itching of the eyes, nose and throat, and rhinorrhea (runny nose);
– to relieve the severity of itching in skin rashes such as urticaria and generalised pruritus (itching);
– to prevent kinetoses and other causes of nausea (nausea).
– in the treatment of terminally ill patients, due to their sedative and antiemetic (suppresses nausea and nausea) effect.
– in emergency treatment in case of severe allergic reactions.
How do antihistamines work?
Histamine is a chemical substance that is produced naturally in various cells of the body. Some cells, called mastocytes, produce a large amount of histamine. They are mainly found in the areas that are particularly exposed to tissue injuries: nose, mouth and feet.
If the skin is injured and the immune system recognizes a foreign substance, the mast cells release histamine, which binds to receptors of other cells.
This triggers a chain reaction that causes an increase in the permeability of the blood vessels located in this area.
In this way, the specialized cells and chemical substances that serve to protect the body can access these areas. This reaction causes redness, swelling and itching.
Allergic reactions, such as hay fever, are triggered by hypersensitivity or by an overreaction of the immune system to a particular allergen. An allergen is a foreign substance that can cause an allergic reaction in certain people. Allergens can be of various nature: food, insecticides, inhaled or absorbed substances, pharmaceuticals.
In most people, the immune response to these foreign substances is normal and appropriate, while in allergic patients, the response is excessive.
For example, people who suffer from hay fever have a much higher histamine release from mast cells than normal when they come into contact with pollen in the nose, throat, and eyes. They develop symptoms such as itching, swelling, runny nose, etc. Antihistamines work by blocking the body’s histamine receptors.
This weakens the body’s reaction to the foreign substances (allergens) and thus helps to reduce the annoying symptoms associated with the allergy.
Antihistamines are also used to treat nausea and vomiting, but the exact reason why they relieve these symptoms is not yet fully understood.
They are thought to block histamine receptors in the brain area that causes nausea in response to certain chemical substances in the body, called the “vomiting center.”
Some antihistamines are less specific and characterized by low selectivity to histamine receptors, with significant antimuscarinic activity (that is, they inhibit the muscarinic receptors of acetylcholine, another important neurotransmitter) at the level of the central nervous system, thereby causing some side effects such as drowsiness, sedation, dry mouth, visual disturbances and water retention.
These effects are mainly caused by first-generation antihistamines, which are described below.
Note: Antihistamines should not be confused with H2 blockers, which reduce gastric acid production.
Even though both types of drugs block the mode of action of histamine, they work on different receptors in different systems of the body.
Are there different types of antihistamines?
Normally, the classification of antihistamines is carried out into two groups:
-First-generation antihistamines or sedatives, which may cause pronounced somnolence (sleepiness) due to their low selectivity to H1 receptors and their ability to cross the blood-brain barrier.
- Dimenhydrinate (Vomex), as a remedy for motion sickness
- Diphenhydramine (Betadorm) for motion sickness and as a sleep aid
These medicines may be used for their sedative effect or for sleep disturbed by itching.
-second-generation antihistamines, which are much more selective and cause less fatigue.
However, those who take these drugs while performing responsible activities, for example while driving, must be aware of the sedative effect, especially in combination with alcohol.
Second-generation antihistamines are: cetirizine, desloratadine, levocetirizine, loratadine, mizolastine and rupatadine.
Are antihistamines available over-the-counter?
Some of these drugs are available on the advice of the pharmacist, others only by prescription of the doctor.
Which antihistamine is best?
All antihistamines work well enough to reduce allergic symptoms. The doctor or pharmacist may recommend or prescribe an antihistamine mainly because of the specific allergy.
As a rule, the antihistamines have the same effectiveness in reducing the symptoms of hay fever and urticaria. However, the second-generation antihistamines are used more often because they cause less fatigue.
Cetirizine and loratadine are often prescribed for urticaria.
Desloratadine may be more helpful for nasal congestion — a symptom that is not controlled by the use of antihistamines.
A sedative antihistamine can be very useful in children at bedtime if they suffer from allergic symptoms.
How are antihistamines taken?
These drugs are sold in different forms: tablets, syrup, spray or eye drops.
Doctor or pharmacist may recommend how to use them.
An antihistamine tablet usually begins to work within 30 minutes of ingestion.
The peak value of effectiveness is usually reached in 1-2 hours.
Antihistamines are more effective when taken daily, rather than occasionally.
This is especially true for people with hay fever. In the spring months, the concentration of bee pollen is usually highest and one often comes into contact with the allergen.
Taking the medicine regularly helps keep symptoms under control.
The effectiveness also depends on the dose taken and the pharmaceutical form.
How long is the therapy required?
This can vary depending on the type of allergy. For example, someone who suffers from hay fever takes the drug throughout the season when there is pollen count.
Sometimes antihistamines can be prescribed over a longer period of time as a basic therapy that accompanies the life of the allergy sufferer on a daily basis, possibly as a substitute for corticosteroids.
There are no risks with prolonged use of antihistamine drugs. If anything, sudden weaning is risky. Although there is no dependence, the “detoxification” of antihistamines must be done gradually to prevent the original allergy from recurring and with greater strength.
Discontinuation should be carried out as directed by the attending physician; one could start with a reduction in the daily dose or stop taking it every other day. Sometimes it may be useful to supplement with homeopathic remedies, mineral salts and vitamins during the period of exposure.
Who is not allowed to take antihistamines?
Most people can take antihistamines with peace of mind. Antihistamines must not be used or should only be used under the control of the doctor in:
- Pregnancy and lactation
- Kidney or liver problems
Most people who take antihistamines do not experience any significant side effects. When these occur, they are usually light.
The most common are:
- Blurred vision
- Urinary retention (difficulty urinating)
- Gastrointestinal complaints (stomach and intestinal complaints)
Some medications interact with antihistamines, such as some antidepressants and antifungal drugs.
Therefore, before using antihistamines, you should talk to the doctor if you are already taking other medications.
If you take antihistamines, you should avoid alcohol, because this can increase fatigue.