Antihistamines are chemicals that inhibit the effects of histamine. Not only do they eliminate histamine itself, but also prevent subsequent cells from reacting to it. Unfortunately, antihistamines have some negative side effects for the body. What are antihistamines and how do they work?
Histamine - what is it?
Histamine is a substance that our body produces naturally. Histamine stimulates, for example, the secretion of gastric juice. It is also used in e.g. skin warming ointments. Histamine is also a tissue hormone and neurotransmitter, but most of all it is a mediator of inflammation. It is she who informs the next cells that there is a "danger" approaching, that some toxic substance has entered the body. This happens, for example, when we are bitten by a mosquito or a spider. But, unfortunately, at this time, we may feel some discomfort, e.g. pain, burning and itching, sometimes redness and swelling are also visible. All of this is to act as a defensive shield.
Histamine in food
All foods that are fermented and matured (e.g. yoghurts, cheeses, fermented products) contain some, low levels of histamine. It is formed from the amino acid L-histidine with the participation of bacterial histidine decarboxylase. However, when the human digestive tract is functional, the oxidase present in the intestinal villi mucosa breaks down this amine and the body does not react to it in an allergic manner. Otherwise, when the structure of the intestinal villi is damaged (in the course of e.g. celiac disease, Crohn's disease or food allergy) and the excess histamine absorbed in the intestines enters the circulatory system. Then, unfortunately, even poisoning of the body can occur.
Antihistamines - what are they and how do they work?
Antihistaminesare chemicals that inhibit the effects of histamine in two ways. First, they block it so that it does not bind to its receptor. Second: they inhibit the activity of histidine decarboxylase converting histidine into histamine. To put it simply - antihistamines are drugs that not only eliminate the histamine itself, but also lead to the fact that subsequent cellsthey do not react to it or to the information that histamine transmits.
Antihistamines - what diseases are they used for?
- allergic rhinitis - they can withstand sneezing, restore its patency, inhibit the excessive production of secretions, reduce tissue swelling and eliminate the symptom of nasal blockage,
Antihistamines are used in the treatment of many allergic diseases. These drugs are designed to endure persistent ailments, improve the well-being and quality of life of the patient. Antihistamines are used primarily to treat:
- allergic conjunctivitis - the newest antihistamines thanks to the additional anti-inflammatory effect - reduce itching, excessive tearing, redness or swelling of the eyes,
- allergic and non-allergic urticaria and angioedema - reduce itching, lead to disappearance of urticaria or swelling of the tissues, reduce any redness. The effectiveness of antihistamines in the treatment of chronic idiopathic urticaria, i.e. of unknown origin, in which causal treatment is impossible, and which is very burdensome for the patient, is particularly important,
- bronchial asthma - inhibit bronchospasm, improve ventilation and reduce the need for ß2-agonists.
- atopic dermatitis - show antipruritic and local anesthetic properties,
Antihistamines - 1st and 2nd generation
In 1937, first-generation antihistamines were introduced to the market. Unfortunately, they caused numerous side effects. It was only in the 1980s that second-generation drugs appeared on the market.
Currently on the pharmaceutical market there are preparations of both groups I and II of various forms - for general use (oral preparations and injection solutions), topical (eye drops, nasal drops, gels or ointments), as well as recently popular combined preparations, which often additionally include pseudoephedrine.
Currently, the basis for people with allergic diseases are second-generation drugs that do not penetrate (or to a small extent) the blood-brain barrier and do not show affinity for other types of receptors, unlike drugs of the first generation.
Due to their selectivity and lack of influence on the CNS, second-generation antihistamines do not cause many side effects.
1st generation antihistamines
- diphenhydramine
- antazoline
- clemastine
- cyproheptadine
- promethazine
- hydroxyzine
- ketotifen
Second-generation antihistamines
Second generation drugs used orally:
- loratadyna
- cetirizine
- mizolastine
- azelastine
- rupatadyna
2nd generation oral combination drugs - they additionally contain a sympathomimetic drug:
- loratadine + pseudoephedrine
- cetirizine + pseudoephedrine
Second-generation drugs administered topically to the mucous membranes of the conjunctiva or nose:
- emedastyna
- azelastine
- levocabastine
Antihistamines - 3rd generation
The newest second-generation antihistamines (fexofenadine, desloratadine, levocetirizine, bilastine) are sometimes called third-generation drugs. They are characterized by a very small number of interactions with other drugs, supplements or food. People suffering from e.g. diabetes or hypertension should, however, pay special attention to antiallergic preparations that are a combination of several active substances, because their very common ingredient is pseudoephedrine, the impact of which on blood pressure and sugar levels is still unpredictable at the moment, and therefore dangerous. The situation is similar with phenylephrine, which can be used interchangeably with pseudoephedrine as an ingredient to fight a runny nose and to decongest the nose. In case of allergies, the above-mentioned patients should therefore use drugs with one active substance, and in case of any doubts it is recommended to consult a specialist.
Antihistamines and pregnancy
Treatment of allergies in pregnant women is a difficult and complex problem. On the one hand, we have a pregnant woman complaining of persistent symptoms, and on the other hand, there is not enough data on the safety of antihistamines in pregnancy because no one is conducting such studies. The use of: cyproheptadine, clemastine, cetirizine, loratadine and diphenhydramine carries a low risk.
The measures showing a low level of risk include:. Nevertheless, if it is possible, pregnant women should refrain from using antihistamines, especially at the beginning of pregnancy, and if they have to take them, they should be under the constant supervision of both an allergist and a gynecologist.
Antihistamines: drug interactions
Always inform your doctor about any other medications you are taking. People with HIV, tuberculosis and those treating fungal infections should be especially careful about drug interactions.
Combinations of allergy medications and medications can also have a negative effectantacids. The latter preparations may result in the absorption of smaller amounts of the antihistamine drug.
Antihistamines - side effects
The most common side effects of taking antiallergic medications are:
- distraction
- sleepiness
- dizziness
- feeling tired
If they do appear, notify your doctor immediately and do not drive.
Less common side effects are:
- nervousness
- nightmares
- sleep disturbance
- diarrhea
- rapid or irregular heartbeat
- itching and rash
Allergy medications can also cause … a severe allergic reaction. Her symptoms are:
- swollen throat
- swollen lips
- tongue swelling
- face swelling
- shortness of breath
- difficulty breathing
People who have an infection in the nasal cavity and those after nose surgery should refrain from taking antiallergic drugs, especially in the form of drops. These types of medications will also not help patients with glaucoma, cataracts, increased intraocular pressure, and vision changes.
Contraindications to taking antihistamines in the form of drops are also: severe kidney disease, adrenal gland dysfunction, liver disease, tuberculosis.
Allergy sufferers with heart disease, thyroid disease, and high blood pressure should also take antihistamines with caution.
For each patient, however, the doctor always decides what drug and in what dose a particular allergy sufferer can take.
It is worth remembering that antihistamines taken with alcohol slow down, cause dizziness and lower blood pressure.
Antihistamines: overdose
An overdose of allergy medications causes a number of symptoms: dizziness, dry mouth, drowsiness, fatigue, and weakness. Suppression of adrenal function, causing muscle weakness, increased s alt requirements, fatigue, decreased blood sugar, darkening of the skin and depression is also likely in the event of an overdose of antihistamines.
Also readAllergy: symptoms, types, treatment
Cross allergy symptoms. Allergen table
Prescription allergy medications: types and uses