Antihistamines are drugs that are frequently prescribed to treat different types of allergies. The function of this medicine is not to cure the disease, but to control the appearance of symptoms so that allergic people can resume their routine without being affected by exposure to the allergen.
To understand the mechanism of action of antihistamines, it is first necessary to understand what happens in our cells when we come into contact with the allergen .
a chain reaction
A person suffering from a pollen allergy, for example, has pollen-specific antibodies in their circulation. These antibodies are like agents of the immune system that roam the body looking for threats.
In this case, the person allergic to pollen has their antibodies ready to detect pollen as a danger and the moment its presence comes into contact with our body, the alarm goes off and the immune response begins . As they pass, antibodies can “settle” on different types of immune cells, such as mast cells.
Histamine releasers, the queen of allergic reaction
These mast cells have specific receptors to receive the antibodies that detect pollen and when they pass by, they capture them and remain attached to them for long periods of time.
This mechanism allows cells to be “charged” and ready to detect pollen as soon as it enters the body. If we continue with the example of pollen allergy, since it is a seasonal allergy, when the amount of pollen in the air increases, the immune system is activated and causes the appearance of the famous allergy symptoms that we all know (sneezing, redness, itching…) .
The pollen is inhaled through the respiratory tract and distributed throughout the interior until it reaches cells that are coated with specific antibodies. Here begins a chain reaction inside the cells that culminates, among other things, with the release of histamine . Histamine is a compound created by cells such as mast cells and has several functions.
In a controlled and punctual situation, the presence of histamine can help our body to get rid of pathogens, heal wounds and modulate circulation in critical or traumatic events . Outside the immune system, histamine also plays an important role in communication between neurons, and is involved in processes associated with diseases such as Alzheimer’s and Parkinson’s. In other words, histamine in the right amounts is good for our bodies.
In the typical symptoms of allergic rhinitis or rhinoconjunctivitis, histamine is involved in itching, sneezing, uncontrolled nasal discharge (rhinorrhea) and vasodilation of blood vessels that facilitates the arrival of other cells of the immune system to the site of reaction. This set of processes, caused mainly by the activation of mast cells and the release of histamine, is the visible part of the allergic reaction and prevents people who suffer from it from carrying out a normal routine during the pollen season .
Most of these symptoms can go away with the use of antihistamines . The mechanism of action of this drug occurs at the end of this chain reaction, by interposing itself between histamine and its receptor.
How does an antihistamine stop the symptoms?
The functions of histamine are so diverse because it is capable of activating different cells by binding to a kind of “buttons” or “antennas” that they have on their surface called receptors. Antihistamines are responsible for searching for these different receptors and blocking them, so that they cannot be activated by the histamine released by mast cells . In this way, the histamine that is produced, unable to activate other cells, ends up degrading and disappearing.
All the previous steps in the chain reaction continue to occur, but if antihistamines are taken, allergic people do not get to present the symptoms, which are nothing more than the final and visible processes of allergy. In addition, the effect of antihistamines is limited in time , since the receptors are blocked for a short period of time and in a reversible way, just enough to avoid symptoms while exposure to the allergen lasts.
For all these reasons, if a person is allergic, antihistamines serve only to control symptoms in a timely manner, but they are not capable of modifying the course of the disease or curing it .
If it is a seasonal allergy, the use of antihistamines should be repeated every time the appearance of pollen appears. In the case of permanent allergies, such as allergies to mites or animals, the medicine may be necessary throughout the year to keep the symptoms at bay or at least reduce their impact.
The design of antihistamines has been optimized over time to reduce side effects and make them more specific for some types of histamine receptors and not others.
Although many antihistamines can be purchased at pharmacies without a prescription, it is imperative that an allergist diagnose the condition and decide, together with the patient, on the best treatment option .
In the case of antihistamines, depending on the type of allergy, you can also choose one type or another depending on the route of administration. It is always advisable to consult all these options with your family doctor or a specialist .
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References:
Randall et al. 2018. Antihistamines and allergy. Aust Prescr. doi: 10.18773/austprescr.2018.013
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