Antihistamines are medicines indicated for the treatment of allergic reactions, such as hives, runny nose, allergic rhinitis or conjunctivitis, for example, as they act by reducing the symptoms of itching, swelling, redness or runny nose. These remedies act by preventing the action of histamine, a substance that causes allergies, which is why they are also called antiallergics.
The type of antihistamine that can be used depends on the condition being treated, and the doctor may recommend the use of first, second or third generation antihistamines, which have differences in the form of action and side effects, such as drowsiness. , for example.
Therefore, it is important to consult a doctor to diagnose the condition to be treated and thus be advised on the best antihistamine, dose of medication and duration of treatment. Furthermore, these remedies should not be used by children, pregnant or breastfeeding women without medical advice.
The main types of antihistamines include:
1. Classic or first generation antihistamines
Classic or first-generation antihistamines were the first to be introduced on the market and act by blocking the release of histamine in the brain and spinal cord. Therefore, they cause more side effects such as severe drowsiness, sedation, fatigue, changes in cognitive functions and memory. Furthermore, they are also more difficult to eliminate from the body and, for these reasons, should be avoided.
The main first generation antihistamines are:
- Promethazinetablet or dermatological cream (Phenergan or Profergan);
- Dexchlorpheniraminetablet, syrup, drops or dermatological cream (Polaramine or Histamin);
- Hydroxyzinetablet, syrup or oral solution (Hixizine or Pruri-gran);
- Clemastinatablet or dermatological cream (Emistin);
- Diphenhydramineinjectable ampoule (Diphenidrin).
These antihistamines are generally indicated for the treatment of allergic reactions, allergic dermatitis, urticaria, allergic rhinitis, vertigo, nausea caused by travel, or prevention of postoperative vomiting, for example, and should be used with medical advice.
Additionally, some first-generation antihistamines, such as diphenhydramine, can be used in hospitals to treat severe allergic or anaphylactic reactions, applied directly to a vein or muscle by a nurse, under medical supervision.
2. Non-classical or second-generation antihistamines
Non-classical or second-generation antihistamines are medications that act by preventing the action of histamine in peripheral tissues, such as blood vessels, the gastrointestinal tract and the respiratory system. These antihistamines penetrate the central nervous system in smaller quantities and are eliminated more quickly, therefore presenting fewer side effects.
The main second generation antihistamines are:
- Loratadinetablet or syrup (Claritin, Histadin or Loratamed);
- Cetirizinetablet, capsule or oral solution (Zyrtec or Reactine);
- Bilastinatablets or oral solution (Alektos);
- Ebastinatablet or syrup (Ebastel);
- Epinastinatablets or eye drops (Talerc or Relestat).
These antihistamines are generally indicated for allergic rhinitis, urticaria, allergic rhinoconjunctivitis, helping to relieve symptoms such as itchy skin, eyes or nose, feeling of a runny or blocked nose, sneezing, red eyes or coughing.
Before starting treatment with second generation antihistamines, you should consult your doctor so that the most appropriate treatment can be recommended according to the symptoms presented. Learn how to recognize allergy symptoms.
3. Third generation antihistamines
Third-generation antihistamines are medicines produced through the modification of second-generation antihistamine molecules, presenting the same action and effectiveness, but with smaller doses and fewer side effects.
The main third generation antihistamines are:
- Levocetirizinatablets or drops (Zyxem, Zina or Rizi);
- Desloratadinatablet or syrup (Desalex, Leg or Esalerg);
- Fexofenadinatablet or syrup (Allegra, Fexx or Allexofedrin).
These remedies are indicated for the treatment of seasonal allergic rhinitis, chronic urticaria, skin allergies, runny nose, allergic conjunctivitis or hay fever, for example, and should be used for the duration of treatment advised by the doctor.
Which antihistamines can be used during pregnancy
During the entire pregnancy, the use of medications, including antihistamines, should be avoided as much as possible, especially in the first trimester of pregnancy, as this is the phase in which the embryo’s cells rapidly multiply and form the main organs, and the use of medicines or other substances can affect the baby’s development.
However, if necessary, the pregnant woman can take antihistamines, but only if indicated by the obstetrician. The antihistamines that are considered safest in pregnancy, and which are in category B, are chlorpheniramine, loratadine and diphenhydramine.
When not to use
Antihistamines can be used by anyone, however, there are some cases that require medical advice, such as:
- Pregnancy and breastfeeding;
- Children;
- Glaucoma;
- High pressure;
- Kidney or liver diseases;
- Benign prostate hypertrophy.
Furthermore, some of these medications may interact with some anticoagulants and central nervous system depressant medications, such as anxiolytics or anti-depressants, and it is advisable to consult your doctor before using them.
