What is Allergic Rhinitis?

Rhinitis is a combination of the words 'Rhino' and 'itis'. "Rhino," which means the nose and "itis," which means inflammation. So allergic rhinitis is inflammation of the nasal mucosa triggered by allergies mediated by immunoglobulin E (IgE). The interaction of allergens with IgE and receptor complex activates the release of inflammatory mediators, one of which is histamine, which causes allergic symptoms.

Which antihistamine is best for Allergic Rhinitis?

Some treatments to treat allergic rhinitis are avoiding allergen triggers, administration of antihistamines, corticosteroids, and even immunotherapy if the patient does not respond adequately to other procedures.

Pathophysiology of allergic rhinitis and the role of antihistamines

The pathophysiology of allergic rhinitis is preceded by a sensitization process by allergens that produce allergen-specific immunoglobulin E (IgE). When sensitized individuals are exposed to certain allergens, there is the release of inflammatory mediators such as histamine, leukotrienes, and prostaglandins, especially by mast cells and basophils.

Inflammatory response due to the release of mediators gives classic symptoms of allergic rhinitis in the form of nasal congestion, rhinorrhea, itchy nose, and sneezing. Other symptoms that can accompany are red and watery eyes, postnasal drip, and cough. In the further phase, the inflammatory mediator forms chronic inflammation of the nasal mucosa, making it more sensitive to allergen exposure, such as pollutants, pollen, and mites.

The antihistamine's role in the management of allergic rhinitis is a competitive antagonist of H1 histamine receptors on the cell surface. There are 4 types of histamine receptors, but H1 receptors most often mediate nasal symptoms. Histamine H1 receptors can be found in various cells in the respiratory tract, but there are also many at the end of nerve cells, smooth muscle, and glandular cells.

A. First-Generation Antihistamines

First-generation antihistamines (such as diphenhydramine and chlorpheniramine) have long been used in treating allergic rhinitis. However,  At present, the use of first-generation antihistamines in treating allergic rhinitis has been avoided because this group has side effects such as high sedation effect, anticholinergic effects (dry eyes and mouth), cardiovascular side effects, and short half-life of the drug. Their side effects appear because they are more fat-soluble and more easily cross the blood-brain barrier than the second generation.

B. Second-Generation Antihistamines

Second-generation antihistamines are preferred because they have a higher selective characteristic of histamine receptors and lower blood-brain barrier penetration. This minimizes the effects of sedatives and psychomotor disorders.

Second-generation antihistamines have high therapeutic effectiveness, fast onset, and long duration of action. Some second-generation antihistamines also show anti-inflammatory effects. Some examples of choices of second-generation antihistamines are fexofenadine, loratadine, and cetirizine.

1. Fexofenadine
Fexofenadine is a second-generation antihistamine that is very selective against H1 histamine receptors and does not penetrate the blood-brain barrier, so it does not cause sedation effects at high and low doses. Fexofenadine does not interact with muscarinic receptors, so it does not cause side effects on the cardiovascular system, such as decreases in heart rate and cardiac output.

A literature review states that fexofenadine is effective in managing allergic rhinitis and has a rapid onset of action compared to other second-generation antihistamines. One study showed that fexofenadine is more effective in overcoming symptoms of nasal congestion, rhinorrhea, nasal itching, and conjunctivitis compared to loratadine and cetirizine. Fexofenadine can be given at a dose of 120 mg/day as much as once given in adults. For children aged 6-11 years, fexofenadine can be given at a dose of 30 mg/day divided into 2 times administration.

Fexofenadine is generally well tolerated by patients, but some of the side effects that have been reported are headache, dizziness, and nausea.

2. Loratadine
Loratadine is another example of a second-generation antihistamine. This drug still has a sedative effect at high doses. Loratadine has a rapid onset of action (75-180 minutes) in relieving the symptoms of rhinitis. The dose of loratadine in adults is 10 mg/day, while the dose for children (≥2 years) is 5-10 mg/day.

3. Cetirizine

Cetirizine has a high binding ability with albumin and low brain uptake and cardiotoxicity compared to first-generation antihistamines. However, the effect of sedation is still reported on the use of cetirizine.

Unlike other drugs, cetirizine does not undergo metabolism in the liver, so there are fewer interactions with other drugs. In some studies, cetirizine also shows anti-inflammatory effects.

Like other second-generation antihistamines, cetirizine has a long duration of action (half-life ± 10.5 hours). Several studies comparing cetirizine 10 mg/day with placebo had shown that cetirizine provided a significant improvement in rhinitis symptoms.

The study by Meltzer et al. reported that cetirizine 10 mg had a faster onset of action and a higher mean reduction in symptoms of rhinitis than loratadine 10 mg or placebo. Cetirizine side effects that have been reported are dry mouth, diarrhea, and excessive fatigue, usually found in the use of larger doses.

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