What are antiallergic medications?
Apr 14, 2022
Source: Cainiu Health
Dr. Gan Liqiang
Introduction
Antiallergic drugs, also known as antihistamines, are divided into two types: H1-receptor antagonists and H2-receptor antagonists. H1-receptor antagonists are primarily distributed in the skin, mucosa, blood vessels, and brain tissue, whereas H2-receptor antagonists are mainly found in the gastrointestinal mucosa. H1-receptor antagonists are further classified into first-generation and second-generation agents. Common first-generation antihistamines include chlorpheniramine, diphenhydramine, promethazine, ketotifen, and cyproheptadine.
Allergy refers to an exaggerated immune response triggered when an individual ingests, touches, or inhales a specific substance. Such substances that provoke this abnormal reaction are known as “allergens.” In allergic individuals, the immune system mistakenly identifies normally harmless substances as harmful. Allergic reactions—also termed hypersensitivity or变态 reactions—are abnormal or pathological immune responses that occur upon re-exposure to the same antigen.
What Are Antiallergic Medications?
Antiallergic drugs—commonly referred to as antihistamines—are classified into two main types: H1-receptor antagonists and H2-receptor antagonists. H1 receptors are predominantly located in the skin, mucous membranes, blood vessels, and brain tissue, whereas H2 receptors are mainly found in the gastrointestinal mucosa. H1-receptor antagonists are further subdivided into first-generation and second-generation agents.
First-generation antihistamines include chlorpheniramine, diphenhydramine, promethazine, ketotifen, and cyproheptadine. Their primary drawback is their ability to readily cross the blood–brain barrier, leading to common side effects such as fatigue, drowsiness, dizziness, and impaired concentration. Some also exhibit anticholinergic effects—including urinary retention. Consequently, these agents are contraindicated or require caution in individuals performing high-risk tasks (e.g., drivers and workers engaged in high-altitude or precision work), as well as in patients with glaucoma, cataracts, or benign prostatic hyperplasia.
Second-generation antihistamines—including fexofenadine, loratadine, cetirizine, and mizolastine—are rapidly absorbed after oral administration. Their principal advantage lies in their limited ability to cross the blood–brain barrier, resulting in minimal central nervous system effects. Typically administered once daily, they are particularly suitable for drivers, high-altitude workers, and patients requiring long-term therapy.We hope this information is helpful to you.
