What is the mechanism of action for antihistamines?

• A. They increase mucus production
• B. They block H1 receptors
• C. They act as anti-inflammatory agents
• D. They reduce fluid secretion from glands

Answer: (B)

Antihistamines are primarily used to alleviate the symptoms caused by allergic reactions and other conditions involving the immune response. Their mechanism of action is centered on the blocking of H1 receptors, which are a specific type of histamine receptor located throughout the body, including the nasal passages, skin, and central nervous system. By inhibiting these H1 receptors, antihistamines prevent histamine from exerting its effects, which include the dilation of blood vessels, increased permeability of blood vessel walls, and stimulation of mucus secretion.

This blockage leads to reduced symptoms of allergies, such as nasal congestion, sneezing, itching, and hives. It is important to note that antihistamines do not directly affect the production of mucus or fluids; rather, their primary function is to counteract the effects of histamine by preventing its binding to H1 receptors. This distinct mechanism is what makes antihistamines effective for treating allergic reactions and other symptoms associated with upper respiratory disorders.