Antihistamine

Definition

An antihistamine is a type of medication that blocks histamine receptors to alleviate symptoms of allergic reactions. They are commonly used to treat conditions such as hay fever, urticaria, and other hypersensitivities.

5 Must Know Facts For Your Next Test

1. Antihistamines can be classified into first-generation and second-generation types, with the former often causing sedation.
2. These medications work by blocking H1 receptors, which prevents histamine from binding and causing allergic symptoms.
3. Common side effects of antihistamines include drowsiness, dry mouth, and dizziness.
4. Antihistamines are effective in treating immediate hypersensitivity reactions but have limited effect on delayed-type hypersensitivity reactions.
5. Over-the-counter antihistamines like diphenhydramine are widely available, but newer prescription-only options like cetirizine offer fewer side effects.

Review Questions

• What is the primary mechanism by which antihistamines alleviate allergic symptoms?
• Differentiate between first-generation and second-generation antihistamines in terms of their side effects.
• Why are antihistamines ineffective against delayed-type hypersensitivity reactions?

Related terms

Histamine:

A compound released by mast cells during an allergic reaction that causes various symptoms like itching and swelling.

H1 Receptor: A receptor that binds histamine and mediates allergic responses such as vasodilation and bronchoconstriction.

Immediate Hypersensitivity: A rapid allergic reaction occurring within minutes of exposure to an allergen, primarily mediated by IgE antibodies.