Antihistamine

Definition

Antihistamines are a class of medications that work by blocking the action of histamine, a chemical released by the body during an allergic reaction. They are commonly used to alleviate symptoms associated with allergies, such as sneezing, itching, and inflammation.

5 Must Know Facts For Your Next Test

1. Antihistamines work by blocking the histamine H1 receptor, which prevents histamine from binding and triggering the allergic response.
2. Antihistamines can be classified as first-generation (sedating) or second-generation (non-sedating) based on their ability to cross the blood-brain barrier.
3. Antihistamines are commonly used to treat the symptoms of allergic rhinitis, hives, and other allergic conditions, as well as motion sickness and nausea.
4. Antihistamines may interact with certain medications, such as antidepressants, and can cause side effects like drowsiness, dry mouth, and constipation.
5. In the context of shock drugs (22.3 Shock Drugs), antihistamines can be used to treat anaphylactic shock, a severe allergic reaction that can be life-threatening.

Review Questions

• Explain how antihistamines work to alleviate allergy symptoms.
  • Antihistamines work by blocking the action of histamine, a chemical released by the body during an allergic reaction. Histamine is responsible for many of the symptoms associated with allergies, such as sneezing, itching, and inflammation. By binding to and blocking the histamine H1 receptor, antihistamines prevent histamine from triggering these allergic responses, effectively reducing the severity of allergy symptoms.
• Describe the differences between first-generation and second-generation antihistamines and how they relate to the treatment of urinary analgesics (35.3 Urinary Analgesics).
  • First-generation antihistamines, such as diphenhydramine, are known to cause sedation and other central nervous system effects due to their ability to cross the blood-brain barrier. In contrast, second-generation antihistamines, like cetirizine and loratadine, are designed to have a reduced ability to enter the brain, resulting in fewer sedative side effects. This distinction is important in the context of urinary analgesics, as the sedative effects of first-generation antihistamines may interfere with the pain-relieving properties of certain urinary analgesics, while the non-sedating second-generation antihistamines may be a more suitable option for managing allergy symptoms in patients requiring urinary analgesics.
• Analyze the role of antihistamines in the management of anaphylactic shock, a type of shock drug (22.3 Shock Drugs), and explain how their mechanism of action contributes to their effectiveness in this context.
  • Antihistamines play a crucial role in the management of anaphylactic shock, a severe and potentially life-threatening allergic reaction. During anaphylaxis, the body releases large amounts of histamine, which can lead to widespread inflammation, constriction of the airways, and a dangerous drop in blood pressure. By blocking the action of histamine at the H1 receptor, antihistamines help to counteract these effects and alleviate the symptoms of anaphylactic shock. This mechanism of action, combined with the ability of antihistamines to reduce swelling and inflammation, makes them an essential component of the treatment protocol for anaphylaxis, alongside other interventions such as epinephrine and corticosteroids.

Related terms

Histamine:

A chemical released by the body during an allergic or inflammatory response, which can cause symptoms like sneezing, itching, and swelling.

Allergic Reaction: An overreaction of the immune system to a normally harmless substance, leading to the release of histamine and other inflammatory mediators.

Decongestant: A type of medication that works by constricting blood vessels and reducing swelling in the nasal passages, often used in combination with antihistamines to relieve allergy symptoms.