Antihistamines

Definition

Antihistamines are Medications that block the action of Histamine, a chemical released by the body’s immune system during an Allergic reaction. They are commonly used to treat symptoms associated with allergies, such as itching, sneezing, runny nose, and hives.

History

The use of antihistamines dates back to the early 20th century, when they were first discovered in small quantities in certain plants, including honeybee venom and the venom of certain animals. In the 1920s and 1930s, antihistamines began to be developed and marketed as Medications for treating allergic reactions.

Mechanism of Action

Antihistamines work by binding to Histamine receptors in the body, which blocks the action of Histamine and prevents it from stimulating immune cells. This leads to a reduction in the release of chemical mediators, such as Histamine, Serotonin, and other compounds that contribute to allergic symptoms.

Types of Antihistamines

There are several types of antihistamines, including:

  • First-generation antihistamines: These include Diphenhydramine (Benadryl) and Loratadine (Claritin). They were the first type of Antihistamine to be developed and have been widely used for decades.
  • Second-generation antihistamines: These include Cetirizine (Zyrtec) and Fexofenadine (Allegra). They are more potent than first-generation antihistamines and tend to cause fewer side effects.
  • Third-generation antihistamines: These include levocetirizine (Xyzal) and Desloratadine (Clonacot). They have a longer duration of action and tend to be less likely to cause sedation or drowsiness than second-generation antihistamines.

Uses

Antihistamines are commonly used to treat the following conditions:

  • Allergic reactions: Antihistamines are often prescribed for the treatment of allergic reactions, such as hives, itching, and swelling.
  • Asthma: Anticholinergics, a type of Antihistamine, are sometimes used in combination with Corticosteroids to treat Asthma symptoms.
  • Hay fever: Antihistamines are commonly used to treat Hay fever (allergic rhinitis) symptoms.

Side Effects

Common side effects of antihistamines include:

  • Drowsiness: Many antihistamines can cause drowsiness or sedation, especially when taken in higher doses.
  • Dry mouth: Antihistamines can cause dryness and dehydration due to their Anticholinergic properties.
  • Headaches: Some people may experience headaches or migraines when taking antihistamines.
  • Constipation: Antihistamines can slow down bowel movements, leading to constipation.

Interactions

Antihistamines can interact with other Medications in several ways:

  • Corticosteroids: Taking an Antihistamine with a corticosteroid (such as prednisone) may increase the risk of side effects.
  • Blood thinners: Antihistamines may increase the risk of bleeding when taken with blood thinners (such as warfarin).
  • ** Sedatives and antidepressants**: Taking an Antihistamine with other Sedatives or antidepressants may increase the risk of side effects.

Precautions

Antihistamines are generally considered safe to use, but there are some precautions to be aware of:

  • Pregnancy and breastfeeding: Antihistamines should be used cautiously during pregnancy and breastfeeding due to their potential effects on fetal development and infant sleep patterns.
  • Allergies in children: Children with allergies may require careful monitoring when taking antihistamines, as they can exacerbate symptoms.

References

  • “Antihistamines”. MedlinePlus. Retrieved 2022-02-20.
  • “Antihistamines: How They Work and Side Effects”. Mayo Clinic. Retrieved 2022-02-20.
  • “Antihistamines: Types, Uses, and Interactions”. RxList. Retrieved 2022-02-20.

Glossary

  • Anticholinergic: A type of Antihistamine that blocks the action of acetylcholine, a neurotransmitter involved in various bodily functions, such as digestion, respiration, and heart rate.
  • Allergic reaction: An overreaction to an allergen, which can cause symptoms like itching, sneezing, runny nose, and hives.