Antihistamine.pptx

Antihistaminic Drugs

1. ANTIHISTAMINIC DRUGS NIDHI SHARMA

2. Histamine- Histamine  is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological function in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus.  Histamine  is involved in the inflammatory response and has a central role as a mediator of itching. Histamine  - a chemical found in some of the body's cells - causes many of the symptoms of allergies, such as a runny nose or sneezing. When a person is allergic to a particular substance, such as a food or dust, the immune system mistakenly believes that this usually harmless substance is actually harmful to the body.

3. . Once formed, histamine is either stored or rapidly inactivated by its primary  degradative enzymes ,  histamine-N-methyltransferase  or  diamine oxidase . In the central nervous system, histamine released into the  synapses  is primarily broken down by  histamine-N-methyltransferase , While in other tissues both enzymes may play a role. Several other enzymes, including  MAO-B  and  ALDH2 , further process the immediate metabolites of histamine for excretion or recycling. Histamine is derived from the decarboxylation of the amino acid histidine, a reaction catalyzed by the enzyme L-histidine decarboxylase. It is a hydrophilic vasoactive amine.

4. Bacteria also are capable of producing histamine using histidine decarboxylase enzymes unrelated to those found in animals. A non-infectious form of foodborne disease,  scombroid poisoning, is due to histamine production by bacteria in spoiled food, particularly fish. Fermented foods and beverages naturally contain small quantities of histamine due to a similar conversion performed by fermenting bacteria or yeasts. Sake contains histamine in the 20–40 mg/L range; wines contain it in the 2–10 mg/L range .

5. Antihistaminic drugs- Antihistamines  are drugs which treat allergic rhinitis and other allergies.  Antihistamines can give relief when a person has nasal congestion, sneezing, or hives because of pollen, dust mites, or animal allergy.  Antihistamines are usually for short-term treatment. Chronic allergies increase the risk of health problems which antihistamines might not treat, including asthma, sinusitis, and lower respiratory tract infection. The Two largest classes of antihistamines are- H 1 -antihistamines   H 2 - antihistamines . H 1 -Antihistamines- They act by binding to histamine H 1  receptors in mast cells, smooth muscle, and endothelium in the body as well as in the  tuberomammillary nucleus in the brain.

6. They are used to treat- A llergic reactions in the nose  (e.g., itching, runny nose, and sneezing). I nsomnia . M otion sickness or  vertigo  caused by problems with the  inner ear . H 2 - Antihistamies - They bind to histamine H 2  receptors in the upper gastrointestinal tract, primarily in the stomach. They are used to treat- Gastric acid conditions (e.g., peptic ulcers and acid reflux).

7. Group Generation Drug Uses Characteristics H1 antihistamines First Dimetindene Diphenhydramine Meclizine Doxylamine Promethazine   Clemastine Dimenhydrinate Brompheniramine Hydroxyzine Antiemetic  agent Sedative agent Anaphylactic shock Antiallergic agent Allergic rhinitis  and  conjunctivitis Contact dermatitis Hay fever ,  urticaria ,  angioedema , and  rhinorrhea Motion sickness Strong sedative action Anticholinergic side effects Second Loratadine  (desloratadine ) Cetirizine  ( levocetirizine  ) Azelastine Fexofenadine Antiallergic agent Adjuvant treatment in  anaphylactic shock Non-sedative/mildly sedative  H2 antihistamines Ranitidine Cimetidine Famotidine Reduce production of  stomach acid Usually used as a  second-line  treatment, or in combination with  PPIs Classification of Antihistaminic Drugs -

8. Mechanism of Action- Blocks action of histamine at receptor Competes with histamine for binding Displaces histamine from receptor