H2 receptor antagonists. by Baqir Naqvi.pptx

H2 receptor antagonists (Antihistamine Drugs)

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2. TOPIC H2 RECEPTOR ANTAGONISTS PRESENTED BY: M. BAQIR RAZA NAQVI M. Phil Pharmacology PRESENTED TO : DR. M. KHALID TIPU Department of Pharmacy Quaid.i.Azam University, I slamabad 2

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4. Histamine Receptors Introduction Histamine receptors  are 7-transmembrane receptors which mediate cellular responses to the  biogenic amine  histamine. Histamine may be released as a transmitter in neuronal preparations or as a mediator of an inflammatory response by mast cells. All histamine receptors are associated with a  G-protein-coupled receptor , a very common target for modern 4

5. TYPES OF HISTAMINE RECEPTORS 5

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8. LOCATION OF HISTAMINE RECEPTORS 8

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10. H2 RECEPTORS ANTAGONISTS 10

11. Overview of H2 Receptor Blockers H2 blockers are a group of medicines that reduce the amount of acid produced by the cells in the lining of the stomach . The selective histamine type 2 receptor antagonists (H2 blockers) are used in treatment of acid-peptic disease , duodenal and gastric ulcers, gastroesophageal reflux disease and common heartburn. The H2 receptor blockers act by binding to histamine type 2 receptors on the basolateral ( antiluminal ) surface of gastric parietal cells, interfering with pathways of gastric acid production and secretion. 11

12. CLASSIFICATION OF H2R ANTAGONISTS 12

13. Cimetidine Cimetidine contains imidazole ring. Molecular formula: C10-H16-N6-S PHYSICAL PROPERTIES: Solubility : sparingly soluble in water Color: white/off white crystalline powder Odor: Unpleasant ordor Melting point: 139-144 °C 13

14. PHARMACODYNAMICS CIMETIDINE inhibit the gastric acid secretions by selectively binding to the H2 receptors in periatal cells of Stomach. It also inhibit some of the isoezymes of hepatic cytochrome P450 enzyme system . 14

15. MECHANISM OF ACTION 15

16. ENZYMES INHIBITION 16

17. PHARMACOKINETICS Absorption: oral/I.V 60% Metabolism: Metabolised in liver, also inhibit microsomal enzymes Excretion : Urine; 48-75% Feces; 2-3% Bioavailability: 60-70% Protien binding: 15-20% Half life : 2-3 hours 17

18. CLINICAL INDICATIONS 18

19. DOSAGE 19

20. ADVERSE DRUG REACTIONS Common side effects of cimetidine include: headache Dizziness, sleepiness Diarrhea, nausea, vomiting Cimetidine inhibits binding of dihydrotestosterone to androgen receptors, inhibits metabolism of estradiol, and increases serum prolactin levels. When used long-term or in high doses, it may cause gynaecomastia 20

21. Ranitidine Ranitidine is a commonly used drug, classified as a histamine H2-receptor antagonist, and belongs to the same drug class as cimetidine and famotidine . Ranitidine is a non imidazole derivative. Chemical Formula : C 13 H 22 N 4 O 3 S This drug helps to prevent and treat gastric-acid associated conditions, including ulcers, because of its ability to decrease gastric acid secretion . 21

22. MECHANISM OF ACTION After a meal, the hormone gastrin, produced by cells in the lining of the stomach, stimulates the release of histamine, which then binds to H2 receptors, leading to the secretion of gastric acid. Ranitidine reduces secretion of gastric acid by reversible binding to (H2 ) receptors, which are found on gastric parietal cells. This process leads to the inhibition of histamine binding to this receptor, causing the reduction of gastric acid secretion. The relief of gastric-acid related symptoms can occur as soon as 60 minutes after administration of a single dose, and the effects can last from 4-10 hours, providing fast and effective symptomatic relief. 22

23. PHARMACOKINETICS Absorption: absorbed with peak concentrations reached within 1-3 hours after administration Metabolism : Metabolized in liver, also inhibit microsomal enzymes Excretion : Urine; 48-75% Feces; 2-3% Bioavailability: 60-70% Protien binding: approximately 15% Half life : 2-3 hours 23

24. CLINICAL INDICATIONS R anitidine oral tablet is used to treat several conditions, including: intestinal and stomach ulcers gastroesophageal reflux disease (GERD) erosive esophagitis conditions where your stomach makes too much acid, such as  Zollinger -Ellison syndrome Ranitidine may be used as part of a combination therapy. This means you may need to take it with other medications. 24

25. ADVERSE EFFECTS Generalized drug effects as that of cimetidine of example headache constipation diarrhea nausea and vomiting stomach discomfort or pain Comparatively, ranitidine and famotidine are more safe than cimetidine. 25

26. CLINICAL COMPARISON OF H2R-BLOCKERS 26

27. REFRENCES: katzung - basic and clinical pharmacology, 12th edition Goodman & Gilman's The Pharmacological Basis of Therapeutics, 12th Edition www.ncbi.net H2-Receptor Antagonists MITCHELL L. SCHUBERT Virginia Commonwealth University's Medical College of Virginia and McGuire Veterans Affairs Medical Center, Richmond 27

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