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Histamine and antihistamin

This document discusses histamine and antihistamine drugs. It begins by introducing histamine as a biogenic amine involved in inflammatory and hypersensitivity reactions. Histamine is synthesized from the amino acid histidine and stored in mast cells. It is involved in processes like gastric acid secretion and allergic responses. Antihistamines work by blocking the action of histamine at receptors. First generation antihistamines are more sedating while second generation ones have less side effects. Common antihistamines and their uses in conditions like allergies and vertigo are described. The document provides an overview of histamine function and the mechanisms of antihistamine drugs.

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Dr.Rakshitha Pharma PG HIMS,Hassan Histamine and antihistamine drugs
Histamine and antihistamine drugs Contents: • Introduction • Synthesis, storage, distribution of Histamine • Role of Histamine • Anti histamine • Its therapeutic uses • Adverse effects • Summary
Introduction Autacoids • Biological agents • act locally (e.g.within inflammatory pockets) at the site of synthesis and release. • k/a “local hormones”
Autacoids • Amine : Histamine Serotonin • Lipid derived: Prostaglandins Leukotrienes • Peptide : Plasma kinins, Angiotensin
Histamine • Histos: Tissue N N NH2 H 1 2 3 45 Histamine
Histamine • Biogenic amine present in -animal and plant tissues -venoms and stinging secretions • One of the mediators involved in inflammatory & hypersensitivity reactions.
Synthesis, storage & metabolism of histamine • Synthesized by decarboxylation of amino acid histidine • Histamine is present in storage granules of mast cells & also found in skin, lungs, liver, gastric mucosa etc.
Histamine Distribution: • Histamine - storage granules of mast cells. Tissues rich in histamine-skin, gastric and intestinal mucosa, lungs, liver and placenta. • Nonmast cell histamine occurs in brain, epidermis, gastric mucosa.
Histamine: Storage and Release Immunologic Release: immunological stimulus. ↓ • In mast cells, if sensitized by surface IgE antibodies, degranulate when exposed specific antigen. • Degranulation is involved in the immediate (type I) allergic reaction.
Histamine: Storage and Release
MoA of Histamine Receptors Histamine H1 Receptors H2 Receptors H3 Receptors (presynaptic auto receptors) ↑ Ca2+ Smooth muscle contraction Increased capillary permeability Vasodilation Sensory nerve endings pain & itching ↑ cAMP ↑ Gastric acid secretion Blood vessels: vasodilation Increased capillary permeability ↓ histamine release ↓secretion Vasodilation ↓ cAMP
Histamine PATHOPHYSIOLOGICAL ROLES 1. Gastric secretion Histamine - ↑ secretion of HCl in the stomach • It is released – feeding, vagal stimulation, cholinergic drugs and gastrin
Histamine
Histamine PATHOPHYSIOLOGICAL ROLES 2. Allergic phenomenon 3. As transmitter -initiates the sensation of itch and pain at sensory nerve endings.
Histamine PATHOPHYSIOLOGICAL ROLES 4. Inflammation -Histamine is a mediator of vasodilatation 5. Tissue growth and repair.
Histamine PHARMACOLOGICAL EFFECTS Exocrine Glands • Gastric glands • Salivary glands • Sweat glands • Pancreas ↑ Secretion • Bronchial glands • Lacrimal glands
Histamine PHARMACOLOGICAL EFFECTS Arterioles, Capillaries & Venules • Vasodilation • Increased permeability, (edema) • Systemic hypotension
Histamine PHARMACOLOGICAL EFFECTS Vascular Smooth Muscles • Bronchial tree • Gastrointestinal tract ↑ Contraction • Uterus
Anti-Histamines General Mechanism of Action of Antihistamines • Blocks action of histamine at receptor • Competes with histamine for binding • Displaces histamine from receptor • Most beneficial when given early
Anti-Histamines H1 ANTAGONISTS PHARMACOLOGICAL ACTIONS 1. Antagonism of histamine block - bronchoconstriction, -contraction of intestinal & smooth muscle and triple response—wheal, flare and Redness.
Anti-Histamine H1 ANTAGONISTS PHARMACOLOGICALACTIONS 2. Antiallergic action -immediate hypersensitivity (type I reactions)are suppressed 3. CNS- variable degree of CNS depression. 4. Anticholinergic action- antagonize muscarinic actions of Ach 5. Local anaesthetic - pheniramine, promethazine, diphenhydramine
Classification of Anti -Histamine Drug DOSE ROUTE I. HIGHLY SEDATIVE Diphenhydramine 25–50 mg Capsule , Syrup Promethazine 25–50 mg oral,, i.m. (1 mg/kg) tab., elixer II. MODERATELY SEDATIVE Pheniramine 20–50 mg oral, Tab, syr, Injection Cyproheptadine 4 mg oral Tab , syrup Cinnarizine 25–50 mg Tab, III. MILD SEDATIVE Chlorpheniramine 2-4 mg Oral,I.M Clemastine 1-2 mg Oral, syrup
Classification of Anti -Histamine DRUG DOSAGE PREPARATIONS Fexofenadine 120–180 mg oral TAB Loratadine 10 mg oral Tab,Suspension Cetirizine 10 mg oral Tab,syrup Levocetirizine 5-10 mg oral Tab,syrup Azelastine 4 mg oral Nasal spray Mizolastine 10 mg oral Tab Ebastine 10 mg oral Tab
Anti-Histamines SECOND GENERATION ANTIHISTAMINICS • Absence of CNS depressant property. • Higher H1 selectivitiy: no anticholinergic side effects. • Also inhibit late phase allergic reaction by acting on leukotrienes or by antiplatelet activating factor effect
Anti-Histamines 2nd GENERATION ANTIHISTAMINICS Fexofenadine: active metabolite of Terfenadine. Terfenadine withdrawn ↓ PVT(Torsades de pointes) + CYP3A4 inhibitors(Erythromycin, Clarithromycin, Ketoconazole, Itraconazole, etc.). Uses: Allergic rhinitis ; Urticaria and other skin allergies • Free of arrhythmogenic potential,
Anti-Histamines 2nd GENERATION ANTIHISTAMINICS Loratadine: • Another long-acting selective peripheral H1 antagonist • lacks CNS depressant effects and is fast acting. • Uses- urticaria and atopic dermatitis Desloratadine - active metabolite of loratadine effective at half the dose.
Anti-Histamines • 2nd GENERATION ANTIHISTAMINICS Cetirizine - metabolite of Hydroxyzine • Affinity for peripheral H1 receptors; • Penetrates brain poorly, but mild sedation • Inhibits release of histamine and of cytotoxic mediators from platelets as well as eosinophil chemotaxis during the secondary phase of the allergic response Levocetirizine - active R(–) enantiomer of cetirizine.
Anti-Histamines USES 1. Allergic disorders. 2. Other conditions- insect bite and ivy poisoning. -Abnormal dermographism is suppressed. -blood/saline infusion induced rigor 3. Pruritides -antipruritic action 4. Common cold
Anti-HistaminesUSES 5. VERTIGO 1. Labyrinthine suppressants (a) Antihistaminics (with anticholinergic action)—Cinnarizine, Dimenhydrinate, Diphenhydramine, Promethazine. (b) Anticholinergics— Atropine, Hyoscine. (c) Antiemetic phenothiazines— Prochlorperazine. 2. Vasodilators —Betahistine , Nicotinic acid. 3. Diuretics —Acetazolamide, Thiazides, Furosemide. 4. Anxiolytics, antidepressants—Diazepam, Amitriptyline. 5. Corticosteroids. Parenteral Prochlorperazine is the most effective drug for controlling violent vertigo and vomiting
Anti-Histamines USES 7. Preanaesthetic medication- Promethazine 8. Cough - Chlorpheniramine, Diphenhydramine and Promethazine 9. Parkinsonism- Promethazine 10. Acute muscle dystonia- Promethazine, Diphenhydramine or Hydroxyzine.
Anti-Histamines Adverse effect • Sedation, • Diminished alertness and concentration, • Light headedness, • Motor incoordination, • Fatigue and tendency to fall asleep • Dryness of mouth, • Alteration of bowel movement, • Urinary hesitancy and blurring of vision
Anti-Histamines H2 receptor antagonists 1. Cimetidine (tagamet) associated with most side effects 2. Rantidine (zantac) 3. Famotidine (pepcid) 4. Nizatidine (axid)
Summary
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