Slides G Bone and Anti-inflammatory.pptx - ANTI-INFLAMMATORY ANTIALLERGIC DRUGS ANTIHISTAMINES Histamine Distribution Present in practically all tissues

Slides G Bone and Anti-inflammatory.pptx -...

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ANTI-INFLAMMATORY, ANTIALLERGIC DRUGS
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ANTIHISTAMINES
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Histamine Distribution Present in practically all tissues Especially high in skin, lungs, and GI tract Low content in plasma
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Histamine Receptors H 1 receptor Vasodilation Increased capillary permeability Bronchoconstriction CNS effects Other
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H 1 Receptors Vasodilation Skin of the face and upper body Extensive: can cause hypotension Increased capillary permeability Edema Bronchoconstriction Not the cause of asthma attack CNS effects Role in cognition, memory, and sleep-waking cycles Other Itching, pain, secretion of mucus
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H 2 Receptors Secretion of gastric acid Act directly on parietal cells to promote acid release Dominant role in acid release
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Histamine Antagonists/Antihistamines Act primarily on H 1 and H 2 receptors Used primarily for two pathologic states 1. Allergic disorders 2. Peptic ulcer disease
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Allergic Responses Mediated by histamine and other compounds Prostaglandins Leukotrienes Tryptase
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Mild Allergic Responses Caused largely by histamine acting at H 1 receptors Rhinitis, itching, localized edema Hay fever, mild transfusion reaction, acute urticaria Usually responsive to antihistamine therapy
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Two Types of Antihistamines H 1 antagonists Produce selective blockade of H 1 receptors Used for treatment of mild allergic disorders H 2 antagonists Produce selective blockade of H 2 receptors Used for treatment of gastric and duodenal ulcers Not used for treatment of allergies
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H 1 Antagonists H 1 antagonists are divided into two major groups: First-generation H 1 antagonists (highly sedating) Second-generation H 1 antagonists Mechanism of action Block the actions of histamine at H 1 receptors Do not block H 2 receptors Some bind to muscarinic receptors
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H 1 Antagonists Pharmacologic effects Peripheral effects Reduce localized flushing Reduce itching and pain Effects on the CNS Therapeutic dose: CNS depression Second-generation negligible CNS depression Overdose CNS stimulation Convulsions Very young children especially sensitive to CNS stimulation
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H 1 Antagonists Therapeutic uses Mild allergy Severe allergy Adjunct only, benefits may be limited Motion sickness Promethazine, dimenhydrinate Insomnia Common cold May decrease rhinorrhea through anticholinergic properties, not H 1 blockade
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H 1 Antagonists Adverse effects Sedation Less with second and third generation Nonsedative CNS effects Dizziness, fatigue, coordination problems, confusion Gastrointestinal effects Can cause nausea, vomiting, loss of appetite, constipation (give with food) Anticholinergic effects Weak atropine-like effects
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H 1 Antagonists Adverse effects Severe respiratory depression Severe local tissue injury Cardiac dysrhythmias Rare
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