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17 Cards in this Set
- Front
- Back
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Histamine Receptors
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1. H1-Gq coupled- allergy and motion sickness
2. H2-Gs coupled- gastric acid release 3. H3-Gi/o coupled- controls NT release 4. H4-Gi/o coupled- mast cell chemotaxis |
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Histamine Receptor Distribution
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H1: **CNS**, bronchial smooth muscle, intestinal smooth muscle, endothelium
H2: Parietal cell, vascular smooth muscle |
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Vascular Physiological Effects of Histamine
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H1- increased permeability
H1, H2- vasodilation |
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Cardiac Physiological Effects of Histamine
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H1, H2- positive inotropism
H2- positive chronotropism H1- slowed AV conduction |
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Pulmonary Physiological Effects of Histamine
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H1- rapid bronchoconstriction, increased mucus viscosity
H2- slow bronchodilation, increased mucus secretion |
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GI Physiological Effects of Histamine
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H2- Increased acid production
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Neuronal Physiological Effects of Histamine
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H1, H2- cutaneous itching and pain
H3- presynaptic inhibition of histamine H3- regulates release of NE, DA, Ach, GABA |
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Pathological Effects of Histamine
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- Uticaria (hives)- localized (bee sting) or all over depending on allergy
- Anaphylactic shock- more serious condition; LOSS OF BLOOD VOLUME- decreased BP - Cardiac arrhythmia- from massive histamine release |
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Causes of Histamine Release
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1. Immune Releasers: food (grains, eggs, seafood); insect stings; venom; drugs (sulfonamide); foreign substances (non-human insulin)
2. Non Immune Releasers: Drugs (Vancomycin "Red Man Syndrome") |
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Triple Response of Lewis
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- Occurs in response to skin injury or histamine injection
1. Small red spot forms (1-2mm) within seconds due to vasodilation 2. Spot grows to 1-2cm due to reflexive vasodilation 3. Wheal forms due to endothelial permeability |
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Types of Antihistamine Drugs
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1. H1 Receptor Antagonists
2. H2 Receptor Antagonists 3. Mast cell stabilizers |
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H1 Receptor Antagonists
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- Prevent the interaction of histamine with H1 receptor
- 2 Generations: 1st generation has sedative effects - Mildly anticholinergic (anti-SLUDE) - Uses: 1. Allergy treatment 2. Motion sickness and nausea (1st gen. ONLY) 3. Sedation (1st gen. ONLY) 4. Supplemental anaphylaxis treatment (must be used with Epi.) |
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H1 Receptor Antagonists- FIRST GENERATION
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1. Chlorpheniramine
2. Cyclizine (mainly for motion sickness) 3. Dimenhydrenate (Dramamine)- mainly for motion sickness 4. Diphenhydramine (Benadryl) 5. Hydroxyzine 6. Meclizine (mainly for motion sickness) 7. Promethazine (for nausea) |
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H1 Receptor Antagonists- FIRST GENERATION: Drug Interactions and Side Effects
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Drug Interactions:
- potentiate anticholinergics (atropine) - must be avoided with MAO inhibitors (b/c exacerbate anticholinergic effects) - metabolized by CYP450 Side Effects: - sedation - dry mouth - upset stomach - OD- hallucinations, ataxia, convulsions, arrhythmia, coma - can enter breast milk and cross placenta |
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H1 Receptor Antagonists- SECOND GENERATION
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1. Acrivastine
2. Cetirizine (Zyrtec)- mild sedation 3. Desloratadine 4. Fexofenadine (Allegra) 5. Loratadine (Claritin) |
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H2 Receptor Antagonists
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- Used to reduce gastric acid production
- Used in treatment of gastric ulcers and GERD - Do NOT affect H1 receptors - Inhibits first pass metabolism of alcohol - Inhibits absorption of drugs favoring acidic envrionment (ketoconazole) - less effective than proton pump inhibitors - Side Effects: headache, dizziness, diarrhea 1. Cimetidine- inhibits CYP450 metabolism 2. Famotidine (Pepcid)- does not interact with CYP450 3. Nizatidine 4. Ranitidine (Zantac) |
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Mast Cell Stabilizers
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1. Cromolyn Sodium
2. Nedocromil - Prevent the release of histamine from mast cells - Use: treatment of asthma (prophylactic) and allergic rhinitis - Very safe drug b/c side effects only include: cough and bitter taste |
