Pharmacology of Histamine and Antihistamines
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Questions and Answers

Which of the following is NOT a characteristic of autacoids?

  • They are formed by the tissues on which they act
  • They are produced by specific endocrine glands (correct)
  • They are produced by many tissues
  • They have differing structures and pharmacological activities

    • What is the primary function of histamine in the brain?

  • Regulating body temperature
  • Neurotransmission in parts of the brain (correct)
  • Mediating allergic and inflammatory reactions
  • Gastric acid secretion

    • Which of the following is NOT a stimulus that triggers the release of histamine?

  • Bacterial toxins
  • Vitamin C (correct)
  • Trauma
  • Cold

    • What is the enzyme responsible for the synthesis of histamine?

    <p>Histidine decarboxylase</p> Signup and view all the answers

    Which of the following receptors is NOT involved in the pharmacological action of histamine?

    <p>H5</p> Signup and view all the answers

    What is the function of amine oxidase enzymes in relation to histamine?

    <p>Inactivating histamine</p> Signup and view all the answers

    Which of the following tissues has a high concentration of histamine?

    <p>Mast cells or basophils</p> Signup and view all the answers

    What is the process by which histamine is stored in mast cells?

    <p>Histamine is stored in granules as an inactive complex composed of histamine and heparin</p> Signup and view all the answers

    Which of the following is a clinical application of histamine?

    <p>There are no clinical applications of histamine</p> Signup and view all the answers

    What is the precursor molecule for the synthesis of histamine?

    <p>Histidine</p> Signup and view all the answers

    What is the primary function of H1 receptors in the bronchial system?

    <p>Constriction of bronchial smooth muscle</p> Signup and view all the answers

    Which of the following is NOT a characteristic of first-generation H1 antihistamines?

    <p>Specific for H1 receptor</p> Signup and view all the answers

    What is the primary mechanism by which H1 antihistamines prevent nausea and vomiting in motion sickness?

    <p>Blockade of central H1 and M1 muscarinic receptors</p> Signup and view all the answers

    Which of the following H1 antihistamines is commonly used for the treatment of vertigo associated with vestibular disorders?

    <p>Meclizine</p> Signup and view all the answers

    What is the average plasma half-life of most H1-receptor blockers?

    <p>4-6 hours</p> Signup and view all the answers

    Which of the following is a common adverse effect of H1 antihistamines?

    <p>Dry mouth, urinary retention, and blurred vision</p> Signup and view all the answers

    What is the primary mechanism by which H1 antihistamines reduce allergic inflammation?

    <p>Blockade of H1 receptors</p> Signup and view all the answers

    Which of the following is a therapeutic use of H1 antihistamines?

    <p>Treatment of allergic conjunctivitis</p> Signup and view all the answers

    What is the primary difference between first-generation and second-generation H1 antihistamines?

    <p>Specificity for H1 receptor</p> Signup and view all the answers

    Which of the following is a potential drug interaction with H1 antihistamines?

    <p>CNS depressants, including alcohol</p> Signup and view all the answers

    What is the primary function of histamine in the GIT?

    <p>Stimulates the release of gastric acid</p> Signup and view all the answers

    What is the effect of histamine on neurotransmission in the brain?

    <p>Enhances neurotransmission</p> Signup and view all the answers

    What is the role of heparin in the storage of histamine?

    <p>Forms an inactive complex with histamine</p> Signup and view all the answers

    Which of the following is a stimulus for the release of histamine?

    <p>Cold temperatures</p> Signup and view all the answers

    What is the role of amine oxidase enzymes in relation to histamine?

    <p>Inactivate histamine</p> Signup and view all the answers

    Which of the following receptors is involved in the pharmacological action of histamine?

    <p>H1</p> Signup and view all the answers

    What is the precursor molecule for the synthesis of histamine?

    <p>Histidine</p> Signup and view all the answers

    What is the primary mechanism of action of H1 antihistamines?

    <p>Block the action of histamine on H1 receptors</p> Signup and view all the answers

    What is a therapeutic use of H1 antihistamines?

    <p>Treatment of allergic reactions</p> Signup and view all the answers

    What is the primary difference between first-generation and second-generation H1 antihistamines?

    <p>Adverse effect profile</p> Signup and view all the answers

    What is the primary effect of histamine on bronchial smooth muscle?

    <p>Constriction</p> Signup and view all the answers

    Which of the following is a characteristic of second-generation H1 antihistamines?

    <p>They are specific for H1 receptors</p> Signup and view all the answers

    What is the primary mechanism by which H1 antihistamines reduce allergic inflammation?

    <p>By blocking H1 receptors, preventing histamine-mediated inflammation</p> Signup and view all the answers

    Which of the following is a therapeutic use of H1 antihistamines?

    <p>Treatment of allergic rhinitis</p> Signup and view all the answers

    What is the effect of histamine on intestinal smooth muscle?

    <p>Contraction</p> Signup and view all the answers

    Which of the following is a common adverse effect of H1 antihistamines?

    <p>Sedation</p> Signup and view all the answers

    What is the primary mechanism by which H1 antihistamines prevent nausea and vomiting in motion sickness?

    <p>Blocking muscarinic receptors in the vestibular system</p> Signup and view all the answers

    Which of the following is a characteristic of first-generation H1 antihistamines?

    <p>They penetrate the CNS and cause sedation</p> Signup and view all the answers

    What is the effect of H1 antihistamines on appetite?

    <p>Increased appetite</p> Signup and view all the answers

    Which of the following is a characteristic of H2 receptors?

    <p>Mediates gastric acid secretion</p> Signup and view all the answers

    Study Notes

    Histamine

    • Histamine is a chemical messenger generated in mast cells, mediating allergic and inflammatory reactions, gastric acid secretion, and neurotransmission in parts of the brain.
    • Found in all tissues, but in high concentrations in skin, lung, GIT, and mast cells or basophils.
    • Synthesized from histidine through histidine decarboxylase.
    • Released in response to stimuli such as cold, bacterial toxins, bee sting venom, trauma, drugs like morphine, and allergies.
    • Acts on H1, H2, H3, and H4 receptors, mediating various pharmacological effects.

    Pharmacological Effects of Histamine

    • H1 Receptor:
      • Exocrine secretion: increases nasal and bronchial discharge.
      • Bronchial smooth muscle: constriction causes symptoms of asthma.
      • Intestinal smooth muscle: constriction causes intestinal cramps and diarrhea.
      • Sensory nerve ending: causes itching and pain.
      • Cardiovascular system: lowers blood pressure by reducing peripheral resistance.
      • Skin: dilation and increased permeability of capillaries result in leakage of proteins and fluids into the tissues.
    • H2 Receptor:
      • Mediates gastric acid secretion.

    Antihistamines (H1 Receptor Blockers)

    • Divided into first- and second-generation drugs.
    • First Generation:
      • Examples: diphenhydramine, dimenhydramine, chlorpheniramine, and promethazine.
      • Effective and inexpensive, but can cause sedation and interact with other receptors.
    • Second Generation:
      • Examples: loratadine, desloratadine, acrivastine, cetirizine, and fexofenadine.
      • Specific for H1 receptor, do not penetrate CNS, and cause less sedation.

    Actions of Antihistamine (H1 Blocker)

    • Blocks H1 receptors, reducing allergic inflammation, itching, sneezing, and rhinorrhea.
    • Can also block cholinergic, adrenergic, or serotonin receptors, causing various effects.

    Therapeutic Uses of Antihistamines

    • Allergic and inflammatory conditions, such as allergic rhinitis, urticaria, and allergic conjunctivitis.
    • Motion sickness and nausea.
    • Vertigo.
    • Insomnia.
    • Parkinson's disease.

    Pharmacokinetics of Antihistamines

    • Well-absorbed after oral administration, with maximum serum levels at 1-2 hours.
    • Average plasma half-life is 4-6 hours, except for meclizine and second-generation agents, which is 12-24 hours.

    Adverse Effects of Antihistamines

    • CNS: sedation, tinnitus, vertigo, fatigue, dizziness, uncoordination, and tremors.
    • Dry mouth, urinary retention, and blurred vision.
    • Hypotension and tachycardia.
    • Increased appetite.

    Drug Interactions and Overdoses

    • Can interact with CNS depressants, MAOIs, and cholinesterase inhibitors.
    • Overdose symptoms include CNS effects, hallucinations, excitement, ataxia, convulsions, coma, and cardiorespiratory collapse.

    Histamine H2-Receptor Blockers

    • Block the actions of histamine at H2 receptors, used as inhibitors of gastric acid secretion.
    • Used in the treatment of ulcers and heartburn.
    • Examples: cimetidine, ranitidine, famotidine, and nizatidine.

    Histamine

    • Histamine is a chemical messenger generated in mast cells, mediating allergic and inflammatory reactions, gastric acid secretion, and neurotransmission in parts of the brain.
    • Found in all tissues, but in high concentrations in skin, lung, GIT, and mast cells or basophils.
    • Synthesized from histidine through histidine decarboxylase.
    • Released in response to stimuli such as cold, bacterial toxins, bee sting venom, trauma, drugs like morphine, and allergies.
    • Acts on H1, H2, H3, and H4 receptors, mediating various pharmacological effects.

    Pharmacological Effects of Histamine

    • H1 Receptor:
      • Exocrine secretion: increases nasal and bronchial discharge.
      • Bronchial smooth muscle: constriction causes symptoms of asthma.
      • Intestinal smooth muscle: constriction causes intestinal cramps and diarrhea.
      • Sensory nerve ending: causes itching and pain.
      • Cardiovascular system: lowers blood pressure by reducing peripheral resistance.
      • Skin: dilation and increased permeability of capillaries result in leakage of proteins and fluids into the tissues.
    • H2 Receptor:
      • Mediates gastric acid secretion.

    Antihistamines (H1 Receptor Blockers)

    • Divided into first- and second-generation drugs.
    • First Generation:
      • Examples: diphenhydramine, dimenhydramine, chlorpheniramine, and promethazine.
      • Effective and inexpensive, but can cause sedation and interact with other receptors.
    • Second Generation:
      • Examples: loratadine, desloratadine, acrivastine, cetirizine, and fexofenadine.
      • Specific for H1 receptor, do not penetrate CNS, and cause less sedation.

    Actions of Antihistamine (H1 Blocker)

    • Blocks H1 receptors, reducing allergic inflammation, itching, sneezing, and rhinorrhea.
    • Can also block cholinergic, adrenergic, or serotonin receptors, causing various effects.

    Therapeutic Uses of Antihistamines

    • Allergic and inflammatory conditions, such as allergic rhinitis, urticaria, and allergic conjunctivitis.
    • Motion sickness and nausea.
    • Vertigo.
    • Insomnia.
    • Parkinson's disease.

    Pharmacokinetics of Antihistamines

    • Well-absorbed after oral administration, with maximum serum levels at 1-2 hours.
    • Average plasma half-life is 4-6 hours, except for meclizine and second-generation agents, which is 12-24 hours.

    Adverse Effects of Antihistamines

    • CNS: sedation, tinnitus, vertigo, fatigue, dizziness, uncoordination, and tremors.
    • Dry mouth, urinary retention, and blurred vision.
    • Hypotension and tachycardia.
    • Increased appetite.

    Drug Interactions and Overdoses

    • Can interact with CNS depressants, MAOIs, and cholinesterase inhibitors.
    • Overdose symptoms include CNS effects, hallucinations, excitement, ataxia, convulsions, coma, and cardiorespiratory collapse.

    Histamine H2-Receptor Blockers

    • Block the actions of histamine at H2 receptors, used as inhibitors of gastric acid secretion.
    • Used in the treatment of ulcers and heartburn.
    • Examples: cimetidine, ranitidine, famotidine, and nizatidine.

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    Description

    This quiz covers the actions of histamine in the body, classification of antihistamine drugs, and their effects, therapeutic uses, and side effects. It also explores the differences between 1st and 2nd generations of antihistamine drugs.

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