Pharmacology: Autacoids and Antihistaminics
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Questions and Answers

Ergot alkaloids are derivatives of ______.

Lysergic acid

Which of the following are adverse effects of Ergotamine? (Select all that apply)

  • Cold extremities (correct)
  • Nausea and vomiting
  • Hypertension (correct)
  • Gangrene (correct)

    • Ergometrine has no CNS distribution. (True/False)

    True

    What is the primary use of Methylergometrine?

    <p>Treatment of postpartum hemorrhage</p> Signup and view all the answers

    What is the main function of histamine in the body?

    <p>Inflammation, immediate allergic reaction, neurotransmitter, neuromodulator</p> Signup and view all the answers

    Which receptors are involved in the actions of histamine?

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

    Histamine agonists are used in the treatment of allergic rhinorrhea.

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

    Histamine antagonists that inhibit degranulation of mast cells are known as ____________.

    <p>histamine release inhibitors</p> Signup and view all the answers

    Match the following serotonin receptors with their effects:

    <p>5-HT1A and 5-HT1B = CNS actions related to mood, behavior, sleep, and anxiety 5-HT2 = Vasoconstriction, platelet aggregation, and contraction in various systems 5-HT3 = Regulates emesis, pain perception, and the chemoreceptor reflex 5-HT4 = Enhances gastrointestinal motility and has a prokinetic effect</p> Signup and view all the answers

    Study Notes

    Autacoids

    Definition and Classification

    • Autacoids: local hormones with heterogenous structures and diverse pharmacological actions
    • Classified into:
      • Amines: histamine, serotonin
      • Ergot alkaloids
      • Vasoactive peptides: angiotensin II, vasopressin, endothelin, natriuretic peptides, substance P, neurotensin
      • Fatty acid derivatives: eicosanoids, platelet-activating factor (PAF)

    Histamine

    Chemistry and Functions

    • Amine formed from amino acid histidine
    • Functions:
      • Inflammation
      • Immediate allergic reaction
      • Neurotransmitter
      • Neuromodulator

    Release of Histamine

    • Release mechanisms:
      • Immunologic reaction (allergy)
      • Mechanical injury
      • Inflammation
      • Chemical stimulation (drugs, toxins)

    Histamine Receptors

    • Four types of receptors:
      • H1: endothelium, smooth muscles, brain, skin
      • H2: gastric mucosa, cardiac muscle, brain
      • H3: presynaptic neurons
      • H4: leukocytes, bone marrow

    Actions of Histamine

    • Vasoactive effects:
      • H1: vasodilation, hypotension, increased capillary permeability
      • H2: positive chronotropic and inotropic effects
      • H3: decreased transmitter release
      • H4: chemotactic effect

    Antihistamines

    • Types:
      • Physiologic antagonists (adrenaline)
      • Histamine release inhibitors (mast cell stabilizers)
      • Adrenal steroids (inhibit antigen-antibody reaction)
      • Pharmacologic competitive antagonists (H1, H2, H3, H4 receptors)

    Antihistaminics (H1 Receptor Blockers)

    First Generation

    • Examples: diphenhydramine, chlorpheniramine, promethazine
    • Characteristics:
      • Lipid soluble
      • Metabolized by liver microsomal enzymes
      • Renal excretion
      • Short duration (4-6 hours)
      • Sedation

    Second Generation

    • Examples: fexofenadine, loratidine, cetirizine
    • Characteristics:
      • Less lipid soluble
      • Metabolized by hepatic microsomal enzymes (CYP3A4)
      • Longer duration (12-24 hours)
      • No sedation

    Pharmacodynamics

    • Reversible competitive blockade of H1 receptors
    • Effects:
      • Relief of allergic symptoms
      • Sedation
      • Antiemetic and antinausea
      • Antiparkinsonian

    Therapeutic Uses

    • Allergic reactions
    • Nausea and vomiting of pregnancy
    • Motion sickness prophylaxis
    • Sedative-hypnotic

    Adverse Effects

    • Sedation
    • Dizziness
    • CNS depression
    • Excitation
    • Dry mouth
    • Constipation
    • Urine retention
    • Teratogenic

    Serotonin (5-HT)

    Chemistry and Functions

    • Formed from amino acid L-tryptophan
    • Functions:
      • Neurotransmitter
      • Neuromodulator
      • Potent stimulant for pain and itching
      • Gastrointestinal tract contraction

    Receptors

    • Five types of receptors:
      • 5-HT1A and 5-HT1B: CNS
      • 5-HT2: CNS, platelets, peripheral blood vessels
      • 5-HT3: CNS, peripheral nerves
      • 5-HT4: GIT (enteric nervous system)

    Agonists and Antagonists

    • Agonists:
      • Buspirone (5-HT1A)
      • Triptans (5-HT1D)
      • Itopride (5-HT4)
    • Antagonists:
      • Cyproheptadine (5-HT2, H1, muscarinic)
      • Methysergide (5-HT2)

    Adverse Effects and Contraindications

    • Agonists:
      • Tingling, dizziness, neck pain, chest pain
      • Contraindicated in angina, hypertension, peripheral vascular disease, pregnancy
    • Antagonists:
      • Drowsiness, dry mouth, retroperitoneal and pleural fibrosis

    Ergot Alkaloids

    Chemistry and Classification

    • Derivatives of lysergic acid
    • Classification:
      • Natural alkaloids
      • Semisynthetic derivatives

    Pharmacokinetics

    • Poor oral absorption
    • Caffeine increases absorption
    • Delayed onset and prolonged duration

    Pharmacodynamics

    • Partial agonist at alpha-1 adrenoceptor and 5-HT2 receptors
    • Stimulates oxytocic effect, cardiac inhibitory center, and chemoreceptor trigger zone

    Uses

    • Acute attack of migraine
    • Postpartum hemorrhage
    • Subinvolution of uterus
    • Variant (Prinzmetal) angina

    Adverse Effects and Contraindications

    • Cold extremities, tingling, numbness, gangrene, hypertension, nausea, and vomiting
    • Contraindicated in coronary heart disease, peripheral vascular disease, hypertension, pregnancy, liver disease, and renal disease

    Migraine Headache

    Definition and Clinical Picture

    • Paroxysmal unilateral headache
    • Preceded by aura
    • Characterized by unilateral throbbing headache, nausea, and pallor

    Prophylaxis

    • Avoidance of precipitating factors
    • Serotonin antagonists
    • Propranolol
    • Amitriptyline
    • Flunarizine

    Treatment

    • Mild attack: analgesics, antiemetics
    • Severe attack: ergotamine or dihydroergotamine with caffeine, sumatriptan

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    Description

    This quiz covers autacoids, antihistaminics, and serotonin agonists and antagonists, including their therapeutic uses and adverse effects.

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