Pharmacology and Histamine Actions

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Questions and Answers

Which receptor is primarily involved in the initiation of a migraine attack?

  • 5-HT2C receptor (correct)
  • 5-HT4 receptor
  • 5-HT3 receptor
  • 5-HT1A receptor

Which of the following drugs is classified as a 5-HT3 antagonist?

  • Dimenhydrinate
  • Ondansetron (correct)
  • Mosapride
  • Meclizine

What is the primary therapeutic use of selective serotonin reuptake inhibitors (SSRIs)?

  • Prevent chemotherapy-induced nausea
  • Elevate mood and treat depression (correct)
  • Control vestibular disturbances
  • Treat motion sickness

Which medication is most effective for the prevention of symptoms of motion sickness?

<p>Meclizine (C)</p> Signup and view all the answers

What does activation of 5-HT3 receptors primarily mediate?

<p>Stimulation of nausea and vomiting (A)</p> Signup and view all the answers

Which first-generation antihistamine is commonly used off-label for insomnia?

<p>Diphenhydramine (A)</p> Signup and view all the answers

Which serotonin receptor mediates platelet aggregation?

<p>5-HT2A receptor (D)</p> Signup and view all the answers

What is a common side effect of medications that are antihistamines?

<p>Sedation (B)</p> Signup and view all the answers

Which of the following is not a function of serotonin?

<p>Preventing insomnia (C)</p> Signup and view all the answers

What is the primary action of 5-HT4 receptors?

<p>Increasing GIT propulsive activity (C)</p> Signup and view all the answers

What is the role of adrenaline in relation to histamine?

<p>It acts as a physiological antagonist. (B)</p> Signup and view all the answers

Which of the following statements is true regarding H1 and H2 blockers?

<p>They compete with histamine at its receptors. (B)</p> Signup and view all the answers

What potential side effect is associated with 1st generation antihistamines?

<p>Sedation due to crossing the blood-brain barrier. (D)</p> Signup and view all the answers

Which generation of antihistamines is less likely to cause sedation?

<p>2nd generation (A)</p> Signup and view all the answers

What action does promethazine exhibit aside from antihistamine effects?

<p>It has central antimuscarinic properties. (B)</p> Signup and view all the answers

Which symptom is NOT typically treated with antihistamines?

<p>Anxiety (B)</p> Signup and view all the answers

What is one common use for H1 blockers?

<p>Treatment of allergic conjunctivitis. (D)</p> Signup and view all the answers

How do corticosteroids function in relation to histamine?

<p>They suppress the effects of antigen-antibody reactions. (C)</p> Signup and view all the answers

What differentiates 2nd generation antihistamines from 1st generation?

<p>Minimal crossing of the blood-brain barrier. (C)</p> Signup and view all the answers

Which condition is specifically treated with adrenaline during an allergic reaction?

<p>Anaphylaxis (B)</p> Signup and view all the answers

What is the main role of COX-1 in the body?

<p>Regulates normal physiological functions. (A)</p> Signup and view all the answers

Which prostaglandin analogue is used to induce labor at term?

<p>Dinoprostone (PGE2) (D)</p> Signup and view all the answers

What is a common pharmacological use of Alprostadil (PGE1)?

<p>Treatment of erectile dysfunction. (C)</p> Signup and view all the answers

How do NSAIDs function in relation to thromboxane A2?

<p>They inhibit it, increasing the risk of bleeding. (A)</p> Signup and view all the answers

What adverse effect is commonly associated with NSAIDs?

<p>Gastric irritation leading to ulceration. (D)</p> Signup and view all the answers

Which drug is specifically used as an antiplatelet agent?

<p>Aspirin (in low dose) (B)</p> Signup and view all the answers

What type of eicosanoid is involved primarily in inflammatory responses?

<p>Leukotrienes (C)</p> Signup and view all the answers

Which of the following is NOT an indication for the use of Misoprostol (PGE1)?

<p>Treatment of erectile dysfunction. (C)</p> Signup and view all the answers

Which of the following correctly describes COX-2?

<p>Inducible enzyme associated with inflammatory conditions. (B)</p> Signup and view all the answers

What is the role of leukotrienes in the body?

<p>They mediate inflammatory and allergic responses. (B)</p> Signup and view all the answers

What is the primary reason selective COX-2 inhibitors have fewer gastrointestinal adverse reactions compared to non-selective NSAIDs?

<p>They preferentially inhibit COX-2. (A)</p> Signup and view all the answers

What condition is specifically associated with Aspirin due to its effect on thromboxane?

<p>Bleeding tendencies (C)</p> Signup and view all the answers

Which of the following is a characteristic of Paracetamol as compared to other analgesics?

<p>It is mainly effective as a central analgesic. (C)</p> Signup and view all the answers

Which adverse reaction is associated with the use of selective COX-2 inhibitors?

<p>Increased arterial thrombosis risk (A)</p> Signup and view all the answers

What is a significant risk in using Selective COX-2 Inhibitors for patients with cardiac conditions?

<p>Increased incidence of myocardial infarction (A)</p> Signup and view all the answers

What serious condition is characterized by acute liver injury with cerebral edema?

<p>Reye syndrome (D)</p> Signup and view all the answers

How does Paracetamol's action on prostaglandins differ from that of other NSAIDs?

<p>It does not inhibit blood clotting. (B)</p> Signup and view all the answers

What is the therapeutic use of Paracetamol?

<p>It is the safest antipyretic for use in children. (A)</p> Signup and view all the answers

What can hypersensitivity reactions from certain medications manifest as?

<p>Urticaria and bronchoconstriction (B)</p> Signup and view all the answers

Why should caution be exercised when administering selective COX-2 inhibitors to cardiac patients?

<p>They may increase chances of arterial thrombosis. (C)</p> Signup and view all the answers

Flashcards

Autocrine signaling

A type of chemical signaling where a cell releases a substance that then binds to receptors on the same cell, leading to a response.

Paracrine signaling

A type of chemical signaling where a cell releases a substance that acts on nearby cells, causing a response.

Histamine

A chemical messenger involved in various physiological processes, including inflammation, allergic reactions, and gastric acid secretion.

Mast cells and basophils

Immune cells that release histamine and other inflammatory mediators, contributing to allergic reactions and inflammation.

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Inflammation

A state of tissue response to injury or infection, characterized by redness, swelling, heat, and pain.

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Antihistamines

Drugs that block the action of histamine at its receptors, reducing allergic and inflammatory responses.

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First-Generation Antihistamines

First-generation antihistamines that cross the blood-brain barrier, leading to sedation and other side effects.

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Second-Generation Antihistamines

Second-generation antihistamines that do not cross the blood-brain barrier, minimizing sedation and other central nervous system effects.

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H1 receptor antagonists

A class of drugs that block the action of histamine at H1 receptors, reducing allergic and inflammatory responses.

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Adrenaline (epinephrine)

The most effective treatment for anaphylaxis, a severe allergic reaction.

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Anti-Motion Sickness Drugs

A group of drugs that prevent or reduce nausea caused by motion sickness. They work by blocking the effects of serotonin and acetylcholine in the brain and body.

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Diphenhydramine

A type of antihistamine used to treat motion sickness and allergies. It has sedative effects.

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Dimenhydrinate

A type of antihistamine used specifically for motion sickness.

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Cyclizine

A type of antihistamine that is used to treat motion sickness. It has anticholinergic effects.

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Meclizine

A type of antihistamine used for motion sickness and vertigo. It has fewer side effects compared to other antihistamines

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Serotonin (5-HT)

A neurotransmitter that plays a critical role in mood, sleep, appetite, and other functions.

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5-HT1A Receptor

A receptor involved in regulating mood and inhibiting serotonin release. It is located in the brain.

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5-HT2A Receptor

A receptor involved in platelet aggregation, vascular, urinary, and gastrointestinal smooth muscle contraction. It also plays a role in learning and memory.

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5-HT2c Receptor

A receptor involved in migraine headache initiation. It is located in the brain.

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5-HT3 Receptor

A receptor involved in mediating nausea and vomiting. They are present in the brain's vomiting center and the gastrointestinal tract.

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Prostaglandins

A type of eicosanoid that is synthesized from arachidonic acid (AA) through the cyclooxygenase (COX) pathway. They are involved in a wide range of physiological processes, including inflammation, pain, fever, blood clotting, and gastric protection.

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Leukotrienes

A type of eicosanoid that is synthesized from arachidonic acid (AA) through the lipoxygenase pathway, also known as the 5-lipoxygenase pathway. They are primarily involved in the inflammatory response, particularly in the airways and immune system.

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Arachidonic Acid (AA)

A precursor molecule for both prostaglandins and leukotrienes. It is a polyunsaturated fatty acid found in cell membranes.

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Cyclooxygenase (COX)

An enzyme that plays a key role in the synthesis of prostaglandins from arachidonic acid. It is also known as COX-1. It is constitutively expressed in most tissues and responsible for the production of prostaglandins that regulate various physiological processes.

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COX-2

A type of COX enzyme that is mainly induced in inflammatory cells and is responsible for the production of prostaglandins involved in inflammation, pain, and fever.

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COX-1

A type of COX enzyme that is constitutively expressed in many tissues and is involved in maintaining normal physiological functions.

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Non-Steroidal Anti-inflammatory Drugs (NSAIDs)

A group of drugs that inhibit the activity of cyclooxygenase (COX) enzymes, thereby reducing the production of prostaglandins., These drugs are used to treat pain, fever, and inflammation.

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Thromboxane A2 (TXA2)

A specific type of prostaglandin that is involved in the aggregation of platelets - the process of blood clotting. They are responsible for forming blood clots, a crucial step in hemostasis.

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Prostacyclin (PGI2)

A type of prostaglandin that is produced by the endothelial cells lining blood vessels, and it has the opposite effect of TXA2: it is responsible for inhibiting platelet aggregation - it prevents blood clotting.

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Aspirin (Acetyl Salicylic Acid)

A specific type of NSAID that is known to irreversibly inhibit COX-1 and COX-2 enzymes, acting as an anti-inflammatory agent, as well as to prevent thrombosis. It is used in low doses to prevent cardiovascular events like heart attack and stroke.

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Selective COX-2 Inhibitors

A group of drugs that primarily target COX-2, an enzyme involved in inflammation, pain, and fever. They are designed to have less impact on COX-1, which is crucial for platelet function and stomach protection.

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Bleeding Tendencies with NSAID

A common side effect of some medications, especially NSAIDs, involving an increased risk of bleeding due to inhibition of thromboxane, a substance involved in blood clotting.

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Reye Syndrome

A serious condition characterized by acute liver damage and brain swelling, potentially associated with the use of aspirin in children with viral infections.

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Paracetamol (Acetaminophen)

Paracetamol (Acetaminophen) is a medication primarily used to relieve pain and reduce fever. Instead of inhibiting COX in the periphery, it mainly acts centrally, making it safer for the stomach and without the antiplatelet effect seen with NSAIDs.

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NSAIDs & Renal/Cardiovascular Effects

A major adverse effect of NSAIDs, especially non-selective ones, involving the impairment of renal function and potential for increased blood pressure.

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Hypersensitivity Reactions with NSAIDs

NSAIDs, particularly non-selective ones, can cause various allergic reactions like asthma attacks, skin rashes, and swelling. This is due to their impact on prostaglandins involved in regulating inflammation and airway function.

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Thromboxane

A specific type of prostaglandin that plays a crucial role in blood clotting and aggregation of platelets.

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Study Notes

Autocrine-Paracrine System

  • Autocrine action involves a cell releasing a signal that acts on the same cell.
  • Paracrine action involves a cell releasing a signal that acts on nearby cells.
  • Endocrine action involves a cell releasing a signal that acts on distant cells via the circulatory system.

Pharmacology of Histamine

  • Histamine is a chemical mediator released during allergic reactions and inflammation.
  • Allergic reactions can be triggered by various factors such as bee stings, medications, pollen, plants, animal products, dust etc.
  • Histamine causes inflammation by activating immune cells like neutrophils.
  • Histamine also plays a role in gastric acid secretion.

Biosynthesis and Storage of Histamine

  • Mast cells and basophils are responsible for the storage and release of histamine.
  • Enterochromaffin cells also store and release histamine.
  • Histamine release is triggered when an allergen is encountered.

Histamine Release

  • IgE receptor activation leads to histamine release from mast cells.
  • Allergens bind to IgE, triggering degranulation.
  • Degranulation releases histamine, kinins, leukotrienes, prostaglandins, and platelet-activating factor.

Histamine Release (Additional Factors)

  • Tissue injury releases histamine along with other mediators like ATP, bradykinin, and prostaglandins in inflammation.
  • Venoms are also a trigger for histamine release.
  • Morphine can trigger or modulate histamine release.

Modulation of Histamine

  • Adrenaline is the physiological antagonist of histamine.
  • H1 and H2 blockers compete with histamine at its receptors.
  • Corticosteroids suppress the effects of antigen-antibody reactions and demonstrate anti-allergic and anti-inflammatory actions.

Histamine Receptor Blockers

  • H1-blockers are antihistamines, which block histamine receptors.
  • Diphenhydramine is a first-generation, central nervous system (CNS) penetrating, antihistamine, for treating allergies and anti-motion sickness.

H1 Receptor Blockers (Generations)

  • First-generation H1-blockers are effective and inexpensive but can cause drowsiness (sedation).
  • Second-generation H1-blockers have less sedation and are effective too.

Pharmacologic Actions of Histamine

  • Histamine binding to receptors in the body leads to pain and itching.
  • The respiratory system is also affected by histamine, causing bronchoconstriction.

Other Pharmacologic Actions of Histamine

  • Histamine affects the body's sedation, anti-motion sickness, and anti-emetic systems in addition to its impact on the immune system.

Therapeutic Uses of Histamine

  • Histamine-blocking agents are used to treat allergic rhinitis, allergic conjunctivitis, and urticaria.
  • Treatment of anaphylaxis may require adrenaline.

Therapeutic Uses (Motion Sickness and Nausea)

  • Diphenhydramine, cyclizine, dimenhydrinate, and meclizine are effective medications to prevent nausea and motion sickness symptoms.

Therapeutic Uses (Sedation/Insomnia)

  • Diphenhydramine, while not specifically targeted at insomnia, can be used off-label for its sedative properties.

Therapeutic Uses (Vertigo and Meniere's Disease)

  • Antihistamines are sometimes used in the treatment of vertigo and Meniere's disease.

Therapeutic Uses (Common Cold)

  • Antihistamines and anticholinergic agents, can potentially help treat common cold symptoms.

Adverse Effects of Histamine Blockers

  • Side effects of histamine blockers include sedation, anticholinergic manifestations, gastrointestinal (GIT) issues (nausea, constipation, diarrhea), and possible teratogenic effects.

Pharmacology of Serotonin

  • Serotonin, also known as 5-hydroxytryptamine (5-HT), is an endogenous amine.
  • 5-HT is derived from the amino acid tryptophan but it has no clinical drug use currently.

Serotonin Receptors & Actions

  • 5-HT1A receptors in the brain are associated with mood control.
  • 5-HT2A receptors are involved in platelet aggregation and other bodily functions.
  • 5-HT2C receptors are involved in migraine initiation.
  • 5-HT3 receptors are connected to the vomiting center.
  • 5-HT4 receptors regulate gastrointestinal motility.

Serotonin Agonists

  • Agonists like buspirone and triptans act on serotonin receptors specifically.

Chemotherapy-Induced Emesis

  • The chemoreceptor trigger zone (CTZ) triggers nausea and vomiting.

Selective Serotonin Reuptake Inhibitors (SSRIs)

  • Fluoxetine and other SSRIs increase serotonin levels by inhibiting reuptake.
  • SSRIs are antidepressants.

Pharmacology of Eicosanoids

  • Eicosanoids are cell signaling molecules, including prostaglandins and leukotrienes, affecting many bodily functions.

Eicosanoid Synthesis

  • Membrane lipids play a key role in eicosanoid synthesis.
  • Lipoxygenase and cyclooxygenase are key enzymes in this synthesis process.

Prostaglandin Types

  • COX-1 produces prostaglandins involved in normal physiological functions.
  • COX-2 produces prostaglandins which are mainly involved in inflammation.

Pharmacological Uses of Prostaglandins

  • Prostaglandins have various obstetric uses, including abortion and postpartum hemorrhage induction.
  • They are also utilized in the treatment of peptic ulcers, open-angle glaucoma, and erectile dysfunction.

Pharmacological Antagonism of Prostaglandins

  • Several medications act as prostaglandin antagonists.

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)

  • NSAIDs like aspirin, ibuprofen, and diclofenac are commonly used to relieve pain, reduce fever, and lower inflammation.
  • Aspirin differs; it's an irreversible enzyme inhibitor.

Therapeutic Uses of NSAIDs

  • NSAIDs are used to treat various inflammatory disorders, pain conditions, fever, common colds and thrombotic events.

Adverse Reactions to NSAIDs

  • Adverse reactions include gastric irritation, high blood pressure, renal problems, bleeding, and hypersensitivity.

Selective COX-2 Inhibitors (Celecoxib)

  • Celecoxib is a selective COX-2 inhibitor and differs from traditional NSAIDS.

Paracetamol (Acetaminophen)

  • Paracetamol is an analgesic and antipyretic, working centrally to reduce fever and provide pain relief.
  • It's not an anti-inflammatory agent; it does not affect prostaglandin production in most tissues.

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