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?

Meclizine Signup and view all the answers

What does activation of 5-HT3 receptors primarily mediate?

Stimulation of nausea and vomiting Signup and view all the answers

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

Diphenhydramine Signup and view all the answers

Which serotonin receptor mediates platelet aggregation?

5-HT2A receptor Signup and view all the answers

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

Sedation Signup and view all the answers

Which of the following is not a function of serotonin?

Preventing insomnia Signup and view all the answers

What is the primary action of 5-HT4 receptors?

Increasing GIT propulsive activity Signup and view all the answers

What is the role of adrenaline in relation to histamine?

It acts as a physiological antagonist. Signup and view all the answers

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

They compete with histamine at its receptors. Signup and view all the answers

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

Sedation due to crossing the blood-brain barrier. Signup and view all the answers

Which generation of antihistamines is less likely to cause sedation?

2nd generation Signup and view all the answers

What action does promethazine exhibit aside from antihistamine effects?

It has central antimuscarinic properties. Signup and view all the answers

Which symptom is NOT typically treated with antihistamines?

Anxiety Signup and view all the answers

What is one common use for H1 blockers?

Treatment of allergic conjunctivitis. Signup and view all the answers

How do corticosteroids function in relation to histamine?

They suppress the effects of antigen-antibody reactions. Signup and view all the answers

What differentiates 2nd generation antihistamines from 1st generation?

Minimal crossing of the blood-brain barrier. Signup and view all the answers

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

Anaphylaxis Signup and view all the answers

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

Regulates normal physiological functions. Signup and view all the answers

Which prostaglandin analogue is used to induce labor at term?

Dinoprostone (PGE2) Signup and view all the answers

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

Treatment of erectile dysfunction. Signup and view all the answers

How do NSAIDs function in relation to thromboxane A2?

They inhibit it, increasing the risk of bleeding. Signup and view all the answers

What adverse effect is commonly associated with NSAIDs?

Gastric irritation leading to ulceration. Signup and view all the answers

Which drug is specifically used as an antiplatelet agent?

Aspirin (in low dose) Signup and view all the answers

What type of eicosanoid is involved primarily in inflammatory responses?

Leukotrienes Signup and view all the answers

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

Treatment of erectile dysfunction. Signup and view all the answers

Which of the following correctly describes COX-2?

Inducible enzyme associated with inflammatory conditions. Signup and view all the answers

What is the role of leukotrienes in the body?

They mediate inflammatory and allergic responses. 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?

They preferentially inhibit COX-2. Signup and view all the answers

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

Bleeding tendencies Signup and view all the answers

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

It is mainly effective as a central analgesic. Signup and view all the answers

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

Increased arterial thrombosis risk Signup and view all the answers

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

Increased incidence of myocardial infarction Signup and view all the answers

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

Reye syndrome Signup and view all the answers

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

It does not inhibit blood clotting. Signup and view all the answers

What is the therapeutic use of Paracetamol?

It is the safest antipyretic for use in children. Signup and view all the answers

What can hypersensitivity reactions from certain medications manifest as?

Urticaria and bronchoconstriction Signup and view all the answers

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

They may increase chances of arterial thrombosis. Signup and view all the answers

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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Description

Explore the pharmacological effects and biological mechanisms of histamine in the body. This quiz covers autocrine and paracrine signaling, allergic reactions, and histamine storage and release processes. Test your knowledge on this crucial mediator involved in immune responses and gastric functions.