Histamine Action and H1 Antagonists
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Questions and Answers

What is the primary effect of activating H2 receptors in the stomach?

  • Marked increase in gastric acid secretion (correct)
  • Decreased gastric secretion
  • Increased production of mucus
  • Stimulation of digestive enzyme production

    • In addition to stimulating gastric acid secretion, what else is enhanced by H2 receptor activation?

  • Pepsin secretion (correct)
  • Trypsin production
  • Bile salt production
  • Lipase activity

    • Which component is chiefly responsible for the acid secretion in the stomach that is influenced by H2 receptors?

  • Acetic acid
  • Hydrochloric acid (HCl) (correct)
  • Gastrin
  • Bicarbonate

    • Where are H2 receptors predominantly found in the human body?

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

    What would most likely occur if there is an inhibition of H2 receptor activation in the stomach?

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

    What is a primary therapeutic use of H1 antagonists in clinical practice?

    <p>Relief from allergic symptoms</p> Signup and view all the answers

    Which of the following is a common adverse effect associated with the use of H1 antagonists?

    <p>Cognitive impairment or sedation</p> Signup and view all the answers

    Which of these pharmacological actions is NOT associated with histamines?

    <p>Bronchodilation in respiratory passages</p> Signup and view all the answers

    How do H1 antagonists primarily function at the cellular level?

    <p>By blocking H1 receptors</p> Signup and view all the answers

    Which of the following is a significant risk when using first-generation H1 antagonists?

    <p>Anticholinergic effects such as dry mouth</p> Signup and view all the answers

    What is one of the primary effects that antagonists of histamine can inhibit?

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

    Which additional activity is associated with Cyproheptadine aside from histamine antagonism?

    <p>5-HT2 receptor blocking</p> Signup and view all the answers

    Which of the following is NOT an effect blocked by histamine antagonists?

    <p>Increased bronchial smooth muscle contraction</p> Signup and view all the answers

    What type of receptor blocking activity is primarily associated with Cyproheptadine?

    <p>5-HT2 receptor</p> Signup and view all the answers

    Which effect of histamines can be counteracted by their antagonists besides bronchoconstriction?

    <p>Increased vascular permeability</p> Signup and view all the answers

    What is one possible reason that H1 antagonists may have additional effects beyond their primary function?

    <p>They reflect binding to other receptor types.</p> Signup and view all the answers

    Which type of receptors may be influenced by H1 antagonists aside from H1 receptors?

    <p>Cholinergic receptors</p> Signup and view all the answers

    The binding of H1 blockers to which of the following receptor types does NOT contribute to their side effects?

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

    What can be inferred about H1 antagonists from their effects on various receptors?

    <p>They can result in a diverse range of physiological responses.</p> Signup and view all the answers

    Which of the following receptors is least likely to be affected by H1 antagonists based on their typical pharmacological profile?

    <p>Histamine H2 receptors</p> Signup and view all the answers

    What condition is NOT indicated for the medication mentioned?

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

    Which of the following characteristics is attributed to the medication's effect on the skin?

    <p>High and longer lasting concentration</p> Signup and view all the answers

    In which of the following conditions is the medication used as an adjuvant?

    <p>Seasonal asthma</p> Signup and view all the answers

    Which of the following is a primary use of the medication, based on its strong efficacy?

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

    What type of allergies does the medication specifically target?

    <p>Upper respiratory allergies</p> Signup and view all the answers

    Autacoids are primarily classified as hormones in the human body.

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

    The understanding of autacoids includes their roles in allergic reactions and inflammation.

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

    Serotonin, a type of autacoid, is primarily involved in the regulation of sleep and appetite.

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

    Autacoids are exclusively produced in the endocrine glands.

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

    Histamines are a type of autacoid that plays a key role in the immune response.

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

    Activation of H2 receptors leads to a decrease in gastric secretion of acid.

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

    H2 receptors are mainly found in the stomach and are responsible for pepsin production.

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

    The primary effect of H2 receptor activation is the enhancement of gastric motility.

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

    Pepsin secretion is unaffected by the activation of H2 receptors.

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

    H2 receptors primarily mediate the secretion of hydrochloric acid in the stomach.

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

    H1 antihistamines can assist in alleviating postoperative vomiting.

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

    H1 antihistamines are only effective for treating motion sickness.

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

    Radiation sickness can be managed using certain H1 antihistamines.

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

    Morning sickness is a condition that H1 antihistamines cannot treat.

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

    H1 antihistamines are ineffective for drug-induced vomiting.

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

    Higher H1 selectivity results in greater anticholinergic side effects.

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

    The principal indications of H1 antagonists include allergic rhinitis and conjunctivitis.

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

    H1 antagonists are characterized by a short duration of action.

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

    The activity of H1 antagonists involves significant antimuscarinic effects.

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

    H1 antagonists are more potent than their H2 counterparts.

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

    Most antihistaminics cause hypotension when administered orally.

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

    Promethazine can cause blood pressure reduction due to direct smooth muscle relaxation.

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

    The effect of antihistamines on blood pressure is only seen with oral routes of administration.

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

    Intravenous administration of antihistamines does not significantly affect blood pressure.

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

    Antihistaminics are not known to affect smooth muscle relaxation.

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

    What types of inflammation are associated with histamines, and which mediators specifically relate to each type?

    <p>Histamines are associated with allergic inflammation, while prostaglandins and leukotrienes are linked to acute inflammation, and interleukins to chronic inflammation.</p> Signup and view all the answers

    Identify the role of interleukins in inflammation and specify which type of inflammation they associate with.

    <p>Interleukins play a role in chronic inflammation.</p> Signup and view all the answers

    Discuss how histamines function in the context of allergic inflammation.

    <p>Histamines mediate allergic inflammation by contributing to vasodilation, increased vascular permeability, and irritation of sensory nerves.</p> Signup and view all the answers

    How do leukotrienes differ from histamines in terms of inflammatory response?

    <p>Leukotrienes are primarily involved in the inflammatory response associated with asthma and allergic reactions, whereas histamines mainly trigger immediate allergic responses.</p> Signup and view all the answers

    What is the significance of prostaglandins in acute inflammation?

    <p>Prostaglandins are significant in acute inflammation as they promote vasodilation, pain, and fever, facilitating the inflammatory response.</p> Signup and view all the answers

    What is the effect of histamine on smooth muscle contraction and which type of smooth muscle is an exception?

    <p>Histamine causes contraction of all smooth muscles except for those in blood vessels, which experience vasodilation.</p> Signup and view all the answers

    Identify the exocrine glands influenced by histamine and their corresponding secretions.

    <p>The exocrine glands influenced by histamine are lacrimal, nasal, and bronchial, leading to lacrimation, nasal discharge, and bronchial secretion.</p> Signup and view all the answers

    Explain why blood vessels are an exception in the response of smooth muscle to histamine.

    <p>Blood vessels respond to histamine by undergoing vasodilation instead of contraction, as histamine promotes relaxation in vascular smooth muscle.</p> Signup and view all the answers

    How does histamine influence the secretion processes in the glands mentioned?

    <p>Histamine stimulates the secretion processes in lacrimal, nasal, and bronchial glands, leading to increased fluid production in these areas.</p> Signup and view all the answers

    What are the primary functions of the exocrine glands affected by histamine?

    <p>The primary functions of these exocrine glands include producing tears (lacrimal), mucus (nasal), and bronchial secretions for respiratory protection.</p> Signup and view all the answers

    What makes first-generation H1-receptor blockers still widely used despite their sedation effects?

    <p>They are effective and inexpensive.</p> Signup and view all the answers

    What is a significant common side effect of first-generation H1-receptor blockers?

    <p>Sedation due to CNS penetration.</p> Signup and view all the answers

    How does the effectiveness of first-generation H1-receptor blockers compare to second-generation drugs?

    <p>They are generally more effective but less selective for peripheral receptors.</p> Signup and view all the answers

    Why might a clinician choose a second-generation H1-blocker over a first-generation drug?

    <p>To minimize sedation and CNS side effects.</p> Signup and view all the answers

    What differentiates first-generation H1 antagonists from second-generation ones in terms of side effects?

    <p>First-generation drugs often cause sedation, while second-generation drugs have fewer CNS effects.</p> Signup and view all the answers

    What distinguishes the membrane stabilizing properties of different local anesthetics such as pheniramine and diphenhydramine?

    <p>Pheniramine has strong membrane stabilizing properties, while diphenhydramine exhibits weaker ones.</p> Signup and view all the answers

    How do the varying strengths of membrane stabilizing properties in local anesthetics impact their clinical use?

    <p>Stronger membrane stabilizing properties allow for more effective pain management, making those anesthetics preferable in acute scenarios.</p> Signup and view all the answers

    What role does the membrane stabilizing action of local anesthetics like promethazine play in medical treatment?

    <p>The membrane stabilizing action can enhance analgesia and reduce nerve excitability, improving patient comfort during procedures.</p> Signup and view all the answers

    Why is it important to understand the differences in membrane stabilizing properties of local anesthetics?

    <p>Understanding these differences aids healthcare providers in selecting the most appropriate anesthetic based on the required potency and duration.</p> Signup and view all the answers

    In what way might weak membrane stabilizing properties of certain anesthetics hinder their effectiveness?

    <p>Weak properties may result in insufficient nerve block, leading to inadequate pain control during surgical procedures.</p> Signup and view all the answers

    How does the atactic activity of desloratadine compare to its precursor, loratadine?

    <p>Desloratadine is the major active metabolite of loratadine, and it is effective at half the dose of loratadine.</p> Signup and view all the answers

    What distinguishes loratadine from other H1 antagonists regarding its central nervous system effects?

    <p>Loratadine is a long-acting selective peripheral H1 antagonist that lacks CNS depressant effects.</p> Signup and view all the answers

    In what way does the fast-acting nature of loratadine influence its clinical application?

    <p>The fast-acting nature of loratadine allows for immediate relief from allergy symptoms, facilitating its use in acute allergic reactions.</p> Signup and view all the answers

    What implication does the metabolism of loratadine to desloratadine have for dosing considerations?

    <p>Since desloratadine is effective at half the dose of loratadine, clinicians can consider lower dosing regimens for optimized efficacy.</p> Signup and view all the answers

    Why might desloratadine be preferred over loratadine in certain therapeutic scenarios?

    <p>Desloratadine may be preferred due to its effectiveness at a lower dose and potential for minimizing side effects.</p> Signup and view all the answers

    Histamine causes broncho-constriction in the ______ of patients with asthma.

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

    Histamine-induced bronchospasm can be effectively antagonized by ______.

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

    Patients with asthma are highly sensitive to ______ during an attack.

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

    The constriction of airways caused by histamine is referred to as ______.

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

    Adrenaline is used to counteract histamine-induced bronchospasm by causing ______.

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

    During inflammation, capillary ______ occurs which causes vascular edema.

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

    First-generation agents tend to interact with other receptors, producing a variety of unwanted adverse ______.

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

    The fluid that leaks from the intravascular component to the injured tissues contains immune cells called ______.

    <p>inflammatory mediators</p> Signup and view all the answers

    Increased vascular permeability during inflammation leads to the leakage of fluid and immune cells to the site of ______.

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

    Second-generation agents are specific for H1 receptors and show less CNS ______ than first-generation drugs.

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

    Second-generation H1 antagonists do not penetrate the ______-brain barrier.

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

    The leaked fluid in inflammation contains ______ that produce local effects.

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

    H1 antagonists have been used to alleviate postoperative ______.

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

    Vascular edema during inflammation results from increased vascular ______.

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

    The primary role of H2 receptors includes mediating the secretion of ______ acid in the stomach.

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

    The medication is indicated in upper respiratory allergies, pollinosis, urticaria, and atopic ______.

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

    The medication may be responsible for superior efficacy in ______/atopic dermatitis due to its high and longer lasting concentration in the skin.

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

    It is also used as an adjuvant in seasonal ______.

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

    The high concentration of the medication in the skin may help in managing ______.

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

    The medication is indicated for treating conditions such as ______ and respiratory allergies.

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

    Certain H1 antihistamines are effective in preventing ______, morning sickness, drug induced and postoperative vomiting.

    <p>motion sickness</p> Signup and view all the answers

    Vomiting of pregnancy and radiation sickness can be managed using certain ______ antihistamines.

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

    H1 antihistamines are ineffective for ______ vomiting.

    <p>drug-induced</p> Signup and view all the answers

    Certain H1 antihistamines can assist in alleviating postoperative ______.

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

    H1 antihistamines are primarily indicated for conditions like allergic rhinitis and ______.

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

    Match the following substances with their effects on bronchial function:

    <p>Histamine = Bronchoconstriction Adrenaline = Bronchodilation Asthma = Increased sensitivity to histamine Bronchospasm = Narrowing of airways</p> Signup and view all the answers

    Match the following effects with their respective substances:

    <p>Bronchoconstriction = Histamine Bronchodilation = Adrenaline Histamine sensitivity = Asthma patients Bronchospasm relief = Adrenaline administration</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Histamine = A compound involved in immune responses and bronchial constriction Adrenaline = A hormone that counteracts the effects of histamine in the bronchi Asthma = A chronic condition characterized by difficulty breathing Bronchospasm = Sudden constriction of the muscles in the bronchi</p> Signup and view all the answers

    Match the following medical concepts with their implications for asthma management:

    <p>Histamine antagonism = Prevention of bronchoconstriction Adrenaline release = Immediate relief from bronchospasm Histamine sensitivity = Increased risk of asthma attacks Bronchoconstriction = Narrowed airways leading to breathing difficulties</p> Signup and view all the answers

    Match the following actions with their corresponding substances in relation to asthma:

    <p>Bronchoconstriction = Histamine Bronchodilation = Adrenaline Sensitivity = Asthma patients to histamine Relief = Adrenaline for bronchospasm</p> Signup and view all the answers

    Match the following effects of histamine with their corresponding antagonistic action:

    <p>Bronchoconstriction = Blocked by H1 antagonists Vasodilation = Blocked by H2 antagonists Increased gastric acid secretion = Blocked by H2 antagonists Increased vascular permeability = Blocked by H1 antagonists</p> Signup and view all the answers

    Match the following receptor activities with their specific drugs:

    <p>H1 receptor antagonism = Diphenhydramine H2 receptor antagonism = Ranitidine 5-HT2 receptor blocking activity = Cyproheptadine H3 receptor antagonism = Pitolisant</p> Signup and view all the answers

    Match the following uses of antihistamines with their associated conditions:

    <p>Allergic rhinitis = Cetirizine Motion sickness = Meclizine Nausea and vomiting = Promethazine Insomnia = Doxylamine</p> Signup and view all the answers

    Match the following statements about the actions of histamine with their respective outcomes:

    <p>Activation of H1 receptors = Increased bronchial smooth muscle contraction Activation of H2 receptors = Increased gastric acid secretion Histamine-induced vasodilation = Decreased blood pressure Histamine-induced itching = Increased immune response</p> Signup and view all the answers

    Match the following types of antihistamines with their characteristics:

    <p>First-generation = Cross the blood-brain barrier and cause sedation Second-generation = Less sedation and longer duration of action Peripheral-selective = Minimal central nervous system effects Non-sedating = Greater risk of anticholinergic effects</p> Signup and view all the answers

    Match the following conditions with their related usages of the medication:

    <p>Urticaria = Indication for high efficacy in skin Atopic Dermatitis = Associated with long-lasting skin concentration Upper Respiratory Allergies = Targeted by the medication for symptom relief Seasonal Asthma = Used as an adjuvant therapy</p> Signup and view all the answers

    Match the following terms with their descriptions regarding the medication:

    <p>Concentration = High and longer-lasting in skin Efficacy = Superior in treating certain allergic conditions Indication = Specific conditions where the medication is used Adjuvant = Additional supportive role in asthma treatment</p> Signup and view all the answers

    Match the following pharmacological effects with their corresponding conditions:

    <p>Pollinosis = Upper respiratory allergies Urticaria = Condition treated for histamine relief Atopic Dermatitis = Skin condition with therapy implications Seasonal Asthma = Condition managed alongside primary treatment</p> Signup and view all the answers

    Match the type of allergy with the relevant symptom it addresses:

    <p>Upper Respiratory Allergies = Nasal congestion and sneezing Pollinosis = Pollen-induced allergic reactions Urticaria = Itchy welts on the skin Atopic Dermatitis = Chronic skin inflammation</p> Signup and view all the answers

    Match the following statements to their correct implications of the medication:

    <p>High Concentration in Skin = May contribute to superior efficacy Indicated for Allergies = Includes multiple types like urticaria Adjuvant in Seasonal Asthma = Supports main therapies Effectiveness Notes = Long-lasting efficacy in certain conditions</p> Signup and view all the answers

    Match the following autacoids with their primary characteristics:

    <p>Histamines = Key role in immune response Prostaglandins = Involved in inflammation Cytokines = Regulate immune responses Leukotrienes = Contribute to allergic reactions</p> Signup and view all the answers

    Match the following types of autacoids with their primary functions:

    <p>Serotonin = Regulation of sleep and appetite Histamine = Promotion of gastric acid secretion Cytokine = Signaling in immune responses Prostaglandin = Induction of fever and pain</p> Signup and view all the answers

    Match the following statements about autacoids with their correct characteristics:

    <p>Autacoids = Collective term for various endogenous substances H2 receptors = Primarily mediate acid secretion in the stomach Leukotrienes = Associated with bronchoconstriction Histamines = Influence allergic and inflammatory responses</p> Signup and view all the answers

    Match the following descriptions of functions to the specific autacoids:

    <p>Cytokines = Control inflammation and immune responses Histamines = Mediate vasodilation and increased permeability Prostaglandins = Support the process of healing and repair Leukotrienes = Promote bronchospasm in asthma</p> Signup and view all the answers

    Match the following types of autacoids with their sources of production:

    <p>Histamines = Mast cells and basophils Serotonin = Enterochromaffin cells in the gut Cytokines = Produced by immune cells Prostaglandins = Formed from cell membrane phospholipids</p> Signup and view all the answers

    Match the following antihistamines with their primary effects:

    <p>H1 antihistamines = Alleviating postoperative vomiting H2 antihistamines = Enhancement of gastric motility Anticholinergic agents = Treatment of Parkinsonism Antitussives = Cough suppression</p> Signup and view all the answers

    Match the autacoids with their respective roles:

    <p>Histamines = Key role in immune response Serotonin = Regulation of sleep and appetite Cytokines = Inflammatory response modulation Prostaglandins = Pain and fever mediation</p> Signup and view all the answers

    Match the following antihistamines with their key characteristics:

    <p>First-generation H1 antagonists = Greater anticholinergic side effects Second-generation H1 antagonists = Short duration of action H2 antagonists = Mediating secretion of hydrochloric acid Antitussives = Effective against coughs</p> Signup and view all the answers

    Match the types of receptor effects with their corresponding clinical outcomes:

    <p>H1 receptor activation = Bronchoconstriction H2 receptor activation = Increase in gastric acid secretion Anticholinergic action = Relief from Parkinsonism symptoms Antitussive action = Reduction of cough reflex</p> Signup and view all the answers

    Match the following conditions with the antihistamines that may be used as treatment:

    <p>Allergic rhinitis = H1 antagonists Gastric acid-related issues = H2 antagonists Postoperative nausea = H1 antihistamines Cough due to cold = Antitussives</p> Signup and view all the answers

    Study Notes

    Histamine Action: H1 Receptor Antagonism

    • H1 receptor antagonists block the effects of histamine, such as bronchoconstriction.
    • Cyproheptadine is a H1 antagonist with additional 5-HT2 receptor blocking activity.

    Therapeutic Uses of H1 Antagonists:

    • Treatment of upper respiratory allergies, pollinosis, urticaria (hives) and atopic dermatitis.
    • Used as adjuvant in seasonal asthma.

    Adverse Effects of H1 Antagonists:

    • Most H1 antagonists have additional effects unrelated to histamine blocking, likely due to interactions with other receptors like cholinergic, adrenergic, or serotonin receptors.

    Action of H2 Receptor Activation:

    • H2 receptors are predominantly found in the stomach and are responsible for increased gastric acid secretion.
    • H2 receptor activation leads to increased production of both hydrochloric acid (HCl) and pepsin.

    Autacoids

    • Autacoids are a diverse group of substances that act as chemical mediators in the body
    • They are produced by various tissues and have a wide range of effects, including inflammation, smooth muscle contraction, and neurotransmission
    • Autacoids can act locally, at the site of release, or systemically, affecting distant tissues
    • They exert their actions by binding to specific receptors on target cells

    Histamine

    • Histamine is an autacoid stored and released from mast cells and basophils
    • It is involved in allergic reactions and inflammatory responses
    • It exerts its effects by binding to histamine receptors, which are classified into four main types: H1, H2, H3, and H4
    • Activation of H1 receptors, which are present in many tissues, causes smooth muscle contraction, vasodilation, increased vascular permeability, and itching
    • Activation of H2 receptors, mainly found in the stomach, causes increased gastric acid secretion
    • H2 receptor activation leads to the release of both hydrochloric acid (HCl) and pepsin
    • Some H1 antihistamines are effective in preventing motion sickness, morning sickness, vomiting induced by drugs or surgery, vomiting during pregnancy, and vomiting due to radiation exposure
    • Antihistamines are also effective in treating allergic conditions, such as allergic rhinitis and conjunctivitis
    • Certain antihistamines can cause a drop in blood pressure when administered intravenously, due to their effect on smooth muscle relaxation or blockage of α adrenergic receptors, as seen with promethazine
    • However, this effect is not usually observed with oral administration
    • Antihistamines with higher H1 selectivity tend to have a longer duration of action, are more potent, and are less likely to cause anticholinergic side effects
    • Antihistamines with higher H1 selectivity often lack antimuscarinic and antiserotonin activity

    Inflammation Mediators

    • Inflammation can be acute or chronic
    • Acute inflammation mediators include histamines, prostaglandins, and leukotrienes
    • Chronic inflammation involves interleukins
    • Histamine is a key mediator in allergic inflammation

    Histamine Effects

    • Histamine causes contraction of all smooth muscles except for the blood vessels
    • Histamine causes vasodilation (VD)
    • Histamine stimulates exocrine glands, including the lacrimal, nasal, and bronchial glands
    • These effects lead to symptoms like lacrimation, nasal discharge, and bronchial secretion

    H1-Receptor Blockers

    • H1-receptor blockers are divided into first- and second-generation drugs
    • First-generation drugs are effective and inexpensive but often cause sedation due to CNS penetration
    • Second-generation drugs are less likely to penetrate the CNS and cause sedation

    H1-Receptor Blocker Examples

    • Loratadine is a long-acting, selective peripheral H1 antagonist that lacks CNS depressant effects and has fast action
    • Desloratadine is the active metabolite of loratadine and is effective at half the dose

    Local Anaesthetic Properties

    • Some H1-receptor blockers, like pheniramine, promethazine, and diphenhydramine, have strong membrane-stabilizing properties
    • Others have weaker membrane-stabilizing properties

    Inflammation

    • During inflammation, capillaries dilate, leading to vascular edema.
    • Increased vascular permeability causes leakage of fluid from intravascular components to the site of injury.
    • The leaked fluid contains immune cells known as inflammatory mediators.
    • Inflammatory mediators produce local effects and are also called autocoids.

    ### Histamine

    • Histamine causes bronchoconstriction in the bronchus.
    • Individuals with asthma are highly sensitive to histamine.
    • Histamine-induced bronchospasm is effectively antagonized by adrenaline.

    H1 Antihistamines

    • Second-generation H1 antihistamines are specific for H1 receptors, resulting in less CNS toxicity compared to first-generation drugs.
    • Certain H1 antihistamines are effective in preventing motion sickness, morning sickness, and various types of vomiting.
    • These antihistamines achieve high and prolonged concentrations in the skin, contributing to their efficacy in urticaria and atopic dermatitis.
    • H1 antihistamines are indicated for upper respiratory allergies, pollinosis, urticaria, atopic dermatitis, and as an adjuvant in seasonal asthma.

    ### Autacoids

    • Autacoids are a collective term for various endogenous peptides, histamines, prostaglandins, leukotrienes, and cytokines.
    • They are also referred to as local hormones.
    • In the bronchus, histamine causes bronchoconstriction, which is particularly impactful in asthma patients.
    • Adrenaline effectively antagonizes histamine-induced bronchospasm.
    • H1 antihistamines block histamine effects such as bronchoconstriction.
    • Cyproheptadine, an H1 antihistamine, has additional 5-HT2 receptor blocking activity.
    • Some H1 antihistamines are also effective antitussives.
    • Some antihistamines possess central antimuscarinic actions, which are beneficial in treating Parkinson's disease.
    • Antihistamines achieve high and prolonged concentrations in the skin, contributing to their effectiveness in treating urticaria and atopic dermatitis.
    • Antihistamines are indicated for upper respiratory allergies, pollinosis, urticaria, and atopic dermatitis.
    • They can also be used as an adjuvant in seasonal asthma.

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