Drugs and Allergy Flashcards
What is an allergy?
An allergy is the body’s immune system response to a substance that is otherwise harmless, leading to symptoms such as swelling, itching, and difficulty breathing.
What is an allergen?
An allergen is the substance that causes an allergic response when the body’s immune system reacts to it.
What happens during the sensitization stage of allergy development?
During sensitization, the body is first exposed to an allergen, and there are no symptoms. Plasma B cells produce IgE antibodies specific to the allergen, which then attach to the surface of mast cells and basophils.
What occurs during an allergic reaction?
During an allergic reaction, the body is re-exposed to the same allergen. The allergen binds to the IgE antibodies on sensitized mast cells and basophils, which then release inflammatory mediators like histamine, leukotrienes, and prostaglandins, leading to allergy symptoms.
What are the effects of inflammatory mediators during an allergic reaction?
Inflammatory mediators cause vasodilation and increased vessel permeability, leading to swelling or hives. They can also stimulate mucus secretion (resulting in a runny nose), activate sensory nerves (causing itching), and induce smooth muscle contraction (leading to bronchoconstriction and difficulty breathing).
How do antihistamines help in treating allergic reactions?
Antihistamines block the action of histamines by acting as inverse agonists on the H1 receptors. They shift the H1 receptors to the inactive state, preventing histamine from activating them, thus reducing allergy symptoms.
What are H1 histamine receptors, and where are they found?
H1 histamine receptors are a type of G protein-coupled receptor (GPCR) that are primarily involved in allergic reactions. They are found on smooth muscle, blood vessels, brain, and nerve cells.
What is the basal activity of the H1 receptor?
The basal activity of the H1 receptor refers to its activity even in the absence of an agonist, meaning the receptor is constitutively active.
What is the mechanism of action of antihistamines?
Antihistamines are inverse agonists that bind to the H1 receptor in its inactive state, shifting the equilibrium toward the inactive state and counteracting histamine’s action, thereby reducing allergic symptoms.
What are the differences between first-generation and second-generation antihistamines?
First-generation antihistamines are lipophilic and can cross the blood-brain barrier, causing sedative effects. An example is promethazine. Second-generation antihistamines are less lipophilic, do not cross the blood-brain barrier, and do not cause sedation. An example is loratadine (Clarityn).
What are the two main stages involved in the development of allergies?
The two main stages are sensitization (first exposure to the allergen) and the allergic reaction (re-exposure to the same allergen).
What is the role of IgE antibodies in allergy development?
During sensitization, plasma B cells produce IgE antibodies specific to an allergen, which then attach to mast cells and basophils. Upon re-exposure, the allergen binds to these IgE antibodies, triggering the release of inflammatory mediators.
What are some common symptoms caused by the release of inflammatory mediators during an allergic reaction?
Common symptoms include swelling or hives (due to vasodilation and vessel permeability), a runny nose (from mucus secretion), itching (due to stimulation of sensory nerves), and difficulty breathing (due to bronchoconstriction).
How do antihistamines work to relieve allergy symptoms?
Antihistamines block histamine’s action by binding to the H1 receptor as inverse agonists, shifting the receptor to its inactive state and preventing histamine from activating it, which reduces symptoms.
What is the difference between the H1 histamine receptor and other histamine receptors like H2, H3, and H4?
The H1 receptor is primarily involved in allergic reactions, while H2, H3, and H4 receptors have different roles in processes such as regulating gastric acid secretion (H2) and modulating immune responses (H3 and H4).
What makes first-generation antihistamines sedating?
First-generation antihistamines are lipophilic, allowing them to cross the blood-brain barrier and interact with receptors in the brain, leading to sedative effects.
What is an example of a first-generation antihistamine, and how is it used?
Promethazine is an example of a first-generation antihistamine. It is used to treat allergic conditions and can also be used as a sleeping pill due to its sedating effects.
What is the key characteristic of second-generation antihistamines that distinguishes them from first-generation antihistamines?
Second-generation antihistamines are less lipophilic, meaning they do not cross the blood-brain barrier, so they do not cause sedation.
Can second-generation antihistamines be used as sleeping aids?
No, second-generation antihistamines, like loratadine (Clarityn), do not cause sedation as they do not cross the blood-brain barrier, so they are not used as sleeping aids.
