anti histamines 1 Flashcards
What are the pKa values of histamine?
5.80 (imidazole) and 9.40 (aliphatic primary amine)
These values indicate the acidity of histamine’s functional groups.
What is the function of H1 histamine receptors?
Allergic inflammatory processes
H1 receptors play a significant role in allergic reactions.
What is the function of H2 histamine receptors?
Gastric acid secretion
H2 receptors are involved in the regulation of stomach acid.
What is the function of H3 histamine receptors?
Release of neurotransmitters
H3 receptors modulate the release of various neurotransmitters in the brain.
What is the function of H4 histamine receptors?
Chemotactic responses
H4 receptors are implicated in the immune response and inflammation.
Name one inhibitor of histamine release.
Khellin, lodoxamide and cromolyn sodium
Khellin is used to prevent histamine release in allergic reactions.
What are the classifications of antihistamines?
First-generation (sedation and anti cholinergic) and second-generation (more diverse) H1 antihistamines
Antihistamines are classified based on their chemical structure and effects.
List the types of first-generation H1 antihistamines.
- Ethylenediamines (Tripenelamine and Thonzylamine)
- Ethanolamine ethers
- Alkyl amines (Chlorpheniramine, Dexbrompheniramine, Triprolidine, Dimethindene)
- Piperazines (cyclizine, meclizine, oxatomide, cetirizine)
- Tricyclic H1 antihistamines
These categories reflect the structural diversity of first-generation antihistamines.
What are some examples of ethanolamine ether antihistamines?
- Diphenhydramine HCl
- Doxylamine
- Carbinoxamine
These are commonly used first-generation antihistamines.
What are some examples of tricyclic H1 antihistamines?
- Promethazine
- Azatadine
- Cyproheptadine
Tricyclic antihistamines are often used for their sedative effects.
What are the types of second-generation H1 antihistamines?
- Fexofenadine
- Loratidine
- Cetirizine
- Mizolastine
- Carebastine
Second-generation antihistamines typically have fewer sedative effects.
What is Log D at pH 7.4 for topical H1 antihistamines?
1.0 ± 0.5
This value indicates the lipophilicity of topical antihistamines.
True or False: First-generation antihistamines are generally less sedating than second-generation antihistamines.
False
First-generation antihistamines are usually more sedating due to their ability to cross the blood-brain barrier.
Fill in the blank: H2 receptors are primarily involved in _______.
[gastric acid secretion]
This role is crucial for digestive processes.
What are the two main roles of histamine in the body?
- Mediating allergic responses
- Regulating gastric acid secretion
Histamine plays a key role in both the immune system and digestive system.
Alkylamines
These agents are characterized by a long duration of antihistaminic action and by a decreased incidence of central sedative side effects, when compared to the ethylenediamines and ethanolamine ether series
Piperazines
The primary use of these compounds remains as treatment of motion sickness and vertigo and for suppression of nausea and vomiting
they have cns effects and anti emetic and anti cholinergic effects
Promethazine
antihistamine. It has significant
antiemetic and anticholinergic properties
. It is has sedative hypnotic properties and
has been used to potentiate the
effects of analgesic drugs.
Cyproheptadine
The (−)-isomer retained antihistaminic, antiserotonin, and appetite-stimulating effects
similar to cyproheptadine, whereas the (+)-enantiomer
had greater anticholinergic potency. Differences of 9- to 60-fold were observed in the reported assays.
treatment of anorexia nervosa and cachexia.
- Second-generation H1 antihistamines
The active agents apparently do not penetrate the blood–brain barrier significantly, perhaps because of their amphoteric nature (most are zwitterionic at physiologic pH) and partitioning characteristics and/or they are substrates for the drug efflux P-glycoprotein transporter or organic anion transporter proteins.
Topical antihistamines
ketotifen
Emedastine
azelastine
Epinastine
