Histamine Flashcards
What are some major histamine-producing cells?
Mast cell
Basophill
ECL cell
Histaminergic neuron
Antihistamines acting at H1 in the CNS can lead to:
- Antiemetic effects
- Sedation
- Impaired cognition, memory and psychomotor function
What are the different types of Histamine receptors and their functions?
H1: allergic inflammation
H2: secretion of gastric acid
H3: neurotransmission
H4: immunomodulation
What are some pathphysiological actions of histamine?
Smooth muscle contraction (bronchoconstriction)
Vasodilation
Increase vascular permeability
stimulation ofgastric acid secretion
snsory neuron to mediate pain and itch
immunomodulation
Allergens trigger mast cell degranulation by…
Cross-linking FcεR1-bound IgEs (Fc epsilon RI)
The triple vascular response of Lewis includes
Flush, Flare and Wheal
Histamine triggers the formation of a wheal (a raised swelling on the skin) due to increased…
Vascular permeability
Histamine triggers the formation of a flush and flare due to…
Dilation of blood vessels and disruption of capillaries
In terms of agonist or antagonist activity, what kind of drugs are clinically used as antihistamine drugs?
Inverse agonists
What are the 1st generation of antihistamine?
Chlorpheniramine
Triprolidine
Ketotifen
Diphenhydramine
Promethazine
which receptors do first generation H1 antihistamines targets?
Muscarinic Cholinergic, alpha-adrenergic, serotonin, H1
List at least THREE examples of 2nd generation antihistamines
Cetirizine, Loratadine, Fexofenadine
List at least TWO examples of drugs sometimes considered 3rd or new generation antihistamines
Levocetirizine, Desloratadine
Which second-generation antihistamine is most likely to still cause some sedation?
Cetirizine are less sedating that first-generation antihistamines but still notably more sedating than fexofenadine and loratadine.
Why do 2nd generation antihistamines cross the blood-brain barrier (BBB) less?
2nd generation antihistamines are less lipophilic and/or have greater affinity for the P‐glycoprotein efflux pump than 1st generation antihistamines
which 1st gen h1 antihistamine can be used to treat motion sickness?
Diphenhydramine
List at least THREE adverse effects of first-generation antihistamines
Sedation, dry mouth, GIT disturbances with nausea and vomiting
What is one effect of 1st gen H1 antihistamine on the CNS?
Decrease neurotrasmission
What is the duration of action of MOST 2nd generation antihistamines?
12 to 24 hours
What is the duration of action of MOST 1st generation antihistamines?
4 to 6 hours
what is the difference in specificity of 1st and new gen antihistamine
old gen: low h1 receptor selectivity
new gen: high h1 specificty
Why is topical application of antihistamine generally avoided?
Can induce contact dermatitis
Can induce systemic allergy to the antihistamine drugs
What are some contraindictation of antihistamine?
- Do not combine with otehr CNS depressants (Alcohol,opioid,antidepressant)
- Do not use late in 3rd trimester of pregnancy
- Do not use when breast feeding
- Do not use first gen H1 antihistamine in closed angle glaucoma
- Elderly patients are particularly susceptible to CNS effects, anticholinergic effects and postural hypotension
Use of promethazine is contraindicated in children under the age of 2 years old because of increased risk of…
Respiratory depression
What must be noted when taking fexofenadine?
Avoid fruit juice from 4 hours before to 1-2 hours aftr dosing
Fruit juice affect absorption
