Antihistamines Flashcards
(30 cards)
How is histamine formed?
Decarboxylation of histidine by histadine carboxylase
What cells generally release histamine?
mast cells and basophils
Which organs have the highest number of mast cells?
lungs, gastrointestinal tract and skin
What does stimulation of H1 receptors cause? (2)
Smooth muscle contraction, vasodilation
What do sedating antihistamines do?
Block/inhibit the actions of histamine at H1 receptor
How do sedating antihistamines sedate?
The cross the blood brain barrier and block H1 receptors leading to drowsiness and sedation
What is another effect that sedating antihistamines can have on other receptors?
they can inhibit acetylcholine at antimuscarinic receptors
What are 3 adverse effects you may have if a sedating h1 antihistamine attaches to a h1 receptor?
CNS neuro-transmission reduction, sedation, appetite increase and cognitive and neuro-psychomotor performance reduction.
What are three other uses for sedating antihistamines?
Motion sickness, insomnia and secretion drying
What is the duration of action of antihistamines?
8-30 hours
What is 1 adverse effect you may have if a sedating h1 antihistamine attaches to a muscarinic receptor?
Xerostoma (or dry mouth), urinary retention or sinustodial tachycardia
What is 1 adverse effect you may have if a sedating h1 antihistamine attaches to an alpha adrenergic receptor?
Hypotension, dizziness or reflex tachycardia
What type of receptors do non-sedative antihistamines target?
H1 receptors
What happens when you stimulate H2 receptors by histamine?
secretion of gastric acid in the stomach and increased HR and CO
What happens when you stimulate H3 receptors by histamine?
Decreases histamine release from histaminergic neurones and decreases acquisition and storage of long and short term memories
What are the three elements of the histamine triple response?
Reddening of the skin, surrounding flare and weal (red swollen mark)
What causes the histamine triple response?
Stimulation of the H1 receptors
What causes type 1 IgE allergic reactions?
Continuous exposure to an allergen in the environment leading to the formation of IgE antibodies and increasing sensitisation from lack of tolerance.
What are the symptoms of hay fever? (5)
vasodilation
increased capillary permeability
itchy and swollen red eyes
itchy runny nose or nasal stuffiness
sneezing
What are the symptoms of hives? (3)
vasodilation
increased capillary permeability
skin rashes
weals
itch
What does FAST stand for in allergies and what is one thing you look for in each letter?
Face- rash, hives, swelling of lips, tongues and eyes
Airway- difficulty breathing, swallowing and speaking
Stomach- ab pain, vomiting and diarrhoea
Total body- Rash, swelling, weakness, paleness, loss of consciousness
What does H3 stimulation cause?
lower histamine release from the histaminergic neurones and lower acquisition of short and long term memories
what does antidromic mean?
back against a normal signal
What does T helper 2 cells produce and what do they do?
they make cytokines promoting allergen sensitising pathways
