Antihistamines Flashcards
Drug class
“amine”, “adine”, “zine”
Antihistamine
Suffix
Antihistamine
“amine”, “adine”, “zine”
Two kinds of Antihistamines
older Sedating
newer Less sedating
Main difference between sedating and less sedating antihistamines
Newer less sedating antihistamines are better tolerated than sedating antihistamines (reduced sedating and anticholinergic effects); cetirizine most likely to cause sedation
Indication
Sedating Antihistamines
- Allergic conditions, eg rhinitis, urticaria (see Practice points below)
- Itch
- Nausea and vomiting
Indication
Less sedating antihistamine
Allergic rhinitis = hayfever
Chronic urticaria = hives
MOA
Sedating antihistamines
Reduce the effects of histamine by binding to the H1 receptor and stabilising it in an inactive form.
They also have anticholinergic activity, some have alpha-blocking activity (eg promethazine) and some have antiserotonin activity
MOA
Less sedating antihistamines
Reduce the effects of histamine by binding to the H1 receptor and stabilising it in an inactive form.
Adverse effects
Less sedating antihistamine
drowsiness, fatigue, headache, nausea, dry mouth
Precautions
Sedating antihistamines
GI obstruction, bladder outlet obstruction (eg prostatic hypertrophy)—may be worsened by the anticholinergic effects of antihistamines.
Adverse effects
Sedating antihistamines
sedation, psychomotor impairment (below), dizziness, confusion, headache, blurred vision, mydriasis, dry eyes, constipation, dry mouth, urinary retention
Psychomotor impairment
Sedating antihistamines can impair alertness, cognition, learning, memory and performance.
Practice points
sedating antihistamines
less sedating antihistamines are preferred for the treatment of allergic rhinitis and chronic urticaria as they are better tolerated and there is more evidence of efficacy
Counselling
All antihistamines
May cause sleepiness
Do not operate heavy machinery
Generic names
Sedating antihistamines
alimemazine
cyclizine
cyproheptadine
dexchlorpheniramine
diphenhydramine
doxylamine
promethazine
Generic names
Less sedating antihistamines
Cetirizine
Desloratadine
Fexofenadine
Loratadine
Drug class and indication
Alimemazine
Sedating antihistamine
Urticaria
Itch
Drug class and indication
Cyclizine
Sedating antihistamine
Nausea and vomiting:
* postoperative
* motion sickness
* radiotherapy-induced
Drug class and indication
Cyproheptadine
Sedating antihistamine
Allergic conditions, eg rhinitis, urticaria
Itch
Drug class and indication
Dexchlorpheniramine
Sedating antihistamine
Allergic conditions, eg rhinitis, urticaria
Itch
Drug class and indication
Diphenhydramine
Sedating antihistamine
Allergic conditions, eg rhinitis, urticaria
Short-term management of insomnia
Drug class and indication
Doxylamine
Sedating antihistamine
Short-term management of insomnia
Drug class and indication
Promethazine
Sedating antihistamine
Allergic conditions, eg rhinitis, urticaria
Itch
Nausea and vomiting, including motion sickness
Sedation (short term)
Drug class and indication
Cetirizine
Less sedating antihistamine
Allergic rhinitis = hayfever
Chronic urticaria = hives
Drug class and indication
Desloratadine
Less sedating antihistamine
Allergic rhinitis = hayfever
Chronic urticaria = hives
Drug class and indication
Fexofenadine
Less sedating antihistamine
Allergic rhinitis = hayfever
Chronic urticaria = hives
Drug class and indication
Loratadine
Less sedating antihistamine
Allergic rhinitis = hayfever
Chronic urticaria = hives
What does Histamine do?
- contraction of smooth muscle tissues of the lungs, uterus, and stomach;
- Vasodilation –> increases permeability and
- lowers blood pressure
- increased heart rate.
in allergy histamine and immune response is hypersensitive. Releases massive amounts of histamine leads to allergy symptoms: runny nose, sneezing, itch.
Can cause anaphalaxis
