Anti Histamines Flashcards
A patient’s urticaria is interfering with sleep. Which class of drugs would be most appropriate to take before bed?
A first-generation antihistamine (e.g., promethazine). A first-generation antihistamine will cross the blood-brain barrier (BBB) and cause sedation helping the patient to sleep.
Which class of antihistamine drugs would be most appropriate for a patient with nausea and vomiting?
A first-generation antihistamine. A first-generation antihistamine will cross the blood-brain barrier (BBB) and block histamine H1 and muscarinic M1 receptors to control nausea and vomiting.
A 28-year-old taxi driver presents with allergic rhinitis. Suggest an appropriate antihistamine drug.
Fexofenadine, desloratadine or loratadine. Any second or new generation antihistamine that does not cause sedation would be appropriate.
A 73-year-old patient with mild cognitive impairment presents with urticaria. Suggest an appropriate antihistamine drug?
Fexofenadine, desloratadine or loratadine. Any second or new generation antihistamine that does not cross the blood-brain barrier (BBB) to cause sedation and block muscarinic cholinergic receptors in the CNS.
Use of promethazine is contraindicated in children under the age of 2 years old because of increased risk of…
Respiratory depression
For how long should patients be warned not to drink fruit juice after taking fexofenadine?
4 hours before dosing and 1-2 hours after dosing
List THREE drugs that should be avoided or taken only with caution together with all first-generation antihistamines.
Alcohol, opioid analgesics, antidepressants and any other CNS depressant drugs
Which class of antihistamine would be preferable for the treatment of
urticaria in a patient with narrow-angle glaucoma?
Second or third/new generation antihistamines without muscarinic receptor antagonism
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
First-generation antihistamines can increase the risk of drug-induced long QT syndrome (LQTS) because of actions at…
HERG potassium channels
What are the major histamine receptors on mast cells?
H1 and H4
Why do 1st generation antihistamines cause sedation?
They cross the blood-brain barrier and inhibit H1 histamine receptors in the CNS. Inhibition of muscarinic receptors in the CNS may additionally further contribute to drowsiness/sedation.
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 due to…
Vasodilation
Allergens trigger mast cell degranulation by…
Cross-linking FcεR1-bound IgEs
List at least THREE examples of 1st generation antihistamines
Chlorpheniramine, Triprolidine, Ketotifen, Diphenhydramine, Promethazine
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}
In terms of agonist or antagonist activity, what kind of drugs are clinically used as antihistamine drugs?
Inverse agonists
Which second-generation antihistamine is most likely to still cause some sedation?
Cetirizine (and also acrivastine) 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
List at least THREE adverse effects of first-generation antihistamines
Sedation, dry mouth, GIT disturbances, weight gain, tachycardia, postural hypotension
