Antihistamines and Related Antiallergic Agents Flashcards
Where does histamine synthesis occur?
in many tissues, including mast cells, parietal cells of the gastric mucosa, and neurons of the central nervous system (CNS) and in the periphery
Histamine gives a ___________ effect
local
What is used in the treatment of allergic inflammatory disorders?
H1 antihistamines
What is used in the treatment of gastric hypersecretory disorders?
H2 antihistamines
Histamine plays a physiologic role at several regions of the CNS via which receptors?
H3 and H4
The stimuli for release of histamine from tissues may include?
- destruction of cells as a result of cold
- allergies and anaphylaxis
- toxins from organisms
- venoms from insects and spiders
- trauma
Why are histamines released by injured tissues?
to recruit white blood cells at the site of injury by inducing vasodilation
What is the effect of H1 receptors on smooth muscle?
relaxation
What is the effect of H1 receptors on capillary permeability?
increases capillary permeability
How does histamine promote vasodilation of small blood vessels?
by causing the vascular endothelium to release nitric oxide
Effect of H1 receptors on bronchioles?
constriction
Which histamine receptors mediate many pathological processes, including allergic rhinitis, atopic dermatitis, conjunctivitis, urticarial, bronchoconstriction, asthma, and anaphylaxis?
H1
What is the main difference between first and second generation H1 antihistamines?
selectivity and side effects
________________ are useful in the treatment of allergy and inflammatory disorders
H1 antagonists
First-generation H1 antihistamines are effective in the treatment of?
allergic responses (e.g., hay fever, rhinitis, urticaria, and food allergy)
Adverse central effects of first-generation antihistamines include?
sedation, drowsiness, decreased cognitive ability,
and somnolence
Peripheral side effects associated with cholinergic blockade include?
blurred vision, dry mouth, urinary retention, and constipation
Second-generation H1 antihistamines give what effects?
separation of CNS depressant and anticholinergic effects from peripheral antihistaminic effects
Are first-generation H1 antihistamines selective?
no
Are second-generation H1 antihistamines selective?
yes
Advantages of second-generation H1 antihistamines?
- more selective for H1 receptor
- less CNS effects
Disadvantages of first-generation H1 antihistamines?
- nonselective which leads to many side effects
- can reach CNS and cause sedation
What happens when H1 antihistamines inhibit cholinergic receptors?
- dry mouth
- urinary retention
- sinus tachycardia
What happens when H1 antihistamines inhibit a-Adrenergic receptors?
- hypotension
- dizziness
- reflex tachycardia
What happens when H1 antihistamines inhibit serotonin receptors?
increased appetite
What happens when H1 antihistamines inhibit histamine H1 receptors?
- lowered allergic inflammation, itching, sneezing, and rhinorrhea
- lowered neurotransmission in the CNS
- sedation
- lowered cognitive and psychomotor performance
- increased appetite
Most H1 antihistamines are?
inverse agonists
What does the structural scaffold of H1 antagonists (first generation antihistamines) include?
- tertiary amine
- spacer
- 2 aromatic or heteroaromatic rings
What is the difference between H1 and H2?
H2 usually has an imidazole but H1 antagonist has only aromatic or heteroaromatic rings
What are the oldest first-generation antihistamine that are not widely used anymore?
ethylenediamines
Do ethylenediamines cause CNS effects mainly sedation?
yes
The prototype of the aminoalkyl ethers is?
diphenhydramine
Do ethanolamine ethers cause significant anticholinergic side effects and sedation?
yes
What type of antihistamines is used as OTC sleep aids?
ethanolamine ethers
Compounds with central anticholinergic and antihistaminic effects have been used as one approach to the treatment of?
Parkinson disease
__________ are widely used OTC antihistamines for mild seasonal allergies.
alkyl amines
Compared to the ethylenediamines and ethanolamine ether series, alkyl amines are characterized by a _________ duration for antihistaminic action and a ________ incidence of central sedative side effects
long; decreased
Do piperazines give anticholinergic side effects and drowsiness?
yes
What is the primary use of piperazines?
treatment of motion sickness and vertigo and for suppression of nausea and vomiting
What is the effect of most tricyclic H1 antihistamines?
sedative effects and long durations of action
Do second-generation H1 antihistamines penetrate the blood-brain barrier?
no because of their amphoteric nature or they are substrates for transporter proteins
Name the second-generation H1 antihistamines with weak potential for producing sedation
- acrivastine
- cetririzine
- levocetirizine
Name the second-generation H1 antihistamines that are nonsedating
- desloratadine
- fexofenadine
- loratadine
