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How do antihistamines work?
Antihistamines: block histamine from binding to the H1 receptor; and therefore we don't get an allergic reaction
What do antiallergic agents do?
Antiallergic agents: prevent mast cells from realising histamine
Where is histamine found?
Found in mast cells and basophilic white blood cells
The largest concentration of histamine is found where?
When an antigen comes in contact with the skin or lungs or bloodstream of sensitive individuals, the mast cells and basophils immediately release histamine where?
- In the blood
- Histamine then interacts with the membrane receptors in certain tissues to produce the symptoms of an allergy.
What are the two types of receptors associated with histamine?
H1 and H2 receptors
Where are H1 receptors located?
- on blood vessels
- bronchiolar smooth muscle
- intestinal smooth muscle
- *there to mediate allergic reactions
Where are H2 receptors located?
- within the stomach
- blood vessels
- and uterine tissue
What is the most important response mediated by H2 receptors?
mediated response of increased gastric acid
Intensity of allergic symptoms is proportional to the amount of....?
Histamine usually produces a transient drop in blood pressure (hypotension) because it.....?
dilates small blood vessels and capillaries
If histamine produces hypotension by dilating small blood vessels and capillaries; with large concentrations of histamine this can result in....
hypotension and circulatory collapse
Capillary dilation in the skin results in localized redness called...
Histamine causes fluids and proteins to leak out of the capillaries.
FYI: When capillary leakage occurs in the nasal mucous membranes, nasal congestion occurs. When capillary leakage occurs in the skin, edema, wheals, or hives are produced. Itching and pain occur because histames irritates sensory nerve endings. The erythema and edema produced by histamine in the skin ar known as the Response of Lewis
Histamine produces contraction of the smooth muscle of the intestine and bronchioles by...?
stimulating H1 receptors
contraction of the bronchiolar smooth muscle results in.....?
Bronchoconstriction; which makes breathing difficult
Histamine usually produces rapid heartbeat; which is directly related to the...
amount of histamine present
At high levels of histamine (histamine shock), cardiac conduction is impaired; which may lead to the development of....what?
- Cardiovascular collapse
Antiallergic agents prevent histamine release from the mast cells--- no effect on histamine receptors
Cromolyn Sodium (Intal, nasalcrom) is the only available drug that selectivily prevents... what?
the release of histamine from mast cells
Drugs like cromolyn sodium, which prevent the onset of symptoms or disease as a result of exposure before the reactive process can take place are called....what?
Cromolyn sodium is inhaled as a fine micronized powder; The powder form allows the drug to reach the pulmonary mast cells before any antigens can dince an allergic reaction.
Cromolyn Sodium is a prophylactic adjuct in the management of chronic bronchial asthma an allergic rhinitis to prevent... what?
Patients must be compliant with dosing at regular intervals otherwise the drug cannot achieve a satisfactory resonse.
Antihistamines are used to relieve actue reactions in which histamine has already been released. All the antihistames available specifically block histamine from interfacing with its....?
Antihistaminic drugs are usually administered orally because they are absorbed well from the intestinal tract but a few are available for; what type of administration?
First generation antihistamines include...?
- chlorpheniramine (Chlor-Trimeton)
- climastine (Tavist)
- diphenydramine (Benadryl)
- promethazine (Phenergan)
*BENADRYL IS STILL CONSIDERED A ANTIHISTAMINE OF CHOICE
Second generation antihistamines are...
- cetirizine (Zyrtec)
- fexofendaine (Allegra)
- loratadine (Claritin)
The 2nd generation appears to be more selective for peripheral...?
The major side effect of antihistamines are....?
Antihistames also have what kind of side effects?
Anticholinergic side effects
Antihistamines are frequently used in acute allergice reactions including: ?
- hay fever
- insect bites
Because of anthistamines inherent sedation, they may be used to ....
induce sleep in OTC sleeping aids (ex:Nytol)
Adverse reactions of anthistamine drugs are: ?
- Drowsiness and sedation
- Anticholinergic side effects
Deffinitioh of : Xerostomia: ?
When administering antihistamine cation is advised in patients thay may have or are ?
- Cardiovascular disease
- urinary retention
- nursing mothers
Caution advised when prolonged topical use of anthistamine may cause....
Drug interactions of anthistamines are....
* may increase the incidence of drowsiness