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Pharm III Unit II > 1 Antihistamines > Flashcards

1 Antihistamines Flashcards

1
Q

Histamine is found in most cells throughout the body, synthesized from _____ in most tissues, particularly ______

A

Histidine

Mast cells, epidermis, gastric mucosa, neurons in CNS, and cells in regenerating/rapidly growing tissues

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2
Q

In the brain, histamine is considered a _______, and is involved in _______

A

Neurotransmitter

Arousal, neuroendocrine control, and weight/temp regulation

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3
Q

Release of histamine from ________ in the fungus of the stomach increases production of ________.

A

Enterochromaffin-like cells

Gastric acid

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4
Q

The highest concentration of histamine is found in tissues that contain ______ as well as _____ in the blood

A

Mast cells

Basophils

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5
Q

How is histamine stored?

A

In a complex with proteases, heparin, or chondroitin sulfate proteoglycans

It is inactive until released from the mast cells

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6
Q

Where in the body are mast cells prominent?

A 
Nose
Mouth
Feet
Near pressure points
Bifurcation of blood vessels
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7
Q

Histamine plays a central role in _______ and _______

A

Immediate hypersensitivity

Allergic reactions

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8
Q

Many substances increase the release of histamine from mast cells and basophils by…

A

Increasing intracellular Ca2+ by various mechanisms

Histamine then causes the release of other auto coins, which contribute to the inflammatory response

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9
Q

Histamine release from mast cells can be triggered by…

A

Interaction of IgE and antigen (classic allergic response)

Many drugs, esp organic bases given IV

Venoms (ie bee venom)

Scratching, cold, sun, non-specific cell damage

Certain cancers

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10
Q

Examples of drugs that increase histamine release

A

MORPHINE

CODEINE

RADIOCONTRAST DYES

VANCOMYCIN (“red man syndrome”)

D-tubocurarine

Succinylcholine

Phenothiazines

Protamine

Guanethidine

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11
Q

Why does bee venom cause histamine release?

A

Contains mast cell degranulating protein

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12
Q

Which histamine receptors are located in the CNS?

A

H1 and H3

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13
Q

Which histamine receptor plays a role in the regulation of gastric acid?

A

H2

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14
Q

The H1 receptor is coupled to _________, and stimulation __________.

A

Gq/11 protein

Increases production of IP3 and DAG

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15
Q

Which histamine receptor is coupled to a Gq/11 protein and increases production of IP3 and DAG?

A

H1

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16
Q

The H1 receptor is structurally very similar to…

A

Muscarinic receptors

Many compounds with block BOTH

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17
Q

The H1 receptor is found in…

A

Smooth muscle
Vascular endothelium
Postsynaptic membranes in the brain

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18
Q

In the CNS, H1 receptors are concentrated in…

A

Hypothalamus - produce wakefulness and inhibit appetite

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19
Q

H1 stimulation in the endothelium of blood vessels releases _____ and causes _____

A

NO

Vasodilation

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20
Q

H1 receptors on smooth muscles other than vascular endothelium cause increased _____ leading to ______

A

Ca2+

Contraction

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21
Q

Classical antihistamines block the ____ receptor

A

H1

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22
Q

The H2 receptor is linked to _____ and increases ______

A

Gs protein

cAMP

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23
Q

Which histamine receptor is linked to Gs proteins and increases cAMP?

A

H2

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24
Q

Where is the H2 receptor found?

A

In the stomach - role in secretion of gastric acid

Heart

Brain

Some smooth muscles

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25
Stimulation of H2 receptors on blood vessels leads to ______
Vasodilation
26
The H3 and H4 receptors are linked to _______ and decrease ______.
Gi protein cAMP
27
Which histamine receptors are linked to Gi proteins and decrease cAMP?
H3 and H4
28
H3 receptors are found in ____ and are primarily ____.
The brain Presynaptic - appear to mediate feedback inhibition of histamine release
29
H3 agonists promote _____
Sleep
30
H3 antagonists increase ______ through stimulation of _________
Wakefulness H1 receptors
31
There are currently no selective ______ agonists or antagonists available for therapeutic use
H3 receptor
32
H4 receptors are found on....
Leukocytes in the bone marrow and circulating blood May have any important role in chemotaxis, esp in inflammation and allergic reactions
33
Principal actions of histamine are on ...
``` CV system Resp system Glandular tissue Nervous system Intradermal tissue ```
34
Effects of histamine on CV system
Vasodilation of small blood vessels • H1-induced release of NO (rapid, short lived effect) • Higher amts —> H2 mediated vasodilation and direct cardiac stimulation - (slow onset, long duration) • Vasodilation —> decreased BP with reflex tachycardia, flushing, warmth, and HA • Increased capillary permeability —> effux of plasma protein/fluid into ECF —> hives and edema
35
Large doses of histamine can result in shock due to ______
Decreased BP (CV effects)
36
Effects of histamine on the respiratory system
Bronchospasm (H1) due to increased Ca2+ Stimulates secretory activity in the lung and increases prostaglandin formation Small H2 bronchodilator effect as well
37
Bronchospasms secondary to histamine are usually mild in normal people but _______ are very sensitive to the effects of histamine
Asthmatics Bronchospasm may also involve irritation of vagal nerve endings
38
Effects of histamine on glandular tissue
Increased secretion of gastric acid and pepsin from gastric mucosa (H2) Increased secretion of catecholamines from adrenal glands with very high doses
39
Intradermal effects of histamine
Lewis triple response (flush, flare, and wheal) - occurs after intradermal injection of histamine Flush: dilation of capillaries in immediate area (in seconds, max by 1 min) Flare: dilation of arterioles —> redness over wider area Wheal: swelling in area of capillary dilation (1-2 mins later) Pain and itching are due to stimulation of nerve endings, which is then transmitted to the CNS
40
Manifestations of histamine release
Hay fever/allergic rhinitis Hives and skin rashes Anaphylaxis
41
What is anaphylaxis
Life threatening reaction to histamine release and other inflammatory mediators from mast cells Drop in BP, shock, resp difficulty, abdominal cramps, edema, hives, throat swelling
42
How is anaphylaxis treated?
Epinephrine Steroids Both H1 and H2 blockers (diphenhydramine & famotidine)
43
All of the antihistamines block _____ receptors
H1 Some are actually inverse agonists, which decrease constitutive activity at the H1 receptor and block the effects of histamine that is released
44
Because antihistamines compete with histamine, their ability to block histamine depends on...
The amount of histamine present In a very severe reaction (ie anaphylaxis), antihistamines alone may be insufficient to block the effect
45
First gen antihistamines have ______ effects and many of them also block _________
CNS effects Muscarinic receptors —> sedation and dry mouth
46
Second gen antihistamines are very selective for the ____ receptor and have little/no ____ effect
H1 CNS
47
All antihistamines block the effects of histamine released in response to allergens or other stimuli, decreasing the itch and Lewis triple response/edema. They are less effective at...
Blocking vasodilation, partly because this is also mediated by H2 receptors
48
Antihistamines decrease bronchospasm to a small degree, but this is not very useful in patients with asthma, as the bronchospasm is mediated more by _______
Leukotrienes
49
Antihistamines that get into the CNS cause both stimulation and depression. _______ is more common with overdose and may result in convulsions. More commonly, H1 blockade causes ______.
Stimulation (some become restless, unable to sleep) Sedation (more common in the older, first gen drugs)
50
Comparing the different first gen H1 antagonists: Diphenhydramine (Benadryl) Muscarinic Block: ______ Sedation: ______ Motion Sickness: _____
Muscarinic block +++ Sedation +++ Motion sickness ++
51
Comparing the different first gen H1 antagonists: Dimenhydrinate (Dramamine) Muscarinic Block: ______ Sedation: ______ Motion Sickness: _____
Muscarinic block +++ Sedation +++ Motion sickness ++
52
Comparing the different first gen H1 antagonists: Hydroxyzine (Vistaril) Muscarinic Block: ______ Sedation: ______ Motion Sickness: _____
``` Muscarinic block (-) Sedation +++ Motion sickness (-) ```
53
Comparing the different first gen H1 antagonists: Cyclizine, meclizine Muscarinic Block: ______ Sedation: ______ Motion Sickness: _____
Muscarinic block (-) Sedation + Motion sickness +
54
Comparing the different first gen H1 antagonists: Bromopheniramine (Dimetane), Chlorpheniramine (Chlor-Trimeton) Muscarinic Block: ______ Sedation: ______ Motion Sickness: _____
Muscarinic block + Sedation + Motion sickness (-)
55
Comparing the different first gen H1 antagonists: Promethazine (Phenergan) Muscarinic Block: ______ Sedation: ______ Motion Sickness: _____
Muscarinic block +++ Sedation +++ Motion sickness +++
56
Main difference with second gen H1 antagonists from first gen
Do not enter brain well —> primarily block peripheral receptors NOT anticholinergic Generally NON-sedating and fewer side effects
57
If any of the second gens causes sedation, it’s most likely ....
Cetirizine (Zyrtec)
58
Second Gen antihistamines may be better at _____ allergic reactions
Preventing, rather than treating them once they occur
59
What is the active metabolite of loratadine?
Desloratadine (Clarinex; Aerius)
60
_______ is teh active R-enantiomer of cetirizine
Levocetirizine - claimed to have fewer side effects but not generally supported by clinical literature
61
Pharmacokinetics of antihistamines
Well absorbed from the GI tract - generally given orally, onset in 15-30 min Duration of action varies, from 4-6 hours to 12-24 hours
62
Most antihistamines are metabolized by the ______
Liver Eliminated more slowly in children, elderly, and patients with liver disease Chronic use can induce hepatic drug-metabolizing enzymes
63
_______ can develop when antihistamines are used long term
Tolerance
64
Some second gen antihistamines are metabolized by ______ and concentrations can increase when treated concurrently with drugs which inhibit metabolism
CYP3A4 Example of inhibitor: Erythromycin
65
Which antihistamines are eliminated only by the kidney and are therefore a good choice for patients with liver disease or drug interaction concerns?
Cetirizine (Zyrtec) Levocetirizine (Zyxal) Acrivastine (Semprex)
66
Clinical indications for antihistamine use
Allergic rhinitis, seasonal rhinitis, and conjunctivitis (response best if used prophylactically - esp 2nd gen) Itching and hives (both first and second gen) Motion sickness (esp first gen drugs with strong anticholinergic effects) Sedation (only first gen - diphenhydramine and doxylamine) Decrease of salivary/lacrimal secretions NOT effective for asthma***
67
What antihistamine works best for conjunctivitis?
Topical eye drops - Levocabastine (Livostatin)
68
Which antihistamines are best for prophylactic treatment of allergic/seasonal rhinitis?
2nd gen antihistamines
69
Which antihistamines are best for motion sickness
1st gen only - need the anticholinergic effects Diphenhydramine (Benadryl) Dimenhydrinate (Dramamine) Promethazine (Phenergan)
70
Which antihistamines are used in OTC sleep aids?
1st gens Diphenhydramine (Tylenol PM) Doxylamine (Unisom)
71
Side effects of first gen antihistamines
SEDATION - potentiated by alcohol and other CNS depressants, worse in elderly patients Contraindicated in children (sedation may impair learning/memory) Anticholinergic effects (dry mouth, dry hot skin, urinary retention, constipation, blurred vision) Other CNS effects (dizziness, tinnitus, poor coordination, etc) May lower seizure threshold
72
Why shouldn’t you give a first gen antihistamine to a seizure-prone patient?
They lower the seizure threshold
73
Side effects of ALL antihistamines
GI - anorexia, N/V, epigastric distress, constipation, diarrhea (effects reduced if taken with food) Possibly teratogenic - avoid in pregnancy Allergic reactions possible with topical preps
74
What drug interactions should you know about for antihistamines?
CNS depressants (alcohol, phenothiazines, benzos, barbiturates) - don’t combine Erythromycin and ketoconazole may inhibit metabolism of 2nd gens Cimetidine (Tagamet) can also decrease metabolism And of course, grapefruit juice
75
Symptoms of acute 1st gen antihistamine poisoning
Similar to atropine poisoning ``` Excitement Convulsions Ataxia Hallucinations Tremors Fixed, dilated pupils Flushed, hot skin Coma CV/Resp collapse Sedation Dried up salivary/bronchial secretions ```
76
Overdose of second gen antihistamines may cause...
Cardiac arrhythmias
77
Which drugs inhibit the release of histamine from mast cells
``` Cromolyn sodium (Intel, Artane) Nedcromil (Tilade) ``` Used to treat asthmas, esp in children Administered in inhaled form, taken chronically
78
Non-competitive H1 blocker applied nasally to decrease teh release of histamine from mast cells
Azelastine (Asteline NS, Astepro) Used for allergic rhinitis
79
_________ is a second gen antihistamine but may also inhibit the release of histamine form mast cells
Cetirizine (Zyrtec)

Pharm III Unit II (8 decks)

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