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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
Q

Stimulation of H2 receptors on blood vessels leads to ______

A

Vasodilation

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26
Q

The H3 and H4 receptors are linked to _______ and decrease ______.

A

Gi protein

cAMP

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27
Q

Which histamine receptors are linked to Gi proteins and decrease cAMP?

A

H3 and H4

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28
Q

H3 receptors are found in ____ and are primarily ____.

A

The brain

Presynaptic - appear to mediate feedback inhibition of histamine release

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29
Q

H3 agonists promote _____

A

Sleep

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30
Q

H3 antagonists increase ______ through stimulation of _________

A

Wakefulness

H1 receptors

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31
Q

There are currently no selective ______ agonists or antagonists available for therapeutic use

A

H3 receptor

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32
Q

H4 receptors are found on….

A

Leukocytes in the bone marrow and circulating blood

May have any important role in chemotaxis, esp in inflammation and allergic reactions

33
Q

Principal actions of histamine are on …

A 
CV system
Resp system
Glandular tissue
Nervous system
Intradermal tissue
34
Q

Effects of histamine on CV system

A

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
Q

Large doses of histamine can result in shock due to ______

A

Decreased BP (CV effects)

36
Q

Effects of histamine on the respiratory system

A

Bronchospasm (H1) due to increased Ca2+

Stimulates secretory activity in the lung and increases prostaglandin formation

Small H2 bronchodilator effect as well

37
Q

Bronchospasms secondary to histamine are usually mild in normal people but _______ are very sensitive to the effects of histamine

A

Asthmatics

Bronchospasm may also involve irritation of vagal nerve endings

38
Q

Effects of histamine on glandular tissue

A

Increased secretion of gastric acid and pepsin from gastric mucosa (H2)

Increased secretion of catecholamines from adrenal glands with very high doses

39
Q

Intradermal effects of histamine

A

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
Q

Manifestations of histamine release

A

Hay fever/allergic rhinitis
Hives and skin rashes
Anaphylaxis

41
Q

What is anaphylaxis

A

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
Q

How is anaphylaxis treated?

A

Epinephrine
Steroids
Both H1 and H2 blockers (diphenhydramine & famotidine)

43
Q

All of the antihistamines block _____ receptors

A

H1

Some are actually inverse agonists, which decrease constitutive activity at the H1 receptor and block the effects of histamine that is released

44
Q

Because antihistamines compete with histamine, their ability to block histamine depends on…

A

The amount of histamine present

In a very severe reaction (ie anaphylaxis), antihistamines alone may be insufficient to block the effect

45
Q

First gen antihistamines have ______ effects and many of them also block _________

A

CNS effects

Muscarinic receptors —> sedation and dry mouth

46
Q

Second gen antihistamines are very selective for the ____ receptor and have little/no ____ effect

A

H1

CNS

47
Q

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…

A

Blocking vasodilation, partly because this is also mediated by H2 receptors

48
Q

Antihistamines decrease bronchospasm to a small degree, but this is not very useful in patients with asthma, as the bronchospasm is mediated more by _______

A

Leukotrienes

49
Q

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 ______.

A

Stimulation (some become restless, unable to sleep)

Sedation (more common in the older, first gen drugs)

50
Q

Comparing the different first gen H1 antagonists:

Diphenhydramine (Benadryl)

Muscarinic Block: ______
Sedation: ______
Motion Sickness: _____

A

Muscarinic block +++
Sedation +++
Motion sickness ++

51
Q

Comparing the different first gen H1 antagonists:

Dimenhydrinate (Dramamine)

Muscarinic Block: ______
Sedation: ______
Motion Sickness: _____

A

Muscarinic block +++
Sedation +++
Motion sickness ++

52
Q

Comparing the different first gen H1 antagonists:

Hydroxyzine (Vistaril)

Muscarinic Block: ______
Sedation: ______
Motion Sickness: _____

A 
Muscarinic block (-)
Sedation +++
Motion sickness (-)
53
Q

Comparing the different first gen H1 antagonists:

Cyclizine, meclizine

Muscarinic Block: ______
Sedation: ______
Motion Sickness: _____

A

Muscarinic block (-)
Sedation +
Motion sickness +

54
Q

Comparing the different first gen H1 antagonists:

Bromopheniramine (Dimetane), Chlorpheniramine (Chlor-Trimeton)

Muscarinic Block: ______
Sedation: ______
Motion Sickness: _____

A

Muscarinic block +
Sedation +
Motion sickness (-)

55
Q

Comparing the different first gen H1 antagonists:

Promethazine (Phenergan)

Muscarinic Block: ______
Sedation: ______
Motion Sickness: _____

A

Muscarinic block +++
Sedation +++
Motion sickness +++

56
Q

Main difference with second gen H1 antagonists from first gen

A

Do not enter brain well —> primarily block peripheral receptors

NOT anticholinergic

Generally NON-sedating and fewer side effects

57
Q

If any of the second gens causes sedation, it’s most likely ….

A

Cetirizine (Zyrtec)

58
Q

Second Gen antihistamines may be better at _____ allergic reactions

A

Preventing, rather than treating them once they occur

59
Q

What is the active metabolite of loratadine?

A

Desloratadine (Clarinex; Aerius)

60
Q

_______ is teh active R-enantiomer of cetirizine

A

Levocetirizine - claimed to have fewer side effects but not generally supported by clinical literature

61
Q

Pharmacokinetics of antihistamines

A

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
Q

Most antihistamines are metabolized by the ______

A

Liver

Eliminated more slowly in children, elderly, and patients with liver disease

Chronic use can induce hepatic drug-metabolizing enzymes

63
Q

_______ can develop when antihistamines are used long term

A

Tolerance

64
Q

Some second gen antihistamines are metabolized by ______ and concentrations can increase when treated concurrently with drugs which inhibit metabolism

A

CYP3A4

Example of inhibitor: Erythromycin

65
Q

Which antihistamines are eliminated only by the kidney and are therefore a good choice for patients with liver disease or drug interaction concerns?

A

Cetirizine (Zyrtec)

Levocetirizine (Zyxal)

Acrivastine (Semprex)

66
Q

Clinical indications for antihistamine use

A

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
Q

What antihistamine works best for conjunctivitis?

A

Topical eye drops - Levocabastine (Livostatin)

68
Q

Which antihistamines are best for prophylactic treatment of allergic/seasonal rhinitis?

A

2nd gen antihistamines

69
Q

Which antihistamines are best for motion sickness

A

1st gen only - need the anticholinergic effects

Diphenhydramine (Benadryl)
Dimenhydrinate (Dramamine)
Promethazine (Phenergan)

70
Q

Which antihistamines are used in OTC sleep aids?

A

1st gens

Diphenhydramine (Tylenol PM)
Doxylamine (Unisom)

71
Q

Side effects of first gen antihistamines

A

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
Q

Why shouldn’t you give a first gen antihistamine to a seizure-prone patient?

A

They lower the seizure threshold

73
Q

Side effects of ALL antihistamines

A

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
Q

What drug interactions should you know about for antihistamines?

A

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
Q

Symptoms of acute 1st gen antihistamine poisoning

A

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
Q

Overdose of second gen antihistamines may cause…

A

Cardiac arrhythmias

77
Q

Which drugs inhibit the release of histamine from mast cells

A 
Cromolyn sodium (Intel, Artane)
Nedcromil (Tilade)

Used to treat asthmas, esp in children

Administered in inhaled form, taken chronically

78
Q

Non-competitive H1 blocker applied nasally to decrease teh release of histamine from mast cells

A

Azelastine (Asteline NS, Astepro)

Used for allergic rhinitis

79
Q

_________ is a second gen antihistamine but may also inhibit the release of histamine form mast cells

A

Cetirizine (Zyrtec)

Pharm III Unit II (8 decks)

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