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Pharmacyology 3 > Antihistamines > Flashcards

Antihistamines Flashcards

1
Q

Antihistamines

A

Histamine H1 receptor antagonists

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2
Q

1st gen antihistamines

A 
Chlorpheniramine
Diphenhydramine
Meclizine
Promethazine
Doxylamine
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3
Q

2nd gen antihistamines

A

Cetirizine

Fexofenadine

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4
Q

When is histamine released?

A

Allergic/inflammatory reactions

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5
Q

Functional histamine antagonists

A

Epinephrine

Cromolyn sodium

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6
Q

Cells that release histamine

A

Mast cells
Basophils
Enterochromaffine like cells (G cells)
Histaminergic neurons

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7
Q

Histamine is what type of hormone?

A

Autocoid (local)

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8
Q

Mast cells

A
  • For pathogen defense
  • in most tissue, near blood vessels
  • enriched at body interfaces (ears, eyes, nose, throat, gut)
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9
Q

Histamine release triggers

A
  • immunologic
  • chemical
  • tissue damage
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10
Q

Enterochromaffin-like cells

A
  • ## release histamine that act on H2 receptors on parietal cells
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11
Q

Which histamine receptor is therapeutically most relevant?

A

H1

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12
Q

Which histamine receptors are involved in allergic reaction?

A

H1, also H2 and H3

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13
Q

Histamine actions in allergic reactions

A
  • VSM dilation
  • increased vascular permeability
  • peripheral sensory nerve excitation
  • nasal congestion
  • bronchial smooth muscle contraction
  • intestinal smooth muscle contraction
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14
Q

VSM dilation in allergic reaction

A

Flushing
Fall in systemic BP
Reflex tachycardia

Small reaction —> H1 stimulated
Large —> H2

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15
Q

Where is H1 receptor?

A

Endothelium (NO)

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16
Q

Where is H2 located?

A

Smooth muscle cells (cAMP)

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17
Q

VSM dilation can cause what?

A

Histamine shock in systemic anaphylaxis

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18
Q

H receptors are what type of receptors?

A

GPCR

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19
Q

Increased vascular permeability in allergic reaction

A

Endothelial cell retraction
Edema/wheal formation (plasma and protein leaking)

H1 recpetor

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20
Q

Peripheral sensory nerve excitation in allergic response

A

Pain and itching

H1 and H3 receptors

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21
Q

Triple response of allergic reaction

A
  • rapid reddening
  • swelling (edema)
  • flare
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22
Q

Rapid reddening in allergic reaction is due to what?

A

Dilation of small vessels

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23
Q

Swelling (edema) in allergic reaction is due to what?

A

Increased vascular permeability

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24
Q

Flare in allergic reaction is due to what?

A

Neural activated vasodilation

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25
Q

Triple response is used for what?

A

Quantify allergic response of an individual

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26
Q

Nasal congestion is from what H receptor?

A

H1

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27
Q

Bronchial smooth muscle contraction in allergic reaction

A

H1
Bronchial hyperactivity to histamine in asthmatics
Involves neural response

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28
Q

Other histamine receptor actions

A
  • H2 on gastric parietel cells
  • H2 on cardiac muscle
  • CNS (wakefullness, analgesic)
  • H4 modulate cytokine production
  • anaphylactic shock
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29
Q

Anaphylactic shock

A
  • bronchospasms
  • severe hypotension
  • angioedema
  • mucous membrane congestion
  • CNS: confusion, anxiety
  • N/V
  • palpitations
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30
Q

What should you give in anaphylactic shock?

A

Epinephrine

H1 blockers not effective

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31
Q

Physiological antagonist of histamine

A
  • occurs when chemicals counterbalance each other by producing opposite effects on same physiological function
  • Epi
32
Q

Epi and histamine reaction

A

A1: NE activation, vasoconstriction (increase BP0
B2: NE activation, bronchodilation

33
Q

Histamine release inhibitor

A

Cromolyn sodium

34
Q

Cromolyn sodium and histamine

A
  • inhibit lung mast cell histamine release

- prophylactic use in asthma, hay fever

35
Q

First gen antihistamine overview

A
  • enter CNS
  • sedation
  • anti-cholinergic effects
  • GI problems
36
Q

2nd gen antihistamine overview

A
  • mostly do not enter CNS
  • less sedating
  • less muscarinic action
  • more metabolized by CYP3A4 —> drug interactions
37
Q

1st generation antihistamine metabolism

A

CYP450 most 2D6

  • don’t have to worry about interfering with other drugs
38
Q

Antihistamine excreteion

A

Urine

Feces (fexofenadine)

39
Q

Antihistamine pharmacodynamics

A
  • inhibit vasodilation and bronchial contraction
  • inhibit increased capillary permeability and edema/wheal formation (does not reverse)
  • anti allergic, anti inflammatory
40
Q

Antihistamine use general information

A
  • best to take before needed
  • symptom relief may be incomplete
  • tolerance usually does not develop
  • less effective with chronic/high antigen exposure
41
Q

T/f tolerance usually develops in antihistamines

A

False

Usually does not

42
Q

Antihistamine PK

A

Most 4-6 hours

2nd gen are 12-24 hour

43
Q

Antihistamine uses

A
  • Seasonal allergic rhinitis and conjunctivitis (hay fever)
  • hives
  • anaphylaxis
  • atopic dermatitis (eczema)
  • CNS and vestibular disorders
44
Q

For seasonal allergic rhinitis what are antihistamines combined with?

A

Pseudoephedrine

Phenylephrine

45
Q

Antihistamines and anaphylaxis

A
  • NOT to replace epinephrine

- only to reduce flushing, itching, urticaria, rhinorrhea

46
Q

Antihistamines for motion sickness

A
  • diphenhydramine
  • promethazine
  • meclizine
47
Q

Antihistamines for antiemetic

A

Promethazine

Doxylamine

48
Q

Antihistamines for insomnia

A

Diphenhydramine

Promethazine

49
Q

Sedation from antihistamines can be enhanced by what?

A

EtOH and CNS depressants

50
Q

CNS adverse effects of antihistamines

A
  • sedation
  • dizziness, HA
  • stimulation in children
51
Q

T/F there are fewer adverse effects with 2nd gen antihistamines

A

True

52
Q

GI adverse effects of antihistamines

A
  • due to muscarinic, adrenergic, serotonin receptor block
  • constipation/diarrhea
  • loss of appetite
  • N/V/ epigastric distress
53
Q

Anti-muscarinic effects of antihistamines

A
  • dry mouth and sinuses

- urinary retention

54
Q

Antihistamines CI

A

Narrow angle glaucoma

Dysuria

55
Q

Allergic reactions from antihistamines

A
  • dermatitis
  • drug fever
  • some photosensitization
56
Q

Antihistamine overdose

A

Tachycardia
Dry mouth
Dilated pupils
Hallucinations

57
Q

T/F caution in pregnancy with antihistamines

A

True

58
Q

T/F generally avoid 2nd gen antihistamines in children and elderly

A

False

1st gen

59
Q

Diphenhydramine uses

A
  • allergic rhinitis
  • dermatologic pain and itching
  • insomnia
  • motion sickness
60
Q

Adverse effects of diphenhydramine

A
  • sedation
  • excitation in children
  • reduce lactation
  • enter breast milk
  • avoid in narrow angle glaucoma
61
Q

Chlorpheniramine use

A
  • allergic rhinitis
  • dermatologic pain and itching
  • OTC cold (>2-4 yo)
62
Q

Adverse effects of chlorpheniramine

A
  • sedation, but less than benadryl
  • less muscarinic effects
  • still glaucoma concern
63
Q

Promethazine use

A
  • antiemetic

- sedative

64
Q

Adverse effects of promethazine

A
  • similar to other 1st gen

- photosensitivity

65
Q

BBW promethazine

A
  • respiratory depression (<2yo)

- severe tissue injury with injection

66
Q

Meclizine use

A
  • vertigo

- prevent motion sickness

67
Q

Adverse effects of meclizine

A

Sedation (less than other 1st gens)

68
Q

Diclegis

A

Doxylamine + pyridoxine (vitamin B6)

69
Q

Diclegis use

A

Morning sickness

Sedative

70
Q

T/F 2nd gen antihistamines have increased 1st pass effect

A

True

71
Q

Cetirizine use

A
  • allergic rhinitis

- dermatologic pain and itch

72
Q

Adverse effects of cetirizine

A
  • very well tolerated
  • some sedation
  • weak anti-muscarinic effects
  • metabolized by CYP3A4
73
Q

Fexofenadine use

A
  • allergic rhinitis (oral only)

- dermatologic pain and itching (better prophylactically)

74
Q

Adverse effects of fexofenadine

A
  • usually well tolerated
  • not sedating
  • dysmenorrhea
  • enters breast milk
75
Q

Which antihistamine should you NOT take with fruit juice?

A

Fexofenadine (reduces absorptioN)

- OATP transport for absorption, not a CYP3A4

76
Q

Decongestant general use

A
  • relief from nasal congestion and pressure

Pharmacyology 3 (12 decks)

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