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Respiratory Block: Pharmacology > Antihistamines > Flashcards

Antihistamines Flashcards

1
Q

Pharmacological effects of Histamine: Which receptors are found in the Nervous System and what is the effect of their simulation?

A

H1 - pain and itching

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2
Q

Pharmacological effects of Histamine: Which receptors are found in the Cardiovascular System and what is the effect of their simulation?

A

H1 & H2 - decreased BP, increased HR

H2 - increased contractility, increased pacemaker rate

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3
Q

Pharmacological effects of Histamine: Which receptors are found in the Bronchial smooth muscle and what is the effect of their simulation?

A

H1 - bronchoconstriction

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4
Q

Pharmacological effects of Histamine: Which receptors are found in the GIT smooth muscle and what is the effect of their simulation?

A

H1 - contraction, diarrhea

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5
Q

Pharmacological effects of Histamine: Which receptors are found in the Secretory tissue (stomach) and what is the effect of their simulation?

A

H2 - increased gastric acid secretion

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6
Q

Pharmacological effects of Histamine: Which receptors are found in the Triple response (capillaries) and what is the effect of their simulation?

A

H1 +++++, H2
= Wheal & flare response, 3 cell types involved:
1. Smooth muscle in microcirculation
2. Capillary and venular endothelium
3. Sensory nerve endings
= increased dilation of small vessels, increased permeability, edema and itch

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7
Q

Pharmacological effects of Histamine: Which receptors are found in the Exocrine Secretion and what is the effect of their simulation?

A

H1 & H2 - Production of nasal and bronchial mucous

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8
Q

Pharmacological effects of Histamine: Which receptors are found in the Central Nervous System and what is the effect of their simulation?

A

H1 - Excitation (arousal, wakefulness) + control of food and water intake
H2 + H3 - Inhibitory

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9
Q

Antihistamines are divided into what groups?

A

1st, 2nd, and 3rd generation

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10
Q

What are the characteristics of the 1st generation?

A

Strong sedative effects, block autonomic receptors.

enter CNS readily

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11
Q

What are the characteristics of the 2nd generation?

A

Less sedation and less complete distribution into the CNS , some are cardiotoxic

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12
Q

What are the characteristics of the 3rd generation?

A

Non-sedative and Non-cardiotoxic

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13
Q

Pharmacokinetics: How rapidly are the drugs absorbed?

A

Rapidly absorbed after oral administration

- peak blood concentration after 1-2 hours

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14
Q

Pharmacokinetics: How are several of the second generation antihistamines metabolized?

A

By the enzyme CYP3A4 which can lead to drug interactions

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15
Q

Pharmacokinetics: What is the duration of action?

A

Between 4-6 hours

- but Meclizine and several 2nd generation antihistamines have longer duration of action: 12-24 hours

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16
Q

Pharmacokinetics: What is the lipid solubility?

A

Newer generations are less lipid soluble than the older generations

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17
Q

What is the active metabolite of Hydroxyzine?

A

Cetirizine

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18
Q

What is the active metabolite of Terfenadine?

A

Fexofenadine

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19
Q

What is the active metabolite of Loratadine?

A

Desloratadine

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20
Q

What is the mechanism of action of the antihistamines?

A

Block the action of histamine by reversible competitive antagonism at H1-receptors, little effect on H2 or H3 receptors.

  • Histamine-induced contraction of bronchial or GIT smooth muscle is completely blocked
  • Effect on gastric acid secretion & heart are unmodified
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21
Q

Other effects of antihistamines (only 1st generation) not caused by H-1 receptor blockage on the CNS (H1)

A
  • Sedation, some useful as sleep acids
  • May cause excitation in children
  • Toxic doses = stimulation, agitation, convulsions, coma
22
Q

Other effects of antihistamines (only 1st generation) not caused by H-1 receptor blockage on the muscarinic cholinergic-receptor block

A
  • Prevents motion sickness, decreased effectiveness when motion sickness is already present
  • anti-vertigo
  • anti-Parkinsonism
  • decreased secretions (peripheral)
23
Q

Other effects of antihistamines (only 1st generation) not caused by H-1 receptor blockage on alpha-adrenoreceptor block

A

Hypotension (promethazine)

24
Q

Other effects of antihistamines (only 1st generation) not caused by H-1 receptor blockage on serotonin receptor block

A
  • appetite stimulation / weight gain

Cyproheptadine

25
Q

Other effects of antihistamines (only 1st generation) not caused by H-1 receptor blockage on Na channel block

A

Local anesthesia

26
Q

Other effects of antihistamines (only 1st generation) not caused by H-1 receptor blockage: which drug inhibits mast cell release of histamine?

A

Cetirizine (active metabolite of hydroxyzine)

27
Q

Which antihistamines should be used for allergic reactions?

A

More the second and third generation antihistamines

28
Q

Which antihistamines should be used for allergic rhinitis

A
  1. Systemic antihistamines - mild cases with / without systemic nasal decongestants (pseudoephedrine), 2nd, 3rd generation less sedation
  2. Topical preparations = LEVOCABASTINE, AZELASTIN - seasonal allergic rhinitis
29
Q

What is Azelastine used for?

A

Topical preparation antihistamine

  • allergic rhinitis
  • blocks H-1 receptors
  • inhibits the release of inflammatory mediators from mast cells
30
Q

What is Levocabastine used for?

A

Topical preparation antihistamine

  • long acting
  • short-term symptomatic treatment of seasonal allergic rhinitis
31
Q

Which antihistamines should be used for atopic dermatitis?

A

Diphenhydramine

- 1st generation, sedative and itching effects

32
Q

Which antihistamines should be used for Hay fever?

A

Alkylamines and second generation

- want to minimize sedation

33
Q

In anaphylaxis, antihistamines are a secondary treatment to what?

A

Adrenaline

34
Q

Which antihistamines should be used as antiemetics (nausea and vomiting)?

A
  1. Doxylamine*
  2. Cyclizine*
  3. Buclizine
35
Q

Which antihistamines should be used for motion sickness and vestibular disturbances (vertigo)?

A 
1st Generation for prevention of motion sickness: 
1. Diphenhydramine 
2. Promethazine 
3. Cyclizine 
(& Meclizine)
36
Q

What drugs should be used with antihistamines for more effective control of motion sickness and vestibular disturbances (vertigo)?

A

Ephedrine or amphetamine

37
Q

Which antihistamines should be used for postoperative medication?

A

Promethazine

- sedation, antimuscarinic & antiemetic

38
Q

Which antihistamines should be used for sedation?

A
  1. Diphenhydramine*
  2. Doxylamine
    = induces sleep, may not however maintain sleep
39
Q

Which antihistamines should be used as an antipruritic?

A

Diphenyhydramine

- reduces itching

40
Q

Which antihistamines should be used as an appetite stimulant?

A

Cyproheptadine

41
Q

Which antihistamines should be used for rhinorrhea in colds and flu?

A

This is primarily the antimuscarinic activity of the 1st generation antihistamines
= drying of secretions, specifically nasal secretions
(also cause dry mouth due to the same effect)

42
Q

How are antihistamines used for rhinorrhea in colds and flu usually found?

A

In polycomponent cold and flu preparations as they:

  • increase tenacity of secretions
  • interfere with normal ciliary function
  • cause drowsiness
43
Q

Which antihistamine is the antidote to “serotonin syndrome”?

A

Cyproheptadine

44
Q

Which antihistamines should be used for anti-Parkinsonism?

A
  1. Promethazine

2. Dophenhydramine

45
Q

Which antihistamines should be used as antitussives?

A

Peripherally acting antihistamines (1st generation) - block cholinergic nerve impulses = dry up secretions = mucous plug formation
- PROMETHAZINE + DIPHENHYDRAMINE

46
Q

When should antihistamines not be used as antitussives?

A

Not for productive coughs or asthmatics

47
Q

Antihistamines as antitussives: Promethazine

A

Causes sedation

48
Q

Antihistamines as antitussives: Chlorpheniramine

A

Causes less sedation than promethazine, however still causes sedation

49
Q

Antihistamines as antitussives: Diphenhydramine

A

Potent antitussive and sedative

50
Q

Antihistamines as antitussives: Mepyramine maleate

A

Less sedating

51
Q

Antihistamines as antitussives: Tripolidine

A

Acts for up to 12 hours

52
Q

Which antihistamines should be used for local anaesthesia?

A
  1. Diphenhydramine
  2. Promethazine
    - when patients are allergic to the usual anaesthetics

Respiratory Block: Pharmacology (8 decks)

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