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Pharmacy Stage 2 > Antihistamines and Antimuscarinics > Flashcards

Antihistamines and Antimuscarinics Flashcards

The histaminergic system and antihistamines.

1
Q

What are autacoids?

A
  • local hormones
  • short acting endogenous mediators
  • act as part of an inflammatory response
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2
Q

define pleitropic?

A

having more than one effect

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3
Q

what cells synthesise, store and release histamine?

A
  1. mast cells (in skin, GI, respiratory tract
  2. Basophils (in blood)
  3. Some neurons (in CNS and peripheral NS)
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4
Q

What is the effect of histamine secretion?

A
  1. acid secretion
  2. mucosal protection
  3. Fluid transport
  4. Neurotransmission
  5. Visceral sensitivity
  6. Motility
  7. Inflammation
  8. Allergy
  9. Tumour growth
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5
Q

How is histamine synthesised?

A

by decarboxylation from an amino acid precursor, histadine. Uses histidine decarboxylase

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6
Q

Where is histamine stored?

A

in granules in mast cells, basophils and enterocytes

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7
Q

Why is histamine released?

A

in response to a stimuli which is a Ca dependent exocytosis

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8
Q

how is histamine eliminated?

A

by oxidative deamination and/or transmethylation

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9
Q

what is produced when histamine undergoes deamination?

A

a ribose conjugate

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10
Q

what is produced when histamine undergoes transmethylation?

A

monoamine oxidase

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11
Q

Where are H1 receptors found and what do they control?

A
  • found in smooth muscle, in endothelium cells and the CNS.

- control bronchoconstriction, vasodilation, pain itching, motion sickness, rhinitis, separation of epithelial cells

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12
Q

Where are H2 receptors found and what do they control?

A
  • in gastric parietal cells, vascular smooth muscle cells, basophils
  • regulate GA secretion, vasodilation, inhibition of IgE-dependent degranulation
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13
Q

Where are H3 receptors found and what do they control?

A
  • in CNS cells and peripheral NS
  • control release of DA, GABA, ACh, 5-HT and NE. Also controls presynaptic feedback, inhibiting histamine synthesis and release
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14
Q

Where are H4 receptors found and what do they control?

A
  • in bone marrow and white blood cells

- mediate mast cell chemotaxis

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15
Q

What are H1 receptors coupled to?

A

Gq proteins which are coupled to phospholipase C (PLC)

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16
Q

What are H2 receptors coupled to?

A

Gs proteins which are coupled to adenylyl cyclase (AC) increasing cAMP.

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17
Q

What are H3 receptors coupled to?

A

Gi/o proteins which are coupled to AC as well as K-channels

18
Q

What is the effect of H3 receptors on calcium influx and presynaptic neurotransmitter release?

A

reduces Ca influx and inhibits the neurotransmitter release.

19
Q

What are H4 receptors coupled to?

A

Gi/o in mast cells and eosinophils

20
Q

What is the effect of H4 receptors, coupled to eosinophils, on calcium?

A

it triggers calcium mobilisation causing mast cell chemotaxis.

21
Q

What is the ‘triple response of Lewis’?

A

a cutaneous reponse that occurs from firm stroking of the skin producing:

  1. an initial red line
  2. a flare around the line
  3. a wheal
22
Q

What happens when histamine is injected transdermally?

A
  1. a red spot appears
  2. flare
  3. wheal (oedema)
23
Q

what is the effect of histamine on the heart?

A
  • forces contraction of atrial and ventricular muscles by promoting Ca2+ influx.
  • speeds heart rate by hastening diastolic depolarisation in SAN
  • slows AV conduction to increase automaticity and elicit arrhythmias
24
Q

Which receptor controls the majority of the effect of histamine on the heart?

A

H2 receptors and cAMP accumulation.

H1 only controls the slowing down of AV conduction

25
Q

Effect of H1 and H2 on the lungs?

A

H1- bronchodilation, increased mucus viscosity, stimulates vagal sensory nerve endings causing cough
H2- slight bronchodilation and increased mucus secretion

26
Q

What are the effects of histamine on H1 receptors?

A
  1. decreased peripheral vascular resistance
  2. Increased vascular permeability
  3. Increased GI motility
27
Q

What are the effects of histamine on H2 receptors?

A
  1. decreased peripheral vascular resistance
  2. Tachycardia (increased heart rate)
  3. Increased gastric acid and pepsin secretion
  4. Increased mucus production
28
Q

What are the effects of histamine on H3 receptors?

A

stimulate nerve endings (pain)

29
Q

What are the pathophysiological actions of histamine?

A
  1. mediates immediate hypersensitivity reactions and acute inflammatory responses
  2. causes anaphylaxis
  3. causes allergic reaction
  4. causes duodenal ulcers
  5. causes systemic mastocytosis
  6. causes gastrinoma
30
Q

What is anaphylaxis?

A
  • a type I allergic response mediated by IgE antibodies
  • IgE binds to receptors on mast cells and basophils
  • Antobody binds to antigen causing release of histamine, leukotrienes, prostaglandins etc
31
Q

What are the effects pf anaphylaxis?

A
  1. decreased blood pressure
  2. decreased cardiac output
  3. bronchoconstriction 4. increased pulmonary secretions
  4. pruritis
32
Q

How is anaphylaxis treated?

A

give epinephrine (a physiological antagonist of histamine, not a pharmacological one)

33
Q

Three mechanistically different approaches

to minimize histamine reactions are…?

A
  1. physiological antagonism
  2. inhibit histamine release
  3. pharmacological antagonism
34
Q

What drugs are given as mast cell stabilisers?

A

cromolyn

35
Q

What drug is given as an H1 receptor antagonist?

A

diphenhydramine or cetirizine

36
Q

What drug is given as an H2 receptor antagonist?

A

ranitidine or cimetidine

37
Q

Properties of 1st generation H1 antihistamines?

A
  1. antiallergy
  2. sedative
  3. antimimetic (prevent motion sickness)
  4. antitussive
  5. given to treat anaphylaxis
  6. lipid soluble - good CNS penetration
  7. well absorbed
  8. metabolised in liver
38
Q

adverse reactions of 1st generation H1 antihistamines?

A
  1. sedation
  2. drowsiness
  3. headache
  4. nausea
  5. vomit
  6. cough
  7. constipation
  8. diarrhoea
  9. dry mouth
  10. blurred vision
  11. urinary retention
39
Q

Properties of 2nd generation H1 antihistamines?

A
  1. lipid soluble
  2. highly ionised functional group so less CNS penetration
  3. well absorbed
  4. metabolised in liver
40
Q

adverse effects of 2nd generation H1 antihistamines?

A
  1. terfenadine and astemizole prolong QT interval in cardiac cycle and they affected the K+ channels. However they are no longer supplied.
41
Q

How are 2nd generation antihistamines excreted?

A

in their unmetabolised form in urine.

Pharmacy Stage 2 (85 decks)

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