Blockers of the Histamine-1 Receptor Flashcards

1
Q

When is histamine released?

A

Released in a variety of allergic conditions e.g. seasonal rhinitis (hay fever), insect stings
Reactions to certain drugs e.g. penicillin, aspirin

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2
Q

Describe the process in which histamine is released

A

IgE binds to the surface of mast cells after first exposure to antigen
After renewed exposure, degranulation (vesicles opened) of the mast cells causes the release of pro-inflammatory mediators (e.g. histamine)

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3
Q

Where does histamine mediate its activity?

A

At the H1 receptor

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4
Q

What properties do blockers of the H1 receptor require?

A

Potent
H1 selective
Hydrophilic - to prevent transport across the BBB = drowsy

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5
Q

List 3 examples of H1 blockers

A

Loratidine
Terfenadine
Fexofanadine

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6
Q

Describe Terfanadine

A

2nd generation H1 blocker = free from anticholinergic (ACh) and CNS-related side effects
Undergoes almost complete first pass metabolism to the pharmacologically active fexofenadine by action of cytochrome P450

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7
Q

Why must terfenadine be metabolised to fexofenadine?

A

Hepatic impairment can lead to a high terfenadine concentration in plasma = serious cardiac events
Fexofenadine does not build up so is devoid of cardiac events

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8
Q

Describe Cetirizine

A

Does not exhibit anticholinergic properties
Only crosses BBB slightly
The *S)-enantiomer displays an improved pharmacological profile compared to the racemate

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