ENT Pharmacology Flashcards
Route of administration
Antihistamines
E.g.:
-Meclizine
-Dimenhydrinate
-Diphenhydramine
Oral (usually every
4-8 hours)
-Dimenhydrinate
can also be given
IV, IM, suppository)
Antihistamines
E.g.:
-Meclizine
-Dimenhydrinate
-Diphenhydramine
Indication Antihistamines
Acute motion sickness and
vertigo (see above notes)
MOA of antihistamines
Histaminergic neurotransmission via
central H1 receptors involved in the link between neural mismatch signal and the emetic centre of brain.
Antihistamines will
reduce the neural mismatch signals
underlying motion sickness and vertigo
Adverse effects of antihistamine
Drowsiness
-Sedation
(meclizine is less
sedating so may
be the better
option)
EG of Anticholinergics
E.g.:
-Scopolamine
Route of administration
Anticholinergics
E.g.:
-Scopolamine
Oral (usually every
4-8 hours)
-Transdermal patch
(effectiveness up to
3 days per patch)
Indication Anticholinergics
-Acute motion sickness and
vertigo (see above notes)
MOA of Anticholinergics
-Like the histaminergic pathways,
cholinergic neurotransmission is involved in pathways underlying sensory inputs and brain emetic centre. Blocking these pathways may reduce the neural mismatch signals underlying motion sickness and vertigo
AE of anticholinergics
Drowsiness
-Sedation
-Dry mouth, dilated
pupils and other
anticholinergic
effects
Route of administration
Benzodiazepines
E.g.:
-Diazepam
-Lorazepam
Oral
-IV
Eg of Benzodiazepines
Diazepam
-Lorazepam
indication of Benzodiazepines
Acute motion sickness and
vertigo (see above notes)
-Relieves anxiety related to
vertigo
MOA of benziodiazepines
-Benzodiazepines such as diazepam act as positive allosteric modulators of inhibitory GABA-A receptors ->
reduces neurotransmission in pathways underlying
neural mismatch
AE of benziodiazepines (8)
Ataxia, euphoria,
Incoordination,
somnolence,
hypotension,
headache,
dizziness, blurred
vision
Why are non-sedating antihistamines such as fexofenadine not effective in treating motion sickness / vertigo?
Non-sedating antihistamines like fexofenadine are not effective in treating motion sickness or vertigo because they primarily target peripheral H1 receptors and do not adequately cross the blood-brain barrier. Motion sickness and vertigo are often mediated by central mechanisms in the brain, particularly involving the vestibular system and central H1 receptors.
In contrast, first-generation antihistamines (like diphenhydramine or dimenhydrinate) are effective for these conditions because they can cross the blood-brain barrier and have sedative properties, which help to reduce the central nervous system’s response to conflicting sensory signals that cause motion sickness. Essentially, non-sedating antihistamines lack the necessary central action to alleviate symptoms related to motion sickness and vertigo.
