Antihistamines & Antitussives

Front 1

Triple response of histamine

Back 1

1. Flush - localised red (NO mediated dilation of arterioles)
2. Wheal - swelling (leakage from post-capillary venules)
3. Flare - large irregular flare sensory nerve axon reflex

also histamine induces SM contraction, pain and itchiness

Front 2

Inhibiting histamine

Back 2

1. functional (physiological) antagonism - e.g. adrenaline opposes histamine induced bronchoconstriction in systemic anaphylaxis

2. Histamine receptor antagonists (antihistamines)

Front 3

1st gen H1-receptor antagonists

Back 3

Promethazine, Diphenhydramine, Cyproheptadine

Acts on other receptors aswell

each has side effects (sedation, dry mouth, postural hypertension)

hence, their primary use is NOT H1 receptor blockade

Front 4

2nd gen H1-receptor antagonists

Back 4

selective antagonists of H1 receptor only - less side effects

Fexofenadine (Telfast)
Cetirizine (Zyrtec)
Loratadine (Claratyne)

Front 5

How do antihistamines stop hayfever

Back 5

Hayfever = "seasonal allergic rhinitis"

1. sneeze & itch - by inhibiting histamine induced activation of sensory nerves
2. rhinorrhea by inhibiting secretion from mucus glands
3. acute congestion by inhibiting microvascular leakage from post-capillary venules

Front 6

Treating chronic nasal congestion

Back 6

fexofenadine good for itch sneezing and rhinorrhea however, chronic nasal congestion is inflammatory

hence, use intranasal glucocorticoids

Front 7

H2 receptor antagonists

Back 7

Ranitidine - for gastric ulcer / gord
supress gastric acid secretion in response to histamine on parietal cells

Front 8

Antitussives

Back 8

1. treat underlying cause

2. nonspecific therapy - codeine
(or methylmorphine - opiates)

good for NONPRODUCTIVE cough

acts centrally on cough receptor

side effects - drowsiness, constipation, nausea & vomiting