Antihistamines

Question 1

Histamine

Answer 1

Biogenic amine
Mast cell pool: circulating basophils and tissue mast cells
Non-mast cell pool: GI, lungs, skin, brain

Question 2

Mast cell granule content

Answer 2

Histamine, serotonin, heparin-protein complex, proteolytic enzymes, autocoids

Question 3

Pre-capillary arteriole

Answer 3

Targets H1 receptor → dilation → hypotension

Question 4

Post-capillary venule

Answer 4

With H1 receptor → increased permeability → edema

Question 5

Cardiac

Answer 5

With H2 receptor → positive ionotrope and chronotrope → tachycardia

Question 6

Smooth muscle

Answer 6

With H1 receptor → contraction in bronchi and GI tract → bronchoconstriction/ spasm/ contraction

Question 7

Lung

Answer 7

Tissue mast cell (systemic anaphylaxis) shock organ for:
Cat, sheep, cows, pig and human

Question 8

GI tract

Answer 8

Tissue mast cell (systemic anaphylaxis) shock organ for:
Horse, pig, dog (hepatic/ GI)

Question 9

H1 receptor

Answer 9

Inflammation
Anaphylaxis, allergies, drug rxs (resp., arteriol, venous)

Question 10

Other histamine receptors

Answer 10

H2: gastric acid secretion
H3: NT release
H4 cells types associated with inflamm.

Question 11

Histamine in the GI tract

Answer 11

Gastric acid secretion
Histamine continually secreted by gastric mucosa
H2 receptor: HCl secreted by parietal cell

Question 12

H1 Antihistamine effects on vasculature

Answer 12

Stabilizes → antagonize arterial vasodilation and venous leaking

Question 13

H1 Antihistamine effects on smooth muscle (resp. system)

Answer 13

Relaxation → ↓ bronchoconstriction

Question 14

H1 Antihistamine effects on extracellular fluid

Answer 14

Decrease → minimize local and systemic

Question 15

H1 Antihistamine effects on inflammatory mediators

Answer 15

Decrease release → ↓inflammatory response

Question 16

Alternate antihistamine approaches

Answer 16

Physiologic antagonists
Opposite response as histamine: don’t block release or compete

Question 17

Clinical situations to use alternate antihistamine approaches

Answer 17

Acute anaphylaxis: sympathomimetics (EP, ephedrine, isoproterenol)
Bronchoconstriction: anaphylaxis, asthma (EP)
↓ histamine associated inflamm response (glucocorticoids - prednisone and dexamethasone, prevent degranualation)

Question 18

Clinical uses for Antihistamines

Answer 18

H1 blockers: allergies, motion sickness, resp. disorders
H2 blockers: gastric ulcers

Question 19

H1 receptor antihistamine classes

Answer 19

Ethylenediamines, ethanolamines, alkylamines, piperazines, phenothiazines (1st gen)
Piperidines (2nd gen)

Question 20

H1 antagonists, 1st gen

Answer 20

Older, more familiar drugs
Cross BBB
Diphenhydramine (Benadryl), hydroxyzine, chlorpheniramine

Question 21

Ethylenediamines

Answer 21

CNS depression or sedation
Gastric upset
Tripelennamine, pyrilamine

Question 22

Ethanolamines

Answer 22

Atropine effects (anti-motion effect, low gastric upset, sedation)
Diphenhydramine

Question 23

Alkylamines

Answer 23

Greatest antihistamine activity
Seldom produce drowsiness (stimulates CNS)
In cold meds

Question 24

Piperazines

Answer 24

Prolonged action
Used for anti-motion
Slight drowsiness
Meclizine, hydroxyzine

Question 25

Phenothiazines

Answer 25

Long acting, good sedative
Good antihistamine activity
Trimeprazine

Question 26

H1 antagonists, 2nd gen

Answer 26

For acute inflamm. and allergic rxs
Doesn’t cross BBB (lack CNS effects- no sedation)
Loratadine (claritin), fexofenadine (allegra), cetirizine (zyrtec)

Question 27

Piperidines

Answer 27

Newest/ second gen
Minimal to no sedation
Loratadine (claritin)

Question 28

Side effects of antihistamines

Answer 28

Sedation (ataxia)
CNS excitement (high doses, irritability, convulsions, hyperexia, death)
GI disturbances (anorexia, V/D, consitpation)

Question 29

Cyproheptadine MOA

Answer 29

Antiserotonergic antihistamine
Serotonin receptor antagonist (inhibit receptors in hypothalamus controlling statiety)
Histamine receptor antagonist

Question 30

Cyproheptadine uses

Answer 30

Cats for appetite stimulant and acute phase of asthma