Antihistamines

Question 1

histamines

Answer 1

chemicals produced in specialized cells through body
role in allergic reaction and regulation of gastric acid secretion

Question 2

histamine effects

Answer 2

Vascular system:
-dilates small blood vessels
- increases capillary permeability

Bronci
- constriction of smooth muscle

Stomach
- secretion of gastric acid

CNS
- acts as a neurotransmitter

Question 3

distribution of histamine

Answer 3

most tissues
- high in skin, lungs, gi tract
- low in plasma

Question 4

synthesis and storage of histamines

Answer 4

mast cells ( in tissues)
basophils (in blood)

stored in secretory granules

Question 5

release of histamine causes

Answer 5

-Allergic and non-Allergic reactions

Question 6

allergic release of histamines

Answer 6

initial requirement
- production of IgE antibodies
- antibodies attach to mast cells and basophils

subsequent
- allergen binds to 2 adjacent IgE (creates a bridge)
- binding causes histamine granules to fuse with cell membrane and release

**REQUIRES PRIOR EXPOSURE

Question 7

Non-Allergic release histamine

Answer 7

Several agents can act directly on mast cells to release histamine

non prior sensitization is required

Question 8

What receptors does Histamine act upon

Answer 8

Histamine 1 (H1)

Histamine 2 (H2)

Question 9

Stimulation of H1 receptors (5)

Answer 9

vasodilation:
dilation of arterioles and venules
- skin becomes warm and flushed
- BP drops

Increased capillary permeability:
capillary endothelial tissue contacts
pores increase in size
fluids, protein and platelets escape

Bronchoconstriction
- constriction of bronchi

CNS
- role in cognition, memory and sleeping/waking cycles

Others
itching and pain

Question 10

Histamine 2 stimulation

Answer 10

activation of GI tract parietal cells
- secretion of gastric acid

Question 11

what are mild allergy symptoms caused by?

Answer 11

Stimulation of H1 receptors

Question 12

Severe Allergic reactions are called
Treatment?

Answer 12

Anaphalactic Shock: bronchoconstriction and hypotension

Treatment: EPINEPHERINE principal mediators

Question 13

Classification of H1 Antagonists

Answer 13

First- generation (highly sedative)

Second-generation antihistamines (not sedative)

Question 14

H1 antagonists mechanism

Answer 14

H1 blockers bind SELECTIVELY to H1 bistamine receptors
- block histamine

H1 blocker also bind to non-histamine receptors (muscarinic receptors)
- side effects

Question 15

H1 antagonists pharmacological effects (6)

Answer 15

Major therapeutic effect of H1 antagonists

Peripheral:

blocking of histamine at H1 receptors

Arterioles and venules
- localized flushing

Capillary beds:
- reduces increased permeability
=REDUCED EDEMA

Sensory Nerves
- reduces itching and pain

Mucous membranes
- suppresses secretion of mucus

CNS effects
- therapeutic doses: CNS depression (slow rxn time)
- Overdose: CNS stimulation ( convulsions)

Question 16

H1 therapeutic uses

Answer 16

Mild Allergy:
- reduce symptoms

Motion Sickness
- block muscarinic receptors in the neural pathway from the inner ear to the medulla vomiting center

Insomnia
- cause drowsiness
- every OTC sleep aid contains H1 antagonists

Question 17

H1 antagonist blocks mast cells from releasing histamines. T/F

Answer 17

False- they prevent the binding of histamines to H1 receptors

Question 18

Do H1 antagonists help with the common cold

Answer 18

NO

Question 19

Adverse effects H1 antagonists

Answer 19

Sedation
- most common side-effect
-IMPAIRED LEARNING AND MEMORY
–> impairment when driving is equal to blood levels over legal limit

GI effect
- nausea, vomiting
- administer with food to help

Anticholinergic effect
- antimuscarinic action
–> dry mouth and throat
–> urinary urgency
–> constipation

Question 20

Second-Generation H1 antagonists drug name

Answer 20

Fexofenadine (F)

Question 21

Second-Generation H1 antagonists

sedation effects
What effects Absorption
Cost

Answer 21

Dont produce sedation
- can’t cross BBB well
- low affinity to CNS H1 receptors

Some fruit juices reduce absorption
- no juices 4 hr before dosing

Relatively expensive