E2: Antihistamines

Question 1

Histamine can cause: (2 conditions)

Answer 1

Immediate hypersensitivity

Allergic rxns

Question 2

Name 3 situations that can cause histamine release

Answer 2

Allergic Response (IgE and Ag)
Drugs
Venoms

Question 3

What 3 drugs can induce a histamine release?

Answer 3

Morphine
Codeine
Radiocontrast dyes

Question 4

List 3 physiologic effects of an H1 receptor.

Answer 4

Allergic response
Vasodilation (stimulates endothelium to release NO)
Bronchospasm (problem in ashthmatics!)

Question 5

What are the 3 components of the Lewis Triple Response?

Answer 5

Flush
Flare
Wheals

Question 6

List 3 skin effects caused by the H1 receptor

Answer 6

Itch
Hives
Edema
(Caused by increased capillary permeability and separation of endothelial cells)

Question 7

List 2 physiologic effects of the H2 receptor.

Answer 7

Gastric acid secretion

Vasodilation (at higher concentrations)

Question 8

When H1/H2 receptors cause vasodilation, what is the body’s physiologic response?

Answer 8

Decreased blood pressure

Reflex tachycardia

Question 9

Describe the H3 receptor

Answer 9

Presynaptic in brain
Responsible for sleep
INHIBITS RELEASE OF HISTAMINE

Question 10

Describe the H4 receptor

Answer 10

Stimulates chemotaxis in inflammation and allergic rxn

Question 11

Large doses of histamine may result in:

Answer 11

SHOCK!

Question 12

Name the 1st gen H1 Antagonists (3)

Answer 12

Diphenhydramine (Benadryl)
Dimenhydrinate (Dramamine)
Promethazine (Phenergan)

Question 13

How do 1st gen H1 Antagonists work? How can histamine overcome this?

Answer 13

Compete directly with histamine

-Effect is dependent on concentration of drug (too much histamine can override the medication effect)

Question 14

What are 1st gen H1 Antagonists used for clinically (4)?

Answer 14

Motion sickness *use prophylactically!
Sedation
Dry up secretions
Anti-emetic (Promethazine)

Question 15

What are 3 adverse effects of 1st gen H1 Antagonists?

Answer 15

Sedation (AVOID OTHER CNS DEPRESSANTS!)
Dry mouth
Decreased seizure threshold

Question 16

What population is contraindicated for use of a 1st gen H1 Antagonist?

Answer 16

Children 4 yo or younger

Question 17

What are the 2nd gen H1 Antagonists?

Answer 17

Loratadine (Claritin)
Certirizine (Zyrtec)
Fexofenadine (Allegra)

Question 18

How do the 2nd gen H1 antagonists differ from the 1st gen?

Answer 18

Non-sedating (little to no CNS penetration)

No anticholinergic effect

Question 19

What are 3 clinical uses of 2nd gen H1 Antagonists? (3)

Answer 19

Allergic rhinitis
Conjunctivitis (topical?)
Itching/hives (topical?)

Question 20

What is the administration of 2nd gen H1 Antagonists and how often are they typically taken?

Answer 20

Oral

1x per day

Question 21

2nd gen H1 Antagonists are metabolized by:

Answer 21

CYP-450

Question 22

What 4 drugs should be avoided with 2nd gen H1 Antagonists?

Answer 22

Erythromycin
Ketoconazole
Cimetidine
Grapefruit juice (Effects heart)

Question 23

What 2nd gen H1 Antagonist is eliminated exclusively by the kidney (therefore great option for pt with liver dz)?

Answer 23

Certirizine (Zyrtec)

Question 24

Name the Nasal H1 Antagonist

Answer 24

Azelastine

Question 25

Name the Histamine Release Inhibitors

Answer 25

Cromolyn
Azelastine
Ceterizine (Zyrtec)

Question 26

What are the general adverse effects of H1 antagonists?

Answer 26

GI upset (take with food)
TERATOGENIC!
Allergic rxn with topical applications

Question 27

Describe the primary sxs associated with acute poisoning of 1st and 2nd gen H1 Antagonists.

Answer 27

1st gen: Just like atropine poisoning
2nd gen: Cardiac arrhythmias

*Overdose usually only happens in kids