Antihistamines (Exam #2)

Question 1

First Generation H1 Antagonists vs. Second Generation H1 Antagonists (think penetration/effect, AEs)?

Answer 1

1st Gen: ENTERS BRAIN = sedating
- AEs involve blocking muscarinic receptors (DRY)

2nd Gen: NON-sedating
- Fewer AEs because no blocking of muscarinic receptors

Question 2

What are the three FIRST Generation H1 Antagonists? What do they all have in common?

Answer 2

SEDATING

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

Question 3

What are the three SECOND Generation H1 Antagonists? What do they all have in common?

Answer 3

NON-sedating

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

Question 4

Which antihistamine drug CAN be used in patients with liver disease, and why?

Answer 4

Certirizine (Zyrtec)

- Excreted by kidney

Question 5

What are the two NASAL H1 Antagonists?

Answer 5

• Cromolyn

- Azelastine (Astelin NS/Astepro)

Question 6

Which three antihistamines can be used to treat motion sickness, and why?

Answer 6

FIRST Generation H1 Antagonists = antimuscarinics

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

Question 7

Which antihistamines are CI in children?

Answer 7

FIRST Generation H1 Antagonists (Diphenhydramine (Benadryl), Dimenhydrinate (Dramamine), Promethazine (Phenergan))

Question 8

What specific AEs are seen with ALL antihistamines (oral vs. topical)?

Answer 8

• Oral: GI issues

- Topical: allergic reactions

Question 9

How might overdose of FIRST Generation H1 Antagonists present? SECOND Generation H1 Antagonists?

Answer 9

• First = atropine poisoning (excitement, convulsions, ataxia, hallucinations, tremors, fixed pupil dilation)
• Second = cardiac arrhythmias

Question 10

Which inhaled form of antihistamines inhibits release of histamine from mast cells? What other drug might do this too?

Answer 10

Cromolyn

- Ceterizine (Zyrtec) also inhibits release of histamine from mast cells

Question 11

Which inhaled form of antihistamines is a non-competitive H1 blocker?

Answer 11

Azelastine (Astelin NS/Astepro)

Question 12

Which three classes/drugs should be avoided with antihistamines? What else?

Answer 12

AVOID:

• Erythromycin
• Ketoconazole
• CNS depressants
• Grapefruit juice (CYP3A4 inhibitor → increase concentration of drugs)

Question 13

Which antihistamine drug is also used as a sleep aid?

Answer 13

Dimenhydrinate (Dramamine, Tylenol PM)

Question 14

What is the recommended tx for anaphylactic shock (4)?

Answer 14

• Epi
• Steroids
• H1 antagonists
• H2 antagonists

Question 15

What unwanted effect of H1 antagonist antihistamines may be seen in asthmatics, and why?

Answer 15

Bronchospasm

- Increase Ca2+