Antihistamines

Question 1

Differentiate H1 receptors from H2 receptors.

Answer 1

H1: histamine binding stimulates allergic reactions in the periphery
H2: histamine binding stimulates acid secretion in the stomach

Question 2

When someone refers to a drug as an antihistamine, which receptor are they referring to?

Answer 2

Drugs that block H1

Question 3

Differentiate allergic rhinitis from non-allergic rhinitis?

Answer 3

Allergic rhinitis is caused by an increase in histamine (HST)
Colds cause rhinitis due to an increase in Ach

Question 4

State the group of AEs that are associated with many antihistamines and specify the individual effects.

Answer 4

Anti-Ach: C-DUST –> constipation, dry mouth, urinary retention, sedation, tachycardia

Question 5

Some antihistamines are sedating, what two properties determine how sedating an antihistamine will be?

Answer 5

Lipophilicity and Anti-Ach properties –> as either or both increase, the more sedating the drug will be.

Question 6

If someone has a cold, would a sedating or non-sedating antihistamine be more effective?

Answer 6

Sedating because they have anti-Ach properties and Ach is the cause of rhinitis in a cold.

Question 7

What are the two primary indications for hydroxyzine?

Answer 7

Anxiety and pruritis –> used a lot in the ED for poison ivy

Question 8

Describe hydroxyzine in terms of its sedative effect.

Answer 8

Highly sedating because it is highly anti-cholinergic

Question 9

By what routes of administration is hydroxyzine available?

Answer 9

IV and PO

Question 10

What is a significant risk associated with administration of hydroxyzine and in what specific population?

Answer 10

Fall risk in the elderly

Question 11

Describe diphenhydramine in terms of its sedative effect.

Answer 11

Highly sedating –> great for insomnia

Question 12

What is the appropriate dose of diphenhydramine in a child 2 years of age or younger?

Answer 12

There is none –> diphenhydramine is activating rather than sedating (paradoxical reaction) in children younger than 2.

Question 13

Other than insomnia and allergic rhinitis, what is another indication for diphenhydramine?

Answer 13

It has some mild anti-tussive (anti-cough) properties

Question 14

List three non-sedating antihistamines.

Answer 14

Cetirizine, Loratadine, Fexofenadine

Question 15

Of the non-sedating antihistamine, which one is most likely to be sedating in some people?

Answer 15

Cetirizine –> it is an active metabolite of hydroxyzine

Question 16

When an antihistamine product is followed by the letter D (Ex, Claritin D) what does this mean and what two drugs are added?

Answer 16

The antihistamine is coformulated with a decongestant.

The antihistamine is combined with either pseudoephedrine or phenylephrine.

Question 17

In what patients would you want to avoid use of antihistamine-D products and why?

Answer 17

Patients with HTN because decongestants are alpha-1 agonists that provide vasoconstriction.

Question 18

Other than use as a decongestant, what condition is pseudoephedrine the drug of choice for?

Answer 18

Post-nasal drip