28 - 189 - ANTIHISTAMINES

Question 1

metabolite of hydroxyzine

Answer 1

cetirizine

Question 2

Identify if first or second generation H1 antihistamines

relatively lipophilic, which enhances penetration of the blood–brain barrier and leads to sedation.

Answer 2

First-generation H1 agents

Question 3

Identify if first or second generation H1 antihistamines

may interact with other drugs metabolized by the hepatic cytochrome P450 system leading to drug–drug interactions.

Answer 3

First-generation H1antihistamines

Question 4

Identify if first or second generation H1 antihistamines

have poor penetration of the blood–brain barrier and thus are less sedating.

Answer 4

Second-generation H1antihistamines

Question 5

Identify if first or second generation H1 antihistamines

bind selectively to peripheral H1receptors and have fewer CNS effects

Answer 5

Second-generation H1antihistamines

Question 6

Identify if first or second generation H1 antihistamines

require less hepatic metabolism and thus are less likely to interact with other medications

Answer 6

Second-generation H1antihistamines

Question 7

Identify if first or second generation H1 antihistamines

There is no evidence of tolerance or tachyphylaxis

Answer 7

Both

Question 8

Identify if first or second generation H1 antihistamines

• bind noncompetitively to the H1receptor, and thus are not easily displaced by histamine
• dissociate slowly, and have a longer duration of action

Answer 8

second-generation antihistamines

Question 9

After oral administration, the sedating effects of first-generation H 1 antihistamines can be observed within how many minutes?

Answer 9

30 minutes to 1 hour and generally persist for 4 to 6 hours

Question 10

2nd generation H1 antihistamines achieve peak plasma concentrations within how many hours?

Answer 10

1 to 2 hours

Question 11

These 2nd gen antihistamines undergo minimal hepatic metabolism, which reduces the likelihood of interactions with other drugs.

Answer 11

Cetirizine, fexofenadine, levocabastine, desloratadine, and levocetirizine

The second-generation antihistamines—loratadine, acrivastine, mizolastine, ebastine, and oxatomide—are metabolized in the liver via the hepatic enzyme CYP 3A4

Question 12

time to reach peak concentration and elimination half-life of cetirizine

Answer 12

In healthy adults, cetirizine and levocetirizine reach peak concentrations approximately 1 hour after administration, with elimination half-lives of 6.5 to 10 hours.

Question 13

Indications for Treatment with H1 Antihistamines

Answer 13

Question 14

First generation H1 antihistamines

Answer 14

Question 15

Examples of second generation H1 antihistmines

Answer 15

Question 16

Doses up to how many times than normally recommended for second-generation H1 antihistamines may be necessary in the treatment of some CIU patients?

Answer 16

4x

Question 17

What drug should not be taken with fexofenadine because this can interfere with drug absorption?

Answer 17

antacids

Question 18

most commonly reported problem with antihistamines

Answer 18

Sedation

Question 19

Contraindications to First-generation H1 Antihistamine Therapy

Answer 19

■ Narrow-angle glaucoma

■ Concomitant use of monoamine oxidase inhibitors

Question 20

Question 21

anticholinergic side effects

Answer 21

Anticholinergic side effects are much more common with first-generation H 1 antihistamines as they have an affinity for cholinergic receptors.

These anticholinergic side effects include dry mucous membranes, urinary retention and hesitancy, postural hypotension, dizziness, erectile dysfunction, and constipation.

Most second-generation H 1 antihistamines are selective for H 1 receptors, and thus lack these anticholinergic side effects

Question 22

most serious, but fortunately rare, cardiac side effects of antihistamines

Answer 22

Arrhythmias, particularly prolongation of the QT interval and torsades de pointes,

These dosedependent effects are mediated through blockade of potassium channels unrelated to the H 1 histamine receptor

Question 23

First-generation H 1 antihistamines are contraindicated for patients receiving what drugs?

Answer 23

monoamine oxidase inhibitors as these medications may interfere with the metabolism of monoamine oxidase inhibitors

Question 24

Examples of H2 antihistamines

Answer 24

cimetidine, ranitidine, famotidine, and nizatidine

These agents bind to H 2 receptors located throughout the body, including epithelial cells, endothelial cells, and chondrocytes, as well as lymphocytes, neutrophils, eosinophils, monocytes, mast cells and dermal dendritic cells

Question 25

Dermatologic Indications for Treatment with H2 Antihistamines

Answer 25

Most often, H 2antihistamines are used in combination with H 1 agents in refractory cases of CIU and angioedema.

Question 26

less inhibitory of the CYP system than cimetidine and may be the preferred H2 antihistamine in situations in which drug interactions are a particular concern

Answer 26

Ranitidine

Question 27

In patients taking the cardiac drug **dofetilide**, this H2 antihistamine is contraindicated because of the risk of prolongation of the QT interval and life-threatening cardiac arrhythmias

Answer 27

cimetidine

Question 28

Question 29

Uncommon side effects of this antihistamine include **gynecomastia** with or without elevated prolactin levels in men; **galactorrhea** with elevated prolactin levels in women; and **loss of libido, impotence, and reduction of sperm counts** in young men

Answer 29

cimetidine

Question 30

Oral doxepin FDA pregnancy category

Answer 30

pregnancy category C drug

Question 31

example of Tricyclic antidepressant

Answer 31

doxepin ## Footnote bind to both H 1and H2 receptors

Question 32

a benzocycloheptathiophene derivative, this is an **H1 antihistamine** with additional **mast cell– and basophil-stabilizing properties.**

Answer 32

Ketotifen ## Footnote Ketotifen has been used successfully in the treatment of CIU, physical urticaria, and symptoms associated with mastocytosis