Antihistamines (Rx)

Question 1

Histamine receptors are ____-type receptors.

Answer 1

G-protein coupled receptors.

Question 2

Describe the H1 type histamine receptor.

Answer 2

H1 receptors are expressed on SM and endothelium. They are responsible for itch, pain, edema and secretion from the mucosa. (increase IP3 and DAG)

Question 3

Describe the H2 type histamine receptor.

Answer 3

H2 receptors are expressed on mast cells, basophils, parietal cells and cardiac muscle. They function in gastric acid secretion, vasodilation and increased heart rate. (increase cAMP).

Question 4

Describe the H3 type histamine receptor.

Answer 4

H3 receptors are expressed on presynaptic histaminergic neurons of the brain, the myenteric plexus and other neurons. They inhibit NT release. (decrease cAMP).

Question 5

Describe the H4 type histamine receptor.

Answer 5

They are expressed on cells of HSC origin: eosinophils, neutrophils, DCs basophils. They play a role in cytokine secretion and adhesion factor, as well as differentiation. (decrease cAMP)

Question 6

Define how an urticarial response relates to histamine.

Answer 6

Urticarial response (H1) is a reaction to stinging insects and plants at peripheral sensory nerve terminals.

Question 7

All first generation H1 antihistamines cause ______ as a side effect. They are primarily used to treat _____.

Answer 7

1st generation (H1) antihistamines treat allergy symptoms, but cause drowsiness (sedation) as a side effect.

Question 8

What is the general function of antihistamines?

Answer 8

Antihistamines block H1/H2 receptors. They are effective if given before histamine release.

Question 9

How do mast cell degranulation inhibitors work? Provide 2 examples.

Answer 9

Inhibitors of mast cell degranulation block Cl- channels and inhibit Ca2+ mobilization to prevent degranulation. They must be inhaled and are used in children to prevent asthma attacks. (ex: Cromolyn and Nedocromil)

Question 10

How does epinephrine function against allergic reactions?

Answer 10

Epinephrine is the BEST treatment for anaphylaxis. It counteracts histamine action since it’s an agonist for alpha and beta receptors. Epi-pen injection stimulates bronchodilation and increases BP.

Question 11

List 4 ways that 1st generation (H1) antihistamines differ from 2nd generation.

Answer 11

1st gen antihistamines:

1. neutral at physiologic pH (cross BBB)
2. Sedative and anti-emetic
3. short-acting (6-12 hours)
4. components of OTC treatments for insomnia, itching and nausea

Question 12

List at least 3 examples of 1st generation (H1) antihistamines.

Answer 12

1. Ethanolamines (Benadryl)
2. Ethylenediamnes (PBZ)
3. Alkylamines

Question 13

List 3 therapeutic applications of H1 antihistamines.

Answer 13

1. Allergic reaction treatments
2. Motion sickness, vertigo and insomnia (cross BBB).
3. Anti-emetics

Question 14

List at least 3 adverse effects of H1 antihistamines.

Answer 14

1. CNS toxicity
2. anticholinergic effects (dilated pupils, blurred vision)
3. Drug interactions (use with alcohol or CYP inhibitors)

Question 15

List 3 clinical uses of H2 antihistamines.

Answer 15

1. Hydrophilic (no CNS interactions)
2. Treats GERD, promotes healing of gastic ulcers.
3. Very specific (no H1 or H3 interactions)

Question 16

List at least 2 adverse effects of H2 antihistamines.

Answer 16

1. Neurological effects in patients with impaired renal or hepatic functions
2. Prolonged use can result in indigestion (low stomach acid)

Question 17

Provide 2 examples of 2nd generation (H1) antihistamines

Answer 17

1. Piperazines (Zyrtec)

2. Piperidines (Claritin) and Fexifenadine (Allegra)

Question 18

Describe the method by which antihistamines can be used to treat gastric ulcers.

Answer 18

1. antihistamines inhibit ACh and Gastrin
2. Calcium and cAMP levels decrease
3. Lower H+/K+ ATPase function (increase Gastric pH)

Question 19

What drugs are more potent than antihistamines in treating gastric ulcers?

Answer 19

Proton-pump inhibitors (PPI’s)