Antihistamines

Question 1

Diphenhydramine

Answer 1

Antihistamine

Inverse agonist of H1 histagenergic receptor (produces opposite effect of histamine since its an inverse agonist)

influences muscarinic acetylcholine receptors, sodium channels and potentially reuptake of serotonin

Predominately used for:

• reducing signs of acute allergic reactions
• treat increase capillary permeability secondary to histamine release.
• reducing symptoms of histamine release from Mast cell tumors.
• crosses the blood brain barrier –> affect CNS; cause sedation or excitement (rare in dogs and cats)

Do not administer SQ because of irritating effects.

Question 2

Meclizine

Answer 2

antihistamine

Used for patients with vestibular disease

Antiemetic and motion sickness

Question 3

Cyproheptadine

Answer 3

antihistamine

serotonin agonist

Used as a mild appetite stimulant

Can also be used to treat serotonin syndrome –> evidence to support efficacy is limited

Question 4

Mirtazapine

Answer 4

antihistamine

Has an effect on serotonin, adrenergic, dopamine and muscarinic receptors

weak appetite stimulant and antiemetic