Pharm One-Liners: Antihistamines and Serotonin

A class of endogenous substances that include histamine, serotonin, prostaglandins, and vasoactive peptides that work in autocrine or paracrine manner

Autacoids

Peptides that increase capillary permeability and edema (2)

Bradykinin and histamine

Tissue distribution of histamine H1 receptors (2)

Smooth muscle and mast cells

Tissue distribution of histamine H2 receptors (3)

Stomach, heart, and mast cells

Tissue distribution of histamine H3 receptors (2)

Nerve endings and CNS

Common adverse effects of 1st generation antihistamines (2)

Sedation, anticholinergic

1st generation antihistamine that is highly sedating

Diphenhydramine

1st generation antihistamine that is least sedating

Chlorpheniramine

Major indication for H1 antihistamines

IgE mediated allergic reaction (allergic rhinitis, urticaria)

Antihistamine that is indicated for allergies, motion sickness, and insomnia

Diphenhydramine

Antihistamine with motion sickness as the only indication

Dimenhydrinate

2nd generation antihistamines (3)

Fexofenadine, loratadine, and cetirizine

H2 antagonist that causes the most interactions with other drugs

Cimetidine

Indication for H2 antagonists (3)

Acid reflux disease, duodenal ulcer and peptic ulcer disease

Major location of serotonin type 1 (5HT-1) receptors

Brain

5HT-1A receptor partial agonist indicated for generalized anxiety disorder; due to longer onset of action, is less effective for acute anxiety

Buspirone

5HT-1D/1B agonist used for migraine headaches

Sumatriptan and -triptans

Ergot alkaloid indicated for migraine headaches

Ergotamine

Reason ergot alkaloids are contraindicated in pregnancy

Uterine contractions

Adverse effects of ergot alkaloids (2)

Prolonged vasospasm and hallucinations resembling psychosis

Medications used off-label for ischemia and gangrene caused by ergot alkaloid overdose (2)

Nitroprusside, nitroglycerin

Serotonin receptor responsible for serotonin syndrome

5HT2

H1 antihistamine with 5HT2 antagonist activity that is mostly used for carcinoid tumor but may be used to treat serotonin syndrome

Cyproheptadine

Location of serotonin type-3 (5HT-3) receptors

GI tract, vomiting center of medulla

5HT-3 antagonist used for the prevention of chemotherapy-induced nausea and vomiting

Ondansetron (-setrons)