Histamine, Seratonin, and Antagonists Flashcards
What is the physiologic effect of histamine on the cardiovascular system?
Immediate fall in BP due to peripheral vasodilation (H1 and H2)
- also, increase in vascular permeability (H1) and increased contractility and HR (H2)
What is the physiologic effect of histamine on the bronchiolar smooth muscle?
Broncoconstriction via H1
What is the physiologic effect of histamine on the GI tract?
- contraction of smooth muscle and diarrhea (H1)
- stimulation of gastric acid, pepsin, and intrinsic factor secretion (H2)
What is the physiologic effect of histamine on the nervous system?
- stimulation of sensory nerve endings: pain and itching (H1)
- feedback inhibition of synthesis and release of histamine (H3)
What are three strategies for pharmacological antagonism of histamine?
- induce opposite actions of histamine via different receptors
- inhibit the degranulation of mast cells
- direct histamine receptor antagonism
What is the use of diphenhydramine (H1 receptor antagonist) and what are the major side effects?
- allergic reactions (benadryl)
- SE: anti muscarinic and sedating
What is the use of tripelennamine (H1 receptor antagonist)?
- OTC sleep aid
What is the use of cyclizine (H1 receptor antagonist)?
- motion sickness
What is the use of promethazine (H1 receptor antagonist) and what are the major side effects?
- antiemetic
- SE: anti muscarinic, sedating
What is the use of chlorpheniramine (H1 receptor antagonist)? How is it different than other 1st gen antagonists?
- component of cold meds
- less sedating!
What is the use of loratadine and fexofenadine (2nd gen H1 receptor antagonists)? What are the rare but important side effects?
- used for allergic rhinitis
- SE: no sedation but CV effects are possible with high doses
What are the uses of azelastine (2nd gen H1 receptor antagonist)?
- allergic rhinitis and allergic conjunctivitis
What is the use of cetirizine (2nd gen H1 receptor antagonist)?
- allergic rhinitis
What is the clinically relevant use of H2 receptor antagonists?
blocks gastric acid secretion from parietal cells; used for dyspepsia and gastric or duodenal ulcers
What are the important side effects of cimetidine (H2 receptor antagonist)?
- antiandrogen (impotence and gynecomastia)
- inhibits P450 enzymes and can increase serum concentrations of other drugs
Name the four H2 receptor antagonists
cimetidine, ranitidine, famotidine, nizatidine
What is a general side effect possible with H2 receptor antagonists?
CNS dysfunction
What is serotonin made from? What can it be made into?
- made from tryptophan
- can be made into 5-hydroxyindolacetic acid or melatonin
What are the actions of 5HT in the GI tract?
- contraction of GI smooth muscle to increase tone and peristalsis
- can be released as a carcinoid syndrome and causes severe diarrhea
What are the actions of 5HT on the cardiovascular system?
- smooth muscle: vasoconstriction
- skeletal muscle: vasodilation
What are the actions of 5HT on the nervous system?
- pain and itching on periphery
- centrally involved in mood, food intake, sleep
How does cyproheptadine work and what are its uses?
- works as an antihistamine and antiserotinergic agent
- used for skin allergies and to treat diarrhea of carcinoid syndrome
How does ketanserin work and what are its uses?
- selective 5HT2A,2C antagonist, α1 antagonist, H1 antagonist
- used as an antihypertensive and as an inhibitor of platelet aggregation
What receptor does odansetron antagonize and what is it used for?
- 5HT3 antagonist
- used for anti nausea/vomiting in chemo
What are triptans used for and what receptors do they work on?
- used for acute migraine
- selective 5-HT1b,d agonists (induces cerebral vasoconstriction)
