Antihistamines Flashcards
Histamine H1 receptor agonists, 1st generation
- Chlorpheniramine
- Diphenhydramine
- Meclizine
- Promethazine
Functional Histamine Antagonists
- Cromolyn (Intal)
- Epinephrine
Histamine H1 receptor agonists, 2nd generation
- Cetrizine
- Fexofenadine
Synthesis of Histamine: Formed from Amino acid _________ in a decarboxylation reaction with the enzyme ________ _____________.
- Occurs primarily in ____ cells and __________.
- Acts on specific histamine receptor
Histadine, Histadine decarcoxylase
-Mast cells and basophils
What cell releases histamine and is for pathogen defense. It is in most tissue, near blood vessels, enriched at body/environment interfaces?
Mast cells
Cell that releases histamine in blood
Basophils
What histamine receptor is widespread and most therapeutically relevant?
H1
What histamine receptor is widespread, gastric, cardiac
H2
What histamine receptor is presynaptic receptors in CNS
H3
What histamine receptor is in hematopoietic cells?
H4
Histamine receptors in allergic response cause:
1) Vascular smooth muscle dilation:
- H1 rec on endothelium (NO)
- H2 rec on smooth muscles cells (cAMP)- Flushing, fall in sytemic BP
2) Increased vascular permeability
3) Peripheral sensory nerve excitation
1) A _____ is rapid reddening due to dilation of small vessels
2) A ______ is due to increased vascular permeability
3) A ______ is due to neural activated vasodilation
1) Spot
2) Wheal
3) Flare
The ___ receptor is involved in bronchial contraction and GI contraction.
H1
The ___ receptor is involved in gastric acid secretion
H2
Histamine Pharmacology: A Physiological antagonist
Epinephrine- used in severe responses, anaphylactic shock
- Vasoconstriction a1
- Bronchodilation-B2
Histamine release inhibitor and MOA
Cromolyn Sodium- Alters Cl- channel function; inhibits lung mast cell histamine release
-Aerosol, prophylactic use in asthma, hay fever
1st generation antihistamines are metabolized by ______. 2nd generation by______.
1st- CYP450
2nd- CYP 3A4
1st generation drugs used to treat Motion sickness and vertigo.
Diphenhydramine, promethazine, meclizine
1st gen drugs for insomnia/sedative
Diphenhydramine, promethazine
1st gen drugs as antiemetic
Promethazine, doxylamine
Diphenhydramine (Benadryl) preparations and uses
Topical and oral.
- Allergic rhinitis; pain and itching
- Dermatologic pain and itching
- Sleep aid (anti-musc.)
- Motion sickness (anti-musc.)
Diphenhydramine Adverse effects and cautions
a) Prominent sedation
b) Topical: allergic dermatitis
c) May reduce lactation and enters breast milk
d) Avoid in narrow angle glaucoma
What drug is this? Used oral or topical. Used for allergic rhinitis, dermatologic pain and itch, and OTC cold remedies. Adverse effects include sedation (less than diphenhydramine) and less effect at muscarinic receptors.
Chlorpheniramine (Chlor- Trimeton)
What drug is this: Oral use. Used as antiemetic, sedative. Adverse effects are similar to others, photosensitivity and additional side effect.
Promethazine (Phenergan)
What drug is this: Oral for vertigo, prevent motion sickness. Less sedating than other 1st gen antihistamines.
Meclizine (Antivert)
What drug is approved by FDA for morning sickness
Doxylamine (+pyridoxine=diclegis)
2nd gen drug in oral prep for allergies. Used for allergic rhinitis and dermatologic pain and itch. Adverse effects include drowsiness and weak anti-muscarinic effects (dry mouth). Metabolized by CYP 3A4
Cetrizine (Zyrtec)
T/F: Fexofenadine has no cardiotoxicity, and is not metabolized by the liver, and excreted unchanged in either urine or feces. It is a metabolite of Terfenadine.
True
An oral drug for allergic symptoms that should not be taken with fruit juice. An OATP inhibitor. Used for allergic rhinitis and dermatologic pain and itching. Not sedating. Can cause nausea,vomiting, dysmenorrhea, drowsiness, and enters breast milk.
Fexofenadine (Allegra)
T/F: 1st gen antihistamines enter CNS readily and 2nd are kept out
True- 2nd kept out by p-glycoprotein pumping=low sedating
T/F: Better to take H1 antihistamines n a regular basis rather than as needed. Tolerance does not develop.
True
- Symptom relief may be incomplete
- Less effective with chronic/high antigen exposure
Adverse effects of 1st gen antihistamines
- Sedation
- GI disorders- due to muscarinic, adrenergic and serotonin receptor block: constipation, diarrhea, loss of appetite, N/V, epigastric distress.
- Anti-muscarinic: dry mouth, sinuses, urinary retention
- Allergic rxns
- Overdose looks like atropine overdose
- Generally Avoid in children and elderly
