Antihistamines Flashcards
H1
Allergic response Gq Brain-wakefullness Smooth muscles Endothelium- activates NO and vasodilation
H2
Gastric acid secretion
increases cAMP via Gs
Histamine effects
Smooth muscle: Bronchospasms (H1) GI: increases acid secretion (H2) Contracts smooth muscle Skin: Itch, pain, sensory, nerve stim decrease BP, increase HR
Triple response of Histamine
1) red spot appears (few seconds)
2) axon reflexes- flush extends out
3) increase capillary permeability– wheal in 2-3 minutes
Effects of antihistamine
inhibits smooth muscle response, inhibits vasodilation due to H1
Counter motion sickness via anticholinergic effects
First Generation H1 sedating antagonists
Cross BBB=SEDATING EFFECT, ANTICHOLINERGIC Diphenhydramine (Benadryl) Dimenhydrinate (Dramamine) Promethazine (Phenergan) Hydroxyzine (Atarax. Vistaril)
First generation H1 moderate-sedating antagonists
Crosses BBB but not as sedating Brompheniramine maleate Chlorpheniramine maleate Clemastine Cyclizine Meclizine
2nd Generation Non-sedating antagonists
DO NOT CROSS BBB=non-sedating No anticholinergic effect=no motion sickness effect Loratadine (Claritin) Desloratadine (Clarinex) Levocetirizine (Zyxal) Certirizine (Zyrtec) Acrivisitine/Pseudoephedrine (Semprex) Fexofenadine (Allegra)
1st gen anti H used for motion sickness
Diphenhydramine (Benadryl)
Dimenhydrinate (Dramamine)
Promethazine (Phenergan)– not as sedating
1st gen anti H used as a sleep aid
Doxylamine (Unisom)
2nd generation antagonists
Metabolized by liver, some by CYP3A4 (erythro, keto, cim, grapefruit juice decrease metabolism)
Better at preventing than treating
older SE: Arrhythmias
newer SE: sinus tachy
Nasal H1 antagonist
Azelastine
Levocabastine
non-competetive H1 BLOCKER that also decrease H release form mast cells
Kidney only metabolism (2nd gen anti H)
Cetirizine (Zyrtec), levocetirizine, acrivastine
CI for first gen H1 antagonists
Children, history of seizures
OD results in same as atropine poisoning (blind as a bat, mad as a hatter, red as a beat, dry as a bone)
