antihistamine H1 blockers Flashcards
how is histamine synthesized?
via decarboxylation of histidine in mast cells, eosinophils, enterochromaffin-cells (stomach), and histaminergic neurons in CNS
function of H1 receptors in CNS
promotes wakefulness, decreased appetite, motion sickness, emesis
function of H1 receptors in periphery
bronchoconstristion, vasodilation, increased vascular permeability, increased noiciception, itch, urticaria
the general classes of drugs affecting histamine action
beta-adrnergic agonists (mast cell stabilization)
chromones (cromolyn) (mast cell stabilization)
H1 receptors antagonists for hypersensitivity/allergic reactions and off-target uses such as sedation/motion sickness
H2 antagonist: inhibition of gastric secretion
therapeutic uses of H1 receptor antagonists
allergic rhinitis
allergic conjunctivitis
atopic dermatitis
colds/cough
anti-nausea,anti-emetic, motion sickness prophylaxis
sedative
adverse effects H1 blockers (CNS)
sedation
impaired cognition/psychomotor coordination
increased appetite
paradoxical excitation in children and elderly
adverse effects H1 blockers (peripheral)
dry mouth
urinary retention
vision problems
postural hypotension
dizziness
prolonged Q-T interval
arrhythmias
1st gen H1 antihistamine drugs
chlorpheniramine diphenhydramine doxylamine promethazine cyproheptadine meclizine
1st gen H1 antihistamine properties
good penetration of BBB
less selective for the H1 receptors vs other receptors (muscarinic, a-adrenergic, serotonin - cyprohetadine, dopamine- promethazine)
more potential for drug-drug interactions with anticholinergics, CNS depressants
2nd gen antihistamine drugs
acrivastine cetirizine desloratadine fexofenadine loratadine
2nd gen antihistamine properties
poor penetration of BBB ( no useful sedative, anti-emetic effect)
more selective for H1 receptor (reduced off-target effects)
less potential for drug-drug interactions
