Antihistamines Flashcards
Histamine effects
- CNS nerve impulse transmission
- capillary dilation
- smooth muscle contraction
- secretion simulation
- ⬆HR
H1 function
smooth muscle constriction in blood vessels
increase cap permeability
too much histamine
anaphylaxis & severe allergy sx
smooth muscle constriction of the stomach and lungs
increase in body secretions
vasodilation and increased cap permeability
when is histamine released?
when there are antigens in the blood
histamine can also trigger the release of more histamine
histamine antagonists
H2 blockers (GERD agents)
H1 blockers (antihistamines)
properties of antihistamines
anthistaminic
anticholinergic
sedative
antihistamine uses
allergies
urticarial (hives)
S/S of common cold and cough
vertigo and motion sickness
insomnia
when should antihistamines be started?
early, before histamine starts to bind
AE
mainly drowsiness
SE
dry mouth
changes in vision
urinary retention/hesitancy
constipation
(anticholinergic)
Loratadine (claritin)
non-sedating
daily
allergic rhinitis and urticaria
lower dose for elderly and renal dz
not for kids <2
few anticholinergic and sedative properties
Diphenhydramine (Benadryl)
- peripheral and central
- high in anticholinergic and sedative properties
- tx of many d/o including insomnia and motion sickness
- tx of anaphylaxis and dystonia when used with epinephrine
- caution in mothers, neonates, lower respir sx/dz, asthma, or risk for pneumonia
- PO, parenteral, topical
- dries secretions
nursing implications
- increased viscosity can occlude airways
- paradoxical rx in older adults
- take w/ food
- tx of dry mouth
- caution w/ other OTC cold meds
- monitor BP
- brain fog (no driving, etc)
paradoxial reaction
irritability
dizziness
confusion
sedation
hypotn
antihistamine MOA
-block H1(histamine) receptors
-inhibit smooth muscle constriction in blood vessels, respir, and GI tract
-decrease capillary permeability
antihistamine contraindications
-narrow-angle glaucoma
-cardiac dz
-kidney dz
-hypertn
-bronchial asthma
-COPD
-peptic ulcer dz
-seizure d/o
-BPH (enlarged prostate)
-pregnancy
Traditional (first gen) antihistamines
diphenhydramine (Benadryl)
diphenhydramine (Benadryl) caution
can easily cross the BB barrier into CNS
diphenhydramine (Benadryl) SE
-drowsiness
-dry mouth, nose, throat
-headache
diphenhydramine (Benadryl) AE
-vision problems
-trouble urinating/dysuria
-hypertn
Non-sedating antihistamines
-loratadine (Claritin)
-fexofenadine (Allegra)
-cetrizine (Zyrtex)
Non-sedating antihistamines SE/AE
same as first-gen
Non-sedating antihistamines caution
-asthma complications
-kidney + liver dz complications
-interact with other drugs
Non-sedating antihistamines interactions
-theophylline
-ketoconazole
-erythromycin
-rifampin
-antacids
Are antihistamines cholinergic or anticholinergic?
anticholinergic
