Ch.34: Antihistamines & Autacoids (Vickroy) Flashcards
Name 2 H2 selective blockers
ranitidine
famotidine
therapeutic uses of antihistamines
- acute/chronic allergic (anaphylactoid) or hypersensitivity reactions (target H1 receptors)
- anti-ulcer therapy (target H2)
- anti-motion sickness (target H1 or H3)
- sedation-behavioral control (target H1 or H3)
what are autacoids
aka local hormones; a diverse group of substances that differ from traditional hormones or transmitters.
-2 main groups: those that are preformed/stored and those that are synthesized in response to stimuli
ex. of preformed autacoid
histamine
ex. of synthesized autacoid
arachidonic acid metabolites (PGs, LTs, TXs) and polypeptide autacoids
common targets of autacoid actions
- smooth m.
- secretory cells
- blood coag components
- immune system
does histamine cross BBB?
no
what is histamine
widely distributed highly polar endogenous decarboxylated amino acid stored and released from intracellular granules
2 major histamine pools
1) mast cell pool
2) non-mast cell pool (Gi mucosa, CNS neurons, epidermal cells
Which species has widest array of rxns to substances that produce histamine release
dogs
release of histamine is called
degranulation; contributes to allergic rxns and inflamm.
should pre-treat with anti-histamine when using which drugs?
morphine amphotericin B polymixin B anti-cancer agents succinylcholine (horses)
things that can trigger degranulation
- Ag-Ab complex
- drugs, toxins
- elevation of Ca
cromolyn sodium
drug that blocks degranulation
non-mast cell pool chars.
- faster turnover of HA stores
- does NOT contribute to allergic/hypersensitivity rxns
- insensitive to conventional HA-releasing agents**
H1 receptor locations and functions
smooth m. (constricts)
vascular endothelium (vasodilation)
sensory nn. (stimulant)
CNS (excitatory)
H2 receptor locations and functions
GI tract (increases acid secretion)
what are anti-histamines?
drugs that competitively block HA receptors (antagonists)
can anti-histamines produce CNS effects?
Y (depression –> coma)
only approved anti-histamine for dogs, cats, horses**
doxylamine (NOT for food animal or horses intended for food)
Name 4 anti-histamines
doxylamine
diphenhydramine
famotidine
ranitidine
disadvantage of older anti-histamine agents
are relatively non-specific and can act on a wide variety of receptors; can result in adverse effects
therapeutic uses of diphenhydramine
- acute allergic rxn
- prevent anaphylaxis from antineoplastic agents
- motion sickness, sedation, anti-tussive
- OP poisoning
how is diphenhydramine eliminated?
liver
contraindications for diphenhydramine use
- aspergillus
- glaucoma
- COPD
- CV dz
properties of newer anti-histamine agents
- more selective for H1 receptors
- more highly charged
- less lipophilic
- uncharacterized in most companion animals (not used much in vet med because we usually WANT the CNS/gastro-protective effects)
efficacy for motion sickness depends of blockade of which receptors?
H1/H3 and/or mACh receptors
full treatment of a SEVERE allergic rxn requires:
- Epinephrine**
- anti-histamines
- Corticosteroid
- Fluids, etc.
EPI mech. of action in allergic rxn
antagonist of histamine actions on bronchiolar smooth m. (beta-2 receptors) and vascular smooth m. (alpha-1 receptors)
cat-specific clinical signs (CS) of histamine (HA) release
*respiratory and GI signs:* yawning coughing sneezing labored breathing
dog-specific CS of HA release
CV signs:
hypotension
white MM
CV collapse
universal CS of HA release
restlessness pruritis anorexia lacrimation red/swollen eyes salivation
H1 receptors mediate most of the major detrimentral actions in which systems?
the CV system, respiratory, and GI tracts
main CV actions of H1 receptors
- relax arteriolar smooth m. via NO release –> dec. BP/shock**
- increase capillary permeability (fluid loss) –> dec. BP/shock**
respiratory actions of H1 receptors
- constriction of bronchiolar smooth m.
- inc. bronchial secretions
- sensory n. ending irritation (coughing, sneezing)
- all of the above lead to POOR VENTILATION*
