martinezdvm's version from 2015-12-06 15:22


Question Answer
H1 effect?Mediates smooth muscle contraction (bronchi, gut, large blood vessels); relaxes small arterioles and reduces peripheral resistance and blood pressure.
G protein linked to the H1 receptor?Gq protein
Mechanism of action of the H1 receptor?Acts through Gq protiein and activated phospholipase C enzyme= initiation of cellular events. Vasodilation achieved through endothelial H1 receptors which activate N2O synthase and release of endothelium derived N2O.
H2 receptor function? Stimulates gastric acid secretion
H2 receptor is linked to which G protein?Gs protein
Mechanism of action of H2 receptor?Acts through Gs protein coupled with adenylyl cyclase enzyme activation, increases synthesis of cAMP which is linked to activation of intracellular protein kinase A = activates parietal cell proton pump to stimulate gastric acid secretion.
H3 receptor function?Modulates neurotransmitter release in the CNS (inhibition of adenylyl cyclcase through Gi); localized on nerve terminals in the CNS.
H4 receptor effect:Involved in inflammation involving eosinophils and other inflammatory cell types.


Question Answer
Autacoids, what are they and what is their stimulus?Biologic factors that are synthesized in the body and play a role in physiologic or pathophysiologic responses to injury.
Autacoid- action, duration of action & metabolismGenerally act locally (termed local hormones) Have brief duration and undergo rapid degradation.
Two places histamines can be found?Mast cell pool & non-mast cell pool
Mast cell pools are foundEverywhere in the body (mainly in CT)
Describe the synthesis of Histamine in the Mast Cell Pool:Histamine is synthesized slowly and stored in secretory granules
Where can we find the Histamine that participates in inflammatory responses, allergies, shock, adverse drug reactions, hypersensitivity reactions, and cellular injury?Mast Cell Pool
Describe synthesis and release of Histamine in the Non-Mast Cell Pool: synthesized and released continuously
Describe turn-over rate of Histamine in the Non-Mast Cell Pool:Turn over rate is rapid.
Describe absorption of histamine through oral routepoor
Describe absorption of histamine via parenteral routehistamine is completely absorbed
Describe metabolism of histamineUndergoes rapid metabolism and distribution in various tissues: Involved methylation and oxidation. Histamine is acted upon by enzyme histamine N-methyltransferase to form methyl histamine - which is acted on by MAO. Minor pathway involves breakdown of histamine by histaminase to form imidazoleacetic acid.
Describe the various roles of histamine: (1) Anaphylaxis, Allergy, (2) Gastric Secretion, (3) NT: emetic response (4) Relaxation of small arterioles & increased vascular permeability (5) Mediator of several pathological states (ruminal bloat)
How is the allergy reaction influencing the body?Induces vasodilation, itching, smooth muscle contraction, and edema. (Humans = flushing of skin, burning, itching.)
In what way does Histamine influence the neurons?stimulates itchy sensation & pain. Release in CNS is involved in the emetic response to vestibular stimulation.
Histamine is involved in which pathological states?ruminant bloating, GI disorders; laminitis, azoturia, retained placenta, pneumonia, gut edema of pigs.
Pharmacological effects of Histamine:Given IV produces smooth muscle contraction, hypotension, increased gastric secretion, dermal reactions.
Histamine effects in the CVS of rabbits:In rabbits it acts as a pressor agent - constriction of arteries is prominent.
Normal CVS effects of histamine:hypotension & increases capillary permeability- induces edema.
Histamine effects on smooth m:CONTRACTION except in Cats & Sheep
Exocrine gland effects of Histamine:Gastric hydrocholric acid secretion mediated through H2. Influences salivary, pancreatic, bronchial, and lacrimal secretions.
Histamine Phosphate use?test agent for achlorhydria (absence of hydrochloric acid) , a negative test would indicate atrophic gastritis
Betazole:H2 receptor. It has a 10-fold selectivity for stimulation of gastric acid production over vasodilation.


Question Answer
What are the differences b/w 1st & 2nd generation anti-histamines?1st generation anti-histamines cause sedation and have antimuscarinic properties
First generation anti-histamines:Chlorpheniramine, Diphenhydramine, Clemastine, Hydroxyzine, Dimenhydrinate, Meclizine, Promethazine, Cyproheptadine.
Second generation anti-histamines:Cetrizine (Zyrtec), Desloratadine (Clarinex), fexofenadine (Allegra), loratidine (Claritin), terfenadine, astemizole.
Two anti-acids:Cemitidine & Ranitidine
Inhibitors of Histamine release (from mast cells) ?Chromolyn Sodium: Inhibits release of histamine and autocoids from mast cells. Mechanism: Facilitates opening of Cl ion channel - hyperpolarizes the cell. (Does not inhibit H1 and H2 receptors.)
Chromolyn sodium pharmacological uses?Prophylactic purposes: Used in pulomnary and nasal allergic reactions. (Mainly used in horses where it is administered by nebulization and delivered with a face mask. A 4% eye drop for allergic conjunctivitis. )
IM or IV preferred for anti-histamines?IM preferred
Anti-histamines are well absorbed orally (T or F)True! Exception = Clemastine
Chlorpheniramine1st gene
Diphenhydramine1st generation
Clemastine1st generation
Hydroxyzine1st generation
Dimenhydrinate1st generation
Meclizine1st generation
Promethazine1st generation
Cyproheptadine1st generation
Cetrizine (Zyrtec)2nd gen
Desloratadine (Clarinet)2nd
fexofenadine (Allegra)2nd
loratidine (Claritin)2nd
terfenadine2nd gen
astemizole2nd gen

Pharmacological effects of anti hist

Question Answer
IV injection of anti-histamines are used in what situations?acute anaphylaxis
Topical administrations of IV are used for? treating topical skin infections.
Describe the metabolism of anti-histaminesUndergo metabolsim by conjugation, excreted by urine and feces.
How are anti-histamines distributed in the body & plasma?Well distributed, bound by plasma proteins.
Effects of anti-histamines on smooth m?relaxation of bronchi & gut
Effects of anti-histamines on CNS?anti-motion sickness & reduce itching by inhibiting sensory nerve stimulation.
Anti-inflammatory mechanism of anti-histamines?Prevent mast-cell degranulation
Effect of anti-hist on blood P?antagonize effects of histaminic hypotension

Therapeutic uses of anti-histamines

Question Answer
Summary the uses of anti-histTreatment of allergic patients, allergic drug reactions, anaphylaxis. Treatment of pruritis assoc. with atopic dermatitis. Synergistic effect of antihistamine with corticosteroids / fatty acids. Treatment of respiratory disorders (Cetrizine.)
Moist eczema, actute eczematous otitis, insect stings, laminitis, paroxysmal myoglobinuria or azoturia, periodic ophthalmia can be treated w?anti-histamines
Therapeutic uses of anti-histamines in bovines?Bloat, acetonemia, acute septic and gangernous mastitis, septic metritis, and retained placenta, pregnancy toxemia.
Therapeutic uses of anti-histamines in pig?Gut edema

Side effects and contraindications

Question Answer
SE in the CNS?CNS depression (sedation, somnolence, ataxia) or CNS excitement in higher doses. CNS Stimulation (irritability, convulsions, hyperpyrexia, death)
Intestinal SE?anorexia, nausea, vomiting, constipation, diarrhea
First generation drugs have anti-muscarinic effects, what are theydry mouth, urinary retention, pupillary dilation, blurred vision, tachycardia.
CVS Side effects?tachycardia, arrythmias, hypertension with high doses.
Can anti-histamines lead to drug tolerance?Yes
Cryptoheptadine can lead to what side effects?polyphagia, sedation, increased vocalization, vomiting in cats.
@ toxic levels, anti histamines cause what?Overdose causes hyperexcitability, convulsions.
Toxic levels of anti-histamines can be tx w/ ?Treat with sedative / ultrashot of acting barbiturates.
Anti- histamines are contra-indicated in patients w/?Hepatic or cardiovascular disease, hypertension, glaucoma, hyperthyroidism, seizures, urinary retention, intestinal atony.

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