Antacids and Antihistamines

Question 1

autacoids

Answer 1

• biological factors which act like hormones
• short duration of action
• act near the site of synthesis/release
• not blood-borne

Question 2

classes of autacoids

Answer 2

• eicosanoids
  
  • prostaglandins, leukotriences, thromboxane
  • mediate inflammatory processes
• polypeptides
  
  • angiotensin, kinins, substance P
• decarboxylated amino acids
  
  • histamine, serotonin

Question 3

histamine

Answer 3

• synthesized in mast cells (tissue) and basophils (blood), ECL cells and CNS
• metabolized in liver
• major mediator of inflammation, anaphylaxis and gastric acid secretion
• neurotransmitter

Question 4

H1-antihistamines

Answer 4

• “H₁ blockers”
• first vs. second generation
  
  • second generation doesn’t cross BBB
• lipophilicity and selectivity profiles
• major uses: allergy, itching, nausea, motion sickness and insomnia
• limited roles in asthma or anaphylaxis

Question 5

diphenhydramine

Answer 5

• used for:
  
  • acute allergic reaction
  • antipruritic
  • prevent reactions
  • motion sickness
  • mast cell tumor
• crosses BBB (1st gen)
• adverse effects: CNS and anticholinergic

Question 6

cyproheptadine

Answer 6

• H₁ blocker
• serotonin (5-HTP) antagonist
• appetite stimulant
• antipruritic effect?
• horses: photic head shaking and PPID
• adverse effects: CNS and anticholinergic

Question 7

meclizine

Answer 7

• H₁ blocker
• motion sickness and vestibular disease
• MOA: partially understood
• antiemetic action through CTZ

Question 8

H₂-Antihistamines

Answer 8

• reversible, competitive antagonists of histamine
• bine to H₂ receptors on gastric parietal cells
• reduce gastric acid secretion

Question 9

famotidine (pepcid)

Answer 9

• H₂ antagonist
• most potent and longest half-life
• first-pass hepatic metabolism
• no prokinetic or antiemetic activity
• side effects are uncommon
• GI effects in healthy dogs?

Question 10

H₃ and H₄ Antihistamines

Answer 10

• not approved for clinical use
• experimental models
• improve attention and wakefulness

Question 11

Serotonin

Answer 11

• 5-HT
• synthesized from tryptophan
• found in GI tissues (ECL cells), CNS and platelets
• ECL cell 5-HT is stored in platelets
• serotonergic projections
  
  • spinal cord (pain perception, motor control)
  • forebrain (mood, cognition)

Question 12

serotonin overdose

Answer 12

• neuro signs
  
  • seizures, depression, tremors, hyperesthesia and ataxia
• GI signs
  
  • vomiting, diarrhea, abdominal pain, hypersalivation
• other
  
  • hyperthermia, blindness

Question 13

amphetamines

Answer 13

• inhibitors of serotonin storage
• displace 5-HT, dopamine and NE from storage vesicles

Question 14

Monoamine Oxidase Inhibitors (MAOI)

Answer 14

• inhibitors of serotonin degradation
• two main types of MAOI-a and MAOI-b
• reversible vs. irreversible

Question 15

selegiline (Anipryl)

Answer 15

• selective MAOI-b, but MAOI-a at high doses
• treatment of canine cognitive dysfunction
• increased dopamine activity
• tx of Cushing’s disease +/- 20%
• adverse effects: GI signs and CNS

Question 16

reuptake inhibitors

Answer 16

• net increase in extracellular 5-HT
• used for tx of anxiety, depression and OCD
• four classes:
  
  • TCAs
  • SSRIs
  • SNRIs
  • NRIs

Question 17

clomipramine

Answer 17

• tricyclic antidepressant (TCA)
• only FDA approved drug for dogs
  
  • tx of OCDs, anxiety and dominance aggressive
• off-label in cats and birds

Question 18

fluoxetine (prozac)

Answer 18

• selective-serotonin reuptake inhibitor (SSRI)
• FDA approved in dogs for tx of separation anxiety in conjuction with behavior modification plan
• adverse effects: anorexia and seizures

Question 19

mirtazapine

Answer 19

• atypical antidepressant
• 5-HT2 and 5-HT3 inhibitor
• central alpha-2 receptor inhibitor (net increase in NE)
• appetite stimulant
• anti-emetic
• adverse effects: drowsiness/sedation, vocalization, tachycardia

Question 20

trazodone

Answer 20

• 5-HT2 inhibitor and SSRI
• adjunctive anxiolytic
• tx of hospitalization-related anxiety and post-op recovery
• adverse effects: GI signs, ataxia, hypotension
• less CV effects

Question 21

cisapride

Answer 21

• 5-HT4 agonist
• enhances acetylcholine release
• prokinetic
• tx of GI stasis, reflux esophagitis, constipation/megacolon (cats)
• adverse effects: well tolerated

Question 22

ondansetron (Zofran)

Answer 22

• serotonin receptor antagonist (5-HT3)
• potent antiemetic
• receptors in vagal nerve terminals and CTZ
• controversial use in cats
• well tolerated in dogs