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PHARMACOLOGY 3 > 3 – Antihistamines and Antifungals > Flashcards

3 – Antihistamines and Antifungals Flashcards

1
Q

*In which tissues is histamine released?

A
  1. **Mast cell pool
    a. Stored in granules within mast cells and basophils
    b. *inflammatory response, allergy, anaphylactic shock
  2. Non-mast cell pool: GI, CNS, dermis, other tissues
    a. Constant production and rapid turnover
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2
Q

*What receptors does histamine bind to?

A
  • *H1: high affinity
  • *H2: lower affinity
  • H3
  • H4
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3
Q

What does H1 receptor activation cause?

A
  • Smooth muscle contraction
    o Bronchioles>GIT>urinary tract
  • Smooth muscle relaxation
    o Vasodilation of arterioles and capillaries
  • *clinical signs: can’t breath, peripheral swelling, heat
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4
Q

What is the importance of H2 receptors?

A
  • Important in HCl secretion from parietal cells
  • Activated=increase translocation of H/K ATPase pumps into apical membrane
  • *lower affinity, but longer duration when activated?
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5
Q

What is a H2 receptor blocker drug? What is it used for in vet med?

A
  • Things ending in ‘azole’
  • Omeprazole (Gastrogard)
  • Anti-ulcers: minimize acid secretion
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6
Q

What happens with a local cutaneous (typically) allergic response?

A
  • Foreign antigen cross-links with IgE on dermal mast cells
  • *this activation of mast cells cause degeneration=HISTAMINE RELEASE
  • *cardinal signs of inflammation
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7
Q

*What are the primary physiological effects of histamine in allergic reactions?

A
  • Vasodilation (redness)
  • Capillary dilation (edema, swelling)
  • Stimulate nerve endings (pain, pruritis
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8
Q

When does anaphylaxis occur?

A
  • Severe, systemic histamine release and widespread activation of H1 receptors
    o Hypotension: vasodilation, decreased peripheral resistance
    o Bronchoconstriction
    o *likely use epinephrine in emergency (not necessarily an antihistamine)
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9
Q

Histamine and neurons

A
  • Histamine is a NT within CNS
  • Peripheral release of histamine can impact sensory neurons
    o Recognized as pruritus and pain
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10
Q

H1-blocking antihistamines: pharmacodynamics

A
  • ‘reversible competitive inhibition’
    o Compete with histamine for H1 receptor binding site
    o Counteracted by high histamine concentrations
  • LIKELY: STABILIZE H1 receptor in NON-ACTIVE state
  • *don’t care on mechanism, either way=prevents histamine/H1 receptor activation
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11
Q

H1 blocking antihistamines in vet med: pharmacodynamics data

A
  • Limited
  • Generally limited oral bioavailability, but lipid soluble
  • High volume of distribution
  • *hepatic metabolism results in ACTIVE metabolites
  • *drug interactions: not an issue in vet med
    o Induce hepatic microsomal enzymes (increase clearance)
    o Elimination may be inhibited by P-gp substrates
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12
Q

Why are drug interactions with H1 blocking antihistamines not an issue in vet med?

A
  • NOT using it chronically compared to humans
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13
Q

*What are the primary categories of antihistamines?

A
  1. 1st generation H1 blocking antihistamines
  2. 2nd generation H1 blocking antihistamines
  3. 3rd generation H1 blocking antihistamines
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14
Q

1st generation H1-blocking antihistamines effects

A
  • Varying degree of anticholinergic effect
    o Can cause sedation (low doses) OR CNS excitement (usually at higher doses)
    o Ex. dry mouth
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15
Q

1st generation H1-blocking antihistamine examples

A
  • Diphenhydramine (Benadryl)
  • Dimenhydrinate (Gravol, Dramamine)
  • *no vet approved formulations in Canada: use human injectable products
  • *may not work well for cutaneous reactions
  • (pyrilamine: OLD)
  • (Trimeprazine)
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16
Q

*What are the commonly used anti-histamines in vet med?

A
  • Diphenhydramine (Benadryl)
  • Dimenhydrinate (Gravol, Dramamine)
    o Diphenhydramine and 8-chlorotheophylline
17
Q

2nd generation of H1 blocking antihistamines

A
  • More selective for PERIPHERAL H1 receptors
    o Less CNS distribution=less antihistamine and anticholinergic effect in CNS (‘non drowsy’?
  • Generally longer half-life and dosing intervals
18
Q

What are some examples of 2nd generation of H1 blocking antihistamines?

A
  • (Cetirizine: Zyrtec)
  • (Loratidine: Claritin)
19
Q

3rd generation H1 blocking antihistamines

A
  • Contains only active moiety
  • Generally decreased AE and increased efficacy
    o Maybe faster acting?
20
Q

*What are the clinical uses of antihistamines?

A
  • ‘treatment of allergic reactions
    o Modulates reaction, but WONT STOP allergen exposure or histamine release
  • *more useful if administered BEFORE allergen contact and subsequent histamine release
    o Realistically does NOT happen
  • *does NOT prevent histamine from being released
21
Q

EXAMWhat actually causes the clinical signs in an allergic reaction?

A
  • *when histamine BINDS to H1, NOT when histamine is released
  • Antihistamines prevent them from binding NOT preventing their release
22
Q

There is limited efficacy when used for atopic dermatitis (dogs/cats)

A
  • May DECREASE pruritus for short time
  • Lots of inter-individual variability in efficacy
  • Actually reduced pruritus OR just cause sedation?
    o Antihistamine/anticholinergic effects
23
Q

What are some other clinical uses of H1 antagonists besides for atopic dermatitis?

A
  • Limited efficacy for reducing bronchoconstriction
  • Antidotes for ‘extrapyramidal reactions’ caused by phenothiazine tranquilizers
  • Adjunctive therapy for anaphylaxis, but does NOT replace sympathomimetics (EPI)
  • **Adjunctive therapy for dogs with mast cell tumours
    o Help prevent pruritus due to degranulation and histamine release
24
Q

H1 blockers can also inhibit muscarinic receptors (anticholinergic): can produce similar but weaker effects as an anticholinergic drug (ex. atropine)

A
  • Dry mouth and mucous membranes
  • Tachycardia
  • Ileus
  • Mydriasis (dilated pupils)
  • *PARASYMPATHOLYTIC SIGNS
25
Q

H1 blockers and CNS depression or excitement. What is it due to?

A
  • Anti-histamine OR anticholinergic OR BOTH?
    o Some sort of balance between them, but variable
    o Lower doses: sedation
    o Higher doses: excitement

PHARMACOLOGY 3 (15 decks)

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