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I3 Exam 3 > Histamine (Ceryak) > Flashcards

Histamine (Ceryak) Flashcards

1
Q

What are H1 first generation drugs?

A

Diphenhydramine, doxylamine, chlorpheniramine

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2
Q

What are H1 second gen drugs?

A

Loratadine, cetirizine, fexofenadine

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3
Q

Describe histamine biosynthesis/metabolism

A
  • biosynthesis: decarboxylation of L-histidine

- metabolism: rapidly broken down to inactive metabolites when released (via enzymes like MAO)

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4
Q

What is it mean that histamine is an autacoid?

A

released and act locally in periphery

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5
Q

Where is histamine most synthesized and stored?

A

mast cells and basophils (in granules complexed with heparin/acidic proteins)

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6
Q

Where is histamine distributed?

A

periphery, CNS (histaminergic neurons)

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7
Q

What is the immunologic release stimuli of histamine?

A
  • allergic rxns (type I hypersensitivity) via IgE:antigen crosslinking
  • inflammation: complement system activation at inflammatory site
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8
Q

What drugs block histamine release?

A

-epinephrine/cromolyn

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9
Q

What are the 2 receptor subtypes and how they differ?

A

H1 - smooth muscle, endothelium, CNS; Gq path (IP3, cGMP)

H2 - vascular smooth muscle, gastric mucosa, cardiac, CNS; Gs path (cAMP)

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10
Q

Endogenous Histamine: vascular SM

A

-H1: vasodilation/edema (relaxation of endothelial cell to decrease blood pressure but increase reflex tachycardia)

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11
Q

Endogenous Histamine: non-vascular SM

A

H1: bronchocontriction

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12
Q

Endogenous Histamine: GI

A

H2: parietal cell gastric acid release

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13
Q

Endogenous Histamine: PNS (autacoid)

A

H1: stimulates primary afferent nerve endings (itch, pain)

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14
Q

Endogenous Histamine: CNS (NT)

A

Mainly H1 (post-synaptic): arousal (wakefulness); appetite, body temp

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15
Q

H1 contracts VSM and relaxes endothelial VSM, while H2 relaxes VSM. What is the net effect?

A

Relaxation! (w/o endothelial H1 it would be contraction)

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16
Q

Is anaphylaxis caused by histamine?

A

no!

17
Q

Are local allergic rxns caused by histamine? (urticaria=hives and allergic rhinitis=hay fever)

A

yes!

18
Q

What are 3 classes of pharmacotherapy for allergies?

A
  • subacute and preventative = inhaled steroids (fluticasone)
  • mast cell stabilizers (cromolyn sodium to inhibit mast cell degranulation)
  • antihistamines
19
Q

What do antihistamines not work against in the allergic response?

A

bronchospasm mediated by leukotrienes

20
Q

First generation H1 antihistamines receptors affected

A
  • cholinergic: dry mouth, urinary retention, sinus tachycardia
  • histamine H1: decreased allergic inflam, itching, sneezing, rhinorrhea, but increased sedation and appetite
21
Q

Diphenhydramine (first gen H1) - duration, anti-ACh, Sed, anti-emetic, other

A
  • 4-6 hours
  • +++
  • +++
  • ++
  • anti-motion sickness, OTC sleep aid
22
Q

Doxylamine (first gen H1) - duration, anti-ACh, Sed, anti-emetic, other

A
  • 6-12 hours
  • +++
  • ++++
  • +++
  • OTC sleep aid, anti-emetic (FDA approved for morning sickness)
23
Q

Chlorpheniramine (first gen H1) - duration, anti-ACh, Sed, anti-emetic, other

A
  • 4-6 hours
  • +
  • ++
  • -
  • OTC cold meds
24
Q

Fexofenadine (second gen H1) - duration, anti-ACh, Sed

A
  • 6-12 hours
  • -
  • +/-
25
Q

Loratidine (second gen H1) - duration, anti-ACh, Sed

A
  • 12-24 hours
  • -
  • +/-
26
Q

Cetirizine (second gen H1) - duration, anti-ACh, Sed

A
  • 12-24 hours
  • +/-
  • +
27
Q

How does second gen compare to first gen H1 antihistamines?

A

-second gen has less BBB penetration so fewer CNS side effects (no anti-emetic effects); second gen not OTC sleep aid

28
Q

H1 antihistamines ADME

A
  • rapidly absorbed, lipid soluble, 95% bound to proteins
  • first gen penetrate BBB, second gen do not bc second gen ionized at physiological pH (increased affinity for PGP
  • second gen longer lasting
  • metabolized in liver (except fexofenadine excreted unchanged in bile)
  • renal clearance
  • crosses placenta but little risk in pregnant women; eliminated in breast milk
29
Q

H1 antihistamines first gen adverse effects (second gen not much): CNS

A

impaired alertness, cognition, learning, memory, performance

30
Q

H1 antihistamines first gen adverse effects (second gen not much): cardiac

A

dose-related sinus tachycardia, reflex tachycardia

31
Q

H1 antihistamines first gen adverse effects (second gen not much): glaucoma

A

contraindicated in persons with glaucoma or prostatic hypertrophy

32
Q

H1 antihistamines first gen adverse effects (second gen not much): toxicity overdose

A 
respiratory depression (potentially fatal)
-adverse CNS effects > adverse cardiac effects
33
Q

H1 antihistamines first gen adverse effects in elderly

A

commonly used but cog and mem impairment, falls, incontinence, etc.

34
Q

H1 antihistamines first gen adverse effects in lactating women

A

cause drowsiness or irritability in nursing infants

35
Q

H1 antihistamines first gen adverse effects in infants and young children

A

adverse effects and occasionally fatalities

36
Q

Any exceptions to H1 antihistamine sedation?

A

some children experience CNS excitation

I3 Exam 3 (9 decks)

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